Spalling uniaxial strength of Al2O3 at high strain rates

In this article research into the uniaxial tensile strength of Al2O3 monolithic ceramic is presented. The experimental procedure of the spalling of long bars is investigated from different approaches. This method is used to obtain the tensile strength at high strain rates under uniaxial conditions. Different methodologies proposed by several authors are used to obtain the tensile strength. The hypotheses needed for the experimental set-up are also checked, and the requirements of the set-up and the variables are also studied by means of numerical simulations. The research shows that the shape of the projectile is crucial to achieve successfully tests results. An experimental campaign has been carried out including high speed video and a digital image correlation system to obtain the tensile strength of alumina. Finally, a comparison of the test results provided by three different methods proposed by different authors is presented. The tensile strength obtained from the three such methods on the same specimens provides contrasting results. Mean values vary from one method to another but the trends are similar for two of the methods. The third method gives less scatter, though the mean values obtained are lower and do not follow the same trend as the other methods for the different specimens

3D meso-scale modelling of concrete material in spall tests

Tensile strength is one of the key factors of concrete material that need be accurately defined in analysis of concrete structures subjected to high-speed impact loads. Dynamic tensile strength of concrete material is usually obtained by conducting laboratory tests such as direct tensile test, Brazilian splitting test and spall test. Concrete is a heterogeneous material with different components, but is conventionally assumed to be homogeneous, i.e., cement mortar only, in most previous experimental or numerical studies. The aggregates in concrete material are usually neglected owing to testing limitation and numerical simplification. It has been well acknowledged that neglecting coarse aggregates might not necessarily give accurate concrete dynamic material properties. In the present study, a 3D meso-scale model of concrete specimen with consideration of cement mortar and aggregates is developed to simulate spall tests and investigate the behaviour of concrete material under high strain rate. The commercial software LS-DYNA is used to perform the numerical simulations of spall tests. The mesh size sensitivity is examined by conducting mesh convergence tests. The reliability of the numerical model in simulating the spall tests is verified by comparing the numerical results with the experimental data from the literature. The influence of coarse aggregates on the experimental test results is studied. The wave attenuation in concrete specimen is analysed, and empirical equations are proposed for quick assessment of the test data to determine the true dynamic tensile strength of concrete material. The contributions of aggregates to dynamic strength in spall tests are quantified for modifying the test results based on mortar material in the literature

Developing a European psychotherapy consortium (EPoC): towards adopting a single-item self-report outcome measure across European countries

Background: Complementing the development of evidence-based psychological therapies, practice-based evidence has developed from patient samples collected in routine care, addressing questions relevant to patients and practitioners, and thereby expanding our knowledge of psychological therapies and their impact. Implementation of assessments in routine care allows for timely clinical decision support and the collection of multiple practice-based data sets by addressing the needs of patients and clinicians (e.g., routine outcome monitoring) and the needs of researchers (e.g., identifying the impact of therapist variables on outcomes). Method: In this article we describe an initiative developed in Europe, through the European Chapter of the Society for Psychotherapy Research, aimed at creating a consortium that has the potential for collecting data on tens of thousands of patients per year. Results: A survey identified one of the main problems in the development of a common data set to be the heterogeneity of measures used by members (e.g., 87 different pre-post outcomes). We report on the results of the survey and the initial stage of identifying a single-item – the Emotional and Psychological Outcome (EPO-1) – measure and the process of its translation into multiple European languages. Conclusions: We conclude this first stage of the overall project by discussing the future potential of the Consortium in relation to the development of procedures that allow crosswalks of outcome measures and the creation of a task force that may be consulted when new data sets are collected, aiming for new common measures to be implemented and shared

Shockless spalling damage of alumina ceramic

Ceramic materials are commonly used to build multi-layer armour. However reliable test data is needed to identify correctly models and to be able to perform accurate numerical simulation of the dynamic response of armour systems. In this work, isentropic loading waves have been applied to alumina samples to induce spalling damage. The technique employed allows assessing carefully the strain-rate at failure and the dynamic strength. Moreover, specimens have been recovered and analysed using SEM. In a damaged but unbroken specimen, interactions between cracks has been highlighted illustrating the fragmentation process