A finite element numerical model for carbon/epoxy woven laminates has been used to predict residual velocity and damaged area when subjected to high impact velocities. Experiments using a gas gun were conducted to investigate the impact process and to validate the model, measuring the two variables previously indicated. A morphology analysis was also made to investigate the different breakage mechanisms that appear during the penetration process. The influence of the impact velocity and obliquity has been studied using the numerical tool, in a wide range of impact velocities and considering two impact angles, 0°and 45°.

In this paper, flexural vibrations of cracked micro-and nanobeams are studied. The model is based on the theory of nonlocal elasticity applied to Euler-Bernouilli beams. The cracked-beam model is established using a proper modification of the classical cracked-beam theory consisting of dividing the cracked element into two segments connected by a rotational spring located at the cracked section. This model promotes a discontinuity in bending slope, which is proportional to the second derivative of the displacements. Frequency equations of cracked nanobeams with some typical boundary conditions are derived and the natural frequencies for different crack positions, crack lengths, and nonlocal length parameters are calculated. The results are compared with those corresponding to the classical local model, emphasizing the differences occurring when the nonlocal effects are significant.

CFRPs Drilling Delamination ModelingDelamination is one of the undesired effects of machining using non appropriate cutting parameters or worn drill. Finite element modeling of drilling of Carbon Fiber Reinforced Polymer (CFRP) composites is an interesting tool for damage prediction. Recently, complete modeling of the process including the rotatory movement of the drill, penetration in the composite plate and element erosion has been developed in the scientific literature. Computational cost of these complex models is a great disadvantage when comparing them with simplified models that consider the drill acting like a punch that pierces the laminate. In this paper both complete and simplified models were developed and compared in terms of delamination prediction. The simplified model, presenting reduced computational cost, slightly overestimates the delamination factor when compared with the complex model. The influence on delamination of thrust force, clamping area at the bottom surface of the laminate and the stacking sequence is studied using the simplified model.

The influence of low temperature on the damage produced on CFRPs by intermediate and high velocity impacts is analyzed. Spherical projectiles were launched against different carbon fiber/epoxy laminates (tape and woven). Experimental tests were done at temperatures ranging from 25 to 2 150 8C. The extension of the damage was measured by C-Scan. Results show a clear dependence of damage on temperature, impact velocity and the type of the laminate. q

a b s t r a c tHydrodynamic ram (HRAM) is a phenomenon that occurs when a high energy object penetrates a fluid filled container. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure increasing the risk of catastrophic failure and excessive structural damage. It is of particular concern in the design of wing fuel tanks for aircraft since it has been identified as one of the important factors in aircraft vulnerability. For the present work, water filled aluminium square tubes (6063 T5) were subjected to impact by steel spherical projectiles (12.5 mm diameter) at impact velocities of 600 900 m/s. The aluminium tubes were filled at different volumes to study how an air layer inside the tank might influence the impact behaviour. The test boxes were instrumented with five strain gauges and two pressure transducers. The formation process of the cavity was recorded with a high speed camera. This work presents the results of these tests.

In this work, a study has been made of the effect of the adhesive layer thickness on the efficiency of alumina/aluminium armours. Full-scale tests were made shooting armour piercing projectile against panels thick enough to arrest the projectile and also close to the ballistic limit. The adhesive layer, of different thickness, was of the toughened epoxy resin. The fire tests revealed the influence of thickness on the response of the lightweight protection. Numerical simulations were performed to analyse the experimental results. The anaysis showed an optimum adhesive layer thickness for the best performance of the lightweight protection considered.

a b s t r a c tHydrodynamic ram (HRAM) is a phenomenon that occurs when a high kinetic energy object penetrates a fluid filled container. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure, increasing the risk of catastrophic failure and excessive structural damage. This is of particular concern in the design of wing fuel tanks for aircraft since it has been identified as one of the important factors in aircraft vulnerability. In the present paper, the commercial finite element code LS DYNA has been used to simulate an HRAM event created by a steel spherical projectile impacting a water filled aluminium square tube. Two different formulations (ALE and SPH) are employed to reproduce the event. Experimental tests which indicate the pressure at different points of the fluid, displacement of the walls and cavity evolution for different impact velocities are compared with the numerical results in order to assess the validity and accuracy of both ALE and SPH techniques in reproducing such a complex phenomenon.

An analytical model to study the impact process of a spherical projectile penetrating at high velocity into a carbon/ epoxy plain woven laminate is developed in this work. The model is based on an energy balance, where the kinetic energy of the projectile is absorbed by the laminate by three different mechanisms: laminate crushing, linear momentum transfer and tensile fiber failure. A non-homogeneous differential equation is obtained. A subsequent simplification using regular perturbation analysis gives a closed-form solution that allows the approximative calculation of the residual velocity and hence the ballistic limit. The model is validated with the results of experimental tests in which the residual velocity is measured by means of high speed cameras.