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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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The modeling of particle-wall impaction in a confined gas-particle flow using both Lagrangian and Eulerian approaches is reported. The Lagrangian method is based on a general computational fluid dynamics (CFD) code, FLUENT (FLUENT...
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The modeling of particle-wall impaction in a confined gas-particle flow using both Lagrangian and Eulerian approaches is reported. The Lagrangian method is based on a general computational fluid dynamics (CFD) code, FLUENT (FLUENT-4.3, 1996). In the Bulerian method, based on our previously developed code [J. Eng. Gas Turb. Power 119 (1997) 709], a computational procedure by decomposing one Eulerian solution of particulate phase into two equivalent Lagrangian solutions for incident and reflected particles has been developed. These two approaches are evaluated versus experimental data for particle-wall impaction using spray droplets. Two test cases, a 45° ramp and an isolated single tube, have been studied using the above two approaches to determine the particle behavior and physical properties of impacting and reflected particles near wall surface. Results show that both approaches are successful in predicting the main features of particulate flow near wall, however, the Eulerian approach is much less expensive than the Lagrangian approach in obtaining the flow solution of impacting particles. The particulate flow predictions using both approaches have been applied for predicting tube erosions that are compared with reported data. Good agreement between predictions using the two approaches and between the predicted and measured erosion results are observed.
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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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This work presents a comparative study on the reliability of auxetic (re-entrant honeycomb) and non-auxetic (diamond lattice and conventional honeycomb) lattice composites. The analyzed specimen consists of two unidirectional carb...
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This work presents a comparative study on the reliability of auxetic (re-entrant honeycomb) and non-auxetic (diamond lattice and conventional honeycomb) lattice composites. The analyzed specimen consists of two unidirectional carbon fiber reinforced composite (CFRP) face sheets and a 3D-printed polymeric core. Low velocity impact tests are conducted first to characterize the unit cell deformation pattern, and we further explore its influence on core structure behavior as well as sandwich panel performance. It is found that the re-entrant topology exhibits lower energy absorption capacity but superior robustness and durability. Consequently, the re-entrant panel performs best in both force mitigation and energy dissipation, provided that the impact energy is appropriate. Furthermore, employing re-entrant core not only stabilizes the occurrences of the face sheet penetration as the impact energy increases, but also grants the sandwich panel consistent behaviors under multi-cycle impacts. These unique performances are due to the global instability of the auxetic structure, which yields more compliant deformation and less stress concentration. Resultant discrepancies shall be interpreted with the sandwich core deformation for validation. These findings pave the way for developing new class of auxetic lattice composites, especially under cyclic loading conditions, through a combination of rational design and 3D printing.
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The crucial parameter in the analysis of impact events is the impact velocity v_i. In case of inertial impactors v_i was assumed to be 85% of the average gas jet velocity, following the work of Marple. Numerical analysis of the im...
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The crucial parameter in the analysis of impact events is the impact velocity v_i. In case of inertial impactors v_i was assumed to be 85% of the average gas jet velocity, following the work of Marple. Numerical analysis of the impact process in low pressure impactors shows that this assumption is inappropriate and leads to overestimation of v_i,- near the inset of particle deposition, while, v_i is underestimated in the regime of high impact velocities. In this paper the whole process of nanoparticle acceleration and impact in low pressure impactors is investigated numerically. In order to assure correct numerical procedures, the employed methods are thoroughly validated by comparison with experimental results. Finally, a new analytical model for the calculation of v_i- on the basis of similarity theory is proposed that is independent of the impactor geometry and particle properties and holds well for the whole incompressible region. The model allows to perform defined collision experiments in low pressure impactors regarding impact velocity, without need of demanding numerical effort that is often beyond the scope of experimental studies. The model replaces the old rule of thumb and allows a quantitative re-evaluation of existing experimental data, e.g. on nanoparticle agglomerate fragmentation.
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the studies have been carried out on the damage initiation behavior of polymer matrix woven fabric composite plates subjected to a transverse central low velocity point impact load. Specifically, the effect of incident impact velo...
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the studies have been carried out on the damage initiation behavior of polymer matrix woven fabric composite plates subjected to a transverse central low velocity point impact load. Specifically, the effect of incident impact velocity and impactor mass for the same incident impact energy on the impact behavior has been investigated with a square plate of 150 mm X 150 mm X 6 mm. The material systems considered are: E-glass/epoxy and T300/5208 carbon/epoxy woven fabric composites. Inplane failure of the layers in the form of matrix cracking/ lamina splitting and delaminations were the primary objectives of the study. The studies have been carried out using an inhouse Finite Element Analysis code. The inplane failure functions and the interalminar failure functions have been predicted using quadratic failure creiteria. It is observed that the use of incident impact energy alone as a parameter to characterize the impact behavior is inadequate. Instead, the effect of both incident impact velocity and impactor mass should be considered separately.
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Experiments were performed, wherein cylindrical projectiles made of hardened steel were impacted on commercially available aluminium plates at different angles. Projectiles were of 12.8 mm diameter and plates were of 0.81 mm, 1.52...
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Experiments were performed, wherein cylindrical projectiles made of hardened steel were impacted on commercially available aluminium plates at different angles. Projectiles were of 12.8 mm diameter and plates were of 0.81 mm, 1.52 mm and 1.91 mm thicknesses. Based on the experimental results, an analytical model has been developed to predict the residual velocity of the projectile and the ballistic limit of the plate.
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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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