Oblique Low-Velocity Impact on Fiber-Metal Laminates

Low-velocity impact of a nanocomposite beam made of glass/epoxy reinforced with multi-wall carbon nanotubes and clay nanoparticles is investigated in this study. Exerting modified rule of mixture (MROM), the mechanical properties of nanocomposite including matrix, nanoparticles or multi-wall carbon nanotubes (MWCNT), and fiber are attained. In order to analyze the low-velocity impact, Euler-Bernoulli beam theory and Hertz's contact law are simultaneously employed to govern the equations of motion. Using Ritz's variational approximation method, a set of nonlinear equations in time domain are obtained, which are solved using a fourth order Runge-Kutta method. The effect of different parameters such as adding nanoparticles or MWCNT's on maximum contact force and energy absorption, stacking sequence, geometrical dimensions (i.e., length, width and height), and initial velocity of the impactor have been studied comprehensively on dynamic behavior of the nanocomposite beam. In addition, the result of analytical model is compared with Finite Element Modeling (FEM).The results reveal that the effect of nanoparticles on energy absorption is more considerable at higher impact energies.

In this work, the normal (0°) and oblique (30° and 45°) ballistic impact behavior of glass fiber-reinforced aluminum laminates (fiber metal laminate, FMLs) impacted by a rigid cylindrical projectile (with a flat nose) has been investigated from an experimental point of view. The ballistic impact tests were conducted on the FMLs using a one-stage gas gun at different impact angels, i.e. 0°, 30° and 45°. A high-speed camera was used to capture and record the experimental images and data during the impacting process. Different failure patterns were observed in the FMLs under oblique and normal impact, with the differences concentrated on the initial crack (in the back surface) and plugging damage (in both the front and back surface). The angular change in direction of the projectile during perforation was only observed during oblique impact tests while the maximum value of the angular change was observed when the impact velocity was close to its ballistic limit velocity. In addition, the angular change decreases with increasing impact velocity and is almost constant when the value of [Formula: see text] reaches a critical value. It can also be observed from the impact test results (both normal and oblique impacts) that FMLs exhibited the lowest ballistic limit velocity when the impact angle was close to 30°. In particular, normal impact shows a higher ballistic limit velocity than that of oblique impact while the ballistic limit velocity at impact angle 45° is slightly higher than that at 30°.

Scaling of oblique impacts in frictional targets: Implications for crater size and formation mechanisms

This research presents the development of a data-driven machine learning-assisted approach to simulate and optimize the design of composite materials subjected to low-velocity impacts. It focuses on a specific type of hybrid composite comprised of fiberglass and Kevlar fabrics stitched with Kevlar threads. The study begins by creating a multiscale finite element simulation for the composite under a low-velocity impact, which operates across three scales: microscale, mesoscale, and macroscale. This simulation accepts various inputs, such as different layer configurations and orientations, and provides impact outputs including maximum load and energy absorption capacity and displacement at failure. Python and MATLAB scripts manage the simulation, automating data generation to create a large dataset for analyzing the composite under low-velocity impacts at both the mesoscale and macroscale levels. This data then trains artificial neural networks (ANNs) at each scale, which are coupled to form a multiscale machine learning-assisted simulation. The mesoscale ANN uses homogenized mechanical properties (HMPs) from the microscale model of the composite layers to predict mesoscale HMPs where a combination of layers and stitching threads are considered in a mesoscale representative volume element (RVE). The macroscale ANN then uses the mesoscale HMPs to produce the composite's impact response, including maximum force and energy absorption capacity and displacement at failure. Finally, the multiscale ANN system is integrated with a particle swarm optimization (PSO) algorithm to explore the design space and find the optimal composite configuration for specific impact conditions and constraints. All simulation results and predictions from the multiscale ANN are validated against experimental data on composites subjected to low-velocity impacts. The multiscale ANN approach introduced in this study is flexible and can be applied to other complex materials and structures where several variables across different scales influence the results. This study shows the efficiency of the introduced approach specifically for the optimization process where several possible combinations of the design space need to be evaluated to find the best combination for a given set of constraints.

This research investigates the ballistic impact performance and energy absorption capabilities of polyurea-coated aluminum alloy plates (250 mm × 250 mm, 6 mm thickness) under high-velocity oblique impacts. Spherical aluminum alloy projectiles with a diameter of 40 mm were used for the impacts. A nonlinear finite-element analysis was conducted using LS-DYNA, replicating the experimental impact test setup from the literature. The numerical findings were validated by comparing them to experimental data available in the literature for flat plates under normal impact at varying velocities, demonstrating a strong correlation with a deviation of only 1.3%. The study explores the effects of various oblique impact angles (0°, 15°, 30°, 45°, and 60°) and panel curvature on the ballistic limit and energy absorption behavior. Results show that the ballistic limit velocity for both flat and curved panels increases significantly with higher impact angles. For flat plates, the ballistic limit increases by 1.6%, 3.3%, 12.2%, and 41.6% at 15°, 30°, 45°, and 60°, respectively, while the curved panels show ballistic limits approximately 11% higher than flat plates. The energy absorption capacity peaks at a 60° angle of incidence, with curved plates absorbing around 20% more energy than flat plates. Damage behavior analysis revealed that delamination, petalling, and spalling were the predominant failure modes, with the extent of delamination increasing with the angle of incidence, particularly at 60°. The study highlights the significant role of impact angle and curvature in improving ballistic performance and energy dissipation, with curved panels exhibiting superior energy absorption and higher ballistic limits compared to flat plates.

This study’s objective is to increase the strength and energy absorption rate of a single-layer honeycomb structure (HCS) with foam under static forces and dynamic impact loads through design of experiments and multi-objective optimization. For the methodology, a set of simulation experiments is conducted using the uniform design (UD) method. Static and dynamic finite element analysis (FEA) is employed to calculate the maximum von Mises stress (VMS) and deformation in the honeycomb core (HCC) under ASTM tension, compression, and impact load testing rules using ANSYS/Workbench. Additionally, the energy absorption of the HCS model is evaluated from dynamic FEA results. By integrating Kriging interpolation (KGI), entropy weighting analysis (EWA), gray relation analysis (GRA), and genetic algorithm (GA), various optimal design results for the HCC model are obtained, considering maximum structural strength and energy absorption rate, respectively. After applying the multi-objective optimal design procedure, the improvement rate for the maximal von Mises stress is 40.5% comparing to the original design. Moreover, the improved rates for the maximum deformation and energy absorption are 16.2% and 21.5%. Consequently, the multi-objective optimization procedure is an effective method and results in a stronger single-layer HCC with foam material and increased energy absorption.

This work compares the low velocity impact (LVI) behavior of conventional fiber metal laminate (FML) with hybrid fiber metal laminates (H-FML) that include an elastomer layer. The aim is to demonstrate the potential of the proposed composite comprising metal, elastomer, and carbon-fiber-reinforced polymer (CFRP) to meet the high demands of emerging products that require lightweight materials. Experimental methodologies and finite element (FE) analysis are used to assess the impact behavior of FML and H-FML. The study evaluates various internal damage processes and the distribution of energy of each ingredient and interaction during the LVI to understand the behavior of the laminates. The results show that the inclusion of elastomer leads to a wider energy distribution and greater participation of the proposed H-FML composites in bearing the load rather than focusing only on the impact area. The materials are used more efficiently in energy absorption since a more extensive energy distribution inside the hybrid laminate takes place. The amount and proportion of energy absorption by each component in laminates are influenced by introduction of the elastomer. The study highlights the potential of using innovative hybrid laminates for energy absorption, and the placement of the elastomer in the laminates affects the extent of energy absorption by each component.

The problem of in-plane damage caused by dynamic impact loading of composite laminates can be enhanced by implanting Z-pins. The effect of Z-pin implantation on the impact resistance of composite laminates is investigated experimentally, and the damage process is analyzed by establishing a low-velocity impact finite element model of Z-pin reinforced laminates. The test results show that the maximum impact contact force of Z-pin reinforced laminates can be increased by 8.23%, and the maximum contact force and absorbed energy of Z-pin reinforced samples both increase gradually with the increase of impact energy. The simulation results show that with the increase of impact energy, the expansion of impact damage is hindered by the Z-pin, and it reduces in-plane matrix damage. The expansion path of the interlaminar crack changes when it reaches the Z-pin enhancement area, and the shape of the interlaminar damage changes from circular to elliptical.

Some achievements have been made in the study on mechanical properties of antler, but they have not been applied in engineering practice, especially in the study of thin-walled tubes similar to antler crashworthiness. In order to improve the crashworthiness and energy absorption of the thin-walled tube structures, a bionic thin-walled tube with the same inner diameter and equal gradient of outer diameter was designed based on the structural characteristics of antler bone and the principle of structural bionics. The finite element method was used to simulate the energy absorption characteristics of 75 kinds of bionic thin-walled tube structures under the oblique impacts with the impact angles of 10°, 20° and 30°. The polynomial regression element model and multi-objective particle swarm optimization algorithm were used to optimize, and the Pareto front optimization principle was used to obtain the optimal allocation scheme of each target. The minimum distance selection method was used in optimization analysis to obtain the optimal structural design parameters of each scheme. The optimization method used in this study can provide reference for the follow-up research on the crashworthiness of thin-walled tubes, and the optimal structure of bionic thin-walled tubes can provide reference for practical engineering application. The results show that when only considering a single impact angle, the optimal number of biomimetic layers n is 6, and the parameter combination of maximum wall thickness and thickness gradient tmax-a is 2.84 mm-0.38 mm, 2.89 mm-0.29 mm, 2.91 mm-0.34 mm, respectively under 10°, 20° and 30° impact angles. Considering various impact angle weight factors and different configuration schemes, the optimal number of biomimetic layers n is 6, and the parameter combination of maximum wall thickness and thickness gradient tmax-a is 2.95 mm-0.28 mm, 2.92 mm-0.30 mm and 2.85 mm-0.33 mm, respectively.

Effects of jet impact angle on cavitation erosion intensity and cavitation cloud dynamics

A helmet is essential protective equipment for the safety of motorcyclists and their passengers. However, motorcycle accidents can cause severe injuries and fatalities, even when wearing helmets, because the strength of motorcycle helmets lacks head protectability in actual impact accidents. Thus, this research investigates the structural performance of commercial motorcycle helmets in Thailand for head injury prevention using finite element analysis via LS-DYNA. The helmet structural model was firstly validated under impact analysis by comparing with the test according to the TIS 369-2557 standard. The finite element results showed that the difference in maximum acceleration was only 4.8%. The protective efficacy of the helmet structure was then studied and analyzed by simulation under various velocities and impact angles according to three cases of accidents. The structural strength was investigated by assessing energy absorption, HIC, and AIS. The worst case was caused when high impact speeds and angles were applied, which showed the highest impact force and HIC. It also enabled a 100% probability of head damage according to AIS 2+, which causes fatality to passengers during impact accidents. The safest conditions in terms of head injury severity occurred when the impact angle was 45 degrees. Finally, at least 75% energy absorption of foam was further recommended for safety design to reduce head injury from motorcycle accidents.

Multi-objective optimization and theoretical analysis of re-entrant structure with enhanced mechanical properties

Measurement of Impact Ejecta from Regolith Targets in Oblique Impacts

Crash-box equipped at the front end of a car, is one of the most important automotive parts for crash energy absorption. In case of frontal crash accident, it is expected to be collapsed with absorbing crash energy prior to other body parts so that the damage of the main cabin frame is minimized and passengers may be saved. Crash-box usually was made a mental thin walled tube. In the paper, automobile crash-box at low-velocity impact was studied by using Finite Element Method. The FE model of the tube was validated by comparing the experimental results and FE model results. Results show that on average the difference of these was within 10％.The good correlation of results obtained show that the numerical analyses are reliable. Crash-box of carbon steel and aluminum alloy materials are compared, it indicates that the peak impact force and maximum energy absorption have certain effect to energy-absorbing component with different materials.

This paper reports the low velocity impact behavior of preloaded E-glass/polypropylene sandwich composite plates. In particular, the effects of the type of preload and pre-strain amount on the impact behavior of composite plates are reported. Low velocity impact tests of specimens subjected to biaxial tension, compression and tension-compression (shear) were carried out using a drop-weight impact machine under a hemispherical impactor. Deformations ranging from 250 to 500 microstrains were imposed by a special fixture fabricated for this purpose. Single impact loadings were applied to the composite sandwich structures at different impact energies which were varied from rebounding case (10 J) to the perforation case (40 J). Impact results were explained in terms of typical contact force – deformation (F-D) curves and energy – time diagrams. The maximum contact force, deformation and absorbed energy of the specimens were compared to investigate the influence of pre-strain amount. In addition to the single impact tests, repeated impact behavior of composite sandwich structures subjected to different preload types were obtained with the same impact energy levels. The experimental results showed that the maximum contact force and maximum absorbed energy were considerably different in these situations. However, the repetition number of the specimens at the higher impact energies subjected to shear preloads was largely unaffected.