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The crack growth behavior in 2324-T39 aluminium alloy was experimentally investigated. Two types of crack branching were observed. The mechanism of an uncommon crack branching which results from the link up of secondary crack with the main crack was focused on. The crack paths were observed with optical microscope and in-situ SEM. Finite element crack tip simulation was performed to investigate the relationship between plastic zone size and the location of the secondary crack. Tests and analysis results indicate that the secondary crack initiates near the plastic zone boundary and from the subsurface. The mechanism of this kind crack branching relates to the interaction of grain size and plastic zone size.

The crack growth behavior in 2324-T39 aluminium alloy was experimentally investigated. Two types of crack branching were observed. The mechanism of an uncommon crack branching which results from the link up of secondary crack with the main crack was focused on. The crack paths were observed with optical microscope and in-situ SEM. Finite element crack tip simulation was performed to investigate the relationship between plastic zone size and the location of the secondary crack. Tests and analysis results indicate that the secondary crack initiates near the plastic zone boundary and from the subsurface. The mechanism of this kind crack branching relates to the interaction of grain size and plastic zone size.

A stress‐based sectional critical plane model is proposed to predict fatigue life under multiaxial constant amplitude loading. The proposed model considers the effects of material properties and loading paths including stress amplitude ratio, phase angle and mean stress. By introducing the ratio of maximum shear stress amplitude to maximum normal stress amplitude, the crack behaviour can be predicted and the critical planes can be divided into three sections: the maximum normal stress plane, maximum damage plane and maximum shear stress amplitude plane. To verify the accuracy and applicability of the proposed model, experimental data of 30CrMnSiA steel conducted by the authors and other test data of different materials from the existing literatures are utilized. The prediction results demonstrate that the proposed sectional critical plane model shows strong applicability for steel, aluminium and titanium alloy materials, especially under the multiaxial loadings with mean stresses. For steel materials, the prediction results of the proposed model are better than the commonly used criteria. [ABSTRACT FROM AUTHOR]

A new material degradation model only with fundamental material properties required is proposed for composite progressive damage analysis based on micromechanics. For different failure modes, the effects of fiber and/or matrix damage on the composite material properties are explored, from which the material degradation factors for these failure modes are deduced. The material degradation model is then implemented for progressive damage analyses, using user subroutines in the commercial code ABAQUS®, accompanying with a modified Hashin type failure criterion and finite element models for six commonly used double-lap composite bolted joints with various layups, geometry dimensions, and fasteners. The numerical predictions of failure loads, failure patterns, and load–displacement curves are compared with results obtained from static tests and further ultrasonic C-scan detection. Good agreements between numerical failure predictions and experimental outcomes indicate the effectiveness and suitability of the proposed model for progressive damage analyses of composite bolted joints. [ABSTRACT FROM AUTHOR]

Stress concentration relief factor, which reflects the linear relationship between the stress concentration factors of composite joint and those of elastic isotropic joint, was proposed by Hart-Smith for the failure prediction of composite multi-bolt joints. It is deemed to be determined by experiments from either unloaded- or loaded-hole laminates and is suitable for investigations of bypass and bearing stress concentration factors. To examine this viewpoint, in this paper, the stress concentration relief factor is determined by tensile tests of open-, filled- and loaded-hole laminates failing in tensile mode, respectively. It can be found that the loaded-hole has obviously high-stress concentration level, while the filled-hole has slightly higher stress concentration than that of open-hole. Detailed 3D-FE analyses are performed to disclose the stress concentration mechanisms of three hole-laminates. Various stress concentration relief factors are combined to calculate bearing and bypass stress concentration factors, which provide the failure envelope for the strength prediction of composite joints. Moreover, both conventional and modified failure envelopes are discussed. Experimental results of two-, three- and four-bolt joints are provided to investigate the suitability of different failure envelopes. It follows that the stress concentration relief factor for bearing stress concentration factor needs to be determined by a loaded-hole laminate, while that for bypass stress concentration factor can be determined by each of open-, filled- and loaded-hole laminates. [ABSTRACT FROM AUTHOR]