Compressive residual strength at low temperatures of composite laminates subjected to low-velocity impacts

7 pages, 8 figures.Compression after impact behaviour of different carbon fibre reinforced composite laminates (tape and woven) was studied at low temperatures. Low-velocity impact tests on thin plates at room temperature were made, followed by compression after impact tests at −60°C and −150°C. The results of these tests were compared with those of non-impacted specimens to study the variation of the residual strength at different impact energies. In tape laminates, the lower temperature decreased compression after impact strength, although no influence was detected regarding temperature in the variation of the compressive-strength-retention factor. However, at low temperatures, the woven laminate showed greater strength and a less loss of the retention factor than at room temperature.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

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

Compression after impact of thin composite laminates

9 pages, 13 figures.The damage tolerance of various lay-ups of thin carbon/epoxy laminates (1.6–2.2 mm thick) is examined by compression after impact (CAI) tests, using a new testing device which adapts to the thicknesses of the specimens and does not require tabs nor any modification of the specimen geometry. The compression stress state was not modified by the presence of the device, as was verified by numerical simulation. With this device, CAI tests were done of different carbon/epoxy laminate lay-ups (quasi-isotropic, cross-ply and woven) and the values of the residual strength and the normalized residual strength of the laminates were obtained as a function of the impact energy. The woven laminate was found to offer the highest residual strength under all the impact energies, and the quasi-isotropic laminate the least loss of normalized strength as the impact energy was raised.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

Response of pre-loaded laminate composite plates subject to high velocity impact

7 pages, 6 figures.-- Issue title: "EURODYMAT 2006 - 8th International Conference on Mehanical and Physical Behaviour of Materials under Dynamic Loading". Eds., J. Cirne, R. Dormeval, et al.An experimental and analytical study of two cases of static preload (uniaxial and biaxial) was made to determine the response of structural plate elements subjected to high velocity impacts under in-plane tensile preloading conditions. The results were compared with those obtained in non-preloading specimens. Rectangular specimens were used for the uniaxial and non-preload tests, while cross-shaped specimens were used for the biaxial tests. The impacts were made by spherical projectiles travelling at velocities from 140 to 525 m/s. As a general result, the existence of a static preloading on the specimen was found to affect the ballistic limit and the damaged area. The biaxial preload specimens showed the higher ballistic limit and the damaged area was slightly bigger in the non-preloaded specimens. From the analytical model, the ballistic limit calculated for the non-loaded specimens showed a difference of 16% from the experimental values, and in the preloaded specimens the model did not show showed the same tendency as that observed experimentally.The authors are indebted to the Comisión Interministerial de Ciencia y Tecnología from Spain (Project MAT2001-0735) for the financial support of this work.Publicad

Ballistic behavior of preloading CFRPs panels

ICCE 12. Twelve International Conference on Composites / Nano Engineering. Tenerife, Spain, August 1-6, 2005In this paper the effect of static biaxial preloading of CFRPs plates under high velocity impact is investigated experimentally. Results are compared with those obtained when no static loads are applied to the specimens. Two magnitudes were measured from the tests: the residual velocity of the impacting projectile and the extension of the damage area in the laminate.The authors are indebted to the Inter-ministerial Commission of Science & Technology of Spain (Project: MAT2001-0735) for the financial support of this work.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

Modelling of the adhesive layer in mixed ceramic/metal armours subjected to impact

11 pages, 14 figures.The effect of the adhesive layer, used to bond ceramic tiles to a metallic plate, on the ballistic behaviour of ceramic/metal mixed armours is analysed mathematically and experimentally. Two types of adhesives, polyurethane (soft adhesive) and rubber-modified epoxy resin (rigid adhesive), and different thicknesses, are considered in the study. Numerical simulations were made of low calibre projectiles impacting on alumina tiles backed by an aluminium plate, using a commercial finite difference code. Full-scale tests were carried out to check the influence of the adhesive. An engineering model was also developed to provide a preliminary design tool taking account of the influence of the adhesive.The authors are indebted to the Dirección General de Enseñanza Superior (DGES) for the financial support of this work (Project PB-0380).Publicad

Modelling of composite sandwich structures with honeycomb core subjected to high-velocity impact

7 pages, 9 figuresIn this study the perforation of composite sandwich structures subjected to high-velocity impact was analysed. Sandwich panels with carbon/epoxy skins and an aluminium honeycomb core were modelled by a three-dimensional finite element model implemented in ABAQUS/Explicit. The model was validated with experimental tests by comparing numerical and experimental residual velocity, ballistic limit, and contact time. By this model the influence of the components on the behaviour of the sandwich panel under impact load was evaluated; also, the contribution of the failure mechanisms to the energy-absorption of the projectile kinetic energy was determined.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project TRA2004 03960) for the financial support of this work.Publicad

Impact behaviour of preloaded glass/polyester woven plates

7 pages, 4 figures.-- Issue title: "16th International Conference on Composite Materials (ICCM-16) -- ONR (Office of Naval Research) sessions on Dynamic Failure and Durability" (Kyoto, Japan, Jul 6–11, 2007).In this work, the effect of a biaxial preload in the behaviour of glass/polyester woven-laminate plates subjected to high-velocity transversal impact was studied. For this, an analytic model based on energy considerations that include the presence of an in-plane preload was used. The results of the analytic model for the biaxial preload state were compared with those found for a non-preload plate, the difference between them being minimal for the pre-stressed level reached in the tests (31% of the static UTS). Therefore, numerical simulations were made in order to study the effect of the preload in greater detail; furthermore, experimental tests were conducted, validating the analytic and numerical model. In general, the two methods revealed minimal differences between the values of the ballistic limit and those of the residual velocity.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2001-0735) for the financial support of this work.Publicad