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Book Review
Fatigue Crack Growth under Variable Amplitude LoadingProceedings of the Third International Spring Meeting of the French Metallurgical Society held in Paris, France, June 1988. Edited by J. Petit, D.L.Davidson, S. Suresh, and P.Rabbe. Elsevier Applied Science, London (1988) 397 pp., $45.00 相似文献2.
Fatigue and fatigue-creep crack growth rate in a bimetal of continuous caster rolls for different loading frequencies and
waveforms is investigated with the use of stress, deformation and energy criteria of fracture mechanics. 相似文献
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Near-threshold fatigue crack propagation behaviour of a cold-worked copper tested with distinct fa-tigue testing systems under different stress ratios has been investigated.The emphasis was placed onthe evaluation of crack closure effect as well as the effective fatigue threshold,It was found that thefatigue threshold for R=0 is higher than those for R=-1 and R=0.4,for which almost the samethreshold value was derived.Compared with the conventional closure evaluation method,the pro-posed new closure evaluation method can generally interpret the dependence of the fatigue thresh-old on stress ratio and loading condition,and leads to a higher and relatively constant effective fa-tigue threshold of about 3 MPa·m~(1/2) for the cold-worked copper at different stress ratios andloading conditions. 相似文献
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Strength of Materials - The short fatigue short crack replica tests using LZ50 axle steel hourglass-shaped specimens of were carried out under rotating-bending cyclic load. Seven sets of effective... 相似文献
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The acoustic emission(AE)characteristicsfrom the fatigue crack propagation in SM50B-Zcsteel were strongly affected by the environment me-dium.The AE feature from the fatigue process bothin air and in 3.5% NaCl aqueous solution mani-fested a periodicity which indicated the fatigue ex-tension was discontinuous.The fatigue striationand secondary cracking were the main AE sourcesduring the fatigue crack growth in air.In contrast,AE during the fatigue crack propagation in 3.5%NaCl solution was released from the intergranularfracture and quasicleavage cracking. 相似文献
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Using thin walled cylindrical specimens subjected cyclic tension and torsion, fatigue crack growth tests under combined stress conditions were carried out. The characteristics of the fatigue crack growth rate (FCGR) and morphology of the fatigue crack were identified.By comparing the experimental results with the results of finite element analyses, it was found that the experimental characteristics of FCGR were related to fatigue damage accumulation before initial crack growth. Damage mechanics approach is indispensable to characterize the fatigue crack growth under combined stress conditions. 相似文献
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Creep crack growth characteristics under various combined mode I and mode II loadings were studied using the compact tension shear (CTS) specimens of polyethylene. Creep crack growth rates da/dtunder combined mode I and mode II loading can be correlated with a single effective stress intensity factor K
Ieffderived from the combined — mode fracture toughness envelope. The steady state or constant crack growth rates which occupy the significant part of creep failure life increase with the increasing initial effective stress intensity factor. 相似文献
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在630℃下,对P92钢进行应力控制下的蠕变-疲劳交互作用实验,研究P92钢高温蠕变-疲劳交互作用下的裂纹扩展行为,并结合断口形貌分析蠕变-疲劳裂纹扩展的机理以及a-N曲线的转折点含义。结果表明:P92钢在蠕变-疲劳交互作用下的断裂属于蠕变韧性断裂,应该用(C_t)_(avg)作为裂纹扩展的断裂参量;P92钢在蠕变-疲劳交互条件下,试样的断口主要表现为蠕变孔洞以及微裂纹。此外,发现a-lg(N_i/N_f)曲线以及(da-dN)-N曲线中的拐点,分别对应蠕变-疲劳裂纹萌生区向扩展区转变周次以及扩展区向瞬断区转变的周次。 相似文献
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Fracture toughness and creep crack growth characteristics under combined mode I and II loadings were studied using the compact
tension shear (CTS) specimens of polypropylene. The K
I
- K
II
envelope for crack initiation was obtained under various combined mode loadings. The creep crack growth rates da/dt under combined mode I and mode II loadings can be correlated with a single effective stress intensity factor K
Ieff
based on the combined mode fracture envelope. 相似文献
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High temperature fatigue in nickel‐base superalloys for aero‐engine applications requires consideration of cycle‐ and time‐dependent phenomena. For waveforms with dwells and/or low frequencies crack growth rates may be significantly accelerated up to the point of fully time‐dependent crack growth. In the paper, the interaction of fatigue (cycle‐dependent) and dwell (time‐dependent) crack growth is addressed using a broad database for IN 718 tested at 600°C. Waveforms with dwells at as well as below maximum load levels are applied to standard CT and CC specimens and blunt notched specimens. It is demonstrated that both the level of dwells with respect to the maximum load level within a cycle as well as the specific conditions at the notch root considerably affect the significance of dwells for fatigue crack growth. 相似文献
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The axle of a load train failed after 5.37?×?106 cycles from its service. Macro-fractography showed clearly the fatigue fracture. The stress distribution in the shaft revealed that the maximum alternating stress was considerably less than the material modified fatigue limit obtained at 107 cycles from the S?CN diagram. Micro-fractography reported from the metallurgical laboratory proved the existence of a surface flaw. Ultimately, fatigue crack growth simulation was performed based on the simple Paris?CErdogan model for estimating the fatigue life of the defective axle. The results showed that the actual life of the axle could be satisfactorily predicted by means of the Paris?CErdogan model. 相似文献
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This paper proposes a nonlinear dynamic model of fatigue crack growth in the state-space setting based on the crack closure
concept under cyclic stress excitation of variable amplitude and random loading. The model state variables are the crack length
and the crack opening stress. The state-space model is capable of capturing the effects of stress overload and underload on
crack retardation and acceleration, and the model predictions are in fair agreement with experimental data on the 7075-T6
aluminum alloy. Furthermore, the state-space model recursively computes the crack opening stress via a simple functional relationship
and does not require a stacked array of peaks and valleys of stress history for its execution; therefore, savings in both
computation time and memory requirement are significant. As such, the state space model is suitable for real-time damage monitoring
and control in operating machinery.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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In order to design structural components using composite materials a deep understanding of the material behaviour and its
failure mechanisms is necessary. To create a better understanding of the initiation, growth and interaction of the different
types of damage, damage monitoring during mechanical loading is very important. To this direction, AE is a powerful non destructive
technique for real time monitoring of damage development in materials and structures which has been used successfully for
the identification of damage mechanisms in composite structures under quasi static and dynamic-cycle loading. In this present
work, pure resin plate and GFRP composite laminates with stacking sequence of [00]6, are fabricated using Hand lay-up method. During the layup a Teflon tape of width 45 mm is kept in the mid plane of the laminate
which serves as an initiator for delamination during loading. As per ASTM STD D5528 01 DCB (Double Cantilever Beam) specimens
are cut out from the laminates and are subjected to tensile test in the transverse direction along with acoustic emission
monitoring. While loading, Markings are made on the sides of the specimen to track the crack front using a magnifying lens.
Parametric analysis is performed on the AE data obtained during crack propagation to discriminate the failure modes. Fast
Fourier Transform (FFT) enabled the calculation of frequency content of each damage mechanism. Further STFFT analysis is performed
on a portion of the waveforms representing the dominant frequency content pertaining to each damage mechanism. 相似文献