An Accurate Mixed-mode Delamination Failure Criterion for Laminated Fibrous Composites Requiring Limited Experimental Input

Abstract

A mixed-mode delamination failure criterion is proposed that may be characterized using test data from only double cantilever beam, end-notched flexure, and single leg bending tests. For validation, a comprehensive literature survey is first performed to obtain toughness versus mode mix data for continuous fiber polymeric matrix composites, and the proposed criterion is then evaluated using those studies where sufficient data are reported. To this end, the criterion is used to obtain an expression for toughness versus mode mixity using only a subset of the experimental data that is presented in any given source. This is done using the toughness data from mode I and mode II tests that are performed, as well as the results from the test with a mode ratio closest to that of the single leg bending test. The failure locus predicted by the new criterion is then compared to the experimentally determined toughnesses over the full range of the experimental data. These results indicate that the proposed criterion is highly accurate for materials spanning a wide range of classifications of fiber reinforced polymeric matrix composites. Further, the accuracy of the proposed criterion is found to be equal to or better than other delamination failure criteria that have been utilized in the past, including those that use a great deal more experimental data for their characterization. It is concluded that the proposed criterion, which can be obtained from only a few simple tests, has predictive accuracy that is similar to that obtained using a failure locus that is fully characterized experimentally. A variety of practical uses of this new criterion are also described.

Fracture Toughness Tests

“…The Vicker's hardness is found from 14) where P /g is the indentation mass (kg), g is the acceleration of gravity and 2d is the indentation diagonal (mm). This is converted to true hardness in GPa by [16] H T = 1.057 × 10 −2 H v .…”

“…On the other hand, the SLB test provides only a single mode mixity of 0.4, but the test procedure and data reduction is very similar to that of the ENF test. In recent work, [14] outlines a method to accurately interpolate any mode I-II mixity from the DCB, SLB and ENF data, negating the advantage of the MMB test. Figure 6.8(b) depicts a typical SLB test.…”

Fracture Mechanics Analyses for Interface Crack Problems - A Review

“…His overall prediction methodology includes the analysis of the energy release rate and the mode mixity along the delamination front in a structure as well as the development of a suitable mixed-mode fracture criterion [88][89][90]. The proposed mixed-mode fracture criterion is based on fracture toughness testing using simple standard type specimens such as the DCB, ENF and MBB specimen.…”

The influence of adhesive constitutive parameters in cohesive zone finite element models of adhesively bonded joints

“…In common practice each has been used to determine a specific constitutive parameter (DCB -G Ic , ENF -G IIc , and SLJ -s IIc ). For each experiment, methods have been established for computing the corresponding constitutive parameter based on the measured load and displacement (or 1 The standard for the ENF test is still evolving (Davidson and Zhao, 2006 other factors). However, there are several uncertainties in each experiment and the computation is not always straightforward.…”