Fatigue Life Design of Mechanical Structure期末答案2023秋

1. Plane strain fracture toughness is 对 material property and regardless of thickness. （ ）
A:对 B:错
答案:错
2. Twice the value of plastic stress is regardless of the plastic relaxation. （ ）
A:正确 B:错误
答案:错误
3. A larger fraction of life for crack growth occurs at lower stress levels. （ ）
A:错误 B:正确
答案:正确
4. Stress ratio of -1 means fully reversed load . （ ）
A:正确 B:错误
答案:错误
5. Fine-grain materials tend to give lower fatigue resistance, while coarse-grain materials give higher creep resistance. （ ）
A:正确 B:错误
答案:正确
6. A crystallite is a small or even microscopic crystal which forms. （ ）
A:错 B:对
答案:对
7. The deformation of the material at the notch root is often inelastic involving plastic strain. （ ）
A:错 B:对
答案:对
8. Plane strain fracture toughness is 对 material property and regardless of thickness. （ ）
A:对 B:错
答案:错
9. Twice the value of plastic stress is regardless of the plastic relaxation. （ ）
A:错误 B:正确
答案:错误
10. A larger fraction of life for crack growth occurs at lower stress levels. （ ）
A:正确 B:错误
答案:正确
11. Stress ratio of -1 means fully reversed load . （ ）
A:错误 B:正确

12. Fine-grain materials tend to give lower fatigue resistance, while coarse-grain materials give higher creep resistance. （ ）
A:错误 B:正确 13. A crystallite is a small or even microscopic crystal which forms. （ ）
A:错 B:对 14. The deformation of the material at the notch root is often inelastic involving plastic strain. （ ）
A:错 B:对 15. The keywords of fatigue do not include （ ）
A:Cyclic loading B:Deformation C:Progressive D:Crack 16. Damage tolerance design is （ ）
A:Anti-crack measures B:Nominal stress C:Crack cannot occur D:Nominal strain 17. Fatigue behavior and life predictions are more complicated at high temperatures because of （ ）
A:Creep deformation B:Time-dependent process C:Cycle-dependent process D:Complex interaction between creep and fatigue 18. The feature of excess deformation does not include （ ）
A:Plasticity B:The most common failure mode C:Maximum tensile stress criterion D:Yielding 19. Fine grain size in room temperature usually means （ ）
A:Low fatigue strength B:Higher fatigue strength C:Short fatigue life D:High crack growth rate 20. The feature of impact or dynamic loading does not include （ ）
A:Fracture B:Lower tensile toughness/ ductile C:Short time/ period D:High strain rate 21. Non-detective inspection techniques include （ ）
A:Drilling a hole B:Ultrasonic testing C:Fatigue testing D:Microscope observation 22. A mean stress may relax fully or partially due to （ ）
A:Plastic deformation B:Environment C:Surface condition D:Residual stress 23. Which is the feature of small crack （ ）
A:Constant threshold value B:Discontinuity C:Regardless of crack size D:Naked-eye visible 24. The number of beach marks is related to （ ）
A:Surface condition B:Defect C:Environment D:Slip 25. The concepts of linear elastic fracture mechanics (LEFM) for crack growth include （ ）
A:Initial crack size B:Stress intensity factor C:Stress concentration D:Stain 26. The following mechanical properties are usually obtained from monotonic tension test（ ）
A:Percent reduction in area B:Modulus of elasticity C:Fatigue limit D:Ultimate tensile strength 27. For Infinite-life design, the correct statement is as follows （ ）
A:Especially for notched members B:The oldest criterion C:Mason-Coffin model D:Fatigue limit is difficult to define 28. Understanding of fracture toughness include （ ）
A:Depends on material, strain rate, environment, thickness and crack length B:Critical value of K C:K at the last cycle of a fatigue fracture D:Used to obtain the critical crack size for fracture 29. The S-N behavior can be affected by many factors （ ）
A:Frequency B:Surface condition C:Size effect D:Microstructure 30. Understanding of strain approach includes （ ）
A:Strain approach is very suitable for fatigue of notched members. B:The strain-based approach to fatigue problems is widely used. C:Strain has a good quantity for correlating with low cycle fatigue. D:Strain is hardly measured. 31. The reason about fatigue failure usually occurring on the surface （ ）
A:Inelastic deformation is easier at the surface B:Surface condition is smooth C:Slip steps are able to develop on the surface D:The stress or strain on the surface is usually maximum 32. The characteristics of fatigue include （ ）
A:Monotonic tension B:Constant or variable amplitude C:Repeated loading D:Crack nucleation/growth 33. Cyclic stabilization is usually reasonably complete within 10 to 40 percent of the total life. （ ）
A:错 B:对 34. Higher frequencies typically allow more environmental interaction to occur. （ ）
A:错 B:对 35. Stress relaxation is the same as the cyclic softening. （ ）
A:错 B:对 36. Most materials exhibit an decrease in fatigue resistance with increasing temperature. （ ）
A:对 B:错 37. Crack growth rates are initially high but decrease, with the decreasing crack length. （ ）
A:对 B:错 38. Only the plastic portion of the strain-life curve is modified to account for the surface finish effects. （ ）
A:错 B:对 39.The mechanism of crack initiation in the very high cycle region has been roughly understood. （ ）
A:对 B:错 40. The characteristics of ductile fracture include （ ）
A:Low strength/ high ductile metals B:Micro-void coalescence (dimpling) C:Substantial plasticity D:High energy absorption 41. Some necessary points about the estimation of crack growth life with mean stress must be again noted （ ）
A:What value of ΔK will cause fracture? B:Does corrosion or temperature play an important role? C:How do we integrate this equation? D:Which crack growth rate equation should be used? 42. The characteristics of ductile fracture include （ ）
A:Micro-void coalescence (dimpling) B:High energy absorption C:Substantial plasticity D:Low strength/ high ductile metals 43. Some necessary points about the estimation of crack growth life with mean stress must be again noted （ ）
A:Which crack growth rate equation should be used? B:Does corrosion or temperature play an important role? C:How do we integrate this equation? D:What value of ΔK will cause fracture? 44. The elastic stress concentration factors are often obtained by （ ）
A:Fracture surface observation B:Fatigue test C:Strain - life D:Finite element method 45. The hysteresis loops at high temperatures are （ ）
A:Discontinuous B:Easy C:Constant D:Regular 46. The elastic stress concentration factors are often obtained by （ ）
A:Fatigue test B:Fracture surface observation C:Strain - life D:Finite element method 47. The hysteresis loops at high temperatures are （ ）
A:Constant B:Regular C:Discontinuous D:Easy