Cracking/cracks finite element modelling

Fig. 9 Dynamic stress intensity factor calculated from a finite element model (o) plotted as a function of crack velocity and compared to experimental data ( ) obtained for PMMA (after [34,35])...

In the high crack velocity regime three different values of Kid can be assigned to one rate of crack propagation depending on the state of crack acceleration. This behaviour was ascribed to inertia effects associated with crack acceleration and deceleration. Such a hypothesis is corroborated by the computed K data (also shown in Fig. 9), which were obtained from a finite element model, taking into consideration the mentioned transient dynamic linear elastic effects [35]. 

The accuracy of the test procedure was validated by room temperature testings of two to three fracture specimens of each material. Additional load data, which were obtained through the bottom load transducer, were used to check the accuracy of the finite element modeling of the load train. A KRAKf gauge at the remaining ligament of the prenotched bar was used to check the master curve which related the crack extension history with the COD data at room temperature. Details of this validation analysis are described in Ref. 57. 

We present recent results on the analysis of the interaction between plasticity and crazing at the tip of a preexisting crack under mode I loading conditions. Illustrations of the competition between these mechanisms are obtained from a finite element model in which a cohesive surface is laid out in front of the crack. 

Fig, 5, With finite element modelled change of compliance due to the occurrence of the first transverse crack as a function of the initial crack length for the [904c/04c]s lay-up. 

Fig. 4. A comparison of the energy release rates calculated from Eq. (4)-(7) with G obtained directly from the finite-element model for different crack length to thickness ratios [2].

Ivanov DS, Lomov SV, Verpoest I. Finite element modelling of inter-ply delamination and intra-yam cracking in textile laminates. In Proceedings of 32nd SAMPE-Europe SEICO conference, Paris 2011. p. CD edition. 

The generation of 3D finite element models suitable for analysis of cracks requires special attention in and around the erack region where focused rings of hex elements are used. In addition, the initial crack front may be straight, a simple elliptic section, or a general curve in space. 

Finite element modelling on a microstructural scale indicates that internal yield has the appearance of a Mode II crack phenomenon (the shear strength of the microstructure depends on the inverse of the square root of the platelet diameter and is independent of the magnitude of the normal stress on the grain). There is a correlation between the macroscopic yield stress Y used in (2) above with the inverse square root of the grain size. 

Since the formation of maincrack could be observed at the AE increasing point, it is understood that the remarkable increase in AE corresponds to the main-crack formation due to microdamage accumulation. Then the critical stress for maincrack formation during thermal shock fracture, oth, can be determined by Disk-on-Rod test. Those values ranged from 220 to 330 MPa. The instantaneous crack path was not determined definitely because of its high growth velocity. Therefore, the thermal stress analysis is no longer valid after maincrack formation because the crack path could not be introduced into finite element models. 

Figure 1. Finite element model and the definitions of evaluated configurations of the interface cracks a) FE mesh with no cracks, b) the crack intercepting the interface between the brick and the mortar and c) the crack at the interface between the mortar and the brick unit. The region marked with the white circle corresponds to the location where the crack configurations (b) and (c) were analyzed.

The analysis of the interface mechanics provides useful insights into crack propagation behavior in adhesively bonded joints. A finite element model for the DCB specimen was constructed using Franc2D/L [64], a convenient code for this task because of its capability for automatic remeshing in the vicinity of a growing crack. An adhesive layer (material 2) with thickness of / = 0.5 mm is sandwiched between two adherends (material 1) with thickness of = 6 mm, and... 

A broad study of this test has been carried out by Blackman et al. (2000), who - on the basis of a series of tests carried out on several types of adhesives, at different speeds and temperatures, and using a high-speed hydraulic machine - have analyzed the effect of the specimen geometry and type of crack growth. The onset and the propagation of the rupture have been observed by means of high-speed photography. Furthermore, the authors have reviewed the methods proposed by the standard to extract the results and have applied a finite element model to reproduce the firacture of the specimen. 

Dom and Liu (1993) used an accumulative plastic strain-based criterion for single lap joint strength prediction. A critical region was identified and the maximum accumulative effective plastic strain in the critical region was used as a parameter for strength prediction. Another approach is to use a hybrid method, for example, a global finite element model used with a localized analytical solution for a circular crack was proposed by Wahab et al. 2004. 

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