Laura Vergani

Politecnico di Milano, Department of Mechanical Engineering, Faculty Member

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Fracture and damage analysis in design

Engineering Fracture Mechanics, 2012

is focussed on several topics, the common matrix being always the (experimental but also numerica... more is focussed on several topics, the common matrix being always the (experimental but also numerical and theoretical) analysis of the state of stress. The attendants to the Conference, which is annual, are always numerous: their works represent the state of art of the research in the topic of Stress Analysis in Italy. The Conference had different sessions, among these latter the ones related to fracture and damage attracted many authors and participants. A part of the papers presented in these sessions (by considering in particular the design application) was selected by the Scientific Committee of the Conference to be submitted for publication on this Special Issue and, after a peer review process that included many international referees, some of them are now published. We thank both the authors and the referees for their remarkable and patient work. The selected works cover both experimental and computational aspects, but are mainly devoted to the application of fracture and damage mechanics and of fatigue life prediction criteria to engineering practical application. This fact reflects very well the aim and the activity of the Association, which would like to consider the Universities competences and the industry technical problems. We hope that the papers selected will be of interest also for the readers of Engineering Fracture Mechanics. Last but not least, a special thank is due, once again, to Professor Karl-Heinz Schwalbe for giving us the opportunity to publish this Special Issue and for his patient and continuous help throughout this project.

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Experimental Determination of Ki, Kii, Kiii of Internal Cracks Under Rolling Contact Loading

The ever increasing research of performances and lightness leads engineers and manufacturers towa... more The ever increasing research of performances and lightness leads engineers and manufacturers toward the development of heavily loaded components, made of materials with improved surface mechanical properties, subjected to multiaxial fatigue loads. In these cases it is not rare the development of internal cracks, whose propagation involves mixedmode conditions; an accurate prediction of the growth rate and of the crack path requires the knowledge of the stress intensity factors concerning mode I, II and III. In this paper an original method for the experimental determination of these quantities is described. It is based on the photoelastic technique and allows to obtain internal cracks with regular shape without using any cutting device.

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Crumpling-based soft metamaterials: the effects of sheet pore size and porosity

Scientific Reports, 2017

Crumpled-based materials are relatively easy to fabricate and show robust mechanical properties f... more Crumpled-based materials are relatively easy to fabricate and show robust mechanical properties for practical applications, including meta-biomaterials design aimed for improved tissue regeneration. For such requests, however, the structure needs to be porous. We introduce a crumpled holey thin sheet as a robust bio-metamaterial and measure the mechanical response of a crumpled holey thin Mylar sheet as a function of the hole size and hole area fraction. We also study the formation of patterns of crease lines and ridges. The area fraction largely dominated the crumpling mechanism. We also show, the crumpling exponents slightly increases with increasing the hole area fraction and the total perimeter of the holes. Finally, hole edges were found to limit and guide the propagation of crease lines and ridges.

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Effect of Morphological and Clinical Parameters on Damage Accumulation in Porcine Trabecular Bone

This thesis is the result of many efforts that required the cooperation of several people who I w... more This thesis is the result of many efforts that required the cooperation of several people who I would like to thank. I am deeply grateful to Prof. Laura Vergani for giving me the opportunity to participate in this intriguing research. With her willingness and curiosity, she allowed me to finish this course of study in the best way imaginable. I would like to thank Eng. Mohammad Mirzaali for patiently guiding me in all stages of the work. I'm sincerely grateful to Eng. Luca Rinaudo and Prof. Fabio Ulivieri for their essential contribution to the success of this work. A sincere recognition goes to Prof. Michele Carboni and Eng. Stefania Cacace for the kindness they have shown me during the endless hours required to complete the tomographic analysis. I would also like to express my gratitude to Prof. Matteo Strano and to Prof. Bruno Cesana for their priceless help and for sharing their invaluable wisdom. Many thanks to Ph.D. Chiara Colombo and Ph.D. Flavia Libonati for their support. And finally, a double thanks to my friends and family who have supported and encouraged me during this five-year experience.

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High-cycle fatigue behaviour of a pultruded composite material used in structural applications

Dealing with composites in polymeric matrix, the pultruded ones are among the more suitable for l... more Dealing with composites in polymeric matrix, the pultruded ones are among the more suitable for large production rates and volumes. For this reason, their use is increasing also in structural applications in civil and mechanical engineering. However, their use is still limited by the partial knowledge of their fatigue behaviour; in many applications it is, indeed, required a duration of many millions of cycles, while most of the data that can be found in literature refer to a maximum number of cycles equal to 3 millions. In this paper a pultruded composite used for manufacturing structural beams is considered and its mechanical behaviour characterized by means of static and high-cycle fatigue tests. The results allowed to determine the S-N curve of the material and to assess the existence of a fatigue limit. Observations at the scanning electronic microscope (SEM) allowed to evaluate the damage mechanisms involved in the static and fatigue failure of the material. 1. Introduction Pu...

$Research paper thumbnail of Bone-inspired enhanced fracture toughness of de novo fiber reinforced composites$

Bone-inspired enhanced fracture toughness of de novo fiber reinforced composites

Scientific Reports, 2019

Amplification in toughness and balance with stiffness and strength are fundamental characteristic... more Amplification in toughness and balance with stiffness and strength are fundamental characteristics of biological structural composites, and a long sought-after objective for engineering design. Nature achieves these properties through a combination of multiscale key features. Yet, emulating all these features into synthetic de novo materials is rather challenging. Here, we fine-tune manual lamination, to implement a newly designed bone-inspired structure into fiber-reinforced composites. An integrated approach, combining numerical simulations, ad hoc manufacturing techniques, and testing, yields a novel composite with enhanced fracture toughness and balance with stiffness and strength, offering an optimal lightweight material solution with better performance than conventional materials such as metals and alloys. The results also show how the new design significantly boosts the fracture toughness compared to a classic laminated composite, made of the same building blocks, also offeri...

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Prediction of the Propagation of an Internal Crack under Rolling Contact Loads by a Weight Function Approach

Key Engineering Materials, 2003

... M. Guagliano, L. Vergani Dip.to di Meccanica, Politecnico di Milano Via la Masa, 34 - 20158... more

On the Fatigue Crack Growth Behavior of a Nitrided and Shot Peened Steel

Key Engineering Materials, 2007

In this paper the fatigue crack growth properties of a nitrided shot-peened steel is dealt with: ... more In this paper the fatigue crack growth properties of a nitrided shot-peened steel is dealt with: different peening intensities were considered and the resulting residual stresses measured by means of an X-ray diffractometer. Rotating bending fatigue tests were executed on specimens with a blind micro-hole, acting as a pre-existent crack. The results allowed determining the threshold of propagation of the nitrided and of nitrided and shot peened material. It was also possible to relate the crack initiation point with the applied and the residual stresses.

Hydrogen Effect on Fatigue Behavior of a Quenched&tempered Steel

Procedia Engineering, 2014

Fatigue Threshold of Nitrided and Shot Peened Specimens

Key Engineering Materials, 2006

Key Engineering Materials Vols. 324-325 (2006) pp 1321-1324 Online available since 2006/Nov/15 at... more

Design of an ankle prosthesis for swimming and walking

Procedia Engineering, 2011

This study presents a particular mechanical device for lower limb amputees, a prosthetic ankle, d... more This study presents a particular mechanical device for lower limb amputees, a prosthetic ankle, designed for swimming and partially for walking in two possible configurations. Experimental static tests are carried out for a compliance according to the standard, in the configuration for walking which is considered the most severe in terms of loading. In parallel, a numerical model is created and validated by a comparison to the experimental test in terms of displacements and strains. The validated FE model is then used for an optimization of the geometry and of the used materials, and to provide a further simulation for the configuration of swimming.

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A Weight-Functions Based Approach to Predict Rolling Contact Fatigue Sub-Surface Crack Propagation in Gears

Volume 4: 9th International Power Transmission and Gearing Conference, Parts A and B, 2003

The problem of the rolling contact fatigue crack propagation in gear teeth is dealt with. An appr... more

Study of an ankle prosthesis for children: adaptation of ISO 10328 and experimental tests

Procedia Engineering, 2011

Object of the present study is an ankle prosthesis for transtibial amputees, designed for childre... more Object of the present study is an ankle prosthesis for transtibial amputees, designed for children. Standards for prostheses compliance available in literature are all related to adults, while very few studies are present for children. In the first part of the paper a discussion on the modification of the standard in terms of loads and distances is presented, to adapt the available data to the test case, a boy of 12 years and 45 kg. In the second part, experimental results are shown, considering four different types of tests: static proof and ultimate tests, fatigue tests and static torsion tests. Results were positive for the designed and tested ankle prosthesis.

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ICM11 Foreword

Procedia Engineering, 2011

From ancient times, the mechanical behavior of materials has been one of the most important facto... more From ancient times, the mechanical behavior of materials has been one of the most important factor for social and economic development and progress of people and countries. This justifies the ever increasing interest to improve our knowledge about the way the materials support mechanical loads and to develop new treatments and materials for engineering applications. But it is from the Industrial Revolution that the characterization of the mechanical behavior of materials became a key factor of development: the possibility to design products more and more sophisticated and daring systems with ever increasing performances leads scientists and engineers both to study in depth the mechanisms of damage and to formulate more accurate design approaches and also to develop new materials with improved mechanical characteristics, suited for tailored applications. Among all the contributions in this field, we like to remember Giulio Natta professor at Politecnico di Milano and Nobel Prize in 1963for having discovered how to obtain the isotactile polypropylene, now a part of everyday life. In this framework of continuous development, the need of cooperation between academics, researchers and engineers is ever more important. Indeed, it is from the beginning of the Seventies of the last century that the International Conference on the Mechanical Behavior of Materials (ICM) is playing an important role in promoting and fostering research on the mechanical behavior of materials, to facilitate related international cooperation among scientists and engineers and to provide means for the public dissemination of the results from these efforts. These conferences are intended to cover progress on all aspects of the mechanical behavior of materials from both the macroscopic and microscopic viewpoints. The ICM holds international conferences every four years and the first one was held in

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Effect of nitriding on low-cycle fatigue properties

International Journal of Fatigue, 1997

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A Simplified Approach to Crack Growth Prediction in a Crankshaft

Fatigue & Fracture of Engineering Materials & Structures, 2007

Fracture mechanics analyses are carried out on a cracked machine element of complex geometry to p... more Fracture mechanics analyses are carried out on a cracked machine element of complex geometry to predict its fatigue behaviour. Usually, in order to obtain reliable values of stress intensity factors, it is necessary to realize three-dimensional meshes or to utilize the energy approach. An alternative, simplified and approximate approach is proposed here. It is based on the construction of simple twodimensional models to obtain accurate values of the geometry factors of the component at the deepest point of the crack. Experimental tests show that the relation between the depth and the length of the crack on the free surface is linear. Hence it is possible to reduce the problem to two dimensions with a consequent saving of calculation time. A comparison with experimental data indicates that a satisfactory prediction is obtained by the proposed method. NOMENCLATURE a = crack length c = surface crack depth I, 11, I11 = modes of fracture K = stress intensity factor K,, = effective stress intensity factor C , n = coefficient and exponent of the Paris law G = strain energy release rate / 3 = shape factor u, v = displacements normal and parallel to crack direction n, b = normal and binormal vectors E = Young's modulus v = Poisson's ratio

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Experimental and numerical analysis of sub-surface cracks in railway wheels

Engineering Fracture Mechanics, 2005

Shelling is the term used to describe the loss of part of the tread of a railway wheel as the res... more Shelling is the term used to describe the loss of part of the tread of a railway wheel as the result of the initiation and growth of a fatigue crack from an internal defect in the rim. Shelling makes the wheel unserviceable and to prevent it, railway wheels are periodically subjected to non-destructive testing. However in order to assess the

Sub-surface crack propagation analysis in hypoid gears

Engineering Fracture Mechanics, 2008

This paper proposes a numerical approach devoted to the investigation of the sub-surface crack pr... more This paper proposes a numerical approach devoted to the investigation of the sub-surface crack propagation mechanism in gear pairs having crossing axis (i.e. hypoid gears). Starting from an accurate 3D description of the complex gear tooth geometry, a numerical analysis carried out by means of an advanced contact solver allows obtaining, over the entire meshing cycle, the contact pressure distribution

An approach for prediction of fatigue strength of shot peened components

Engineering Fracture Mechanics, 2004

In this paper the problem of predicting and optimising the fatigue strength of shot peened specim... more In this paper the problem of predicting and optimising the fatigue strength of shot peened specimens is dealt with. A series of notched cylindrical specimens, peened by using different parameters, was fatigue tested, being the aim to determine the improvement of the fatigue limit of the treated specimens. After the tests, the specimens were observed at the SE microscope and

Damage assessment of composite materials by means of thermographic analyses

Composites Part B: Engineering, 2013

Composite materials are widely used for structural applications, thanks to their excellent mechan... more Composite materials are widely used for structural applications, thanks to their excellent mechanical properties combined with a low material density. It is difficult to perform a complete characterisation of these materials, due to the influence of several factors on their mechanical behaviour. Generally, the mechanical characteristics of composites are influenced by the manufacturing process parameters (i.e. curing time-temperature) and the experimental parameters (i.e. specimen shape, the use of tabs for testing, the test velocity, and the loading conditions). These materials show different failure mechanisms (i.e. interfacial debonding, delamination, fibre rupture, matrix cracking), which depend on the type and direction of the applied load. In this study, an E-glass/vinylester pultruded material is mechanically characterised by means of static tests, performed on specimens with different fibre orientations. Thermal analyses are also performed, by means of a Thermal imaging camera (FLIR Thermacam SC 3000), to determine the static damage parameters (i.e. Temperature). Thermal maps of the damaged area, evaluated from the experimental data, are used to get information related to the damage evolution and the failure mode. The aim of this work is the evaluation of composites damage under static loading conditions, by using the thermographic method.

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