Low Velocity Impact Simulations Research Articles

Numerical Investigation of the Effects of Impactor Geometry on Impact Behavior of Sandwich Structures

The aim of this study is to examine the impact performance and damage behavior of sandwich composite structures with a core material of aluminum and a facesheet of glass fiber composites using the finite element method. In the study, the effects of impactor shape, impact velocity and number of core layers on peak force, absorbed energy efficiency, maximum displacement and damage deformation were examined. For low velocity impact simulation, progressive damage analysis was performed based on the Hashin damage criterion using the MAT 54 material model in the LS DYNA finite element program. While providing the connection between the core structure and its surfaces, a Cohesive Zone Model (CZM) based on the bilinear traction-separation law was created and examined. At the end of the study, it was determined that the shape of the impactor had a significant effect on impact resistance. Energy absorption efficiency may vary as impact energy changes. However, as the impact energy increases, the energy absorption efficiency increases. It was determined that the largest and dominant damage type for all three impactors was matrix damage.

Effect of geometric configurations and curvature angle of corrugated sandwich structures on impact behavior

AbstractThe aim of this study is to numerically investigate the low‐velocity impact behavior of carbon fiber reinforced orthogonal woven fabric composite sandwich structures with five different geometric configurations and four different curve angles. Low velocity impact simulations were performed in LS DYNA finite element program to investigate the effects of core configuration and curve angle on peak contact force, energy absorption efficiency and damage mode. A progressive damage analysis based on the combination of the Hashin damage criterion and the Cohesive Zone Model (CZM) with bilinear traction‐separation law was performed using the MAT‐54 (ENHANCED_COMPOSITE_DAMAGE) material model. Among the five different cores, Trapezoidal core has the highest peak force average of 2.9 kN while Triangular core sandwich structure has the lowest with 1.23 kN. Absorbed energy efficiency average was highest for rectangular core with 0.95 and lowest for sinusoidal core with 0.69. The specific absorbed energy value was highest for Triangular core with 0.312 J/g and lowest for Sinusoidal core with 0.178 J/g. The damage area on the structure increased with increasing curve angle. It was determined that the core structure and curve angle is an effective parameter on peak force and energy absorption efficiency.Highlights Impact behavior of sandwich composite structures was examined. The effects of core type and curve angles on peak force, energy absorption efficiency and specific absorption energy were investigated. Specific absorption energy rates were compared with studies in the literature.

Experimental and Simulation Study on Low-velocity Impact Damage of Composite Laminates under Temperature Environment

The composite material casing of aero-engine operates in different temperature environments and is inevitably impacted by external objects during use. The resin matrix composite materials are sensitive to temperature, which leads to more complex damage propagation and failure modes of materials under temperature environment. The influence of temperature environment on low-velocity impact damage of composite materials needs to be studied. In this paper, the T300/QY8911 composite laminates were subjected to low-velocity impact test and simulation study under three different temperature environments of 20°C, 120°C, and 180°C. The impact damage detection was carried out by visual inspection and ultrasonic C-scan to analyze the influence of temperature on the damage of composite laminates. Finite element simulation analysis was also conducted on the gradual expansion process of impact damage of composite laminates under different temperature environments to predict the impact damage area of laminates. The results show that the main damage forms are matrix cracking and delamination and the temperature has a significant effect on the low-velocity impact damage of composite laminates. Under the same impact energy, the length of the back crack and the cracking damage of the matrix of the laminate decreases as the temperature increases; the impact damage area and the delamination damage of the laminate increases as the temperature increases.

Low-velocity impact simulation of carbon fiber reinforced composite laminate using IFF-criterion based on BP-ANN

Damage characteristics of composite materials after low-velocity impacts are hard to predict and numerical simulation is time-consuming. This paper explores a study in carbon fiber reinforced composite (CFRP) laminates low-velocity impact (LVI) simulation with Puck inter-fiber failure (IFF) criterion based on the back-propagation neural network (BP-ANN) model. LVI numerical simulations under three different energy levels were conducted and the resulting element stress components were extracted. After data screening and stratified sampling, a training set including five stress tractions as input and the corresponding fracture angle as output was generated. With this dataset, a fracture angle search algorithm based on the BP-ANN model containing three hidden layers was established. Through Matlab coding and ABAQUS subroutine tests, the algorithm exhibits high efficiency compared with other common algorithms and distinctly accelerates the simulation progress (reduce cost time 22.75% and 38.06% compared with Puck's method and SRGSS algorithm). In addition, the simulation results, including the predicted damage size, impact force, displacement and absorbed energy, are in good agreement with experimental results. This work provided a referable thought to accelerate the impact simulation process with the fracture angle-based criteria.

Strain rate-dependent failure modelling of impact damage in laminated CFRP structures

This work focuses on the development, implementation, and validation of a constitutive model for unidirectional composites, aiming to numerically simulate impact damage in laminated structures. The model incorporates a failure criterion that accounts for the influence of strain rate on failure initiation and distinguishes between four failure modes. Failure initiation criteria are 3D phenomenological-based criteria according to the previous work of Puck and Schürmann (1998) and Pinho (2006). Additionally, a mesh-objective damage propagation model is implemented to simulate the impact damage. The impact simulations are performed using Abaqus/Explicit, with the constitutive model implemented through the user subroutine VUMAT. Validation of the strain rate effects on failure initiation is performed using strain rate-dependent bi-axial failure curves for IM7/8552 and AS-4/3506. The analyses indicate that the properties governing the strain rate dependence of failure initiation are consistent. Therefore, the hypothesis was tested in which the same strain rate scaling approach could be used for CFRP materials for which only static properties are available. This hypothesis was tested in high and low-velocity impact simulations at laminated IMS60/977–2 CFRP plates. The results demonstrate that the model accurately replicates the experimentally observed impact-induced contact forces and effectively captures the damaged state in the impacted plate.

High-fidelity simulations of low-velocity impact induced matrix cracking and dynamic delamination progression in CFRP beams

A high-fidelity finite element model is constructed to simulate the low-velocity line-impact experiments conducted by Bozkurt and Coker on [05/903]s CFRP beams. The simulations utilize a user-implemented three-dimensional continuum damage model with the LaRC05 criterion for matrix cracking, and a built-in cohesive zone model for delamination in ABAQUS/Explicit. The significant influence of boundary supports on the global impact response leads to proposing a heuristic boundary conditions approach using spring elements that replicate the experiment boundaries. Results then demonstrated an excellent agreement with the experiments in terms of the global impact response, the strain field, and damage pattern and sequence. Simulations reveal intersonic delamination with crack tip speeds around ∼5000 m/s, while the experimental crack speeds were measured as sub-Rayleigh speeds reaching ∼1000 m/s. When a crack tip definition based on the crack tip opening is introduced in the simulations, crack tip speeds in the range of 490–1500 m/s are measured which are within the range of experimental speeds, suggesting that the sliding mode might be physically hidden in the experiments. The potential use of delamination crack tip speeds as a benchmark for refining numerical simulations is demonstrated by increasing the effective interface toughness leading to a decrease in crack tip speeds with no noticeable effect on the global responses.

A numerical study on the low-velocity impact response of hybrid composite materials

Composite materials are advanced engineering materials with superior properties to traditional materials. One of the most important disadvantages is the high cost of composite materials. Therefore, producing composite materials from the first to the last stage is a very important process. Homogenization is the most important parameter in production since composites contain more than one material type in their structure. In addition, composite structures are sensitive materials against low-velocity impacts. In this study, the effect of reinforcement material combination and stacking sequence on mechanical properties used in the production of composite materials was investigated by low-velocity impact simulations using LS-DYNA software. The mass of the 12 mm diameter spherical impactor used in the analyzes was determined as 10 kg and low-velocity impact tests were applied at 20 J, 30 J and 40 J energy levels. The composite samples were modeled with 180x100mm dimensions and the contact between the impactor and the sample was made from the center of the composite structure. Numerical analyzes were performed using the Tsai-Wu damage criterion in the LS-DYNA software, and material properties were defined using the "Mat_Enhanced_Composite_Damage (MAT 055)" material card.

Research of composite resistance and design of the test matrix of low-speed impacts

In this paper, low-velocity impact resistance for composite laminates is introduced. The resistance function for the parameters of low-velocity impact performs 2-order Taylor’s series expansion. The orthogonal design and Latin hypercube design are presented and their strongpoint and shortcoming are also indicated. The low-velocity impact simulation model of the composite plate is established. The computed results are compared with the existing standard test from ASTM D7136M-05 and the simulation parameters of the model are modified. By calculating and analyzing typical honeycomb sandwich models with different configurations, the damage-area resistance is extracted from the results. The discrete and abstract variables are treated as continuous integer variables to fit the resistance formula of the composite material. Response surface approximation is used to form a hyper surface formula for parameters. The sensitivity analysis of it reveals that the two most influential factors, related to the resistance definition, which is convenient for the subsequent structural design of the composites. In contrast to the previously defined Taylor’s series expansion, the initial coefficients of the resistance formula are obtained. The resistance hyper surface function obtained from the simulation data is used to design the 7-point low-speed impact tests using Latin hypercube design, which employed to verify and validate the simulations, for purposes of saving on the cost of testing and improving the accuracy of analysis.

Experimental and numerical investigation of mechanical behavior of plain woven CFRP composites subjected to three-point bending

The mechanical behavior of plain woven Carbon Fiber-Reinforced Polymer (CFRP) composites under Three-Point Bending (TPB) is investigated via experimental and numerical approaches. Multiscale models, including microscale, mesoscale and macroscale models, have been developed to characterize the TPB strength and damages. Thereinto, Representative Volume Elements (RVEs) of the microscale and mesoscale structures are established to determine the effective properties of carbon-fiber yarn and CFRP composites, respectively. Aimed at accurately and efficiently predicting the TPB behavior, an Equivalent Cross-Ply Laminate (ECPL) cell is proposed to simplify the inherent woven architecture, and the effective properties of the subcell are computed using a local homogenization approach. The macroscale model of the TPB specimen is constructed by a topology structure of ECPL cells to predict the mechanical behavior. The TPB experiments have been performed to validate the multiscale models. Both the experimental and numerical results reveal that delamination mainly appears in the top and bottom interfaces of the CFRP laminates. And matrix cracking and delamination are identified as the significant damage modes during the TPB process. Finally, the quasi-static and dynamic behaviors of plain woven composites are discussed by comparing the results of Low-Velocity Impact (LVI) and TPB simulations.

Fracture Prediction of Steel-Plated Structures under Low-Velocity Impact

In this paper, a validation study of a recently proposed rate-dependent shell element fracture model using quasi-static and dynamic impact tests on square hollow sections (SHS) made from offshore high-tensile strength steel was presented. A rate-dependent forming limit curve was used to predict the membrane loading-dominated failure, while a rate-dependent ductile fracture locus was applied for predicting failure governed by bend loading. The predicted peak force and fracture initiation using the adopted material and fracture model agreed well with the experimental results. The fracture mode was also captured accurately. Further simulations were performed to discuss the importance of the inclusion of dynamic effects and the separate treatment of failure modes. Finally, the shortcomings of the common practice of treatment of rate-effects in low-velocity impact simulations involving fracture were highlighted.

Buckling and post-buckling characteristics of axially loaded channel-section CFRP/aluminum laminate profiles under the influence of impact damage

Damage caused by random impact incidents can greatly reduce the load bearing capacity of composite structural components. In this study, numerical simulations were performed to investigate the influence of impact damage on the buckling and post-buckling performance of carbon fiber reinforced polymer (CFRP)/aluminum laminate (CARALL) channel-section profiles. Low-velocity impact experiments and simulations were performed first on CARALL panel with the exact stacking configuration of the profiles to characterize the possible failure mechanisms for such hybrid components. Then, the dynamic responses of the channel-section profiles with the corner, web and flange impacted respectively, and the corresponding residual properties under axial compression were numerically revealed. Results showed that the residual deformation of specimens after impact was the dominate factor concerning its residual buckling load, and the post-buckling strength was mainly determined by the material damage propagation in the post-buckling stage. The specimens with corner impacted exhibited the highest residual axial buckling load and the lowest failure load compared with the ones with web or flange impacted. This work intended to provide insight into developing novel fiber reinforced polymer/metal hybrid structural components with high impact resistance.

Numerical and predictive analysis of the low-velocity impact response of UD composite plate under a controlled environment

The present paper proposes an investigation and analysis study of a low velocity impact on a unidirectional S2-Glass/Polyester composite plate subject to a controlled environment. A set of simulations of low velocity impact on unaged and aged samples in a bending configuration were carried out. A mass diffusion is studied in order to use its outputs as a predefined field which will be combined with the velocity of the impact loads. The diffusive and mechanical responses, such as moisture concentration, the effect of temperature, energy dissipation and impact force are highlighted and analysed. To ensure the validity of the finite element model, a comparison study has been carried out and compared against experimental investigation founded in the literature. The adopted finite element model performance for the low velocity impacted composite plate under hygrothermal conditions strongly matches with the experimental findings and represents a clear improvement of the model. The impact of the moisture concentration on recorded contact force and energy is highlighted, particularly the delayed contact time and the reduction of the contact forces and the recorded energies intensity. Accordingly, two main factors have affected the contact force responses. These two factors are the drop height and the humidity concentration. An analysis of the maximum contact forces using the design of experiments (DOE) is performed. The effect of both factors namely, the drop height and the humidity concentration, on the response is highlighted as well as the effect of their interaction. The predictive model is highly effective and eases the reproducibility of other mechanical responses.

On the applicability of rate-dependent cohesive zone models in low-velocity impact simulation

This paper studied the applicability of logarithmic, exponential and power cohesive zone models by carrying out experiments and simulations of low-velocity impact on composite laminates. The results show that the dynamic mechanical response and delamination damage under low-velocity impact simulated by the logarithmic rate-dependent CZM have the best agreement with experimental ones than other two models. The delamination damage simulated by exponential model are significantly higher than experimental results, which indicates that the delamination initiation strength and fracture toughness are less estimated under impacting load. The simulation by power model also generally has a good agreement with experimental result but the predicted dynamic mechanical response is a little bit worse than logarithmic model. This study suggests that logarithmic rate-dependent CZM is optimal during low-velocity impact simulation, followed by power model and exponential model.

Aluminium plates with geometrical defects subjected to low-velocity impact: Experiments and simulations

In this paper, an experimental and numerical program investigating impact in the low-velocity regime (≤10 m/s) on 1.5 mm thick AA6016 aluminium plates in three different heat treatments (T4/T6/T7) is presented. The tests were carried out in a drop tower where the force was continuously monitored by a strain-gauge instrumented striker. Results from both intact plates and plates with geometrical defects in the form of pre-cut slits are presented. The heat treatments result in materials with different strength, work-hardening and ductility. It was observed that the intact plates in high-strength material are more resilient to low-velocity impact whereas high ductility is preferred for the plates with pre-cut slits as the crack growth is more restrained. Quasi-static tests on the same plates showed a significant reduction in force only for plates in temper T6 and T7. The experiments are complemented by nonlinear finite element simulations using linear brick elements in Abaqus/Explicit. A von Mises plasticity model was calibrated from notched tension tests. The global response from single edge notch tension (SENT) tests was used to calibrate the failure criterion. The numerical model was able to sufficiently predict the force response and deformation of the intact plates, and the global response and crack propagation of the SENT tests. While the force response in the dynamic simulation of low-velocity impact on plates with slits was in agreement with the observed quasi-static response for all tempers, it was in general underestimated for temper T6 and T7 when compared to the data from the dynamic experiments. For plates in temper T4, the predicted response also agreed with the dynamic experiments.

On the Effects of Core Microstructure on Energy Absorbing Capabilities of Sandwich Panels Intended for Additive Manufacturing.

Increasing transportation safety can be observed as one of the biggest engineering challenges. This challenge often needs to be combined with the need to deliver engineering solutions that are able to lower the environmental impact of transportation, by reducing fuel consumption. Consequentially, these topics have attracted considerable research efforts. The present work aims to address the previously cited challenges by maximizing the energy absorption capabilities of hybrid aluminum/composite shock absorbers with minimal thickness and mass. This engineering solution makes it possible to lighten vehicles and reduce fuel consumption, without compromising safety, in terms of crashworthiness capabilities. A numerical sensitivity study is presented, where the absorbed energy/mass (AE/m) and the absorbed energy/total panel thickness (AE/Htot) ratios, as a consequence of low-velocity impact simulations performed on six different shock absorbers, are compared. These hybrid shock absorbers have been numerically designed by modifying the core thickness of two basic absorbers’ configurations, characterized, respectively, by a metallic lattice core, intended to be produced through additive manufacturing, and a standard metallic honeycomb core. This work provides interesting information for the development of shock absorbers, which should be further developed with an experimental approach. Indeed, it demonstrates that, by integrating composite skins with a very light core producible, by means of additive manufacturing capabilities, it is possible to design shock absorbers with excellent performance, even for very thin configurations with 6 mm thickness, and to provide a significant increase in AE/m ratios when compared to the respective equal volume standard honeycomb core configurations. This difference between the AE/m ratios of configurations with different core designs increases with the growth in volume. In detail, for configurations with a total thickness of 6 mm, the AE/m increases in additive manufacturing configurations by approximately 93%; for those with a total thickness of 10 mm, the increase is 175%, and, finally, for those with a total thickness of 14 mm, the increase is 220%.

Assessment of degraded stiffness matrices for composite laminates under low-velocity impact based on modified characteristic length model

This study aims to evaluate the applicability of the degraded stiffness matrix and the redefined characteristic length models in the finite element analysis of composite laminates under low-velocity impact. Implemented by the user-defined VUMAT subroutine in ABAQUS, various damage models are used to predict the damage behavior in the composite laminates, meanwhile, the user-defined VUCHARLENGTH subroutine is applied to define the characteristic length to match the damage mode. Cohesive elements are inserted between the adjacent piles to model the delamination. The applicability of different damage models is investigated by comparing the global mechanical response and local damage behavior. A new characteristic length calculation method is proposed to apply in the low-velocity impact simulation for laminates. The numerical results show that the degraded stiffness matrix proposed by both Maimi and Matzenmiller can accurately predict the global mechanical responses in the complicated damage accumulation case, while the model of PEE (the principle of energy equivalence) and Linde aren’t suitable for the low-velocity impact simulation. As for the characteristic length model, the redefined characteristic length model can obtain more accurate global mechanical responses with the impact energy increasing compared with the predictions of default characteristic length model.

Modelling of low-velocity impact and compression after impact of CFRP at elevated temperatures

In this study, temperature-dependent material properties are implemented into a continuum-damage-based (CDM) model to describe the progressive failure of CFRP under temperature influence. Low-velocity impact (LVI) simulations showed that the material model could accurately represent the damage resulting from LVI at different temperatures and impact energies. The simulations show that an increase of the interlaminar ERR does not cause the reduction in delamination size, but the change in intralaminar damage and overall structural response. Compression after impact (CAI) simulations are in good agreement with experimental data. The results emphasise that an increased temperature during compression has a more decisive influence on residual strength than the impact of energy. The proposed approach and CDM model can predict the material behaviour of CFRP under temperature influence and complex load cases.

Use of enriched shell elements compared to solid elements for modelling delamination growth during impact on composites

Simulation of damage in composite laminates using currently available three-dimensional finite element tools is computationally demanding often to the point that analysis is not practical. This paper presents an enriched shell element that can provide a computationally efficient means to simulate low-velocity impact damage in a composite. The enriched element uses the Floating Node Method and a damage algorithm based on the Virtual Crack Closure Technique that is capable of simulating progressive damage growth consisting of delamination and delamination-migrations from ply to ply during a dynamic impact load. This paper presents results from the shell model in a test-analysis correlation for impact testing of 7-ply and 56-ply laminates. Analysis results from a separate high-fidelity three-dimensional finite element analysis are included also for comparison in the case of the 7-ply laminate, but not in the case the 56-ply laminate due to excessive computational demand. This paper serves as the first application of both models in low-velocity impact simulation. The shell model is considerably more computationally efficient than the high-fidelity model by at least an order of magnitude and is shown to produce results, while not as accurate as the high-fidelity model, potentially sufficiently accurate for a wide range of engineering applications including structural design and rapid prototype assessments.

Simulations and Tests of Composite Marine Structures Under Low-Velocity Impact

Abstract Due to their excellent performance, composite materials are increasingly used in the marine field. It is of great importance to study the low-velocity impact performance of composite laminates to ensure the operational safety of composite ship structures. Herein, low-velocity drop-weight impact tests were carried out on 12 types of GRP laminates with different layup forms. The impact-induced mechanical response characteristics of the GRP laminates were obtained. Based on the damage model and stiffness degradation criterion of the composite laminates, a low-velocity impact simulation model was proposed by writing a VUMAT subroutine and using the 3D Hashin failure criterion and the cohesive zone model. The fibre failure, matrix failure and interlaminar failure of the composite structures could be determined by this model. The predicted mechanical behaviours of the composite laminates with different layup forms were verified through comparisons with the impact test results, which revealed that the simulation model can well characterise the low-velocity impact process of the composite laminates. According to the damage morphologies of the impact and back sides, the influence of the different layup forms on the low-velocity impact damage of the GRP laminates was summarised. The layup form had great effects on the damage of the composite laminates. Especially, the outer 2‒3 layers play a major role in the damage of the impact and the back side. For the same impact energy, the damage areas are larger for the back side than for the impact side, and there is a corresponding layup form to minimise the damage area. Through analyses of the time response relationships of impact force, impactor displacement, rebound velocity and absorbed energy, a better layup form of GRP laminates was obtained. Among the 12 plates, the maximum impact force, absorbed energy and damage area of the plate P4 are the smallest, and it has better impact resistance than the others, and can be more in line with the requirements of composite ships. It is beneficial to study the low-velocity impact performance of composite ship structures.

Influence of the impact position on scarf repair composite under low velocity impact: FEA investigation

The influence of impact location on internal scarf repaired composite is determined through numerical analysis. For this purpose, the finite element model (FEM) of the composite repair was developed and four special impact locations were chosen on the scarf repaired laminates to subject the impact load. Low velocity impact simulation was carried out on the repaired samples with various impact energies (15 J, 20 J and 25 J), and damage analysis was examined based on impact parameters (peak contact force, impact time interval, and energy absorption). Hashin failure criteria damage model was adopted for the computational analysis to visualize the fiber and matrix damages. Results of the simulation shows that when impact location was exterior to the repaired region, it displayed the least damage, conversely when the impact location was at the bond edge, greater damage was observed. Afterwards, a correlation was established among impact parameters and the impact energy that was subjected to the laminates.