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A multiple crack weight technique with a level set method is proposed to model multiple cracks using a coarse meshfree nodal discretization. A new level-set structure is presented to handle multiple cracks and their propagation using the maximum tangential principal stress criterion. The level sets are updated with respect to the new crack tip positions. The problem of modelling interacting cracks in isotropic and bi-materials is studied using a new variant of the element-free Galerkin method. The stress intensity factors (SIFs) and energy release rates for interacting cracks in isotropic and homogenous materials, including a crack at a bi-material interface are determined using the standard interaction integral. Case studies involving crack-crack interactions, doubly and triply kinked cracks are analysed to demonstrate the simplicity and the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

• A first study of the effect of full creepage on RCF crack growth behaviour. • Predicted crack growth directions show a good agreement with field observation. • Lateral and spin creepages can significantly affect K II and K III evolutions. • Increase in spin creepage is more detrimental to RCF crack driving force. In heavy-haul railway systems, the experience of high traction force of rails in curved tracks significantly accelerates the rolling contact fatigue crack growth. The overall level of traction force and its detailed distribution within a contact patch can be determined by the extent of wheel slips in different directions, also referred to as creepage. However, few studies have focused on quantifying the influence of creepage on rolling contact fatigue crack growth behaviour. In this paper, a numerical method is proposed to investigate the non-proportional mixed-mode rolling contact fatigue crack growth behaviour in the presence of severe longitudinal, lateral and spin creepages. To partially validate the proposed numerical method, the predicted crack growth directions on the rail surface are compared with the cracking patterns obtained from field observations. A parametric study is also conducted to further quantify the influence of different creepage combinations on the evolution of stress intensity factors at the crack front. Results show that both lateral and spin creepages can significantly affect the phase and maximum magnitude of K II and K III during one complete loading cycle. Moreover, the increase of spin creepage is found to have a more detrimental effect on overall RCF crack driving force than the increase of the other two creepage components. [ABSTRACT FROM AUTHOR]

The failure envelope of the matrix in composite laminates under tensile loads has not received much attention in literature. There are very little to no experimental results to show a suitable failure envelope for this constituent found in composites. With increasing popularity in the use of micromechanical analysis to predict progressive damage in composite structures, it is important that matrix behaviour under tension is modelled correctly. In this paper, the authors present and test a new biaxial specimen design to investigate tensile matrix failure in composite structures. Through the use of micromechanical analysis, the authors developed a method in which the matrix stresses at failure can be extracted. Comparing to the existing off-axis test, it was shown that the presented specimen design and test methodology can improve the accuracy of the obtained matrix failure stresses, i.e., the matrix failure envelope for EP280 resin. Additionally, the results indicate that matrix failure takes place earlier than that predicted by von-Mises failure criterion and that the 1st Stress Invariant criterion can better predict matrix failure under tensile loading. [ABSTRACT FROM AUTHOR]

• An approach to investigate fatigue performance of heavy-duty truck trailers based on the damage tolerance concept is proposed. • An approach to develop a representative simulated loading spectrum from both multi-body dynamics simulation analysis and static stress analysis is proposed. • Simple geometric modification of local regions in trailer structure can improve their fatigue resistance and extend their fatigue life. • Damage tolerance approach can be further utilized to improve the structural integrity of truck trailer structures when integrated with an advanced optimization algorithm. To understand and analyse fatigue cracking that occurred in heavy truck trailers, a framework based on the damage tolerance concept was proposed to investigate the structural integrity of a high-strength steel trailer structure and to improve its fatigue resistance through local geometric modifications. To illustrate the framework, the fatigue behaviour at a critical region located at a circular cut-out in the trailer was studied. Firstly, a simulated loading spectrum was developed based on the dynamic analysis of a trailer under different driving scenarios together with the FEA analysis of the trailer structure. After that, for the fatigue analysis, crack growth rate at the critical region was computed using the NASGRO equation, and the fatigue life associated with the simulated loading spectrum was predicted. This damage tolerance approach was further applied to explore possible new designs of trailer structures with either improved fatigue performance or reduced tare weight. The results indicate that the proposed framework can be utilised to both monitor the structural integrity of current vehicle structures and design future trailers with longer life and lighter weight. [ABSTRACT FROM AUTHOR]

Abstract: The fracture toughness and mode I fatigue crack growth (FCG) tests for open cell stainless steel foam with 45 pores per inch (ppi) have been carried out. In this study, the R-curve of crack propagating from a pre-crack was measured for a compact tension specimen by fracture toughness test. The fracture mechanics response was simulated by using an inverted spherical foam modeling approach. The results attained for crack extension rates were described by ΔK, using the Paris-power law approach. The compact tension porous stainless steel specimens have shown full plastic collapse along the ligaments. The microstructure of the foam had a significant influence on the fatigue crack propagation rate. It was found that stainless steel foam has higher Paris exponent than solid stainless steel and the high Paris exponent was explained by crack bridging. The simulation results showed that initiation toughness values strongly depend on failing struts, resulting in cracks that are significantly curved and kinked along their weakest path in stainless steel foam. The results from this study help in predicting and improving mechanical properties of metallic foams with open cell structure. [Copyright &y& Elsevier]

Abstract: There is an urgent need to understand the failure behavior of titanium foams because of their promising application as load-bearing implant materials in biomedical applications. Following our recent study on fracture toughness of titanium foams , this paper investigates the mode I fatigue crack propagation in 60% porous open pore titanium foams both with and without solid coated surface. Fatigue crack propagation tests were performed on compact tension specimens at load ratios of R =0.1 and R =0.5 and the fracture surfaces were examined using scanning electron microscopy. The crack growth rate, da/dN, versus the stress intensity factor range, ΔK, curves were measured and compared using two different techniques; image processing and compliance methods. The crack extension rates were well described by ΔK, using the Paris-power law approach. Coated and non-coated titanium foams with 60% porosity had a significantly higher Paris exponent than solid titanium, which can be explained by crack closure and crack bridging. It was also shown that the fatigue crack grows along the centerline, following the weakest path throughout the foam. The results obtained from this work provide important information for evaluating the structural integrity of porous titanium components in the future biomedical applications. [Copyright &y& Elsevier]

Abstract: The fracture behavior of titanium open foam is characterized and the R-curves of crack propagation from pre-cracks are measured. The crack growth has been optically observed, the measured initiation toughness, J IC, has been analyzed and the effect of material morphology on the J IC is discussed. The fracture toughness was found to be dependent on the expanding crack bridging zone at the back of the crack tip. The compact tension specimens also have some plastic collapse along the ligaments and it has shown that the titanium foam with a higher relative density is tougher. The non-uniform stressing within the plastic zone at the crack tip and the plastic collapse of cell topology behind the tip was found to be the primary cause of the R-curve behavior in low relative density titanium foams. [ABSTRACT FROM AUTHOR]