A Contribution to Time-Dependent Damage Modeling of Composite Structures
The paper presents a new damage model for predicting stiffness loss due to creep loading and cyclic fatigue. The model, developed within a continuum damage mechanics framework, is based on the idea of a time-dependent damage spectrum, some elements of which occur rapidly and others slowly. The use of this spectrum allows a single damage kinematic to model creep and fatigue damage and to take into account the effect of stress amplitude, R ratio, and frequency. The evolution equations are based on similar equation than the one describing the viscoelasticity model and are relatively easy to implement. The new model is compared to the experimental results on carbon fiber/epoxy tubes. Quasi-static, creep and fatigue tests are performed on filament-wound tubular specimens to characterize the elastic, viscoelastic and plastic behavior of the composite material. Varying amounts of damage are observed and discussed depending on stress level and R ratio. The experimental work aims to develop and validate the damage model for predicting stiffness loss due to creep loading and cyclic fatigue.
Time-dependent response of thermoplastic matrix composite material under the cyclic loadings
Under the service conditions, steel pipelines coated with the thermal protection system are subjected to cyclic loadings of axial tension and hydrostatic pressure. The finite element method generally used to simulate the behavior of composite structures under these loadings allows us to estimate the stresses generated in the system and to conclude on several origins of damage. However, for the framework of displacement or deformation analyses in such multilayer systems, these calculations do not allow a better prediction of their behavior. The methods used do not take sufficiently into account the characteristics of the different coating materials to predict their response in service conditions under cyclic loading. In this paper, we consider the viscosity of the thermoplastic materials used for the five layers coating system. Finite element calculations allow us to observe the areas of highest stress concentration at the interface with the steel pipe. Simulations allowed us to observe that the applied loads lead to increases in residual deformation in the thermoplastic matrix composite material. Cyclic tensile loading causes cracks in the matrix of the syntactic foam material. The study carried out here makes it possible to justify the origin of the failure mechanism in the composite material at the time of the installation of the pipelines which could limit the duration of their use in an offshore environment. The tensile failure of the syntactic foam considered as the polypropylene matrix composite material on which cyclic loads have been applied, is due to the stress level at a given temperature.
Test security in medicolegal cases: proposed guidelines for attorneys utilizing neuropsychology practice.
In the context of forensic neuropsychological assessments, the professional interaction of law and psychology is viewed primarily as one where the retaining attorney or court dictates its needs to psychologists when resolving legal disputes. While this perspective is conceptually accurate, the positive and practical collaboration of law and psychology also relies on attorneys adhering to basic protections of sensitive psychological assessment procedures and tests. Objective testing is undermined when a practitioner of law engages in actions prior to, during, or following a neuropsychological examination in a manner that threatens the test security. An appreciation among practitioners of law and psychology regarding the necessity of test security is essential. This article reviews attorney actions that can affect test security, proposes a distinction by psychology between appropriate and problematic client preparation for a neuropsychological examination, integrates the available legal precedent regarding test security, and suggests productive measures to protect test security in medicolegal settings.