Failure strain

The maximum strain failure criterion is quite similar to the maximum stress failure criterion. However, here strains are limited rather than stresses. Specifically, the material is said to have failed if one or more of the following inequalities is not satisfied ... 

The only difference between the maximum strain failure criterion. Equation (2.125), and the maximum stress failure criterion, Equation (2.118), is the inclusion of Poisson s ratio terms in the maximum strain failure criterion. 

As with the maximum stress failure criterion, the maximum strain failure criterion can be plotted against available experimental results for uniaxial loading of an off-axis composite material. The discrepancies between experimental results and the prediction in Figure 2-38 are similar to, but even more pronounced than, those for the maximum stress failure criterion in Figure 2-37. Thus, the appropriate failure criterion for this E-glass-epoxy composite material still has not been found. 

Figure 2-38 Maximum Strain Failure Criterion (After Tsai [2-21])...

The Tsai-Hill failure criterion appears to be much more applicable to failure prediction for this E-glass-epoxy composite material than either the maximum stress criterion or the maximum strain failure criterion. Other less obvious advantages of the Tsai-Hill failure criterion are ... 

Interaction between failure modes is treated instead of separate criteria for failure like the maximum stress or maximum strain failure criteria. 

Identify which subcriterion for failure applies for each segment of the multiseg-mented maximum stress and maximum strain failure criteria cun/es in Figures 2-37 and 2-38 for uniaxial off-axis loading c . 

Tsai—Hill The maximum stress and maximum strain failure criteria consider each stress component individually. This is a simplification. Test results show that if more than one stress is present in a ply, they can combine to give failure earlier (or later) than the maximum stress or maximum strain failure criterion would predict. One example that shows this effect is the case of a unidirectional ply under shear on which a tensile or a compressive stress is applied parallel to the fibers. The situation is shown in Eigure 6.7. 

In a number of design situations, piles have to be designed for effect of lateral soil movement. These include piles in or near an embankment built on soft clay, bridge abutment piles in soft ground, piles adjacent to an excavation, piles in unstable slope and piles in a marginally stable riverbank. These piles are called passive piles (De Beer 1977). As these piles will experience additional stress and strain, failure to assess the effect in design will result in unacceptable pile movement or stress or both. 

P(l) When lap and strap joints are loaded simultaneously by more than one of the above listed loadings, the joint resistance shall be determined using the maximum strain failure criterion applied to the resultant shear strain vector in the adhesive. 

The strain failure envelope for an isotropic material can be adjusted to account for an orthotropic material having multiple Poisson s ratios, the transverse one of which is small for most fibre/polymer composites. The development of the failure envelope, starting from a single measured strength, is illustrated in Figure 4.13. By considering failure in the strain plane it becomes possible to superimpose failures, by different mechanisms, on a common reference plane. 

A load versus deflection curve can be produced by a recorder, and from this, or directly from machine load/movement readings, measurement of flexural strength (crossbreaking strength), breaking strain, flexural stress at a conventional deflection (often 1.5 times the thickness) and elastic modulus in flexure can be carried out. The nature of the material s failure will also indicate if its behaviour is brittle (low-strain failure of less than 0.05) or tough (sample bends appreciably or yields). Other relevant standards include ISO 178 (1975), ASTM D 790 (1971) and DIN 53452 (1977). 

CRITICAL SHEAR STRAIN FAILURE DEVELOPS ONLY AT LESS STIFF END OF JOINT -... 

As the crack grows there is less material available to withstand the applied stress or strain. Failure... 

Bueche attempted to calculate the distribution of local strain (2) he used the inverse Langevin function for the local stress-strain behavior (3) he assumed a critical strain failure criterion and (4) his representation was one-dimensional. In my model, I proposed a simple representation wherein the local stress-strain function and the distribution of local strains were arbitrary and for the case of a critical strain failure criteria, I have described how these two functions can be assessed from experimental tests. This portion of my work can be looked upon as an extension of Bueche s research. The main difference between my work and Bueche s is that I also handle the case when the local... 

Fig. 3.5. Failure in multiaxial stress, o PMMA tubes (Broutman et al., 1231), a 6 PA tubes, A buckling (Ely, 1241), x PUR tubes (Lim, 1221), SBR membranes (Dickie et al., (251) ------maximum strain failure criterion, - - - octahedral shear stress failure criterion.

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