摘要 :
? 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...
展开
? 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.
收起
摘要 :
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...
展开
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.
收起
摘要 :
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...
展开
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.
收起
摘要 :
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...
展开
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.
收起
摘要 :
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...
展开
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.
收起
摘要 :
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...
展开
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.
收起
摘要 :
Brittle intermetallics are easily formed during welding of dissimilar metals in many alloy system such as Al-Ti, Al-Fe, and Ti-Ni, usually resulting in poor mechanical performance. In this study, laser impact welding (LIW) was app...
展开
Brittle intermetallics are easily formed during welding of dissimilar metals in many alloy system such as Al-Ti, Al-Fe, and Ti-Ni, usually resulting in poor mechanical performance. In this study, laser impact welding (LIW) was applied for joining of Ni-Ni, Al-Cu, Al-Ni and Al-Ti similar and dissimilar metal combinations. A series of experiments were conducted using a 3-Joule pulsed laser to study the influence of LIW parameters on the launch of the flyer component as well as the bonding between the flyer and target. Metallurgical bonds between Ni-Ni, Al-Cu, Al-Ni and Al-Ti combinations were successfully produced. A characteristic wavy interface was observed in all LIW samples. The impact angle plays a key role in the bonding between the flyer and target. The bonding area was significantly increased (up to 30 % of the impact region) when an appropriate impact angle was applied (nominally 7.5 degrees). In addition, Photon Doppler Velocimetry (PDV) was used to measure the impact velocity of the flyer during the LIW process. The full velocity of the flyer (over 400 m/sec) can be achieved within 1.1 mu s. The impact velocity of the flyer was maintained at almost the same velocity even at relatively large standoff distance (32.5 mm). However, severe deformation of the flyer occurred when the displacement exceeded 3.0 mm.
收起
摘要 :
The model of the oblique rigid body impact with a granular matter is studied. The force acting on the body is a linear superposition of a static (velocity-independent) friction force and a dynamic (velocity-dependent) resistance f...
展开
The model of the oblique rigid body impact with a granular matter is studied. The force acting on the body is a linear superposition of a static (velocity-independent) friction force and a dynamic (velocity-dependent) resistance force. The impact of a sphere, a mathematical and a compound pendulum are modeled and simulated using different initial impact velocity conditions and different impact angles. We analyze how rapidly the rigid body impacting a granular media slows upon collision. For most of the analyzed cases the rigid body under high-force impact (higher initial velocity) comes to rest faster in a granular matter than the same body under low-force impacts (lower initial velocity). Researchers were able to explain this interesting phenomena, not shared by solids or liquids, for the vertical impact of spheres. The simulations for some configurations with small initial impact angles show that as the speed at which the rigid body impacts the media increases, the later it will come to rest.
收起
摘要 :
Simulation and analysis of the projectile impact and penetration problem and its effects are among the practical topics that can be used to design bulletproof panel and military equipment, construction of impact and penetration re...
展开
Simulation and analysis of the projectile impact and penetration problem and its effects are among the practical topics that can be used to design bulletproof panel and military equipment, construction of impact and penetration resistant structures, design of projectiles with appropriate penetration strength and High performance noted. One of the most important parameters affecting penetration is the impact velocity of the projectile. The mechanism of penetration varies in different speed ranges. In this paper, Ansys Autodyn software is used for intrusion simulation. The simulation carried out in this study is based on the accuracy and physical conditions of the problem and the compatibility of numerical simulation with the governing analytical relationships indicates the validity and accuracy of the assumptions made in the simulation. In this study, we selected materials such as material behavior, grating, contact surfaces, and controls, as well as collision of the blunt projectile with angles of 0o,15o,30o,45o by of high velocity impact 1000 m/s with the same mass and diameter and shape of the projectile nose and properties. Ceramic materials are discussed. The result of the numerical simulation comparison shows relatively good agreement between them.
收起
摘要 :
This study presents the impact with friction of a rigid or a flexible body against a half-space, each with a small region of contact compliance where the compliance is obtained from the Jackson and Green theory. The model consists...
展开
This study presents the impact with friction of a rigid or a flexible body against a half-space, each with a small region of contact compliance where the compliance is obtained from the Jackson and Green theory. The model consists of a system of nonlinear differential equations which considers a nonlinear contact force as well as frictional effects at the contacting end, and allows one to predict the motion after the impact. The initial incidence angle, the initial impact velocity, and the contact radius of the link are found to influence the coefficient of restitution with friction. Analytical and experimental results were compared to establish the accuracy of the model.
收起
原文获取