Abstract: The interaction behavior of two non-aligned through-wall cracks in flat plates is
investigated by the finite element method (FEM) under extensive creep condition. The
time-dependent fracture parameter C*-integral along the crack tips are calculated and compared to
the results of a single crack of the same size. For comparison purpose, the interaction of stress
intensity factors (SIFs) is also examined in the study. The results indicated that interaction of
multiple cracks is different between the time- dependent fracture characterized by C*-integral and
linear elastic fracture noted by SIF. The magnifying factors of time-dependent fracture are obviously
larger than that of the linear elastic fracture cases. Therefore, the current re-characterization rule for
multiple cracks developed from linear elastic fracture analysis may lead to a non-conservative result
and should be modified when it is used in the assessment of time dependent failure.
Authors: Zahid R. Khokhar, Ian A. Ashcroft, Vadim V. Silberschmidt
Abstract: Fibre reinforced polymer composites (FRPCs) are being increasingly used in structural applications where high specific strength and stiffness are required. The performance of FRPCs is affected by multi-mechanism damage evolution under loading which in turn is affected by microstructural stochasticity in the material. This means that the fracture of a FRPC is a stochastic process. However, to date most analyses of these materials have treated them in a deterministic way. In this paper the effect of stochasticity in FRPCs is investigated through the application of cohesive zone elements in which random properties are introduced. These may be termed ‘stochastic cohesive zone elements’ and are used in this paper to investigate the effect of microstructural randomness on the fracture behaviour of cross-ply laminate specimens loaded in tension. It is seen from this investigation that microstructure can significantly affect the macroscopic response of FRPC’s, emphasizing the need to account for microstructural randomness in order to make accurate prediction of the performance of laminated composite structures.
Abstract: The wedge splitting (WS) test is now a promising method to perform stable fracture mechanics tests on concrete-like quasi brittle materials. Fracture parameters, such as fracture toughness and critical crack opening displacement and et.al, are however not easy to determined since formulae available from stress intensity factor manual are restricted to standard specimen geometry. The paper attempts to compute expressions for commonly used fracture parameters for a general wedge splitting specimen. By means of finite element analysis program, test simulation was performed on non-standard wedge splitting specimen with different depth and initiation crack length, and thereafter expressions were proposed for stress intensity factor at the pre-cast tip and crack mouth opening displacement on the load line. Based on the work above, size effect on the unstable fracture toughness and crack extension were investigated, and the consistency of fracture toughness data for various specimen depth as well as initiation crack length is demonstrated. The crack extension is little sensitive to the initiation crack length, it increases with the depth of specimen, which can be explained by the boundary influence of the specimen.
Authors: Zhi Fang Zhao, Qiu Yu Wang, Zhi Hua Yang, Yang Yang
Abstract: The softening curves of four groups specimens with different sizes were obtained by inverse analysis based on the fictitious crack model（FCM）and the P-CMOD curve achieved by a three-point bending notched beam (TPB) test. According to the softening curves obtained by inverse analysis, size effect of softening curves was investigated，which shows both the tail of calculated softening curve, namely the maximum crack width wc and fracture energy GF have an increasing trend with the increase of the specimen size, but no longer to increase when the specimen size attains to a certain level.
Authors: Yan Jun Chang, Gui Qiong Jiao, Ke Shi Zhang
Abstract: Based on the analysis of the woven structure, the compressive fracture process and strength of a 2.5D-C/SiC ceramic matrix composite were investigated by the classical laminate theory. The porous composite was regarded as a spatial layered structure, and the two classes of the warps and wefts in the 2.5D-C/SiC composite were treated as the corresponding layers. The strengths of the C/SiC bundle and C/SiC lamina were determined, and the compression strength for the composite was calculated by progressive fracture method of the layers and elastic degradation. The failure mechanisms and the angles of the compressive fracture surfaces coincided with the experimental result well. It was demonstrated that the strength predictive method of the classical laminate theory can be applied to the analysis of 2.5D-C/SiC composite.