Influence of shear plugging in the energy absorbed by thin carbon-fibre laminates subjected to high-velocity impacts

This work examines the energy-absorption process in thin woven laminates made from carbon fibres, with the aim of analysing the energy employed in the formation of a shear plug. This study was conducted with a simplified model which considered five energy-absorption mechanisms. The model was validated with experimental tests and numerical simulations, with regard to the residual velocity of the projectile and perforation velocity. The model makes it possible to evaluate the influence of the shear plugging in laminates of different thickness. It has been demonstrated that this energy-absorption mechanism needs to be considered in the analysis. The main energy-absorption mechanisms for impact at low velocity (i.e. below the perforation velocity) are related to the elastic deformation of fibres and shear plugging, whereas when a higher impact velocity is considered (i.e. above the perforation velocity) such mechanisms are related to the acceleration field of the laminate and the shear plugging.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project TRA2007-0440-001) for the financial support of this work.Publicad

Influence of areal density on the energy absorbed by thin composite plates subjected to high-velocity impacts

This work analyses the influence that the areal density of a composite thin-plate, made of glass-fibre woven laminates and subjected to high-velocity impact, exerts on perforation-threshold energy, contact time, and energy-absorption mechanisms. The perforation-threshold energy increased with the areal density. Also, the contact time increased at impact energies above the perforation-threshold energy and decreased below this threshold. The main energyabsorption mechanisms at impact energies close to that causing perforation were found to be the deformation and failure of the fibres, regardless of the areal density. For higher impact energies, the main mechanisms were fibre failure and the energy absorbed by acceleration of the laminate.This study was supported by the Autonomous Community of Madrid and the University Carlos III of Madrid (Project CCG10-UC3M/DPI-4694).Publicad

A non-dimensional theoretical approach to model high-velocity impact on thick woven plates

A theoretical energy-based model to capture the mechanical response of thick woven composite laminates, which are used in such applications as maritime or aerospace, to high-velocity impact was developed. The dependences of the impact phenomenon on material and geometrical parameters were analysed making use of the Vaschy-Buckingham Theorem to provide a non-dimensional framework. The model was divided in three different stages splitting the physical interpretation of the perforation process: a first where different dissipative mechanisms such as compression or shear plugging were considered, a second where a transference of linear momentum was assumed and a third where only friction took place. The model was validated against experimental data along with a 3D finite element model. The numerical simulations were used to validate some of the new hypotheses assumed in the theoretical model to provide a more accurate explanation of the phenomena taking place during a high-velocity impact.L. Alonso, S.K.García Castillo and C.Navarro are indebted to the project 'Acción Estratégica en Materiales Compuestos y Análisis Numérico simplificado de Estructuras y protecciones ligeras sometidas a impacto balístico' (2010/00309/002) of the University Carlos III of Madrid for the financial support of this work. D.Garcia-Gonzalez acknowledges support from the Talent Attraction grant (CM 2018 - 2018-T2/IND-9992) from the Comunidad de Madrid

Experimental analysis of perforation of glass/polyester structures subjected to high-velocity impact

3 pages, 3 figures.In this paper the ballistic behaviour of several glass/polyester laminate structures was studied, evaluating the residual velocity of the projectile and the damage area. Three monolithic laminates of different thicknesses and two multiplate laminate structures were analyzed: one of a sandwich type with face-sheets of glass/polyester and a foam core, and another made with the same face-sheet, which were separated by a distance equal to the thickness of the core. It was found that laminates of greater thickness show a larger damage area and a greater ballistic limit. The influence of the core on the ballistic limit of multiplate laminate structures is negligible but, nevertheless, the extension of the damage area in the back face-sheet is increased.Publicad

Analytical models for the perforation of thick and thin thickness woven laminates subjected to high-velocity impact

This paper deals with the problem of high-velocity impact of a low-mass projectile on woven composite plates. A nondimensional formulation of two analytical models has been developed (one for thin laminates and the other for thick ones). Both analytical models are based on energy conservation and have been applied for the ballistic impact on E-glass woven fibres/polyester composite plates. The results of the models (mainly the ballistic limits) have been compared with experimental results. The value of the ratio target thickness/projectile diameter determining whether the laminate behaves as thick or thin has been established.The authors are indebted to the project "Accion Estrategica en Materiales Compuestos y Analisis Numeric simplificado de Estructuras y protecciones ligeras sometidas a impacto balistico" (2010/00309/002) of the University Carlos III of Madrid for the financial support of this work

Damage in preloaded glass/vinylester composite panels subjected to high-velocity impacts

This paper examines the influence of in-plane preloading on the damage of thin composite panels under high-velocity impact loading. The composite was a tape laminate made with a glass-fibre and vinylester matrix. Impact on a preloaded laminate was analysed experimentally, comparing their behaviour with the condition in which the laminate was load-free. Two preload cases representative of actual structures were selected, uniaxial and biaxial load cases. An experimental device was developed to apply the load in two perpendicular directions. This device was combined with a gas gun to carry out impact tests in a broad range of impact velocities. The static preload altered the perforation-threshold velocity and the damage area in the laminate. Decrements of the both variables were detected in the preloaded specimens, both with uniaxial and biaxial loads. The reduction of the damage area was greater for impact velocities close to the perforation-threshold velocity in all the cases analysed.Publicad

Morphological study of damage evolution in woven-laminates subjected to high-velocity impact

The aim of this experimental work was to study the evolution of damage in woven E-glass fiber/polyester laminates of four different thicknesses. After being impacted, these plates were inspected by nondestructive inspection techniques: ultrasound by C-Scan and B-Scan and visual inspection in order to confirm the qualitative and quantitative results. The damage presented an opening cone shape towards the rear face of thin laminates. On the other hand, two different opening cones of delamination grew towards the front and rear faces after a certain thickness in thick laminates.Publicad

Impact Behavior of In-plane Pre-stressed Pannels

The 3rd International Conference on Structural Stability and Dynamics,, June 19-22, 2005, Kissimmee, FloridaIn this paper the behaviour of plates when they are subjected to normal impact under in-plane pre-stressed conditions was studied. Two kinds of lightweight materials were considered: aluminium alloy 7075 and quasi-isotropic glass fibre-reinforced vinylester resin. The residual velocity, the ballistic limit and, in the case of the composite material, the delaminated area, were measured in each test. Unstable cracks, that generate the catastrophic failure of the panel, were observed in the case of the aluminium at pre-stressed load levels lower than those inducing material yielding.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2001-0735) for the financial support of this work.Publicad

Comportamiento frente a impacto de placas de vidrio/vinilester

Presentado en: VI Congreso Nacional de Materiales Compuestos organizado por Asociación Española de Materiales Compuestos, Departamento de Ingeniería Mecánica y de Materiales-UPV, Departamento de Ingeniería de la Construcción y Proyectos de Ingeniería Civil-UPV (Valencia, Junio 27-29, 2005).Los elementos estructurales de fibra de vidrio en matriz polimérica pueden verse expuestos durante su montaje, mantenimiento y vida en servicio a cargas impulsivas, lo que hace necesario estudiar su comportamiento frente a este tipo de cargas. En este trabajo realizaron ensayos de impacto sobre placas de un tejido equilibrado vidro/vinilester, utilizando los siguientes dispositivos experimentales: torre de caída, barra Hopkinson y cañón de gas, que permitieron trabajar en un rango de velocidades desde los 4 m/s hasta los 350 m/s. Se determinó la extensión del área dañada en todas las placas sometidas a impacto, por medio de técnicas de inspección no destructiva (CScan). En los ensayos de baja velocidad se midió el desplazamiento máximo de la placa; y en el caso de la torre de caída se obtuvo la energía absorbida. Por último, en los ensayos de impacto balístico se estableció la relación entre la velocidad residual y la de impacto. De los resultados obtenidos, se puede concluir que a bajas velocidades de impacto la relación existente entre la energía de impacto y la absorbida presenta una tendencia lineal; al igual que la relación entre la extensión del daño y la energía de impacto. Mientras, que para los impactos de alta velocidad se presenta un punto de inflexión a partir del cual la extensión del área dañada disminuye, con el aumento de la velocidad.Publicad

Design tool to predict the open-hole failure strength of composite laminates subjected to in-plane loads

A design tool based on Whitney-Nuismer model is proposed to predict the failure strength of open-hole composite plates subjected to in-plane loads, both tensile and compressive. One of the limitations of this model is the use of characteristic distances, which have to be estimated, and which are mostly considered constant material properties. In this work, it is demonstrated that these characteristic distances are a function of the plate geometry and are not a material property. Different analytical expressions are proposed to estimate the characteristic distances by using the results of only three experimental tests. This approach enables an accurate and fast estimation of the failure strength when the parameters of the plate are modified without using numerical simulations that require a longer time to be carried out.The authors are indebted for the financial support of this work to the Ministry of Economy and Finance of Spain (project DPI2013-42240-R).Publicad