Fracture Energy

Background: Acrylic resins constitute about 90% of polymeric materials used in prosthetic dentistry. However, they are not devoid of drawbacks. Their weakness includes poor resistance to fracture and abrasion, as well as changes in volume and shape during fabrication and use. The aim of this study is to evaluate and compare the mechanical strength in fracture force test of maxillary palatal denture bases, fabricated from different acrylic resins. Materials and Methods: Twenty five maxillary edentulous stone casts were constructed from a standard silicon model of maxillary edentulous jaw. Five palatal denture bases were made from each of the following materials; conventional heat cure acrylic (Control Group), rapid cure acrylic, high impact acrylic and Biostar pure acrylic, according to the manufacturer's instructions. The fracture force test was carried out on a universal testing machine (GUNT HAMBURG) at a crosshead speed of 10mm/min. The results were analyzed using ANOVA and t-test to determine the significant differences between tested groups at a significant level (P<0.05). The high impact acrylic resin showed the highest fracture force value, while the Biostar pure acrylic resin showed the lowest value as compared with other tested materials. The results revealed highly significant differences between the high impact acrylic and conventional heat cure acrylic (P<0.001), and other tested denture base materials (P<0.05). Also, rapid heat cure acrylic resin showed significantly higher fracture force value than those obtained by both conventional heat cure acrylic resin and Biostar pure acrylic resin (P<0.05),(P<0.001) respectively. Finally, significantly lower fracture force value was obtained by the Biostar acrylic resin as compared to the conventional heat cure acrylic (P≤0.05) and other tested denture base materials (P<0.001). Under the limitation of this study for those patients who fracture their dentures on regular basis, it is possible to consider a high impact and rapid cure acrylic resins denture base, which shows a higher degree of resistance to fracture in comparison with conventional heat cure acrylic resin. However, this is unlike the Biostar pure acrylic resins that showed undesirable results as compared with conventional heat cure acrylic and other tested denture base materials.

This paper deals with numerical analyses of concrete subjected to triaxial compressive loading. For this purpose, two different 3D-constitutive models for concrete are considered. The Leon model, a single-surface plasticity model previously formulated by Etse , is reformulated with respect to the ductility function for the description of ductile concrete behavior. This model accounts for the dependence of the concrete strength on the Lode angle. The second model is a multi-surface plasticity model consisting of three Rankine yield surfaces for the description of cracking of concrete and a Drucker-Prager yield surface for the description of compressive behavior of concrete. This model is reformulated to account for the dependence of both strength and ductility of concrete on confinement. Consideration of confinement is controlled by the major principal stress. The model behavior under different confinement levels is compared with experimental results reported in . Within a finite element (FE) analysis of a pull-out test, the predictive capabilities of the models are investigated.

Polytetrafluoroethylene (PTFE) exhibits excellent non-stick properties and a very low coefficient of friction under tribological stress, but it is incompatible with almost all other polymers. In the first part of this study, we presented the generation of the novel tribological material based on unsaturated oil, radiation-modified PTFE and Polyamide 66 (PA66). To get a better understanding of the chemical properties and chemical composition of the compounds, the PA66-PTFE-oil-cb (chemically bonded) compounds were examined by differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). In this part, the mechanical properties of the compounds are compared with plain PA66 and PA66-MP1100-cb. The tribological investigation was carried out using the block-on-ring tribometer. It was detected that the mechanical properties of PA66-PTFE-oil-cb with 20 wt% PTFE-oil-cb only show slight differences compared to PA66, but the tribological properties of the compounds were significantly improved through chemical coupling between the three components.

Hat-shaped specimen geometries were developed to generate high strain, high-strain-rates deformation under prescribed conditions. These geometries o↵er also the possibility to investigate the occurrence of ductile rupture under low or negative stress triaxiality, where most failure models fail. In this work, three tophat geometries were designed, by means of extensive numerical simulation, to obtain desired stress triaxiality values within the shear region that develops across the ligament. Material failure was simulated using the Continuum Damage Model (CDM) formulation with a unilateral condition for damage accumulation and validated by comparing with quasi-static and high strain rate compression tests results on OFHC copper. Preliminary results seem to indicate that ductile tearing initiates at the specimen corner location where positive stress triaxiality occurs because of local rotation and eventually propagates along the ligament.

Ductile damage evolution assessment in high purity copper and stainless steel subjected to different shock-loading profiles using cohesive modeling ANDREW RUGGIERO, NICOLA BONORA, LUCA ESPOSITO, University of Cassino, GEORGE T. (RUSTY) GRAY III, Los Alamos National Laboratory -At continuum level, the triaxiality of the stress state has the major effect to reduce the ductility that the material can exhibit. As a result of this, ductile metals under uniaxial strain loading condition, such as that experienced in flyer plate impact experiment, should show a very limited ductility that is often in contrast with the energy dissipation estimated from the pull-back signal amplitude. In this paper, it is proposed that the developing of damage in form of voids causes a dramatic drop of the stress triaxiality giving the material the ability to sustain much larger deformation and consequent plastic work dissipation. Thus, a numerical model using cohesive elements has been developed to account for this dissipation in the energy balance. The model has been used to investigate the damage evolution and plastic strain accumulation in plate impact experiments with different loading profiles, for both high purity copper and stainless steel, in order to achieve a better comprehension of the processes related to spall fracture. Comparisons of numerical results with experimental data, available in term of both velocity profiles and optical metallography of soft-recovered samples, seem to confirm the capability of the proposed model to correctly capture distinctive features of spall event.

The American Physical Society Embedded Cohesive Elements (ECE) Approach to the Simulation of Spall Fracture Experiment NICOLA BONORA, LUCA ESPOSITO, ANDREW RUGGIERO, University of Cassino, Italy -Discrepancies between the calculated and observed velocity vs time plot, relatively to the spall signal portion in terms of both signal amplitude and frequency, in numerical simulations of flyer plate impact test are usually shown. These are often ascribed either to material model or the numerical scheme used. Bonora et al. (2003 ) [Bonora N., Ruggiero A. and Milella P.P., 2003, Fracture energy effect on spall signal, Proc. of 13 th APS SCCM03, Portland, USA] showed that, for ductile metals, these differences can be the imputed to the dissipation process during fracturing due to the viscous separation of spall fracture plane surfaces. In this work that concept has been further developed implementing an embedded cohesive elements (ECE) technology into FEM. The ECE method consists in embedding cohesive elements (normal and shear forces only) into standard isoparametric 2D or 3D FEM continuum elements. The cohesive elements remain silent and inactive until the continuum element fails. At failure, the continuum element is removed while the ECE becomes active until the separation energy is dissipated. Here, the methodology is presented and applied to simulate soft spall in ductile metals such as OHFC copper. Results of parametric study on mesh size and cohesive law shape effect are presented.

The amount of concrete utilized worldwide has lately grown due to rising populations and urbanization. The gas emissions during cement manufacturing and the usage of common resources result in a significant environmental threat. As a result, researchers are attempting to minimize the amount of cement consumed by using waste materials while lowering building costs. This research aims to minimize the amount of cement used in concrete by partially replacing it with ceramic powder waste while also increasing the mechanical qualities of concrete mortar by substituting cement with nanoclay hydrophilic bentonite. Mortar samples were prepared using five different replacement percentages of cement by nanoclay, including 0, 2, 4, 6, and 8%, and two replacement percentages of cement by ceramic powder, including 0% and 20%. Compressive and flexural strength tests were performed on mortar samples for 7, 14, and 28 days of moist curing. The toughness was also measured for all mixes by measuring the area under the load-deflection curve. Also, water absorption and relative densities for all mortar mixes were measured. The results show that replacing cement with 2% nanoclay and 20% ceramic powder increases the flexural strength by 11%.

Since the development of the wedge splitting test (WST), techniques have been used to extract material properties that can describe the fracture behavior of the tested materials. Inverse analysis approaches are commonly used to estimate the stress-crack width relationship; which is described by the elastic modulus, tensile strength, fracture energy, and the assumed softening behavior. The stress-crack width relation can be implemented in finite element models for computing the cracking behavior of cementitious systems. While inverse analysis provides information about the material properties of various concrete mixtures there are limitations to the current analysis techniques. To date these techniques analyze the result of one WST specimen, thereby providing an estimate of material properties from single result. This paper utilizes a recent improvement to the inverse analysis technique, which enables the stress-crack width response to be determined simultaneously from multiple experimental tests. The effect of water-to-cement ratio and aggregate size are discussed. A comparison of epoxy-impregnated cracked WST specimen and material properties indicate a relationship between fracture properties and characteristics of load induced cracks.

The paper investigates and models the mechanism of pre-split cutting, a technique used in excavations in hard rock and based on creating large splits by simultaneous blasting or slow pressurising of closely placed holes. Only the case of initially intact rock (no discontinuities comparable with the dimension of pre-split fracture) is considered. The critical spacing between the holes is found separating the case of splitting from the case of bulk fracturing of the rock. The determination of the critical spacing is based on the comparison between the hole pressure required to start the pre-existing cracks with the pressure required to bring the cracks to the length at which the interaction between them will make their propagation unstable. If the initial cracks are relatively large such that the pressure of the crack start is less than the pressure of unstable growth, other cracks will appear fracturing the bulk of material. If the initial cracks are small enough, the starting pressure will be high, hence the cracks will propagate dynamically until the coalescence with the neighbours, which produces splitting. For the case of pre-splitting prepared parallel to a free boundary, the influence of the latter is minor, so the dominant mechanism of pre-splitting is the crack interaction.

This research evaluates the fracture behavior of concrete with reactive magnesium oxide (MgO). Replacing cement with MgO is an attractive option for the concrete industry, mainly due to sustainability benefits and reduction of shrinkage. Four different MgO’s from Australia, Canada, and Spain were used in the concrete mixes, as a partial substitute of cement, at 5%, 10%, and 20% (by weight). The fracture toughness (KI) intensity factor and the stress–strain softening parameters of the wedge split test were evaluated after 28 days. The experimental results showed that the replacement of cement with MgO reduced the fracture energy between 13% and 53%. Moreover, the fracture energy was found to be correlated with both compressive strength and modulus of elasticity. A well-defined relationship between these properties is important for an adequate prediction of the non-linear behavior of reinforced concrete structures made with partial replacement of cement with MgO.

In this paper, experiences on the development of an assessment method for existing bridges are presented. The method is calibrated using the results of full-scale testing to failure of a prestressed bridge in Sweden. To evaluate the key parameters for the structural response, measured by deflections, strains in tendons and stirrups and crack openings, a sensitivity study based on the concept of fractional factorial design is incorporated to the assessment. Results showed that the most significant parameters are related to the tensile properties of the concrete (tensile strength and fracture energy) and the boundary conditions. A finite element (FE) model in which the results of the sensitivity analysis were applied, was able to predict accurately the load-carrying capacity of the bridge and its failure mode. Two additional existing prestressed concrete bridges, that will be used to improve further the method, are also described, and discussed.

Improving of epoxy adhesive tensile joint strength is a major interest relevant to many industries. In this study, four types of fillers were chosen (tungsten carbide, silicon carbide, iron, and glass). Fillers were in the form of powder with a particle size of 140 µm. Adherents were 6061-T6 aluminium alloys fabricated according to ASTM D 2094-00 (2014). Bonding surfaces were prepared by grinding using 400 grit emery paper. The surfaces were then chemically etched using CSA solution. Two distance copper wires were used per specimen having a diameter of 180 µm. Five replicas per adhesive condition were adopted. Four volume filler fractions were chosen (10%, 15%, 20%, and 25%). A comparison of average tensile adhesive joint strength was made between the reference (no filler specimen) and other fillers. It was concluded that SiC and iron fillers had negative results on the joint strength, with the worse results occurring at high fractions. Glass with low fractions slightly enhanced the joint strength but showed negative results when the volume fraction was increased. Tungsten carbide showed a slight improvement at 10% fraction, but a major improvement was achieved. In particular, at 20% fraction the strength was enhanced by 41.33%.

Ultrasonic consolidation (UC) is a solid freeform fabrication technique developed for the manufacture of metal parts. The mechanisms by which bonds are formed, during the UC process, are based on a combination of the surface effect and the volume effect. Based on the outcomes of peel tests and microstructural analysis, this paper will consider the influence of these two phenomena on the weld strength of specimens. A model is presented to describe how calculations for weld strength may be derived on the basis of the theory of surface and volume effects. Through the application of the model, it was possible to demonstrate that the weld strength may be 7 per cent greater than the tensile strength of the base metal. The identification of the phenomena and the development of a model for weld strength have led to the modification and production of an enhanced test procedure which is described in this paper.

The Charpy test has been used for over a hundred years as an important tool in the qualification of materials in engineering projects and in the development of new metal alloys. The instrumentation of the Charpy test allowed its use in determining the dynamic fracture toughness parameters (K Id , J Id ), and thus the verification of the effects of temperature and loading rate on the performance of metallic materials. The small sample sizes, ease in preparing these samples and execution the tests have been guaranteeing their use in the various areas of engineering. Prof. Telmo R. Strohaecker was one of the pioneers in the use of the Instrumented Charpy test in the country in determining parameters of the dynamic fracture mechanics for the characterization of the fracture toughness of high-strength low-alloy steels.

The scaling of earthquake source displacement spectra is analytically studied based on the continuous form of one-dimensional dynamical spring-slider model in the presence of either linearly slip-weakening friction or linearly velocity-weakening friction. The main parameters of the model are the natural angular frequency, wo, and the (dimensionless) decreasing rate, D, of friction with slip (or the characteristic displacement) for slip-weakening friction as well as the (dimensionless) decreasing rate, u, of friction with velocity (or the characteristic velocity) for velocity-weakening friction. The analytic solution includes the complementary and particular parts. The former shows the travelling wave and the latter denotes vibrations at a site. The complementary solution exhibits w-1 scaling in the whole range of w for both friction laws. For the particular solution, slip-weakening friction results in spectral amplitudes only at three values of w. For velocity-weakening friction wit...

The scaling of earthquake source displacement spectra is analytically studied based on the continuous form of one-dimensional dynamical spring-slider model in the presence of either linearly slip-weakening friction or linearly velocity-weakening friction. The main parameters of the model are the natural angular frequency, ~o, and the (dimensionless) decreasing rate, D, of friction with slip (or the characteristic displacement) for slip-weakening friction as well as the (dimensionless) decreasing rate, y, of friction with velocity (or the characteristic velocity) for velocity-weakening friction. The analytic solution includes the complementary and particular parts. The former shows the travelling wave and the latter denotes vibrations at a site. The complementary solution exhibits ~-1 scaling in the whole range of ~for both friction laws. For the particular solution, slip-weakening friction results in spectral amplitudes only at three values of ~. For velocity-weakening friction with y>0.5, the log-log plot of spectral amplitude versus ~exhibits almost ~0 scaling when ~is lower than the corner angular frequency, ~c, which is independent on y and increases with ~o. When ~>~c, the spectral amplitude monotonically decreases with ~following a line with a slope value of -1, which is the scaling exponent.

Seismicity is dynamically simulated by one-dimensional mass-spring model with fractal distribution of breaking strengths. -A linearly rapidly-weakening-and hardening friction law controls the sliding of the mass. The frequency-magnitude relations from synthetic seismicity for five values of friictal dimension show that b values for events with intermediate magnitudes are close to 1, while those for events with larger magnitudes are from 1.68 to 2.52. For small events, the logN values are almost constant.

The very large glued laminated timber columns that are needed for tall timber buildings are too large to be physically tested in most facilities. To safely design these columns, it is necessary to identify and extrapolate behaviour from the physical testing of smaller specimens. Compression testing of 27 glue-laminated timber columns showed a reduction in strength with increased member size. This phenomenon is known as a size effect. The laminated timber exhibited a compressive strength much higher than the characteristic strength that it was graded it. Comparisons between columns of different lengths and widths, suggests that the homogenisation of laminated timber may mitigate the size effect. An extrapolation of the size effect from the column sizes tested, to an ultra-large column for a timber skyscraper, indicated that the magnitude of the effect could be large enough to reduce the compressive strength of the glulam to below its characteristic strength.

The paper presents detailed measurements of midspan total pressure loss, secondary flow field, static pressure measurements on airfoil surface at midspan, near hub and near the end walls in a transonic turbine airfoil cascade. Numerous low-speed experimental studies have been carried out to investigate the performance of turbine cascades. Profile and secondary loss correlations have been developed and improved over the years to include the induced incidence and leading edge geometry and to reflect recent trends in turbine design. All of the above investigations have resulted in better understanding of flow field in turbine passages. However, there is still insufficient data on the performance of turbine blades with high turning angles operating at varying incidences angles at transonic Mach numbers. In the present study, measurements were made at +10, 0 and -10 degree incidence angles for a high turning turbine airfoil with 127 degree turning. The exit Mach numbers were varied within a range from 0.6 to 1.1. Additionally, the exit span is increased relative to the inlet span resulting in one end wall diverging from inlet to exit at 13 degree angle. This was done in order to obtain a ratio of inlet Mach number to exit Mach number which is representative to that encountered in real engine and simulates the blade and near end wall loading that is seen in an engine. 3D viscous compressible CFD analysis was carried out in order to compare the results with experimentally obtained values and to further investigate the design and off-design flow characteristics of the airfoil under study. All aerodynamic measurements were compared with CFD analysis and a reasonably good match was observed.

A theoretical model is proposed to estimate the fracture toughness of ferritic steels in the transition region from ball indentation test data. The key concept of the model is that the indentation energy to a critical load is related to the fracture energy of the material. By applying the new model, the fracture parameters of reactor pressure vessel steel base and weld metals were estimated from the indentation load-depth curves. The estimated fracture stresses agreed well with those of the Wilshaw et al. model. The temperature dependence of the estimated K JC was almost the same as that of the ASTM K JC master curve. Also, the reference temperature obtained from the estimated K JC versus temperature curve correlated well with the index temperature of 41 J Charpy impact energy, T 41 J . Additionally, the ball indentation deformation was simulated by ABAQUS code to evaluate the stress state and the result was compared with that at the crack tip.

This paper investigates the manufacturing and mechanical properties of thermoplastic composite-metal hybrid laminates based on DP500 steel sheets bonded to a glass fiber-reinforced polypropylene (PP) or to a self-reinforced PP composite materials. Single cantilever beam (SCB) tests revealed that a good level of adhesion can be achieved by using a hot dip zinc surface treatment on the DP500 steel and incorporating an interlayer based on modified polypropylene at the interface between the composite and metal plies. In addition, SCB tests have shown that the interfacial fracture energy of the hybrid laminates increased with increasing crosshead displacement rate. Additional testing of a number of laminates has shown that the tensile properties of these composite-metal hybrid laminates are strongly dependant on the tensile properties of the constituent materials and that a modified rule of mixtures could be used to predict such properties.

This paper presents a nonlinear local bond-slip model for fiber reinforced polymer (FRP) laminates externally bonded to concrete at elevated temperature for future use in the theoretical modeling of fire resistance of FRP-strengthened concrete structures. The model is an extension of an existing two-parameter bond-slip model for FRP-to-concrete interfaces at ambient temperature. The two key parameters employed in the proposed bond-slip model, the interfacial fracture energy and the interfacial brittleness index , were determined using existing shear test data of FRP-to-concrete bonded joints at elevated temperature. In the interpretation of test data, the influences of temperature-induced thermal stress and temperature-induced bond degradation are properly accounted for. As may be expected, the interfacial fracture energy is found to be almost constant initially and then starts to decrease when the temperature approaches the glass transition temperature of the bonding adhesive; the interfacial brittleness index exhibits a similar trend. The proposed temperature-dependent bond-slip model is shown to closely represent the test data upon which it is based, despite the large scatter of the test data.

This research presents analytical and mathematical modelling of coating failures within industrial components, structures, mobile assets and systems due to corrosive degradation and mechanical fracture. These failures lead to several surface problems; therefore, contact mechanics and electrochemistry approaches incorporating induced residual stresses have been adopted to develop a comprehensive solution for the prediction and prognostic of such failures. Experimental study of film cracking and its propagation into substrates, interfacial transient behaviours and film-substrate system has been conducted. A parallel study of corrosive degradation to include cathodic delamination, cathodic blistering and tribo-corrosion of films has been conducted. Experimental and analytical studies of induced residual stresses within the coating and their effects on failure mechanisms and propagation have been completed. A detailed investigation of elastic mismatch at the interfacial contact and interfacial crack tip field has been performed and a complex stress intensity factor is presented. Mathematical derivation of oscillatory singularity, mode mix and interfacial fracture criterion to include adhesion are presented. This paper presents novel mathematical modelling incorporating interfacial crack propagating, diffusion of corrosive species and cathodic blistering for prediction and prognoses of coating failures.

Since ancient times randomly distributed quartz is routinely included in ceramic earthenwares as an aid to drying. Although it has been noticed that this practice also provides the ware with higher capability for flaw tolerance so that a crack does not become readily unstable in the event of overloading during service, no systematic study of the effect or a satisfactory model has been reported in the open literature. This work reports the results of such an investigation on the influence of grain size and volume fraction of quartz on the elastic modulus, strength and fracture energy dissipation of such composites based on fired clays. In addition, we have studied the fracture micromechanisms by dynamic in situ optical microscopy and scanning electron microscopy and introduced a simple model to explain the results, based on the local effects of the stress field of the inclusions.

This paper presents results for the fracture energy of concrete (GF) obtained from a wide range of high-strength concretes. Strength levels up to I00 MPa, a99regate type and a99regate surface texture were included as variables. The determination of GF was performed accordin9 to the recommendation of the RILEM 50-FMC Committee. Compressive and tensile strengths and the modulus of elasticity are also presented. Measured values of G v are compared with those proposed in the last CEB Model Code. NOTATION E f; f(s) f,,et GF MR Modulus of elasticity Compressive strength Tensile strength (splitting test) Modulus of rupture, central (notched beams) Fracture energy lch point loading Modulus of rupture, four-point loading (unnotched beams) Maximum displacement Characteristic length

The paper analyses the size dependency of the fracture energy (G F ) and the effective length of fracture process zone (C f ) of concrete determined as per the Bazant's Size effect method and RILEM Work-of-fracture methods. The fracture parameters (G F ,C f ) are determined by measuring the maximum loads of geometrically similar notched plain concrete (M25) specimens of different sizes in a size ratio of 1:5 with different pre-cast notch depths (a/d=0.15, 0.30 and 0.45) under three point bending through load-deflection curves. In each notch depth ratio, 15 beams are cast and tested with 03 similar specimens in each size of the beams. Total beams tested are 45.The variation of both the fracture energy and the effective length of fracture process zone as a function of the specimen size and notch depth is determined using Bazant's Size effect method and RILEM Work-of-fracture method. Fracture energy and Fracture process zone length determined by Size effect method are found to be decreasing with the increasing notch depth ratios. Fracture energy calculated using Work-of-fracture method is increasing with the increase in size of specimen and decreasing with the increasing notch depth ratios.

A combined compression and AE test is proposed, in order to study the scaling of fracture and Acoustic Emission in concrete-like specimens with different size and slenderness. The cylindrical concrete specimens were drilled from two pilasters sustaining a viaduct along an Italian highway built in the 1950s. A two-dimensional FEM numerical model of the pure compression tests is also presented, which is able to describe both the discrete cracking at the matrix-aggregate interface and the smeared cracking of the matrix. The adopted mesoscale modeling directly accounts for the aggregate dimensional distribution, being each aggregate explicitly represented. The distribution of aggregate size and position was generated according to the Füller distribution. In this way, the crack patterns can be simulated correctly, as well as the load displacement curve. During microcrack propagation, acoustic emission events can be clearly detected experimentally. Therefore, the number of acoustic emissions can be put into relation with the number of Gauss points in the finite element model where cracking takes place. A good correlation is found between the amount of cracking simulated numerically and the experimental acoustic emission counting for different specimen sizes, and the two quantities show the same exponent with respect to the considered volume. This evidence reconfirms the assumption, provided by fragmentation theories, that the energy dissipation during microcrack propagation occurs in a fractal domain comprised between a surface and the specimen volume.

Clayey gouges are common in fault slip zones at shallow depths. Thus, the fault zone processes and frictional behaviors of the gouges are critical to understanding seismic slip at these depths. We conducted rotary shear tests on clayey gouge (~41 wt % clay minerals) at a seismic slip rate of 1.3 m/s. Here we report that the gouge was melted at 5 MPa of normal stress and room humidity conditions. The initial local melting was followed by melt layer formation. Clay minerals (e.g., smectite and illite) and plagioclase were melted and quenched to glass with numerous vesicles. Both flash heating and bulk temperature increases appear to be responsible for the melting. This observation of clayey gouge melting is comparable to that of natural faults (e.g., Chelungpu fault, Taiwan). Due to heterogeneous fault zone properties (e.g., permeability), frictional melting may be one of the important processes in clayey slip zones at shallow depths.

Pseudotachylyte formed by frictional melting has been the only unequivocal evidence of past seismogenic fault slip. We report from high-velocity friction experiments on sideritebearing gouge that mineral decomposition due to frictional heating also can leave evidence of paleoseismic events along shallow crustal faults other than pseudotachylyte. Experiments were conducted room dry on simulated gouge composed of siderite or mixture of siderite, calcite, and quartz, initially at room temperature, under normal stresses of 0.6-1.3 MPa and at seismic slip rates of 1.3-2.0 m/s. In all cases, gouge exhibited dramatic slip weakening and siderite was decomposed into nanocrystalline magnetite and CO 2 gas, as confi rmed by CO 2 measurement, X-ray diffraction analyses, and transmission electron microscopy. The weakening was caused by the low frictional strength of ultrafi ne decomposition products at seismic slip rates. Magnetite formation during shearing changed gouge color to black and increased magnetic susceptibility by a few orders of magnitude. Those changes can be recognized in natural fault zones, and black gouge in the Chelungpu fault zone in Taiwan is perhaps such an example. Thus our results suggest that thermal decomposition in shallow crustal faults can be an important co-seismic process not only for dynamic fault weakening, but also for leaving seismic slip records.

We investigated stress change parameters during ruptures for earthquakes globally with M w ≥ 6.0 from 1991 to 2023. Employing a formulation and alternative graphical method, we analyzed variations between initial and final stresses as compared to frictional stress during rupture. Our goal was to assess the validity of Orowan's model (final stress equals frictional stress) across different environments, crucial for recurrent source studies. Our findings reveal significant deviations among event types: reverse-type events diverge slightly from Orowan's model, while normal events show even larger discrepancy. Strike-slip events exhibit a blend of stress difference mechanisms, with around 30% displaying overshoot (final stress smaller than average frictional stress). The partial stress drop (final stress larger than average frictional stress) percentage for reverse and normal types indicates that approximately 21-23% of the available stress for rupture was not relieved. Our results suggest that partial stress drop is a widespread phenomenon across all event types. This observation implies higher energy at higher frequencies than expected for an ω 2 frequency decay in the source spectra (Brune, 1976), potentially leading to underestimation of expected damaging accelerations. Our observations underscore the complexity of stress dynamics during earthquakes, with potential implications for energy release and damaging effects.

Advanced numerical modeling of high-strength concrete (f c >60 MPa) structures designed to withstand severe thermal conditions requires detailed and reliable information on the mechanical properties of the material exposed to elevated temperatures. The only uniaxial compressive strength variation with temperature is not enough to satisfy the large number of parameters often required by advanced nonlinear constitutive models. For this reason, a complete experimental investigation is required. The paper takes a commonly used high-strength concrete (f c ¼ 73 MPa) as an example to describe a comprehensive experimental approach instrumental to the parameter definition and calibration of common constitutive models for concrete. The present study not only studied the overall compressive and tensile behavior of the case study material, but also investigated the effect of elevated temperatures on the specific fracture energy and the evolution of internal damage, in residual conditions after a single thermal cycle at 200°C, 400°C, and 600°C.

A new cohesive zone model is developed in order to study the mechanisms of adhesive and cohesive failures of soft rubbery materials. The fracture energy is estimated here using a strategy similar to that of Lake and Thomas (LT) by considering the dissipation of stored elastic energy followed by the extension and relaxation of polymer chains. The current model, however, departs from that of LT in that the force needed to break an interfacial bond does not have a fixed value; instead, it depends on the thermal state of the system and the rate at which the force is transmitted to the bond. While the force required to rupture a chain is set by the rules of thermomechanically activated bond dissociation kinetics, extension of a polymer chain is modeled within both the linear and nonlinear models of chain elasticity. Closed form asymptotic solutions are obtained for the dependence of crack propagation speed on the energy release rate, which are valid in two regimes: (I) slow crack velocity or short relaxation time for bond dissociation; (II) fast crack velocity or long relaxation time for bond dissociation. The rate independent and the zero temperature limit of this theory correctly reduces to the fracture model of LT. Detailed comparisons are made with a previous work by Chaudhury et al. which carried out an approximate analysis of the same problem.

The strengths of epoxy/aluminum joints reinforced with a zirconium-silicon based sol-gel adhesion promoter were investigated using an ADCB (Asymmetric Double Cantilever Beam) wedge test. The fracture energies and loci of failure of these joints were shown to depend upon the mixity of the normal and shear modes of stress acting at the crack. The ADCB geometry enabled the crack to propagate along the epoxy/aluminum interfaces so that the effect of surface pretreatment and the processing conditions of the adhesion promoter on adhesion strength could be directly evaluated. The dry strength of these joints depends on the thickness of the sol-gel film derived from different concentrations of the precursors. Thinner films are more fully crosslinked and thus give higher adhesion strengths than those obtained with thicker films. The differences in the wet strengths of the sol-gel reinforced joints for various surface pretreatments suggest that the sol-gel films are subject to moisture degradation with certain surface pretreatments. The loci of failure of many of these joints alternate between the sol-gel/aluminum and epoxy/sol-gel interfaces. This behavior is similar to that observed more generally in adhesively-bonded joints tested in DCB (Double Cantilever Beam) geometry. The brittle versus ductile behavior associated with the failure process reveals important information about how the sol-gel films affect the adhesion strength.

Transverse cracking is a prevalent problem that occurs in asphalt pavement binders in cold climates and diminishes the integrity of the road as well as shortens the life span of the road leading to premature failure. Current specification for testing asphalt pavement binders for transverse cracking fails to accurately model the behavior of modified asphalt binders because it does not take into account the effects of physical hardening. Furthermore, current specification, which employs the use of the bending beam rheometer (BBR) and direct tension tests, was developed through the use of unmodified asphalt pavement binders and so it does not accurately model the behavior of modified asphalt pavement binders at colder temperatures. This study sought to come up with a new specification criterion for testing for transverse cracking as well as modeling the behavior of modified asphalt pavement binders at colder temperatures. This was achieved by the fracture energy method through the use of a single edge notched beam (SENB). The results showed that the fracture energy method proved to be an effective tool for modeling the behavior of modified asphalt pavement binders. However, when comparing the stiffness calculated from the SENB with that of the BBR we found that the stiffness in the SENB was much higher than that of the BBR. The increase in stiffness could very well be attributed to the differences in the way the samples are tested. Further research is necessary to come up with a way to compare the stiffness calculated from the SENB with that of the BBR before the fracture energy method can replace the BBR method.

The aim of this study is the characterization of the mechanical properties of typical masonry components in Portugal and the definition of mortar compositions, with direct implication to the National Annex of EC6. For masonry units the following were evaluated: the dimensions; water absorption and compressive strength. To assess mortar parameters such as, consistence, air content, compressive and flexural tensile strength, fracture energy and shrinkage, an analysis with various types of traditional and ready-to-use mortars was also performed. For several traditional mortars with different compositions and various strength classes, by varying the type of binder (cement, hydrated lime and hydraulic lime) and the type of sand (natural or artificial), it was possible to draw some conclusions about the parameters mentioned, such as: for the same strength class, the study compositions presented higher values of binder than the EC6 compositions and the shrinkage of cement mortars develops quicker than that of mixed mortars; for the same kind of sands there is a straight relationship between the maximum load applied and fracture energy. An experimental characterization of mechanical properties of masonry specimens was also made including flexural strength, compressive strength and Young's modulus.

This study compares high-speed bondtesting (shear and pull) with board level drop testing (BLDT) of BGA packages using Sn4.0%Ag0.5%Cu solder balls and either an ENIG or OSP package substrate surface finish. High-speed shear and pull testing were carried out at various speeds; failure modes were recorded, together with force and fracture energy data. In addition, detailed microscopic analysis (SEM and EDX) was executed on both complementary surfaces (ball and pad) of brittle fracture failures from both shear and pull test samples. The results of these studies showed close similarity to those from brittle fractures generated during BLDT of the same packages. Furthermore, there was strong correlation between various bondtesting parameters at which brittle fractures occurred and the number of drops to failure seen in BLDT. In summary, it is suggested that brittle fractures obtained in high-speed bondtesting are a strong indicator of BLDT behavior.

Six different AC-20 asphalt cements were used in a Pennsylvania project in September 1976. Two of the six test pavements developed low-temperature cracking in January 1977. The remaining four test pavements started to develop cracks to different degrees tier three years. This project has been well documented in the literature during its 7 years service life. Data such as theological properties of original and aged asphalt cements, hourly air and pavement temperature, and yearly crack surveys, have been reported. The samples of these six asphalt cements which were saved from 1976 to 1995 (19 years) have now been tested using Superpave binder test procedures such as bending beam rheometer (BBR). This research project was undertaken to verify whether these Superpave test procedures and specifications could have predicted the lowtemperature cracking of the six AC-20 asphalt cements in the Pennsylvania project. The maximum stiffness criteria of 300 MPa and the minimum m-value criteria of 0.30

The use of interfacial reactions to control the structure and shear strength of metal-ceramic interfaces was studied in the NiO-Pt system. Interfaces were formed by hot pressing together thin NiO single crystals and thick Pt polycrystalline films. Suitable choice of the annealing temperature, time and oxygen partial pressure allowed the introduction at the interface of a layer of either an intermetallic compound NiPt with thickness between 1 and 65 nm or a Ni-Pt solid solution. The shear strength of the NiO-Pt interface with and without the different interlayers present was measured by the periodic cracking method. Compared to its originally hot pressed state the shear strength of the NiO-Pt interface was increased by a factor of at least 4 by the presence of the NiPt and by ~ 10 by the solid solution. The use of interfacial reactions to control interfacial strength may also be applicable in other metal-ceramic systems where the metal and the cation form intermetallic compounds, and where the oxidation potentials of the metal and the cation are significantly different. Rrsumr---On 6tudie l'utilisation des rractions d'interfaces pour contr61er la structure et la rrsistance au cisaillement d'interfaces mrtal~,,rramique dans le systrme NiO-Pt. Les interfaces sont formres en comprimant ensemble fi chaud des monocristaux minces de NiO et des films polycrystallins 6pais de platine. Un choix convenable de la tempgrature et du temps de recuit, et de la pression partielle d'oxygrne permet l'introduction fi rinterface d'une couche du compos6 interm&allique NiPt avec une 6paisseur de 1 fi 65 nm, ou d'une solution solide Ni-Pt. La rrsistance au cisaillement de l'interface NiO-Pt avec et sans les diffrrentes intercouches prrsentes est mesurre par la mrthode de la fissuration prriodique. Comparge fi l'6tat original comprim6 ~i chaud, la rrsistance au cisaillement de l'interface NiO-Pt augmente d'un facteur au moins 6gal fi 4 par suite de la prrsence du NiPt et 6gal ~ ~ 10 par la prrsence de la solution solide. L'utilisation des rractions d'interface pour contrrler la rrsistance mrcanique interfaciale peut aussi 6tre appliqure fi d'autres systrmes m&al-c6ramique off le mrtal et le cation forment des composrs intermrtalliques et off les potentiels d'oxydation du m&al et du cation sont trrs diffrrents. Znsammenfassung--Die M6glichkeit, Graenzfl/ichenreaktionen zur Beeinflussung von Struktur und Scherfestigkeit metallkeramischer Grenzfl/ichen einzusetzen, wurde am NiO-Pt-System untersucht. Die Grenzfl/ichen wurden hergestellt durch gemeinsames HeiBpressen d/inner NiO-Einkristall-und dicker Pt-Polykristallfilme Geeignete Wahl yon Auslagerungstemperatur und -zeit und des Sauerstoff-Partialdruckes erm6glichten, in die Grenzfl/iche eine Schicht entweder einer intermetallischen Legierung NiPt, zwischen 1 und 65 nm dick, oder einen Ni-Pt-Mischkristall einzuffihren. Die Scherfestigkeit der Ni-Pt-Grenzfl/iche mit und ohne diese verschiedenen Zwischenschichten wurde mit der Methode des periodischen Brechens gemessen. Im Vergleich zum heil3gepreBten Ausgangszustand erh6ht sich die Scherfestigkeit der NiO-Pt-Grenzfl/iche um mindestens den Faktor 4 bei der NiPt-Schicht und um ~ 10 bei dem Mischkristall. Dieses Ausnutzen der Grenzfl/ichenreaktion k6nnte auch bei anderen Metall-Keramiksystemen anwendbar sein, bein denen das Metall und das Kation intermetallische Verbindungen bilden und bei denen die Oxidationspotentiale des Metalls und des Kations deutlich verschieden sind.

Glass microballoons (GMBs), which are hollow microspheres, were tested to obtain uniaxial compressive properties. Individual GMBs with diameters between approximately 5 and 90 lm were tested in compression using a nanoindentation instrument equipped with a flat ended sapphire tip. GMBs failed at loads ranging from 2.4 to 49.7 mN, and showed a direct relation between diameter and load to failure and between diameter and fracture energy.

To analyze a concrete structure according to fracture mechanics, its fracture parameters are needed to be determined at first. Many non-linear fracture models have been proposed by design codes and investigators to determine fracture parameters of concrete. These models can be classified as the cohesive crack models and the effective crack models. Although the notched beam specimens have been commonly used in concrete fracture, there have been some the advantages of the cubical/cylindrical specimens such as compactness and lightness. The notched splitting-cube specimens have only been investigated for the cohesive crack models, while the splitting-cylinder specimens have commonly been studied for the fracture approaches based on both the effective crack and the cohesive crack. In this study, the splitting-cube specimens were analyzed for fracture models based on the effective crack. To investigate how well the split-cube tests would simulate the fracture behavior of concrete, one series experimental study on cubical and beam specimens was performed. The test results were analyzed according to two most popular elastic crack models: two-parameter model and size effect model. The results of the split-cube tests look viable and very promising. Beton bir yapıyı kırılma mekaniğine göre analiz edebilmek için ilk önce kullanılan malzemenin kırılma parametrelerinin belirlenmesi gerekir. Betonun kırılma parametrelerini belirlemek için şartnameler ve araştırmacılar tarafından birçok lineer olmayan kırılma mekaniği modelleri önerilmektedir. Bu modeller kohezif ve eşdeğer elastik çatlak yaklaşımları olarak sınıflandırılmaktadır. Betonun kırılma mekaniğinde kiriş numuneler yaygın olarak kullanılmakla birlikte küp ve silindir numunelerin taşınabilirlik ve hafiflik açısından bazı avantajlara sahiptir. Bu çalışmada küp yarma deneyi kullanılarak eşdeğer elastik çatlak yaklaşımlarına göre (İki Parametreli Model ve Boyut Etkisi Modeli) betonun kırılma parametrelerinin nasıl tayin edileceği ve uygulama potansiyeli deneysel olarak tartışılmıştır. Beton ve betonarme yapıların göçme analizi için birçok lineer ve lineer olmayan yaklaşımlar kullanılmaktadır. Ancak özellikle sismik yüklemelere maruz beton/betonarme yapılarda göçme meydana gelmeden taşıyıcı sistemlerde yerelleşen çatlak veya çatlaklar oluşabilmekte brought to you by CORE View metadata, citation and similar papers at core.ac.uk

Beton ve betonarme yapılarda göçme analizi yapılırken birçok lineer ve lineer olmayan yaklaşımlar kullanılmaktadır. Betonarme bir yapıyı kırılma mekaniğine göre analiz edebilmek için ilk önce, kullanılan malzemenin kırılma parametrelerinin belirlenmesi gerekir. Betondaki neme ve zamana bağlı olarak mekanik sabitlerin değişmesi ve boyut etkisinden dolayı, Lineer Elastik Kırılma Mekaniği (LEKM), kırılma parametrelerinin tespitinde yetersiz kalmıştır. Bunun nedeni çatlağın ucunda yer alan diğer malzemelere göre daha büyük bir yer işgal eden kırılma süreci bölgesinin (KSB) var olmasıdır. Betonun kırılma parametrelerini belirlemek için şartnameler ve araştırmacılar tarafından birçok lineer olmayan kırılma mekaniği modelleri önerilmektedir. Bu lineer olmayan yaklaşımlardan boyutun dayanım üzerindeki etkisini inceleyerek betonda daha büyük bir KSB olduğunu öne sürmüş ve 'Boyut Etkisi Kanunu' geliştirmiştir. Betonun kırılma mekaniğinde kiriş numuneler yaygın olarak kullanılmakla birlikte, taşınabilirlik ve hafiflik açısından bazı avantajlara sahip olduğundan küp ve silindir numuneler son zamanlarda kullanılmaya başlanmıştır. Bununla birlikte karşılıklı basınç kuvveti uygulanan küp yarma testi ile ilgili deneysel ve teorik çalışmalar oldukça sınırlıdır. Sunulan bu çalışmada, su/çimento oranı 0.6 olan, maksimum agrega çapı 8 mm'lik kesikli ve sürekli granülometrili beton karışımları hazırlanmıştır. Aynı geometriye sahip farklı boyutlu (4:2:1) küp numuneler üzerinde boyut etkisi incelenmiştir. 50x50x50 mm 3 , 100x100x100 mm 3 , 200x200x200 mm 3 'lük küp numunelerin 28 günlük yarmada-çekme dayanımları belirlenmiş, elde edilen deney sonuçları Bazant'ın "Boyut Etkisi Kuralı"na göre analiz edilmiştir. Sonuç olarak kesikli granülometriye sahip betonların daha sünek davrandığı tespit edilmiştir.

To analyze a concrete structure using fracture mechanics, its fracture parameters need to be determined. Many nonlinear fracture models have been proposed in design codes and by investigators for use in determining fracture parameters of concrete. The two-parameter fracture model (TPM) requires two fracture parameters to describe fracture-dominated failure of concrete structures: the critical stress intensity factor, , and the critical crack tip opening displacement, CTODc. In this model, the fracture parameters are obtained from one of two experimental methods: the compliance method and the peak-load method of which the theoretical basis is to solve four simultaneous nonlinear equations. However, eccentric compression prisms, beams and notched split-tension specimens, namely, cubes, cylinders, diagonal cubes, holed cylinders have been used in the peak-load method based on the two-parameter fracture model. In this study, the peak-load method was initially applied to compact-tension ...

The results of He et al. (1995) for the Double Cleavage Drilled Compression (DCDC) specimen are extended to cover the case where both the hole and crack are offset from the centerline of the specimen. The effect of the thickness of an adhesive layer on the value of the energy release is also investigated. The applicability of the results to experimental studies is presented.

A Hookean material containing an increasing number of non-interacting microcracks is studied from the aspect of continuum thermodynamics. Rectilinear microcracks in a two-dimensional body are examined. The former model by Basista ( ) is enhanced to describe the response of microcracks to compression. Microcrack densities introduced here enter into the formulation of continuum thermodynamics as internal variables. The strong physical foundation of these internal variables makes them more attractive quantities for damage mechanics than variable damage, the physical background of which is sometimes unclear. The model is coded as an Abaqus VUMAT subroutine and applied to the creep of ice.

In this paper the numerical FEM model developed to simulate the behaviour of the NSM strengthening system for concrete elements is presented. The plane model introduces the non linear bond law of the system by an interface element between the composite reinforcement and the concrete considered linear. The results of two experimental programs are analysed and used to calibrate the parameters of the bond shear-slip relationship by means the numerical model. The procedure is based on the inverse analysis of the experimental data in order to have the better fitting of the global pull-out load-displacement curves.

Damage that might originate from climate fluctuations can be observed on decorated oak wooden panels in historical Dutch cabinets and panel paintings. A thorough analysis of the damage mechanisms is needed to obtain a comprehensive understanding of the causes of damage and to develop sustainable conservation strategies. For this purpose, the combined experimental and numerical characterisation of the fracture behaviour of historic and new oak wood is studied. Three point-bending tests are performed, and the measured failure responses and fracture paths are compared against results computed with a finite element model, in which discrete fracture behaviour is simulated with an interface damage model. The experimental and numerical results are in good agreement. The experiments show a quasi-brittle fracture response for the oldest samples and a more brittle fracture response for the new samples. In addition, the strength required for crack initiation along a radial-longitudinal fracture plane is higher than for a tangential-longitudinal fracture plane and the strength depends on the specimen size. Photographs and scanning electron microscopy photos illustrate that fibre bridging is more apparent for the oldest samples, and that the location of crack initiation is set by geometrical imperfections. Moreover, differences in density characterize the crack propagation path.

High temperature alloys and coatings rely on the formation of adherent scales to protect against further oxidation, but scale spallation is often problematic. Despite the technical importance of the problem, "practical adhesion", which refers to the separation of the oxide from the metal, has mainly been treated qualitatively in the past. Various techniques now exist such that the subject can be assessed in quantitative or semiquantitative terms. Some of the techniques are described in this paper, and their weakness and strength are discussed. The experimental methods addressed here include: ',tensile pulling, micro-indentation, scratch test, residual stress induced delamination, laser or shock wave induced spallation, double cantilever beam and several 4-point beam bending approaches. To date, there is not an universal, easy test for oxide adhesion measurement that can provide reproducible information on interfacial fracture energy for a variety of oxide/metal systems. Much experimentation is still needed to increase confidence in many of the existing tests, and the fundamental mechanics for some present techniques also require further development.

Holes with round or rectangular shapes in monolithic glued laminated timber (GLT) beams represent a frequent construction necessity. The holes disturb the stress flow within the beam, resulting in stress concentration areas at the periphery of the hole. The holes cause stresses perpendicular to the grain, previously not existing, but also shear and normal stress concentrations depending on the shape, size and placement of the opening. The basic mechanics of the load and stress redistribution in the orthotropic, or better said, cylindrical anisotropic material wood are well understood. This applies to the material resistance, too, which has to account for the stochastic defect distribution within the timber.