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International audience; This paper deals with low velocity and medium velocity impacts on thin car-bon/epoxy hybrid laminates made of unidirectional plies and woven fabric layers. Drop weight and gas gun impact tests were performed to compare the damage mechanisms of thin hybrid laminates with those of woven laminates of equivalent stiffness and mass. The results show that hybrid laminates present a better impact behaviour in terms of post impact damage extent. These tests were then modeled using a semi-continuous approach. The numerical results well correlate the experiments.

This paper represents experimental and numerical investigations into the dynamic response of woven carbon fiber reinforced thick composite laminates under low-velocity impact. Experiments with nine impact energies are carried out by the drop weight testing machine. The force-displacement curves are extracted from experimental data, and the influence of impact energy on impact response is discussed. The relationships between impact energy and impact performance such as peak force, maximum displacement, and absorbed energy are analyzed. The damage morphology obtained by digital microscope and ultrasonic C-scan is used to analyze the damage mechanisms. Experimental results show that woven composite laminates considered here exhibited several failure modes, including indentation, delamination , matrix cracks and fiber breakage . The finite element model is established to study the complex damage and failure mechanisms by employing ABAQUS/Explicit. Good consistency is achieved between the experimental and numerical results by comparing the force-time curves, impact resistance and damage status. Finally, the impact damage behavior of woven composite laminates with helicoidal layups is explored.

In this paper, the impact response of unidirectional cross-ply GF/epoxy laminates with different shape memory alloys (SMAs) positions was investigated. According to vacuum assisted resin injection (VARI) process, we manufactured the laminates without SMAs, the laminates with one layer of SMAs were inserted in 1/8 thickness, in 1/2 thickness, in 14/16 thickness, and in 15/16 thickness of specimen, respectively, the laminates with two layers of SMAs were inserted in the 15/16 and 14/16 thickness, in 15/16 and 1/2 thickness, in 15/16 and 1/8 thickness, in 14/16 and 1/2 thickness, in 14/16 and 1/8 thickness, and in 1/2 and 1/8 thickness of specimen, respectively. The low-velocity impact experiment was performed by Dynatup 9250HV Drop Weight Impact Testing Machine under the impact energy of 28 J to analyze the impact response, and the impact parameters such as contact force (F), displacement (D) and energy (E) of the laminates were obtained. To further observe and analyze the impact damage morphology, we also adopted visual inspection and scanning electron microscope (SEM) technology. The experimental results showed that impact performance of laminates improved by embedding SMAs. By contrast, the impact performance of the laminates with two layers of SMAs was optimum.

This paper reports the low-velocity impact damage behaviors of 3-D angle-interlock woven carbon fiber/epoxy composites which have undergone the accelerated aging for 4-day, 8-day, 16-day and 32-day at 90 °C and 180 °C in air environment. The low-velocity impact behaviors of the un-aged composite specimens were compared with those of the aged composites. The impact load-displacement curves were recorded and the damage morphologies were observed for analyzing the aging effect on the impact behaviors. It was found that the aging influenced the impact behaviors significantly. For the aging at 90 °C, owing the post-curing of the epoxy resin, impact peak loads and modulus increased with the aging time. While the impact behaviors at the room temperature and 180 °C decreased with the aging time due to the thermal oxidative degradation of the epoxy resin and the fiber/resin interface crack.

The low-velocity impact behavior of intralayer hybrid composite laminates made from warp-knitted fabrics with carbon (C) and glass (G) fibers was investigated. The impact testing at varying energy levels was performed using drop weight impact tests. The impact response was evaluated in terms of peak force and absorbed energy, and damage mechanism were characterized by visual observations and fluorescent dye penetration. Furthermore, the damage modes was assessed through quasi-static indentation (QSI) and acoustic emission (AE) techniques. The results from this study indicated that the hybrid structure exhibited a positive hybrid effect in peak force and the absorbed energy, and failure mechanism were significantly affected by the hybrid ratio and intralayer structure. The intralayer hybrid laminate of C:G = 1:1 revealed better impact resistance, and that of C:G = 1:4 exhibited less damage accompanied by the least carbon fiber content, however, more fiber damage appeared in C:G = 1:2 laminates.

Results of an experimental investigation into the low-velocity impact response of carbon fibre reinforced laminates and sandwich structures are presented. Six different impact tests have been performed on the composite laminates and sandwich panels with impact energy levels ranging from 17.13 to 154.18 J. Two types of loading conditions were implemented: (1) impacts by the impactors having the same mass and variable impact velocities resulting in different impact energy levels; (2) impacts with the same level of energy (equivalent energy impacts) and different impactor masses with corresponding (different) velocities. The experiments probed the effects of impactor mass, velocity, and different impact energy levels by analysing the patterns of induced damage, energy absorption, penetration resistance and force-displacement response. Microscopic non-intrusive damage assessment procedures were employed to investigate various damage modes induced by the drop weight impact depending on the impact of velocities and impactor masses.

This paper presents an optimization procedure to design laminated composites with improved damage resistance and tolerance. The ant colony optimization algorithm is used to minimize the predicted induced damage during a low velocity drop weight impact event on a dispersed panel. The orientation angle for each layer can be selected as a discrete variable in the domain of −85° to 90°, at 5° intervals. Two case studies are analyzed. In the first one the predicted damage area is minimized whereas, in the second one, the absorbed elastic strain energy is maximized. The results show that this problem is a multi-optimum problem. By using this methodology on dispersed laminates, the predicted impact damage area can be reduced by more than 20% while the objective function of the second case can be improved by 8% compared to the traditionally designed configurations. These results evidence the possibility to improve the damage tolerance using dispersed laminates.

The three-dimensional impact behaviours of functionally graded (FG) circular plates were studied under a drop-weight. The functionally graded circular plate was composed of ceramic (SiC) and metal (Al) phases and the through-thickness mechanical properties through the region between the metal and ceramic layers vary continuously according to a power-law distribution of the volume fraction of the ceramic. The through-thickness material properties of the FG circular plate were determined using the Mori-3Tanaka scheme. The effects of layer number and compositional gradient exponent as well as impactor velocity and plate radius on the elastic impact response of the FG circular plates were investigated. The compositional gradient exponent, impactor velocity and plate radius played an important role on the impact response of the FG circular plates, whereas the layer number through the plate thickness had a minor effect. In addition, the failure strains in all layers were determined using Tamura-Tomota-Ozowa (TTO) model in order to predict the damage regions in each layer through the thickness of FG circular plates. (C) 2010 Elsevier Ltd. All rights reserved.

Fiber reinforced plastics lack design codes and appropriate specifications for the structural engineer to use these materials as a construction material. The need for the development of definitive guidance and criteria for the design and performance of fiber reinforced plastics and composite materials is essential for widespread applications of these materials. This investigation, like many others, is expected to contribute to the better understanding of the behavior of fiber reinforced plastics. The findings of an experimental study are presented here. The study focuses on the effect of velocity on the impact behavior of pultruded composite box-beams. The investigation concentrates on determining the critical design parameters for using pultruded box-beams as roadside barriers. A standard drop weight MTS machine is used for the impact tests. All tests specimens are simply supported and are impacted at mid-span. Static tests and impact tests at different impact velocities are performed to determine the loading rate sensitivity of the pultruded box-beams. In addition, the effect of the impact velocity on the failure mode is investigated. Two different resin systems are considered. These resins are polyester and vinylester.

This paper describes an alternative estimating method for the current drop weight impact test used to determine the mechanical properties of fibre reinforced composites. The method proposed here measures the strain variations in time of the drop weight and uses the one-dimensional wave theory to convert the measurements into the load and displacement variations in time without any filtering technique. As a result, it is shown that the measurements with high accuracy can contribute to determine the real mechanical properties and to obtain further information on the composites under drop weight impact.