Transverse matrix crack

Keywords Boundary Finite Element Method, composite laminates, stress localization, laminate free-edge effect, free-edge stresses, crack problems, transverse matrix crack, numerical methods, boundary discretization... 

In the following results are presented for the application of the Boundary Finite Element Method both for the case of the laminate free-edge effect and for the case of a single transverse matrix crack in the framework of linear elasticity theory. 

Fig. 3 Application of the BFEM analysis for transverse matrix cracking...

The Boundary Finite Element Method is presented as a numerical method which combines characteristics of the finite element method and the boundary element method. For certain geometric situations, this method allows an easy investigation of stress localization problems with less discretizational effort in comparison with the finite element method. For both the example of a transverse matrix crack and the example of the laminate fr( e-edg( effect, the results are shown to be in excellent agreement with comparative finite clement results. 

Equation 1 assumes that the shear stress at the interface is constant as a result of complete interfacial debonding. With good adhesion, only partial debonding or other micro-mechanical events such as transverse matrix cracking are observed, which invalidate the assumption of a constant interfacial shear stress. As a result, alternative data reduction techniques have been developed. For example, Tripathi and Jones developed the cumulative stress-transfer function, which deals with the limitations given above. This has been further refined by Lopattananon et al into the stress-transfer efficiency from which an ineffective length of that fibre in that resin can be determined. In this model, the matrix properties and frictional adhesion at debonds can be included in the analysis. It is also possible to use the three-phase stress-transfer model of Wu et al to include the properties of an interphase. 

Zang W. and Gudmundson P. (1993) An analytical model for the thermoelastic properties of composite laminates containing transverse matrix cracks. International Journal of Solids and Structures, 30, 3211-3231. 

Figure 11. Optical micrographs of longitudinal section of ZMI-3. This isothermally tested sample showed only a small number of transverse matrix cracks.

The maximum stress failure criterion is applied to investigate ply level damage related to transverse matrix cracking and longitudinal tensile and compressive failure. 

Conventional progressive models deal with the stiffness reduction caused by matrix cracking as a function of microcrack densities, resulting in strength reduction of a laminate [7-9]. If transverse matrix cracking is encountered in layers, q, and... 

Assuming that transverse matrix cracking will occur when 22r/ Y >i> transverse matrix cracking of IM7/977-2... 

IM7/5250-4 laminate originally has one ply transverse matrix cracking at -253°C and ISOOKPa. Six updates of laminate stiffness matrix and iteration left three plies undamaged using the conventional progressive failure model (Table 6). However, if the updated laminate stiffness matrix is combined with thermal redistribution associated with the inner surface matrix cracking-... 

IM7/977-2 and IM7/5250-4 are between 0.9 to 1 (Table 4 to7), which means it is hard to say that plies are safe to avoid the transverse matrix cracking against the thermal stresses applied on each ply. Preventing the cryogenic temperature contact with the inside wall of the fuel tank could be accomplished by insulating the laminate in order to minimize thermal residual stresses on each ply. If the inner surface temperature of IM7/977-2 and IM7/5250-4 laminates can be maintained to LN2 temperature which is -196"C, (cr r/ Y at ISOOKPa of both laminates can be... 

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