tailieunhanh - Standard Handbook of Machine Design P15

CHAPTER 12 STRENGTH UNDER STATIC CIRCUMSTANCES Charles R. Mischke, ., RE. Professor Emeritus of Mechanical Engineering Iowa State University Ames, Iowa Joseph E. Shigley Professor Emeritus The University of Michigan Ann Arbor, Michigan PERMISSIBLE STRESSES AND STRAINS / THEORY OF STATIC FAILURE / STRESS CONCENTRATION / FRACTURE MECHANICS / NONFERROUS METALS / STOCHASTIC CONSIDERATIONS / REFERENCES / GLOSSARY OF SYMBOLS a A D, d F I / K K' KC Kt Kts M n qs Crack semilength Area Diameter Force or load Second moment of area Second polar moment of area. | CHAPTER 12_ STRENGTH UNDER STATIC CIRCUMSTANCES Charles R. Mischke . RE. Professor Emeritus of Mechanical Engineering Iowa State University Ames Iowa Joseph E. Shigley Professor Emeritus The University of Michigan Ann Arbor Michigan PERMISSIBLE STRESSES AND STRAINS THEORY OF STATIC FAILURE STRESS CONCENTRATION I FRACTURE MECHANICS NONFERROUS METALS I W STOCHASTIC CONSIDERATIONS REFERENCES GLOSSAR Y OF SYMBOLS a Crack semilength A Area D d Diameter F Force or load I Second moment of area J Second polar moment of area K Stress-intensity factor K Stress-concentration factor for static loading Kc Critical-stress-intensity factor K Normal-stress-concentration factor Kts Shear-stress-concentration factor M Moment n Design factor qs Sensitivity index STANDARD HANDBOOK OF MACHINE DESIGN r Radius or ratio Ssy Yield strength in shear Ultimate compressive strength Su Ultimate tensile strength Sy Yield strength T Factor of safety o Normal stress o von Mises stress x Shear stress xo Octahedral shear stress or nominal shear stress PERMISSIBLE STRESSES AND STRAINS The discovery of the relationship between stress and strain during elastic and plastic deformation allows interpretation either as a stress problem or as a strain problem. Imposed conditions on machine elements are more often loads than deformations and so the usual focus is on stress rather than strain. Consequently when durability under static conditions is addressed attention to permissible stress is more common than attention to permissible strain. Permissible stress levels are established by Experience with successful machine elements Laboratory simulations of field conditions Corporate experience manifested as a design-manual edict Codes standards and state of the art During the design process permissible stress levels are established by dividing the significant strength by a design factor n. The design factor represents the