Shear-mode failure

Fig. 10.8. Located AE sources in reinforced concrete beams of (a) bending-mode failure and (b) shear-mode failure.

A crack in a body may grow as a result of loads appHed in any of the three coordinate directions, lea ding to different possible modes of failure. The most common is an in-plane opening mode (Mode I). The other two are shear loading in the crack plane (Mode II) and antiplane shear (Mode III), as defined in Figure I. Only Mode I loading is considered herein. 

Bonded-bolted joints generally have better performance than either bonded or bolted joints. The bonding results in reduction of the usual tendency of a bolted joint to shear out. The bolting decreases the likelihood of a bonded joint debonding in an interfacial shear mode. The usual mode of failure for a bonded-bolted joint is either a tension failure through a section including a fastener or an interlaminar shear failure in the composite material or a combination of both. 

One of the most important properties which control the damage tolerance under impact loading and the CAI is the failure strain of the matrix resin (see Fig. 8.8). The matrix failure strain influences the critical transverse strain level at which transverse cracks initiate in shear mode under impact loading, and the resistance to further delamination in predominantly opening mode under subsequent compressive loading (Hirschbuehler, 1987 Evans and Masters, 1987 Masters, 1987a, b Recker et al., 1990). The CAI of near quasi-isotropic composite laminates which are reinforced with AS-4 carbon fibers of volume fractions in the range of 65-69% has... 

Figure 13.35 Basic modes of failure of structural materials ( ) opening or tensile mode (II) sliding or in-plane shear mode (III) tearing or antiplane shear mode.

The variety of materials possible results in specimens having a range of behaviors. Thus, even in a single test, such as interlaminar shear, unacceptable failure modes may occur depending on the material characteristics. 

Figure 113 Failure modes in composite bolted joints (a) bearing failure, (b) net-tension failure, (c) shear-out failure, (d) cleavage failure, (e) fastener puU-through, (f) bolt failure.

The shear-out failure mode shall if possible be avoided by selecting an appropriate ply-orientation and by using a minimum value of the e/d ratio. 

The failure analysis is carried out according to section 5.2.2.4 of the EUROCOMP Design Code. The net-section, bearing and shear-out failure modes were evaluated. For... 

Figure 20.26 Variation of longitudinal compressive strength of carbon fiber epoxy resin laminate with temperature showing transition from shear mode to buckling mode failure. Failure depends on the shear modulus of the matrix and shear strength of the fibers and a similar effect is observed with the uptake of water. Source Reprinted with permission from Ewins PD, Potter RT, Phil Trans R Soc London, A294, 507-517, 1980. Copyright 1980, The Royal Society of Chemistry.

Ducept et al., [13] studied mixed mode failure criteria for a glass/epoxy composite and an adhesively bonded composite joint. In their study, the initiation failure point detected by acoustic signal and by the non-linearity point on the load/displacement curve and found good correspondence. Magalhaes et al., [14] studied the application of acoustic emission to investigate the creep behavior of composite bonded lap shear joints. 

We can consider there to be three possible modes of failure axial tensile failure parallel to the fibres shear failure parallel to the fibres and transverse tensile failure perpendicular to the fibres. Adopting the approximation that each mode of failure occurs independently of the others (see text), identify failure stresses corresponding to each mode. Failure stresses [Pg.243]

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