Local dynamics of a randomly pinned crack front during creep and forced propagation: An experimental study

We have studied the propagation of a crack front along the heterogeneous weak plane of a transparent poly(methyl methacrylate) (PMMA) block using two different loading conditions: imposed constant velocity and creep relaxation. We have focused on the intermittent local dynamics of the fracture front for a wide range of average crack front propagation velocities spanning over four decades. We computed the local velocity fluctuations along the fracture front. Two regimes are emphasized: a depinning regime of high velocity clusters defined as avalanches and a pinning regime of very low-velocity creeping lines. The scaling properties of the avalanches and pinning lines (size and spatial extent) are found to be independent of the loading conditions and of the average crack front velocity. The distribution of local fluctuations of the crack front velocity are related to the observed avalanche size distribution. Space-time correlations of the local velocities show a simple diffusion growth behavior.Comment: Physical Review E (2011); 62.20.mt, 46.50.+a, 68.35.C

Contract Damages and Investment Dynamics

The present article provides an economic analysis to examine how contract damages affects both breach and investment decisions over time. Unlike the standard static model, this article studies a model in which, upon signing a contract, a seller invests over two periods, and a buyer may breach at the end of each period. The dynamic structure of the model allows us to investigate investment dynamics under alternative contract damages. First, under expectation damages, the seller has an incentive to invest only in the first period (front-loading of investment). Second, under reliance damages, a similar front-loading of investment occurs, and the degree of front-loading is excessive relative to the expectation damages. Third, under restitution damages, the seller has an incentive to invest only in the second period. We also examine efficiency properties of new hybrid measures of damages in which damages depend on the timing of breach.Contract Damages, Investment Dynamics

Competition and Growth in Neo-Schumpeterian Models

We study the effect of product market competition on the incentives to innovate and the economy’s rate of growth in an endogenous growth model. We extend previous works in industrial organization by assuming that innovation is sequential and cumulative, and early endogenous growth models by accounting for the possibility that in each period many asymmetric firms (i.e., an endogenously determined number of successive innovators) are simultaneously active. We identify the price effect, the front loading of profits, and the productive efficiency effect associated with an increase in competitive pressure. The price effect reduces the incentives to innovate, but both the front loading of profits and the productive efficiency effect raise the incentives to innovate. We demonstrate circumstances in which the productive efficiency effect dominates the price effect. In these circumstances, the front loading of profits and the fact that the productive efficiency effect dominates the price effect compound to make the equilibrium rate of growth increase with the intensity of competition.

Crack front instabilities under mixed mode loading in three dimensions

The evolution of a crack front under mixed mode loading (I+III) is studied using a phase field model in 3 dimensions with no stress boundary conditions. As previously observed experimentally in gels, there is a relaxation toward a geometry where $K_{III}=0$ without any front fragmentation even for high values of the initial mode mixity $K_{III}/K_{I}$. The effects of the initial condition is studied and it is shown that irregularities in the initial slit can lead to front fragmentation for smaller values of the ratio $K_{III}/K_{I}$ as is observed in experiments.Comment: 6 pages, 7 figures, accepted for publication in EuroPhysics Letter

Effect of crack curvature on stress intensity factors for ASTM standard compact tension specimens

The stress intensity factors (SIF) are calculated using the method of lines for the compact tension specimen in tensile and shear loading for curved crack fronts. For the purely elastic case, it was found that as the crack front curvature increases, the SIF value at the center of the specimen decreases while increasing at the surface. For the higher values of crack front curvatures, the maximum value of the SIF occurs at an interior point located adjacent to the surface. A thickness average SIF was computed for parabolically applied shear loading. These results were used to assess the requirements of ASTM standards E399-71 and E399-81 on the shape of crack fronts. The SIF is assumed to reflect the average stress environment near the crack edge

Average crack-front velocity during subcritical fracture propagation in a heterogeneous medium

We study the average velocity of crack fronts during stable interfacial fracture experiments in a heterogeneous quasibrittle material under constant loading rates and during long relaxation tests. The transparency of the material (polymethylmethacrylate) allows continuous tracking of the front position and relation of its evolution to the energy release rate. Despite significant velocity fluctuations at local scales, we show that a model of independent thermally activated sites successfully reproduces the large-scale behavior of the crack front for several loading conditions

Metode Dempster-shafer untuk Sistem Pakar Deteksi Kerusakan Mesin Cuci Berbasis Web

Front loading washing machine is one household items needed in daily life . But its use is often experienced problems caused obstacles both human error and resilience of spare parts has limited capacity . To resolve this may be accomplished by a novice technicians who have the basic skills of front loading washing machine . But sometimes to overcome these problems also requires a high level of ability of front loading washing machines that require a qualified technician to fix it. Shafer Demster method used to combine separate pieces of information ( evidence ) to calculate the probability of an event . So that the application of such methods in an expert system to detect damage to the front loading washing machine with a problem-solving solution is expected to provide appropria

A model to distribute mark-up amongst quotation component item

The outline of a proposed new unbalanced bidding model is discussed. Background is provided as regards the role of item price loading, otherwise known as unbalanced bidding. Three types of loading are described, namely those of ‘front-end loading’, ‘back-end loading’ and ‘quantity error exploitation’ (otherwise known as ‘individual rate loading’). It is proposed that one single mathematical model could embrace all three of the above types and that the aspect of risk may be addressed partially by means of using the quadratic programming techniques employed within the field of Modern Portfolio Theory. MPT is a field pioneered by Markowitz in 1959 and was developed to identify optimum portfolios of investments, typically equities. It is hypothesized that MPT presents a basis by which to distinguish Efficient Item Pricing combinations from inefficient ones and thereby provide a scientific tool by which rational contractors may optimally price a project’s items. A brief history of unbalanced bidding describes the field that was pioneered in the 1960’s by Marvin Gates and Robert Stark, as well as the subsequent contributions by the leading researchers in the field.unbalanced bidding, bidding models, item price loading, modern portfolio theory, construction industry, mathematical models, bidding strategies

Downscaling of fracture energy during brittle creep experiments

We present mode 1 brittle creep fracture experiments along fracture surfaces that contain strength heterogeneities. Our observations provide a link between smooth macroscopic time-dependent failure and intermittent microscopic stress-dependent processes. We find the large-scale response of slow-propagating subcritical cracks to be well described by an Arrhenius law that relates the fracture speed to the energy release rate. At the microscopic scale, high-resolution optical imaging of the transparent material used (PMMA) allows detailed description of the fracture front. This reveals a local competition between subcritical and critical propagation (pseudo stick-slip front advances) independently of loading rates. Moreover, we show that the local geometry of the crack front is self-affine and the local crack front velocity is power law distributed. We estimate the local fracture energy distribution by combining high-resolution measurements of the crack front geometry and an elastic line fracture model. We show that the average local fracture energy is significantly larger than the value derived from a macroscopic energy balance. This suggests that homogenization of the fracture energy is not straightforward and should be taken cautiously. Finally, we discuss the implications of our results in the context of fault mechanics