Academia.eduAcademia.edu

Figure 2 – uploaded by Dr. YOGESH Y. MAHAJAN

See full PDFdownloadDownload figure
Fig. 2 Appearance of spring fracture, Region I and II and diameter of the helical tension spring There were total three springs fractured, each into two parts. The wire diameter is measured and found to be as per the specification and also confirms to the Gr.III. Fig. 2 shows the fracture appearance of one spring with a wire diameter 2.8 mm. The upper and lower portions of the failed springs are analyzed separately. Visual examination of the spring samples under the stereoscopic microscope at 20X magnification revealed a brittle surface. In all the three spring samples fracture occurs,at the ends. The plane of fracture is from the maximum bending location. Also, the broken portions did not show any perceptible deformation in the region of cracking. Macroscopic investigation of normal spring supplied by the supplier doesn’t reveal any surface abnormality and confirms to specification.

Figure 2 Appearance of spring fracture, Region I and II and diameter of the helical tension spring There were total three springs fractured, each into two parts. The wire diameter is measured and found to be as per the specification and also confirms to the Gr.III. Fig. 2 shows the fracture appearance of one spring with a wire diameter 2.8 mm. The upper and lower portions of the failed springs are analyzed separately. Visual examination of the spring samples under the stereoscopic microscope at 20X magnification revealed a brittle surface. In all the three spring samples fracture occurs,at the ends. The plane of fracture is from the maximum bending location. Also, the broken portions did not show any perceptible deformation in the region of cracking. Macroscopic investigation of normal spring supplied by the supplier doesn’t reveal any surface abnormality and confirms to specification.

Related Figures (12)

Earlier failure analysis reports indicated the criticality of the hook design. A typical raw material defect is the existence of a foreign material inside the steel, such as non-metallic inclusions [4]. Surface defects, tool marks and other stress concentrations were found to be the main source of the failure of springs. in the spring body. Hook stresses can be reduced by using forming radii, not to exceed one-half the I.D. and by reducing the end coil diameter relative to the body coils. The hook stress in torsion should not exceed 40-45 percent of tensile strength, while hook stress in bending should not exceed 75% of tensile strength.
Earlier failure analysis reports indicated the criticality of the hook design. A typical raw material defect is the existence of a foreign material inside the steel, such as non-metallic inclusions [4]. Surface defects, tool marks and other stress concentrations were found to be the main source of the failure of springs. in the spring body. Hook stresses can be reduced by using forming radii, not to exceed one-half the I.D. and by reducing the end coil diameter relative to the body coils. The hook stress in torsion should not exceed 40-45 percent of tensile strength, while hook stress in bending should not exceed 75% of tensile strength.
Fig. 3 Optical microstructure of low carbon unalloyed helical tension spring wire
Fig. 3 Optical microstructure of low carbon unalloyed helical tension spring wire
Fig. 5 Appearance of the helical tension spring fracture in area I It indicates shear marks at different locations of upper portion of failed spring [5]. The fractures occurring in the tension spring are basically consistent with those opened artificially along the circumferential cracks. The fracture consists of two areas. Area Tis even fracture, near the spring inner surface, while Area II is quite rough and has large height difference, called slanted fracture as can be seen from the SEM images no. 4, 5, and 6. Area I of the fractures accounts for about 65% of the spring cross section.
Fig. 5 Appearance of the helical tension spring fracture in area I It indicates shear marks at different locations of upper portion of failed spring [5]. The fractures occurring in the tension spring are basically consistent with those opened artificially along the circumferential cracks. The fracture consists of two areas. Area Tis even fracture, near the spring inner surface, while Area II is quite rough and has large height difference, called slanted fracture as can be seen from the SEM images no. 4, 5, and 6. Area I of the fractures accounts for about 65% of the spring cross section.
Fig. 6 Appearance of the helical tension spring fracture in area II
Fig. 6 Appearance of the helical tension spring fracture in area II
Observation of the helical tension spring is conducted by scanning electron microscopy (SEM). A series of SEM images of upper and lower part of the tension spring were taken. Fig. no 7 and 8 shows the full morphology of upper and lower fractured surface of a tension spring, respectively. Very little indication of ductile behavior during failure as revealed from its SEM appearance as indicated in Fig. no. 7 and 8. Fig. 7 Fracture zone of the helical tension spring (Upper fractured portion/Hook side)
Observation of the helical tension spring is conducted by scanning electron microscopy (SEM). A series of SEM images of upper and lower part of the tension spring were taken. Fig. no 7 and 8 shows the full morphology of upper and lower fractured surface of a tension spring, respectively. Very little indication of ductile behavior during failure as revealed from its SEM appearance as indicated in Fig. no. 7 and 8. Fig. 7 Fracture zone of the helical tension spring (Upper fractured portion/Hook side)
Fig. 8 Fracture zone of the helical tension spring (Lower fractured portion)
Fig. 8 Fracture zone of the helical tension spring (Lower fractured portion)
Fig. 9 Surface irregularities on the outer surface of the helical tension spring (Upper fractured portion/Hook side)
Fig. 9 Surface irregularities on the outer surface of the helical tension spring (Upper fractured portion/Hook side)
Fig. 11 Fracture zone of the helical tension spring and direction of crack propagation The red marked area is further magnified in SEM images 12 and 13 (Upper fractured portion/Hook side) Fig. 10 Surface cracks on the outer surface of the helical tension spring near the fractured end (Lower fractured portion)
Fig. 11 Fracture zone of the helical tension spring and direction of crack propagation The red marked area is further magnified in SEM images 12 and 13 (Upper fractured portion/Hook side) Fig. 10 Surface cracks on the outer surface of the helical tension spring near the fractured end (Lower fractured portion)
Fig. 13 Crack Morphology in the helical tension spring at X350 (Upper fractured portion/Hook side)
Fig. 13 Crack Morphology in the helical tension spring at X350 (Upper fractured portion/Hook side)
Fig. 14 Effect of presence of surface crack on cross section of the helical tension spring
Fig. 14 Effect of presence of surface crack on cross section of the helical tension spring
Related topics:
Geology
580 California St., Suite 400
San Francisco, CA, 94104
© 2025 Academia. All rights reserved