Disorder induced brittle to quasi-brittle transition in fiber bundles

We investigate the fracture process of a bundle of fibers with random Young modulus and a constant breaking strength. For two component systems we show that the strength of the mixture is always lower than the strength of the individual components. For continuously distributed Young modulus the tail of the distribution proved to play a decisive role since fibers break in the decreasing order of their stiffness. Using power law distributed stiffness values we demonstrate that the system exhibits a disorder induced brittle to quasi-brittle transition which occurs analogously to continuous phase transitions. Based on computer simulations we determine the critical exponents of the transition and construct the phase diagram of the system.Comment: 6 pages, 6 figure

Crumpling wires in two dimensions

An energy-minimal simulation is proposed to study the patterns and mechanical properties of elastically crumpled wires in two dimensions. We varied the bending rigidity and stretching modulus to measure the energy allocation, size-mass exponent, and the stiffness exponent. The mass exponent is shown to be universal at value $D_{M}=1.33$. We also found that the stiffness exponent $\alpha =-0.25$ is universal, but varies with the plasticity parameters $s$ and $\theta_{p}$. These numerical findings agree excellently with the experimental results

Evaluation of thermal and mechanical loading effects on the structural behavior of a SiC/titanium composite

Composite specimens of titanium-15-3 matrix reinforced with continuous SCS-6 silicon carbide fibers were tested under a variety of thermal and mechanical loadings. A combined experimental/finite element approach was used to estimate the effective in-situ modulus of the matrix material and to evaluate changes in modulus due to the applied loads. Several fiber orientations were tested. Results indicate that the effect of the thermal loads on composite stiffness varies with fiber orientation. Applications of this method to test specimens damaged by uniaxial tension, thermal cycling, and isothermal fatigue loadings are used to illustrate that by monitoring overall structural behavior, changes in stiffness caused by thermomechanical loading can be detected

An investigation on the stiffness of timber sleepers for the design of fibre composite sleepers

This paper presents an experimental investigation on timber railway sleepers with a view to select a suitable stiffness and a modulus of elasticity for the design of a fibre composite railway sleeper. Eight full size timber sleepers were tested using a four point bending test arrangement. An overview of existing material for railway sleepers is also presented. Based on the tests, it is concluded that timber sleepers have significant variation in strength and stiffness as can be inferred from the modulus of elasticity (Esleeper) which ranged between approximately 9520 MPa and 27600 MPa. It is desirable to develop a concept fibre composite sleeper within a similar range of modulus of elasticity. Based on the statistical analysis, it is proposed to use the lower tail value that is 12000 MPa as design modulus of elasticity for the fibre composite railway sleeper

Stiffness modulus properties of hot mix asphalt containing waste engine oil

This study presents the effect of waste engine oil (WEO) on the mechanical properties of hot mix asphalt mixtures containing waste lubricating WEO. It was added into mixture at 0%, 3%, 5%, 7%, 10% and 15% by weight of binder. The mechanical properties of the mixes were evaluated by conducting indirect tensile stiffness modulus (ITSM) at temperatures of 25°C and 40°C. The results indicated that modified mixes exhibited lower stiffness modulus with the increasing amount of WEO as well as testing temperature. The increasing amount of WEO was found to have a good linear correlation to the decreasing of stiffness modulus. The finding showed that the WEO has the significant role as a softening agent which affected the stiffness modulus even at low percentag

Consideration of the restriction of lateral contraction in the elastic behaviour of cohesive zone models

Cohesive zone models do not consider the lateral contraction of adhesive layers under tensile loads. The constraint of the lateral contraction by the adherents which depends on the geometry of the adhesive layer has a major influence on the normal stiffness of the joint. Two methods to improve the accuracy of the stiffness of cohesive zone models of rectangular adhesive layers are proposed in this paper. Both approaches use existing closed-form solutions for rectangular elastic layers between rigid plates. The first assigns an effective stiffness to the entire cohesive zone, the second approach defines a spatially varying stiffness to account for the difference in constraint of the adhesive close to the free surfaces and in the centre of the layer. The accuracy in joint stiffness for cohesive zone models gained by the two methods is tested in two extensive parametric studies considering both rigid and flexible adherents

Relationship of structure and stiffness in laminated bamboo composites

Laminated bamboo in structural applications has the potential to change the way buildings are constructed. The fibrous microstructure of bamboo can be modelled as a fibre-reinforced composite. This study compares the results of a fibre volume fraction analysis with previous experimental beam bending results. The link between fibre volume fraction and bending stiffness shows that differences previously attributed to preservation treatment in fact arise due to strip thickness. Composite theory provides a basis for the development of future guidance for laminated bamboo, as validated here. Fibre volume fraction analysis is an effective method for non-destructive evaluation of bamboo beam stiffness