Laminates failure analysis

Laminate failure analysis predicts the criticality of a loading condition by comparing actual ply stresses and strains with ply stresses and strains corresponding to the failure of the laminate. Failure criterion functions are used to take into account the combined effect of stress or strain components. The criticality of the loading condition is indicated with a reserve factor which defines how much the load can be increased before failure occurs. The importance of the analysis is evident. The need for a computer code is also obvious since the failure analysis is even more complicated than the load response analysis. 

Laminate failure analysis was performed using a step-by-step stiffness reduction pro-... 

The procedure of laminate strength analysis outlined in Section 4.5.2, with the Tsai-Hill lamina failure criterion will be illustrated for cross-ply laminates that have been cured at a temperature above their service or operating temperature in the manner of Tsai [4-10]. Thus, the thermal effects discussed in Section 4.5.3 must be considered as well. For cross-ply laminates, the transformations of lamina properties are trivial, so the laminate strength-analysis procedure is readily interpreted. 

Andreasson N, Mackinlay CP, Soutis C. Experimental and numerical failure analysis of bolted joints in CFRP woven laminates. RAeS Aeronaut J 1998 102(1018) 445—50. 

Puck A, Schurmann H. Failure analysis of FRP laminates by means of physically based phenomenological models. Compos Sci Technol 2002 62 1633-62. 

As at this stage, accurate modeling of failure after hrst damage is very complicated and not very accurate. For general laminates, failure theories used in practice conservatively equate hnal failure with failure of the first ply in the laminate. The procedure requires determination of the stresses or strains in each ply in the ply axes and uses one of the many failure criteria. The steps followed in a typical failure analysis are as follows ... 

Reddy YS, Reddy JN. Three-dimensional finite element progressive failure analysis of composite laminates under axial extension. J Compos Technol Res 1993 15 73-87. 

Knight Jr NF, Rankin CC, Brogan FA. STAGS computational procedure for progressive failure analysis of laminated composite structures. Int J Non-Linear Mech 2002 37(4) 833—49. 

Quinn BJ, Sun CT. A critical evaluation of failure analysis methods for composite laminates. In Proceedings of 10th DoD/NASA/FAA conf on fihrous composites in structural design, vol. V 1994. V21—37. 

Berbinau P, Filiou C, Soutis C. Stress and failure analysis of composite laminates with inclusions under multi-axial compression-tension loading. Appl Compos Mater 2000 8(5) 307-26. 

Chen WH, Lee SS. Numerical and experimental failure analysis of composite laminates with bolted joints under bending loads. J Compos Mater 1995 29(1) 15—36. 

Sleight DW. Progressive failure analysis methodology for laminated composite structures. NASA/TP-19999-209107, Washington DC, 20546-0001 1999. 

Langdon GS, Lemanski SL, Nurick GN, Simmons MC, Cantwell WJ, Schleyer GK. Behaviour of fibre-metal laminates subjected to locahsed blast loading part I — experimental observations and failure analysis. Int J Impact Eng 2007 34(7) 1202—22. 

Wang CH, Gunnion AJ. Optimum shapes of scarf repairs. Comp A 2009 40(9) 1407—18. Soutis C, Hu FZ. Failure analysis of scarf-patch-repaired composite laminates loaded in compression. AIAA J 2000 38(4) 734—40. 

C.I. (1985) Failure analysis of a graphite/epoxy laminate subjected to combined thermal and mechanical loading./. Compos. Mater., 19(5), 216-235. 

Laminate failure envelope analysis determines the combinations of selected load components that cause the failure of a laminate. Envelopes are constructed from the results of consecutive failure analyses, A computer code for creating failure envelopes is useful since the envelope in graphical form displays clearly the load-carrying capability of the laminate. Such a tool should allow the designer ... 

Daniel IM, Strain and failure analysis in graphite/epoxy laminates with cracks, Exp Mech, 18, 246-252, 1978. 

Guedes R M, De Moura M F S F, and Ferreira F J. Failure analysis of quasi-isotropic CFRP laminates under high strain rate compression loading. Composite Structures, 84(4), 2008, pp. 362-368. 

Failure Analysis of Composite Laminates. Seminar notes. San Diego Technomic, 1986. 

FAILURE ANALYSIS OF COMPOSITE LAMINATES WITH FREE EDGE... 

For laminates which are prone to open-mode delamination, progression of delamination as the applied load increases must be modeled first. In addition, the effect of delamination on ultimate strength must be estimated. This failure analysis is not an easy task. 

The analysis of stresses in the laminae of a laminate is a straight-fonvard, but sometimes tedious, task. The reader is presumed to be familiar with the basic lamination principles that were discussed earlier in this chapter. There, the stresses were seen to be a linear function of the applied loads if the laminae exhibit linear elastic behavior. Thus, a single stress analysis suffices to determine the stress field that causes failure of an individual lamina. That is, if all laminae stresses are known, then the stresses in each lamina can be compared with the lamina failure criterion and uniformly scaled upward to determine the load at which failure occurs. 

If no laminae have failed, the load must be determined at which the first lamina fails (so-called first-ply failure), that is, violates the lamina failure criterion. In the process of this determination, the laminae stresses must be found as a function of the unknown magnitude of loads first in the laminate coordinates and then in the principal material directions. The proportions of load (i.e., the ratios of to Ny, to My,/ etc.) are, of course, specified at the beginning of the analysik The loaa parameter is increased until some individual lamina fails. The properties, of the failed lamina are then degraded in one of two ways (1) totally to zero if the fibers in the lamina fail or (2) to fiber-direction properties if the failure is by cracking parallel to the fibers (matrix failure). Actually, because of the matrix manipulations involved in the analysis, the failed lamina properties must not be zero, but rather effectively zero values in order to avoid a singular matrix that could not be inverted in the structural analysis problem. The laminate strains are calculated from the known load and the stiffnesses prior to failure of a lamina. The laminate deformations just after failure of a lamina are discussed later. 

Note that the lamina failure criterion was not mentioned explicitly in the discussion of Figure 4-36. The entire procedure for strength analysis is independent of the actual lamina failure criterion, but the results of the procedure, the maximum loads and deformations, do depend on the specific lamina failure criterion. Also, the load-deformation behavior is piecewise linear because of the restriction to linear elastic behavior of each lamina. The laminate behavior would be piecewise nonlinear if the laminae behaved in a nonlinear elastic manner. At any rate, the overall behavior of the laminate is nonlinear if one or more laminae fail prior to gross failure of the laminate. In Section 2.9, the Tsai-Hill lamina failure criterion was determined to be the best practical representation of failure... 

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