Analysis and modelization of lightweight structures subjected to impact

Mechanics of Advanced Materials research group (Department of Continuum Mechanics and Structural Analysis) of the University Carlos III of Madrid (Spain) offers their experience in the analysis and modelization of high and low velocity impact behaviour of composite structures. Their research focuses on both numerical analysis and non-standard experimental methodologies)

Development of methologies to study the damage tolerance of aeronautical and aerospace composite structures

Mechanics of Advanced Materials research group (Department of Continuum Mechanics and Structural Analysis) of the University Carlos III of Madrid (Spain) offers their experience in the analysis and modelization of high and low velocity impact behaviour and damage tolerance of composite structures

Stiffness control in adaptive thin-walled laminate composite beams

The aim of this paper is to verify the control of the stiffness that is feasible to achieve in a thin-walled box-beam made from a laminate by including an adaptive material with variable stiffness. In this work, a material having a strongly varying Young Modulus under minor temperature changes was included in the cross-section. An analytical model was used to estimate the position of shear centre and the axial, bending, torsional, and shear stiffnesses of the cross-section. Two cross-sections were analysed, one with an adaptive wall and another with two adaptive walls. In both sections, the torsional stiffness could be strongly altered with minor temperature variations. In the section with one adaptive wall, the shear centre and thus the bending twist coupling was also strongly modified. A study was made of the influence on the control of stiffnesses exerted by the overall cross-section thickness and the thickness of the adaptive walls

Experimental study of agglomerated-cork-cored structures subjected to ballistic impacts

The present paper examines the high-velocity impact behaviour of agglomerated cork-cored structures. The ballistic performance was studied by impact-perforation tests. Three different types of specimens were tested: an agglomerated cork, two spaced thin aluminium plates, and a pair of thin aluminium plates separated by an agglomerated-cork core. The behaviour of the agglomerated cork and the effects of the cork core were analysed in terms of the ballistic limit, residual velocity, and energy absorption. The ballistic limit of cork-cored structures increased slightly, whereas the absorbed energy was strongly augmented by the presence of the cork core.The Spanish Ministerio de Educación y Ciencia (Project HP2006-0024) and the Portuguese Ministério da Ciência, Tecnologia e Ensino Superio

Analysis of the dynamic flexural behaviour of composite beams at low temperature

17 pages, 18 figures.In this study, the dynamic flexural behaviour at low temperatures of beams of three carbon/epoxy laminates is evaluated, analysing the influence of temperature on the mechanical strength, stiffness and absorbed energy until failure. Three-point bending tests were performed under dynamic conditions at three different temperatures (20 °C, −60 °C and −150 °C), and the results were compared with those found under static conditions at the same temperatures. Both the mechanical strength and the absorbed energy decreased when the temperature diminished in all the laminates. No significant influence of temperature was noted on the effective flexural modulus. Two analytical models, using the classical laminated theory and the first-order shear deformation laminate theory, and a numerical model were used to analyse the experimental results of the tests. The models allowed to ensure the use of the equations, which do not consider inertia forces, to calculate the test parameters, and they provided the specimen support span to neglect shear effects. They served also to determine the origin of the noise present in the load measured in the dynamic tests.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT-98/0273) for the financial support of this work.Publicad

Residual flexural strength after low-velocity impact in glass/polyester composite beams

6 pages, 5 figures.This work focuses on an experimental study of flexural after impact behaviour of glass/polyester composite beams. The influence of impact energy, beam width, and impactor-nose geometry on the residual flexural strength was evaluated. Two widths of plain woven laminate specimens were selected. For each specimen width, the geometries of two impactor-noses (Charpy and hemispherical) were chosen to carry out impact tests using a three-point bending device, so that four different test configurations were executed. The residual flexural strength of damaged specimens, evaluated by quasi-static three-point bending tests, was found to depend on the extent of the damage, so that the residual flexural strength was lower in the specimens in which the damage reached the edges of the beam. For this reason, the residual strength was lower in specimens impacted with a Charpy-nose impactor than in the specimens impacted with a hemispherical-nose impactor. Analogously, the narrower specimens presented a lower residual flexural strength than did the wider ones.Publicad

On the estimation of percentiles of the Weibull distribution

3 pages, no figures.Advanced ceramics exhibit brittle behavior. The lack of ductility and the presence of flaws and defects of different sizes and orientations lead to scatter in failure strength. This variability depends also on the specimen size, stress distribution and stress state. The Weibull theory explains correctly this dependence, so the fracture strength of ceramic materials has been studied using the Weibull statistic as recommended by ASTM Standards for reporting uniaxial strength data of these materials.The authors are indebted to the Fundación Ramón Areces (Área de Materiales, IX Concurso Nacional) for its financial support of this research.Publicad

Statistical distribution of the estimator of Weibull modulus

3 pages, 3 figures.The Weibull statistic has been widely used to study the inherent scatter existing in the strength properties of many advanced materials, as well as in the fracture toughness of steels in the ductile-brittle transition region.The authors are indebted to the Fundación Ramón Areces (Área de Materiales, IX Concurso Nacional) for its financial support of this research.Publicad

Statistical analysis of the mechanical properties of composite materials

7 pages, 6 figures.The Weibull statistic is currently used in designing mechanical components made of composite materials. This work presents useful formulae to describe the behaviour of the Weibull modulus estimator, which in turn may be described by means of a three-parameter Weibull distribution. Expressions for the parameters of this latter distribution, dependent on the sample size, are also given in the paper, so, the percentage points, published until now in tabular form, may be directly calculated. Empirical expressions are derived for determining the A-basis and the B-basis material properties as a function of the sample size.The authors are indebted to the Fundación Ramón Areces (Área de Materiales, IX Concurso Nacional) for the financial support of this research.Publicad

A comparison of progressive-failure criteria in the prediction of the dynamic bending failure of composite laminated beams

28 pages, 8 figuresHou and Hashin criteria were compared under dynamic conditions, analyzing the failure of beams subjected to low velocity impacts in a three point configuration. To accomplish this goal a progressive failure model was implemented in a finite element code to predict the failure modes (fibre tensile failure, fibre compressive failure, matrix cracking, matrix crushing, and delamination), considering both Hou and Hashin criteria. The experimental results, from tests conducted in a drop-weight tower and available in the literature, were used to validate the numerical model. This model, using both criteria, was used to analyse the failure modes of two lay-ups (unidirectional and cross-ply) tested in two experimental devices (drop-weight tower and split Hopkinson pressure bar). The main failure mechanisms in both laminate lay-ups were also identified.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (TRA2007-66555) for the financial support of this work.Publicad