摘要:

Abstract—A theoretical development based on a simple physical model is proposed to help the designer predict high strain multi‐axial fatigue behaviour. This approach hypothesises that the maximum shear strain γ*, on planes driving the crack through the thickness, controls the fatigue crack propagation rate and hence the life. The direct strain δ*nacting normal to the plane of γ* can exert a secondary modifying influence. Experimental results from several research laboratories have been analysed in this manner with some s

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01101.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—A test facility has been developed in which a thin walled tube can be subjected to fully reversed fatigue cycles for all biaxial stress or strain ratios. Twin loop servo‐control allied to high resolution gauge length extensometry, load and pressure transducers permits stress or strain controlled testing. The rig is unique in that cyclic stress‐strain hysteresis loops can be obtained for both axial and circumferential directions during a test.Results from a strain controlled series of low cycle fatigue tests on a ferritic 1Cr‐Mo‐V steel obeyed the Manson‐Coffin relationship with the exponent being sensibly constant for all strain ratios. For a given maximum principal biaxial strain, the damaging effect increased as the strain ratio φ increased from –1 to +1. By comparing results from solid and hollow cylindrical specimens, geometry effects on fatigue life were revealed. Data on shakedown and cyclic softening under biaxial strain conditions were

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01102.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—Strain controlled continuous cycling fatigue tests are reported on three casts of Type 316 steel; the results obtained are shown to be consistent with published data.Strain controlled creep/fatigue tests are reported involving a hold period per cycle of between 0·2 and 168 h on one batch of Type 316 steel. An empirical extrapolation of the data and one involving a linear damage summation suggest that the existing Code Case N47 creep/fatigue design curve and rules are over‐conservative. A stress relaxation/fatigue endurance correlation shows some promise for predictive purposes. Although many of the mechanical test and metallurgical features observed are consistent with a fundamental crack growth extrapolation approach, further consideration of detailed aspects are necessary before it can be used with confidence. It is concluded that there are no entirely reliable methods of extrapolation currently available for Type 316 steel and longer term tests are therefore essential to reduce the extrapolation uncertain

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01103.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—The plastic work to propagate a fatigue crack by a unit area,U, measured by the foil strain gage technique requires an extrapolation to estimate the contribution closer than 100 μm to the crack tip. This is due to the size of the strain‐gages used, 200 × 210 μm. Conversely, the electron channeling technique for determiningUis useful mainly close to the crack tip where subgrains form. In the present workUwas measured by both techniques in the same low carbon steel at ΔK= 8 MN/m3/2. The contribution toUfrom closer than 100 μm of the crack tip was determined to be 1·7 × 106J/m2using electron channeling and 2·0 × 106J/m2by extrapolation. The measured contribution toUfrom further than 100 μm from the crack tip was 3·6 × 106J/m2giving 5·3 × 106J/m2forU.Thus, a large amount of energy is absorbed outside the region where sub‐grains form. The non‐hysteretic plastic work was found to be about four orders of magnitude smaller than the hysteretic plastic work, and may be neglected. A map of the plastic zone results from the strain‐gage measurement. Rice's theory predicts the measured plastic zone sizeif the proper material's strength is

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01104.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—Cyclic deformation behaviour of medium carbon steel, armco iron and copper has been investigated. A model based on the energy absorbed for the fracture process at the crack tip, given in the form (Δw*p)ywhere Δw*pis the hysteresis energy at the crack front and the exponentydecides the energy spent for the fracture process, is proposed for the crack growth in low cycle fatigue. The value of the exponentyhas been found to be around 0·26 to 0·28 for medium carbon steel and armco iron and around 0·52 for copper. These values ofygive good prediction of the relations between the total fracture energy and the stress amplitude and the total fracture energy versus the fatigue life. The energy based approach has been extended to predict the cumulative damage in a single step stress variation. Good correlation has been obtained between the experimental data and the theoretical pred

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01105.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

Abstract—Fatigue crack propagation tests were carried out in different environments on 7075–T6 and 2024–T3 centre‐cracked sheet specimens. Observations were made on the macroscopic transition from tensile mode to shear mode. The transition is suppressed by an aggressive environment, whereas it is promoted by an inert environment. As a consequence there is no unique correlation between the state of stress and the mode of cracking. Both the state of stress and the environment have a significant effect on the mode of cracking. A simple model for the effect of environment on fatigue crack growth is presented. The implications for crack growth under corrosion fatigue conditions are di

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1980.tb01106.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY