Effects of loading rate and temperature on cracking resistance in steel

A study has been made on the effects of loading rate and temperature on cracking resistance in steels. A method has been devised for estimating the carrying capacity of a steel structure under actual working conditions. Test data and published evidence give general temperature-dependence curves for the cracking resistance in static and dynamic loading, and a criterion for the carrying capacity is devised.Translated from Problemy Prochnosti, No. 7, pp. 30–33, July, 1992.     

Effects of temperature on the bending strength and static cracking resistance in specimens of abrasive material

Conclusion Smooth specimens with rectangular cross sections and specimens with such cross sections and notches of radius 0.1–0.2 mm have been used in three-point bending to examine the effects of temperature on the bending strength _b and the static cracking resistance K_Ic. The specimens were made from silicon carbide with one of three binders: epoxide, epoxide-phenol, and bakelite ones. As the temperature increased towards the critical valuet _c, those characteristics altered little, but abovet _c, _b and K_Ic decreased considerably. Specimens with the epoxide binder hadt _c1 = 85°C, while the epoxide-phenol ones hadt _c2 = 110°C, and the bakélite ones hadt _c3 = 200°C.Translated from Fiziko-khimicheskaya Mekhanika Materialov, Vol. 27, No. 1, pp. 88–91, January–February, 1991.     

Effect of plasma cutting on the fatigue and cracking resistance of steel

The results are presented of detailed examination of the effect of plasma cutting on the fatigue and cracking resistance of 14KhGNMDAFBRT steel.The thermal effect of the plasma arc increases the endurance limit of the hardened surface and heat-affected zone in comparison with the initial nonhardened material. The crack growth rate does not change.Translated from Problemy Prochnosti, No. 12, pp. 23–25, December, 1990.     

Effect of vacuum plasma surface treatment on the titanium alloy resistance to static and cyclic loading

We present the results of the experimental investigations on the static and cyclic strength of titanium alloy VT20 with a TiN vacuum plasma coating. This coating has been found to increase the static strength characteristics and to reduce the plasticity characteristics. Under conditions of low-cycle loading, the coating application results in the improvement in the cyclic strength characteristics in quasistatic fracture and in their deterioration in fatigue fracture. __________ Translated from Problemy Prochnosti, No. 1, pp. 100–106, January–February, 2007.     

Loading rate effects on cracking behavior of flaw-contained specimens under uniaxial compression

To investigate the loading rate effects on the cracking processes of flaw-contained specimens under compressive loading, rectangular parallelepiped specimens containing centrally located single and double flaw(s) are numerically loaded using the bonded-particle model (BPM). The study reveals that the uniaxial compressive stress ( $\upsigma _\mathrm{c})$ and coalescence stress ( $\upsigma _\mathrm{cc})$ increase significantly, while the first crack initiation stress ( $\upsigma _\mathrm{ci})$ only subtly increases with the increase of loading rate. The trajectories of the first and secondary cracks become shorter while the amount of discrete micro-cracks increases as the loading rate increases. The mode of coalescence cracks changes from tensile-segments-dominant to shear-band-dominant when the loading rate increases. The shape of the stress-strain curves of specimens loaded at different rates also varies. Based on the present study, an upper limit of loading rate of 0.08 m/s deems to be acceptable for cracking processes analysis under static load using the BPM.     

Effect of loading rate on the failure resistance of economically alloyed steels at low temperatures

Results are presented for an experimental study of the effect of cooling to 77 K on the dynamic crack resistance and impact strength of steels ON9 and 07Kh13N4AG20. Features are noted for the change in failure resistance of these metals in the temperature range 293-77 K with an increase in loading rate to 1.5 m/sec. It is established that crack resistance characteristics of the test steels are somewhat higher in the case of dynamic loading than with static loading, but impact strength of the materials decreases with cooling.Translated from Problemy Prochnosti, No. 10, pp. 43–46, October, 1990.     

Crack resistance of structural steels under static and cyclic loading

The article deals with the investigation of static and fatigue crack resistance of normalized steels 40Kh and 30KhGSA, and also of steel 40Kh after hardening and tempering at 500°C with the object of working out recommendations for the use of normalized steel 40Kh for making axles of tractor trailers produced at the Chelyabinsk Engineering Works. The article presents the results of static tests of cylindrical specimens with annular cracks under conditions of axial tension which showed that the crack resistance K_1C of heat-treated steel 40Kh is up to 20% higher than after normalization. The crack resistance K_1C of normalized steel 30KhGSA has intermediate values. We carried out fatigue tests of the above-mentioned steels by concentrated bending, and from the results we plotted kinetic diagrams of fatigue failure and determined the threshold values of the characteristics of fatigue crack resistance K_th and K_fc which confirmed the data of the static tests. It was established that normalized steel 40Kh can be recommended as material of axles for tractor trailers with a load capacity of up to 10 tons for which the safety factor K_s is at least 2–2.5.Translated from Problemy Prochnosti, No. 7, pp. 28–31, July, 1990.     

Effects of nonlinear viscoelastic behaviour and loading rate on transverse cracking in CFRP laminates

The progressive multiplication of matrix transverse cracks in cross-ply laminates made of long carbon fibre reinforced polymer (CFRP) is addressed in this study. Monotonic tensile tests performed on [0₃/90₃]_S laminates at 120 °C have shown a marked dependence of cracking development on loading rate. This paper aims to assess the impact of the material nonlinearity on the loading rate sensitivity of the damaging process. A “shear-lag” damage analysis, using the nonlinear correspondence principle and appropriate failure criteria, is carried out to numerically predict the cracking evolution. This work shows that, though important, the material nonlinearity of the undamaged material does not significantly enhance the loading rate sensitivity of the cracking process and it cannot explain alone the phenomenon. On the other hand, taking into account the loading rate dependence of the critical strength, together with the R-curve effect, which gives good predicted cracking curves, suggests that the observed rate effect pertains to the viscoelastic character of the damaged material in the process zone close to crack fronts.