Experimental and numerical study of AA5086-H111 aluminum plates subjected to impact

An experimental and numerical study of medium-velocity impact (within the range of 120 m/s) has been conducted on thin AA5086-H111 aluminum square plates. Targets with different thicknesses (between 2.5 and 4 mm), stratifications and aluminum alloys have been normally impacted by projectiles with 30 mm diameter and 127 g weight. Experimental results show that a compromise is to be found between the alloy strength and ductility, taking into account the impact velocity and energy. Ductile aluminum like AA5086-H111 grade subjected to medium-velocity impacts, showed the best perforation resistance. A finite element analysis was carried out using the ABAQUS finite element code. Slightly modified versions of the JohnsoneCook models of flow stress and fracture strain were applied. A good correlation between experimental and numerical results was found. The effect of strain rate appears to be predominant in the rupture initiation for the aluminum under consideration. Stratification seems to be advantageous compared to monolithic solutions. However, there are limitations to this tendency

Experimental study of compression after impact of asymmetrically tapered composite laminate

This paper presents an experimental study of CAI (compression after impact) of tapered composite laminate. Two types of layup with thickness changing from 4 mm to 6 mm are considered. A new CAI testing rig, suitable for the specimens and a brief description of impact damage are presented first. Then, the behavior of impacted specimens under compressive loading is discussed along with the effects of ply drop-off parameters (taper angle, ply drop-off disposition and configuration) and impact point location on the failure mechanism. Finally, the residual strength in CAI of tapered laminates is compared with equivalent flat laminates. The results show that compressive behavior of the specimens is mostly governed by a coupling between compression and bending, generated by the discontinuity of the neutral axis in the tapered region. Despite this difference of behavior with flat laminates, the presence of ply drop-off has little effect on the residual strength in CAI

Numerical simulation of impact and compression after impact of asymmetrically tapered laminated CFRP

This paper presents a numerical simulation of impact and compression after impact (CAI) of a tapered composite laminate using a discrete ply model. Three types of damage: matrix cracking, delamination and fiber rupture are considered in the model. The presence of ply drop-off generates some discontinuities in the stress field and therefore adds difficulties to the simulation. Analyses of numerical results are performed to understand the damage and failure mechanisms in both tests. Numerical results in terms of force-displacement curves, delamination shape, CAI displacement field and residual strength are compared with experimental data. Impact simulation is in good correlation with the tests. CAI strength is under predicted and depends on quality of the meshing of the transition region. This study highlights the importance of modeling intra-ply matrix cracking for impact simulation

Study of impact damage tolerance of composite structure at ply drop-off

La tenue résiduelle à l'impact basse vitesse est un critère dimensionnant des structures composites minces pour l'aéronautique. La majorité des travaux réalisés jusqu'ici porte sur l'analyse du comportement en zone courante. Ce travail élargit le domaine d'étude aux zones de variation d'épaisseur. L'objectif est d'étudier la tolérance aux dommages d'impact d'un stratifié comportant une zone de reprise de plis (ZRP) dans le cadre d'un dialogue essai/ calcul, en menant en parallèle une campagne d'essais expérimentaux et l'adaptation d'un modèle numérique de l'endommagement des composites.Le volet expérimental étudie successivement l'impact, la compression et la fatigue à R=-l après impact (CAI et FAI) d'éprouvettes comportant une ZRP. L'analyse des essais d'impact a permis d'identifier la résistance à l'impact et le mécanisme d'endommagement des éprouvettes. Ensuite, un outillage d'essai adapté à la géométrie des éprouvettes a été conçu pour les essais de CAI et de FAI. Les essais de compression montrent une tenue résiduelle statique après impact similaire à celle des éprouvettes sans perte de plis. Les essais de fatigue menés à 60 070 de la tenue résiduelle statique montrent une propagation des délaminages d'impact (en dessous du BVID) qui mène à la rupture des éprouvettes pour un nombre de cycles relativement faible. Alors que la tolérance aux dommages d'impact des ZRP sous chargement statique est comparable à celle des zones courantes lisses, on constate une forte vulnérabilité de ces zones sous chargement de fatigue.Le volet numérique a permis de tester l'approche DPM (Discrete Ply Model), développé lors de travaux précédents, sur une configuration particulière. Un maillage spécifique a été réalisé pour tenir compte des discontinuités de la ZRP. Au niveau de la loi matériau, une formulation unifiée de la rupture de fibres en traction/compression a été implémentée. Les résultats de la simulation d'impact sont en bonne corrélation avec les données expérimentales. Le modèle est capable de prédire la réponse globale de l'éprouvette ainsi que l'étendu des dommages internes. La modélisation de la CAI a permis de confirmer les mécanismes de rupture identifiés lors des essais. Ces résultats numériques sont remarquables puisqu' aucune modélisation locale particulière n'a été faite pour les arrêts de plis. L'approche DPM s'est révélée suffisamment robuste et bien adaptée à la modélisation de l'endommagement des stratifiés unidirectionnels.The residual strength after low velocity impact is a sizing criterion of thin composite structures in aeronautics. The majority of work on the subject is focused on the analysis of plain laminates. This study expands the field of interest to tapered area. The objective is to study the impact damage tolerance of a laminate with ply drop-off using an experiment/ modelling dialogue: on one hand carrying experimental test campaign and on other hand adapting numerical modelling of composite damage. The experimental part successively examines the impact, compression and fatigue R=-l after impact (CAI and FAI) of specimens with ply drop-off. Analysis of the impact results has enabled the identification of impact resistance and damage mechanism. Then, a testing tool for CAI and FAI was specially designed to suit the geometry of the specimens. Compression tests show a static residual strength after impact similar to plain laminates. Fatigue tests carried at 60% of CAI strength show a propagation of impact delamination (below B VID). Failure of specimens occurs after a relatively small number of cycles. While the impact damage tolerance of tapered laminates is comparable to plain laminates under static loading, high vulnerability is observed under fatigue loading. The numerical part allowed to test the Discrete Ply Model (DPM), developed in previous works, on a particular configuration. A specific meshing was realized to account for the discontinuities in the ply drop-off area. Regarding the material law, a unified formulation of the fiber breakage in tension/ compression is implemented. Impact simulation results correlated well with the experimental data. The model is able to predict the overall response of the specimen and internal damage. The modeling of the CAI enabled to confirm the failure mechanisms identified during tests. These numerical results are remarkable since no particular local modeling has been realized for the ply drop-off area. DPM approach has proven robust enough and well suited to damage modeling of unidirectional laminates

Damping evaluation of a ballistic foam: from tests to simulations

The perpetual evolution of soldiers light weight armors include now high technology ceramic, composite and polymeric in ballistic vest that are optimized by simulations. Knowledge of individual material response in the strain, strain rate regime closed to the threat stays mandatory and thus collecting parameters to fit material models guarantees reliable numerical investigations. Since 2015, THIOT INGENIERIE Shock Physics Laboratory has been selected by the French Defence procurement agency DGA-Land Systems to perform materials characterization in three main families of ballistic materials [1-2]. A coupled approach between laboratory experiments and numerical simulations has shown its relevance with ceramic and an Ultra High Molecular Weight PolyEthylene composite (UHMWPE). This paper presents succinctly the last part of those experimental investigations on a polymeric foam that is implemented on the soldier’s chest [3]. The material behavior under dynamic loading has been first evaluated using Split Hokinson Pressure Bars (SHPB) up to 5000s-1. Ballistic tests have been performed in a second time using Digital Image Correlation (DIC) with ultrahigh speed cameras at the back of the target plate to evaluate the damping behavior. Numerical simulations are under progress and the first results are promising

Study of the ballistic behaviour of UHMWPE composite material: experimental characterization and numerical simulation

This paper presents a comprehensive mechanical study of UHMWPE (Ultra High Molecular Weight Polyethylene) composite material under dynamic loadings. The aim of the study is to provide reliable experimental data for building and validate the composite material model under impact. Four types of characterization tests have been conducted: dynamic in-plane tension, out-of-plane compression, shear tests and plate impact tests. Then, several impacts of spherical projectiles have been performed. Regarding the numerical simulation, an intermediate scale multi-layered model (between meso and macro scale levels) is proposed. The material response is modelled with a 3d elastic orthotropic law coupled with fibre damage model. The modelling choice is governed by a balance between reliability and computing cost. Material dynamic response is unconventional [1, 2]: it shows large deformation before failure, very low shear modulus and peeling strength. Numerical simulation has been used both in the design and the analysis of tests. Many mechanical properties have been measured: elastic moduli, failure strength and EOS of the material. The numerical model is able to reproduce the main behaviours observed in the experiment. The study has highlighted the influence of temperature and fibre slipping in the impact response of the material

Study of the ballistic behaviour of UHMWPE composite material: experimental characterization and numerical simulation

This paper presents a comprehensive mechanical study of UHMWPE (Ultra High Molecular Weight Polyethylene) composite material under dynamic loadings. The aim of the study is to provide reliable experimental data for building and validate the composite material model under impact. Four types of characterization tests have been conducted: dynamic in-plane tension, out-of-plane compression, shear tests and plate impact tests. Then, several impacts of spherical projectiles have been performed. Regarding the numerical simulation, an intermediate scale multi-layered model (between meso and macro scale levels) is proposed. The material response is modelled with a 3d elastic orthotropic law coupled with fibre damage model. The modelling choice is governed by a balance between reliability and computing cost. Material dynamic response is unconventional [1, 2]: it shows large deformation before failure, very low shear modulus and peeling strength. Numerical simulation has been used both in the design and the analysis of tests. Many mechanical properties have been measured: elastic moduli, failure strength and EOS of the material. The numerical model is able to reproduce the main behaviours observed in the experiment. The study has highlighted the influence of temperature and fibre slipping in the impact response of the material

Influence of internally dropped-off plies on the impact damage of asymmetrically tapered laminated CFRP

International audienceThis paper presents an experimental study of low velocity impact response of carbon/epoxy asymmetrically tapered laminates. The tests are realised at energy between 10 and 30 J on two types of layup with multiple terminated plies. The type and localisation of damage are analysed using C-scan and micrographs. Then, the data is compared with the response of corresponding respective plain laminate.The effects of some tapering parameters (taper angle, drop-off disposition and configuration) on the impact damage mechanisms are also investigated. Very similar impact damage phenomena are found between tapered and plain laminates. The presence of material discontinuity due to the resin pocket affects less the damage mechanism than the structural difference between the thick and the thin sections

Kinetic Energy Penetrator (KEP) impact on confined concrete

Understanding concrete response facing warheads threats is important for both the design of strategic infrastructure protection and the prediction of warhead performances. This ongoing study aims at building a robust approach for the characterisation of concrete behaviour under ballistic impact of Kinetic Energy Penetrator (KEP). A set of tests has been developed and performed to fit the main parameters of the Holmquist Johnson Cook Concrete material model. Highly instrumented tests are conducted to improve the model prediction capability and to identify its limits. After a brief description of the test configuration, the paper focuses on the analysis of an impact test and presents preliminary simulation results