Stress-based failure models

There are four main types of models for predicting failure under monotonic loading. The first type is stress-based failure models. A stress-based failure model, in its most general form, can be written/(ct ) > 0. Since stress is a tensor quantity, the failure model becomes a function of the six independent stress components. Thanks to the difficulty and the experimental effort needed to determine the six-dimensional failure envelope in stress space, the prob-... 

The part stress analysis prediction section contains failure rate models for a broad variety of parts used in electronic equipment. This method includes the effects of part quality factors and environmental factors. The tabulated values of the base failure rate are "cut off" at the design temperature and stress of the part. 

References 46 and 47. These approaches have been based on models of cracks in viscoelastic materials in which finite crack tip stresses are obtained by considering a small failure zone or damage region to exist ahead of the crack, somewhat analogous to the Dugdale model... 

Al-Shawaf A (2011), Modelling wet lay-up CFRP-steel bond failures at extreme temperatures using stress-based approach , Int J Adhes Adhes, 31(6), 416 28. 

Four degraded components of the wind turbine are considered. The failure models are based on onshore ones and derived using an empirical approach based on stress factors for mechanical systems. Generalized Stochastic Petri Nets (GSPN)... 

An age-based imperfect PM combined with CM replacements was modelled for an offshore wind turbine using GSPN with predicates coupled with MCS and considering the logistics, times and costs, and weather constraints. The PM repairs were modelled to be performed after a repair threshold age, p X MTTF, of the components. The failure models of the components were obtained from onshore ones using an empirical approach based on stress factors for mechanical systems. 

For inelastic analysis, phenomenological axial, shear, and flexural constitutive relations should be specified, possibly with cracking and post-failure modeling capabilities and, if possible, interaction of axial/flexural and shear stresses. Where this is not possible and given that the variation of axial loads is not high for low-rise buildings, uncoupled values may be assumed based on initial state vertical load levels. 

Maximum-stress-and-strain-based failure criteria were used by Harris and Adams (1984) to predict the failure of single lap joints. A nonlinear finite element analysis with an elasto-plastic material model for the adhesive and adherends was carried out. The selection of stressor strain-based failure criterion was based on the results of uniaxial tensile test results. For an un-toughened adhesive, a brittle failure was observed and a maximum stress criterion was used, while for a toughened adhesive, failure was ductile and a maximum-strain-based criteria was used. However, these criteria are difficult to implement when highly localized stress concentrations or stress singularities exist in an adhesive joint. 

Typical factors used in determining a part s failure rate include a temperature factor (%), power factor (tip), power stress factor (%), quality factor (icq) and environmental factor (itp) in addition to the base failure rate A.b. For example, the model for a resistor is as follows Afiejjjtor = ... 

As shown in Sect. 2, the fracture envelope of polymer fibres can be explained not only by assuming a critical shear stress as a failure criterion, but also by a critical shear strain. In this section, a simple model for the creep failure is presented that is based on the logarithmic creep curve and on a critical shear strain as the failure criterion. In order to investigate the temperature dependence of the strength, a kinetic model for the formation and rupture of secondary bonds during the extension of the fibre is proposed. This so-called Eyring reduced time (ERT) model yields a relationship between the strength and the load rate as well as an improved lifetime equation. 

Theoretical analyses of interfacial debonding and frictional pull-out in the fiber pull-out test were initially modeled for ductile matrices (e.g. tungsten wire-copper matrix (Kelly and Tyson, 1965, Kelly, 1966)) assuming a uniform IFSS. Based on the matrix yielding over the entire embedded fiber length, as a predominant failure mechanism at the interface region, a simple force balance shown in Fig. 4.19 gives the fiber pull-out stress, which varies directly proportionally to the cylindrical surface area of the fiber... 

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