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A demand raised is how to improve the survivability of aircraft and naval structures concerning low- and high-velocity impacts. Since fundamental failure is due to mainly by fracture, a fundamental understanding of both mechanisms...
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A demand raised is how to improve the survivability of aircraft and naval structures concerning low- and high-velocity impacts. Since fundamental failure is due to mainly by fracture, a fundamental understanding of both mechanisms and mechanics of the material is crucial. It is important to understand the deformation and damage mechanisms involved in the impact to improve the design of composite structures. Several approaches have been exploited to improve the impact damage resistance of composite laminates in different conditions. Among these, the development of composite laminates stacking different fibres in the same matrix results very interestingly. This paper deals to investigate on the high and low speed impact performance of hybrid composite configurations made of glass/carbon and basalt fibres. Low-velocity impact at penetration and high speed tests at different impact velocity were carried out at the room and low temperatures to evaluate the goodness of hybridization proposed and the temperature effect on the composite performances. Among the three proposals, a hybrid basalt carbon configuration was identified as the best both at low speeds and at high impact speeds for both temperatures tested.
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? 2022 Elsevier LtdThis paper is devoted to Reinforced Concrete (RC) beams that can be subjected to accidental falls of substantial masses (hard impacts at low velocities), such as the beams of bridges, industrial buildings, or fa...
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? 2022 Elsevier LtdThis paper is devoted to Reinforced Concrete (RC) beams that can be subjected to accidental falls of substantial masses (hard impacts at low velocities), such as the beams of bridges, industrial buildings, or factories. Here the reference is to existing RC beams, which have no purposely designed reinforcement to resist impacts. The paper focuses on a mass that falls around the midspan, where the capacity of a RC beam to resist an impact is minimum, due to a potential primary cracking pattern that consists of vertical cracks. The impact here is defined by the combination of the mass that falls down and its velocity at the impact. The paper provides an analytical formulation to predict the combinations that trigger the collapse of a RC beam (i.e., ultimate combinations). After having framed the research question, the paper presents the two possible failure modes, the derivation of the equations, the sensitivity of the bearing capacity to the main parameters, comparisons with existing results from literature, and two applications, whose results are discussed.
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In this paper, the most important parameters including material, thickness, shape and impact condition are studied for design and analysis of an automotive front bumper beam to improve the crashworthiness design in low-velocity im...
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In this paper, the most important parameters including material, thickness, shape and impact condition are studied for design and analysis of an automotive front bumper beam to improve the crashworthiness design in low-velocity impact. The simulation of original bumper under condition impact is according to the low-speed standard of automotives stated in E.C.E. United Nations Agreement, Regulation no. 42, 1994. The bumper beam analysis is accomplished for composite and aluminum material to compare the weight and impact behavior. The strength in elastic mode is investigated with energy absorption and impact force in maximum deflection situation.
A good design of this part of automotives must prepare for the safety of passengers; meanwhile, should have low weight. Beside the role of safety, fuel efficiency and emission gas regulations are being more important in recent years that encourage manufacturer to reduce the weight of passenger cars.
In this research, a front bumper beam made of three materials: aluminum, glass mat thermoplastic (GMT) and high-strength sheet molding compound (SMC) is studied by impact modelling to determine the deflection, impact force, stress distribution and energy-absorption behavior. The mentioned characteristics are compared to each other to find best choice of material, shape and thickness. The results show that a modified SMC bumper beam can minimize the bumper beam deflection, impact force and stress distribution and also maximize the elastic strain energy. In addition, the effect of passengers in the impact behavior is examined. The time history of the calculated parameters is showed in graphs for comparison. Furthermore, beside the above-mentioned benefits, some more advantages like easy manufacturing due to simple shape without-ribs, economical aspects by utilizing low-cost composite material and reducing weight with respect to others can be achieved by SMC material.
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The complete modeling for impact on flexible structures can always be done through a three-dimensional finite element model. The FEM approach is often very costly both from modeling and calculation duration point of views, so it c...
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The complete modeling for impact on flexible structures can always be done through a three-dimensional finite element model. The FEM approach is often very costly both from modeling and calculation duration point of views, so it can be simplified by using simplified impact models. The selection of an impact model depends on the structural response, thus one should be able to predict the expected structural response a priori in order to select an appropriate impact model. Impact duration is an important parameter that can be helpful for predicting the expected structural response. This paper provides guidelines for the prediction of the structural response on the basis of impact duration and the fundamental period of the impacted structure. A criterion for defining a precise upper limit of low velocity impact is also developed.
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Due to the improved impact performance characteristics, composites are widely used in engineering and military applications to absorb the impact energy. Determination of impact response of composite materials provides the engineer...
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Due to the improved impact performance characteristics, composites are widely used in engineering and military applications to absorb the impact energy. Determination of impact response of composite materials provides the engineer and the manufacturer with critical knowledge to understand the failure criteria, initiation of the first failure and damage growth through the laminates. This study covers the investigation of impact damage growth and determination of Hertzian failure and maximum force thresholds in three different types of composites. Unidirectional E-Glass, woven E-Glass and woven Aramid composite samples with dimensions of 100 × 100 mm are subjected to low velocity impact with an instrumented impact test system. Rebound, on-set of perforation and perforation limits of composites are found out Also, energy profile diagrams of both unidirectional and plain weave E-Glass composites are obtained. According to test results, woven composites are found to be superior to unidirectional composites in the protection limit of low velocity impact. It is also observed that damage growth in woven composites is restricted within a smaller area. Impact tests conclude that strength of the composite materials under dynamic loading increases considerably compared to static loading case as a result of strain rate sensitivity.
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Laminated carbon fiber reinforced polymer (CFRP) composites have gained popularity in engineering applications due to their lightweight and strong in-plane mechanical properties. This material, however, performs poorly with respec...
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Laminated carbon fiber reinforced polymer (CFRP) composites have gained popularity in engineering applications due to their lightweight and strong in-plane mechanical properties. This material, however, performs poorly with respect to out-of-plane impact resistance. The objective of this research was to investigate the effect of bistability on the low velocity impact resistance of laminated CFRP composites. Bistable composites have the ability to alternate between two different geometric equilibria through external loading, and when unloaded, do not require external forces to maintain either geometry. Laminated CFRP composite specimens of bistable, flat symmetric, and curved symmetric configurations were subjected to low velocity impacts of 20 J. The acceleration and force of each impact was recorded using an accelerometer and a load cell mounted on the impactor. The sensor data was used to analyze the dynamic response and calculate the energy absorption of each impact. Post-impact crack length measurements and damage characterization were used to conduct a damage resistance analysis. The effects of geometry, stacking sequence, and bistability of the impacted specimens were determined. The results showed that bistability improves the low velocity impact damage resistance of laminated CFRP composites through increased energy absorption and specimen kinetic energy.
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This paper presents an investigation into the damage characteristics and failure strengths of composite laminates at low velocity impact tests. Three E-glass fabrics, non-crimp fabric, woven fabric, and nonwoven mat, were selected...
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This paper presents an investigation into the damage characteristics and failure strengths of composite laminates at low velocity impact tests. Three E-glass fabrics, non-crimp fabric, woven fabric, and nonwoven mat, were selected as reinforcements for the composite laminates. Impact tests were conducted using a guided drop-weight test rig in ascending energy to 24 J/layer nominal impact energy. Metallographic microscopy was used to observe the damage characteristics of the perpendicular cross-section of the impacted laminates after a micropowder polishing treatment. When the load-time and the energy-time histories were compared with the fractographics, it was found that fiber breakage had occurred prior to the major damage. When the impact energy increased over the threshold energy of the major damage, matrix cracking, delamination, and fiber breakage were observed at the back surface, below a nearly undamaged zone, which were attributed to the bending stresses.
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Impact and compression after impact characteristics of a typical plain weave fabric E-glass/epoxy composite have been studied for plates with different thicknesses and the same incident impact energy. Impact studies have been carr...
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Impact and compression after impact characteristics of a typical plain weave fabric E-glass/epoxy composite have been studied for plates with different thicknesses and the same incident impact energy. Impact studies have been carried out on an instrumented drop weight impact test apparatus. Post-impact compressive strength has been obtained using NASA 1142 test fixture. Compressive strength of an unnotched specimen has been obtained using Lockheed test fixture with modified specimen geometry. Power fits for peak contact force and maximum plate displacement have been given as a function of plate thickness. It is observed that the impact damage area has quasi-lemniscate shape. Further, damage mechanism has been studied during the post-impact compressive testing. The residual compressive strength as a function of a plate thickness has been obtained.
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? 2022 Elsevier Inc.We compare low velocity impacts that ricochet with the same impact velocity and impact angle into granular media with similar bulk density, porosity, and friction coefficient but different mean grain size. The ...
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? 2022 Elsevier Inc.We compare low velocity impacts that ricochet with the same impact velocity and impact angle into granular media with similar bulk density, porosity, and friction coefficient but different mean grain size. The ratio of projectile diameter to mean grain length ranges from 4 in our coarsest medium to 50 in our finest sand. Using high speed video and fluorescent markers, we measure the ratio of pre- to post-impact horizontal and vertical velocity components, which we refer to as coefficients of restitution, and the angle of deflection caused by the impact in the horizontal plane. Coefficients of restitution are sensitive to mean grain size with the ratio associated with the horizontal velocity component about twice as large for our coarsest gravel as that for our finest sand. This implies that coefficients for hydro-static-like, drag-like and lift-like forces, used in empirical force laws, are sensitive to mean grain size. The coefficient that is most strongly sensitive to grain size is the lift coefficient which decreases by a factor of 3 between our coarsest and finest media. The deflection angles are largest in the coarser media and their size approximately depends on grain size to the 3/2 power. This scaling is matched with a model where momentum transfer takes place via collisions with individual grains. The dependence of impact mechanics on substrate size distribution should be considered in future models for populations of objects that impact granular asteroid surfaces.
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