Low Velocity Impact Research Articles

Prediction of compression after impact strength from surface profile of low-velocity impact damaged CFRP laminates using machine learning

Prediction of compression after impact strength from surface profile of low-velocity impact damaged CFRP laminates using machine learning

Dynamic behaviour of ultra-high performance concrete beams with rectangular openings subjected to impact loads

To facilitate residents’ needs, contemporary building structures often incorporate prefabricated transverse openings in reinforced concrete (RC) beams to accommodate pipeline installations. However, these openings can potentially impact the load-bearing capacity of the beams, particularly as structures increasingly need to consider dynamic loading effects. The use of ultra-high performance concrete (UHPC) has proven effective in enhancing the dynamic resistance of RC beams with openings. This study employs numerical simulations in ANSYS/LS-DYNA to investigate the dynamic response of UHPC beams with rectangular openings exposed to low-velocity impact. The calibrated Continuous Surface Cap (CSC) model is primarily validated through quasi-static four-point loading tests on UHPC beams with openings. Following this validation, numerical simulations of drop hammer impact are carried out to comprehensively analyse the behaviour of UHPC beams with openings. Furthermore, parametric investigations are performed to evaluate the impact response of UHPC beams with large or small openings, considering various design factors such as opening size, opening position, stirrup quantity and UHPC strength level.

Low-velocity impact damage characteristics of flax/glass epoxy hybrid laminates on the influence of different temperatures: Experimental and numerical analysis

Low-velocity impact damage characteristics of flax/glass epoxy hybrid laminates on the influence of different temperatures: Experimental and numerical analysis

A Novel Spring-Actuated Low-Velocity Impact Testing Setup

Evaluating the behavior of materials and their response under low-velocity dynamic impact (less than 30 m/s) is a challenging task in various industries. It requires customized test methods to replicate real-world impact scenarios and capture important material responses accurately. This study introduces a novel spring-actuated testing setup for low-velocity impact (LVI) scenarios, addressing the limitations of existing methods. The setup provides tunable parameters, including adjustable impactor mass (1 to 250 kg), velocity (0.1 to 32 m/s), and spring stiffness (100 N/m to 100 kN/m), allowing for flexible simulation of dynamic impact conditions. Validation experiments on steel plates with a support span of 800 mm and thickness of 5 mm demonstrated the system’s satisfactory accuracy in measuring impact forces (up to 714.2 N), displacements (up to 40.5 mm), and velocities. A calibration procedure is also explored to estimate energy loss using numerical modeling, further enhancing the test setup’s precision and utility. The results underline the effectiveness of the proposed experimental setup in capturing material responses during low-velocity impact events.

Low-Velocity Impact Resistance and Compression After Impact Strength of Thermoplastic Nanofiber Toughened Carbon/Epoxy Composites with Different Layups.

This study investigates the effectiveness of polyether block amide (PEBA) thermoplastic elastomeric nanofibers in reducing low-velocity impact damage across three carbon fiber composite lay-up configurations: a cross-ply [0°/90°]2s (CP) and a quasi-isotropic [0°/45°/90°/-45°]s (QI) lay-up utilizing unidirectional plies, and a stacked woven [(0°,90°)]4s (W) lay-up using twill woven fabric plies. The flexural strength and interlaminar shear strength of the composites remained unaffected by the addition of nanofibers: around 750 MPa and 63 MPa for CP, 550 MPa and 58 MPa for QI, and 650 MPa and 50 MPa for W, respectively. The incorporation of nanofibers in the interlaminar regions resulted in a substantial reduction in projected damage area, ranging from 30% to 50% reduction over an impact energy range of 5-20 J. Microscopic analysis showed that especially the delamination damage decreased in toughened composites, while intralaminar damage remained similar for the cross-ply and quasi-isotropic lay-ups and decreased only in the woven lay-up. This agrees with the broad body of research that shows that interleaved nanofibers result in a higher delamination resistance due to toughening mechanisms related to nanofiber bridging of cracks. Despite their ability to mitigate delamination during impact, nanofibers showed limited positive effects on Compression After Impact (CAI) strength in quasi-isotropic and cross-ply composites. Interestingly, only the woven fabric composites demonstrated improved CAI strength, with a 12% improvement on average over the impact energy range, attributed to a reduction in both interlaminar and intralaminar damage. This study indicates the critical role of fiber integrity over delamination size in determining CAI performance, suggesting that the delaminations are not sufficiently large to induce buckling of sub-layers, thereby minimizing the effect of nanofiber toughening on the CAI strength.

Recycled PET foam core sandwich panels with reinforced hybrid composite facesheets: A sustainable approach for enhanced impact resistance

This research explores the Low-Velocity Impact behavior of thermoplastic composite sandwich panels with 100% recycled Polyethylene Terephthalate (PET) foam sourced from post-consumer plastic water bottles. Being recognized as a reliable technique, hybridization using stainless-steel mesh layers was employed to reinforce the panels’ composite facesheets of sandwich panels accessible for modular housing, cold storage rooms and cargo trucks. Adequate impregnation of the reinforcement metallic mesh layer alongside proper skin-to-core adhesion was accomplished by optimizing a two-phase compression molding method. The effect of hybridization on impact response of sandwich panels with two different PET foam core thicknesses, and stacking sequence were evaluated. It was revealed that reinforcing the impacted surface of the composite sandwich panels significantly increased the perforation threshold. Moreover, analyzing the post-impact section view of the samples indicated that hybridization modified the damage propagation response of the PET foam core sandwich composites, through which the energy absorption capacity was improved.

Investigation into the Role of Z-Fiber Orientation in Low-Velocity Impact Behavior of Sandwich-Structured Composite: Numerical and Experimental Analysis

Investigation into the Role of Z-Fiber Orientation in Low-Velocity Impact Behavior of Sandwich-Structured Composite: Numerical and Experimental Analysis

Investigation of Low Velocity Impact Behavior of Aluminum Honeycomb Sandwich Structures with GFRP Face Sheets by Finite Element Method

The aim of this study is to examine the low velocity impact behavior of aluminum honeycomb sandwich structures with glass fiber reinforced plastic (GFRP) face sheets with the help of finite element method. In the study, low velocity impact tests were carried out in the LS DYNA finite element program to examine the effects of face sheets thickness, core number, wall thickness, impact location and impact velocity on maximum contact force, absorbed energy efficiency and damage mode. Progressive damage analysis based on the Hashin damage criterion and the combination of Cohesive Zone Model (CZM) and the bilinear traction-separation law was performed using the MAT-54 material model. At the end of the study, it was determined that the face sheets thickness in sandwich structures had a significant effect on the impact resistance up to a certain impact energy. It has been observed that as the impact velocity gradually increases, there is a decrease in the contact force after a certain threshold value. As the impactor velocity increases, the energy absorption efficiency also increases. It has been determined that the location of the impact is very effective on peak force and energy absorption efficiency. The effect of the number of core layers depends on the face sheets thickness. When the face sheets thickness was not damaged at first contact, the peak force value increased in parallel with the number of layers. It was determined that the dominant damage mode after impact was matrix damage. It has been observed that as the energy level of the impactor increases, damage also occurs on the back surfaces.

Low-velocity impact on a CFRP sandwich plate with a reentrant auxetic core

Theoretical analysis is utilized to model the low-velocity impact (LVI) on a Carbon-Fiber Reinforced Polymer (CFRP) sandwich plate with reentrant auxetic core. The Zig-Zag theory is employed to formulate the displacement field of the sandwich plate. The mechanical characteristics of the reentrant auxetic core unit cell are determined through the application of Gibson’s equations. The influences of the unit cell thickness, the unit cell angle, the number of layers of the unit cell along the plate thickness, the impactor radius, and the impactor initial velocity on the LVI study of CFRP sandwich plate with reentrant auxetic core are investigated in detail.

Classification, Localization and Quantization of Eddy Current Detection Defects in CFRP Based on EDC-YOLO.

The accurate detection and quantification of defects is vital for the effectiveness of the eddy current nondestructive testing (ECNDT) of carbon fiber-reinforced plastic (CFRP) materials. This study investigates the identification and measurement of three common CFRP defects-cracks, delamination, and low-velocity impact damage-by employing the You Only Look Once (YOLO) model and an improved Eddy Current YOLO (EDC-YOLO) model. YOLO's limitations in detecting multi-scale features are addressed through the integration of Transformer-based self-attention mechanisms and deformable convolutional sub-modules, with additional global feature extraction via CBAM. By leveraging the Wise-IoU loss function, the model performance is further enhanced, leading to a 4.4% increase in the mAP50 for defect detection. EDC-YOLO proves to be effective for defect identification and quantification in industrial inspections, providing detailed insights, such as the correlation between the impact damage size and energy levels.

Research on low-velocity impact performance of polyurethane foam-filled M-type GFRP foldcore sandwich plate

The M-type GFRP (Glass Fiber Reinforced Polymer) foldcore was prepared by thermal pressing method, and was bonded with the panel to obtain the complete foldcore sandwich structure and filled the core with polyurethane foam. The influence of foam filling, impact energy and impact position on the damage mode and impact dynamic response under the low-velocity impact of GFRP M-type foldcore sandwich structure is studied through low-velocity experiment. The results show that the impact resistance of N-side impact is better than the B-side impact. Foam filling could effectively closing the gap between the N-side impact and B-side impact. In addition, foam filling could absorb about 15%-25% more energy than the empty core sandwich plate.

Predicting low-velocity impact on the CNTs-reinforced plate using machine learning models

Purpose The study aims to predict a low-velocity impact on a plate reinforced with carbon nanotubes (CNTs) using machine learning models. Design/methodology/approach The first-order shear deformation plate theory (FSDT) is used to express the plate displacements filed. The Hertz nonlinear contact law is used to predict the contact between impactor and plate. Using the energy method and Hamilton’s principle, the motion equations are extracted. The six main parameters considered as inputs to machine learning models are CNTs percentage, impactor radius, plate thickness, plate length and width, CNTs distribution profile and impactor initial velocity. These input parameters are used to predict two impact targets including contact force and contact time. Findings As the values of the targets are continuous, the machine learning task is considered a regression problem. Therefore, this study uses different regression models to predict the targets. These regression models include linear regression, stochastic gradient descent regressor, Bayesian regression, partial least squares regression, Gaussian process regression, multilayer perceptron regressor, support vector regression and decision tree regression. To validate the effectiveness of the regression models, experiments are designed based on different evaluation metrics. The results of the experiments demonstrate that the machine learning models achieve promising performance in predicting the contact force and contact time based on the input parameters. Originality/value Due to the volume of high numerical calculations of impact mechanics to reach the response, the targets of the impact problem are predicted using a variety of machine learning methods.

Effect of Star-like Polymer on Mechanical Properties of Novel Basalt Fibre-Reinforced Composite with Bio-Based Matrix.

This study is aimed at developing a fibre-reinforced polymer composite with a high bio-based content and to investigate its mechanical properties. A novel basalt fibre-reinforced polymer (BFRP) composite with bio-based matrix modified with different contents of star-like n-butyl methacrylate (n-BMA) block glycidyl methacrylate (GMA) copolymer has been developed. n-BMA blocks have flexible butyl units, while the epoxide group of GMA makes it miscible with the epoxy resin and is involved in the crosslinking network. The effect of the star-like polymer on the rheological behaviour of the epoxy was studied. The viscosity of the epoxy increased with increase in star-like polymer content. Tensile tests showed no noteworthy influence of star-like polymer on tensile properties. The addition of 0.5 wt.% star-like polymer increased the glass transition temperature by 8.2 °C. Mode-I interlaminar fracture toughness and low-velocity impact tests were performed on star-like polymer-modified BFRP laminates, where interfacial adhesion and impact energy capabilities were observed. Interlaminar fracture toughness improved by 45% and energy absorption capability increased threefold for BFRP laminates modified with 1 wt.% of star-like polymer when compared to unmodified BFRP laminates. This improvement could be attributed to the increase in ductility of the matrix on the addition of the star-like polymer, increasing resistance to impact and damage. Furthermore, scanning electron microscopy confirmed that with increase in star-like polymer content, the interfacial adhesion between the matrix and fibres improves.

Particularities on the Low-Velocity Impact Behavior of 3D-Printed Sandwich Panels with Re-Entrant and Honeycomb Core Topologies

This work describes, through experimental and numerical investigations, the mechanical behavior and energy absorption characteristics of 3D-printed sandwich panels with cellular cores subjected to low-velocity impact. Using fused deposition modeling techniques (FDM), three different sandwich panels, one with a regular hexagonal core and two with re-entrant cores at 0 and 90 degrees, were fabricated. The sandwich panels were subjected to low-velocity impact, at impact energies of 10 J and 15 J. A comprehensive investigation of the panels’ behavior through experimental testing and numerical simulation was conducted. The results indicate that the sandwich panel with a 90 degrees re-entrant core is stiffer and absorbs the largest amount of impact energy but, at the same time, suffers significant damage to the upper facesheet. The 0 degrees re-entrant core is compliant and provides both impact resistance and good energy absorption characteristics. Such a sandwich panel finds its application in the construction of personal protective equipment, where the aim is to minimize the forces transmitted during low-velocity impacts and maximize the total absorbed energy. Re-entrant core sandwich panels prove to be very good candidates for replacing the honeycomb core sandwich, depending on the desired engineering application.

Discrete element model of low-velocity projectile penetration and impact crater on granular bed

The present study investigates the low-velocity impacts of a spherical projectile into a bed of spherical particles using Discrete Element Method (DEM) simulations and laboratory experiments. The findings reveal intricate forces and energy transformations, indicating the phenomena leading to projectile impact, penetration, cessation, and crater formation. The DEM result indicates that the penetration stopping time of the projectile is not influenced by impact velocity. Further, simulations show that projectile penetration depth correlates with 1/2.7 power of total impact height, while crater diameter and depth scale with 1/4.32 power of nondimensional impact energy. The shape of the resulting crater appears independent of impact velocity and the maximum diameter of the fluidized region varies with the 1/2.68 power of impact velocity. Experimental validation confirms the accuracy of predicted penetration depths and crater diameters, enhancing confidence in DEM simulations. These findings extend scaling laws and reveal the influence of larger particles on low-velocity impact dynamics, addressing unexplored aspects of granular cratering.

Investigation of mechanical behavior of reinforced u-profile composites under low velocity impact

In this study, the impact resistance of reinforced composite panels with unsupported, and U profile supported by I profile was numerically examined. For this purpose, firstly, unsupported glass fiber/epoxy composite panels were designed, and then I-profile composite supports were added to these panels. The impact strength, and damage behavior of supported, and unsupported specimens under low-velocity impact were compared numerically. In the analysis, the MAT22 material card, also known as the Chang-Chang damage model for composite material, was used in the LS-DYNA program. As a result of the analysis, maximum damage load of the unsupported specimen is determined to be approximately 294 N. It was determined that by adding an I profile to the structure, the maximum damage load increased to 543 N. It was seen that the added I profile supports increased the maximum contact force of the composite structure by approximately 85%. Fiber breakage damages were observed in both supported, and unsupported specimens. However, with the use of I profile support, the damaged area was further reduced. It has been determined that under low-velocity impact, supported specimens exhibit more rigid material behavior than unsupported specimens.

Prediction of low-velocity impact responses for bio-inspired helicoidal laminates based on machine learning

The inherent capacity of natural protective systems to withstand impact loadings, attributed to their microscale helicoidal architectures, has garnered significant interest. Drawing inspiration from this mechanically robust design, this study aims to introduce the composite laminates with a helicoidal distribution and to accurately and efficiently predict their Low-Velocity Impact (LVI) responses. Initially, the Latin hypercube design (LHS) was employed to generate 500 samples representing various pitch angles. An experimentally verified finite element model was then established to capture the load-displacement curves and energy-time curves for these 500 samples. Subsequently, the Convolutional Neural Network (CNN) model was utilized to accurately predict the load-displacement curves and energy-time curves for bio-inspired helicoidal laminates across different pitch angles. The principal component analysis (PCA) was used to enhance the efficiency of learning the load-displacement and energy-time curves in a reduced dimensional space, and the SHapley Additive exPlanations (SHAP) method was employed to investigate the feature importance of pitch angle. Finally, the helicoidal laminate with the highest energy absorption for a given volume was obtained by the genetic algorithm (GA) combined with the CNN model. This optimized laminate demonstrates a remarkable 9.5 % improvement in energy absorption compared to the best-performing sample within the original data set. Furthermore, the "spiraling" delamination damage of the helicoidal laminates was studied, which indicates that the delamination with small pitch angle is more pronounced for that with large pitch angle. The proposed method offers significant advantages in terms of cost reduction and efficiency enhancement for predicting the LVI responses of helicoidal laminates, holding immense potential in structural design and optimization of composite materials.

Prestressed concrete slabs subjected to low-velocity impact: Theoretical analysis model and design method

Bidirectional bonded prestressed concrete (PS) structures are widely used in energy engineering structures due to their excellent impermeability. Owing to the particularity of the structure and the severity of damage consequences, the impact dynamic performance of bidirectional bonded PS structures has been widely concerned. Nonetheless, the existing researches focus on the test and finite element, and lacks the theoretical analysis model that can consider the whole process of load action, let alone the corresponding anti-impact design method. Therefore, based on the existing test and finite element results, the resistance function model of bidirectional bonded PS slab is proposed in this paper, and the anti-impact design method is formed. Firstly, the performance of specimens under low-velocity impact loading and quasi-static loading conditions is compared, and the effects of inertia force and material strain rate on the dynamic performance of specimens under low-velocity impact are further explored. Then, a resistance function theoretical analysis model that can consider the whole process of load action is proposed with a quadrilinear form, and the analytical expressions of resistance and stiffness at characteristic points are derived. Subsequently, the accuracy of the resistance function model is verified based on the existing test results. Furthermore, based on the resistance function model, the influence laws of compressive strength of concrete, prestressing degree, reinforcement ratio of reinforcement and slab thickness on slab resistance are analyzed. Finally, an anti-impact design method considering perforation and scabbing failure is proposed, and the feasibility of the design method is verified by impact test results.

Energy absorption of the kirigami-inspired pyramid foldcore sandwich structures under low-velocity impact

Foldcore sandwich structures offer a promising alternative to conventional honeycomb sandwiches in the field of lightweight structures, demonstrating significant potential as efficient energy absorption devices. The dynamic behavior of foldcore sandwich structures is crucial in response to low-velocity impacts in various engineering scenarios such as bird strikes, airdrops, and vehicle collisions. This study investigates the dynamic responses of a kirigami-inspired pyramid foldcore sandwich subjected to low-velocity impacts, which has previously exhibited remarkable energy absorption efficiency under quasi-static compression. Through a combination of experimental investigations and numerical simulations under impact conditions, it is observed that the pyramid foldcore initially undergoes pronounced localized deformation which results in a sensitivity to the loading rate and causes the high initial peak stress. Different from the mechanism observed under quasi-static compression, additional stationary plastic hinges on the facets are triggered during the post-buckling stage, thereby slightly enhancing the overall energy absorption. Moreover, the multi-layer pyramid foldcores with graded geometries are proposed, characterized by varying height and wall thickness for each layer. The graded pyramid foldcores significantly reduce the initial peak stress while maintaining energy absorption efficiency. In comparison with the conventional square honeycomb and Miura-ori foldcore under the impact velocity of 10 m/s, the uniformity ratio of the graded pyramid foldcore decreases by 70.9 % and 80.5 %, while the specific energy absorption improves by 0.97 % and 138.37 %, respectively. To summarize, the graded pyramid foldcore shows outstanding energy absorption efficiency, indicating its potential as a high-performance sandwich structure for impact applications.

Investigation of Residual Strength in CFRP Double-Adhesive Single Lap Bonded Joints after Low-velocity Impact

ABSTRACT Single lap adhesive joints are prone to debonding and delamination during impact, affecting the residual tensile strength and mechanical properties. To improve the stress distribution and withstand larger loads, this paper proposes to use Araldite 2015 ductile adhesive at both ends of the joint and AV 138 brittle adhesive in the middle. Through finite element analysis and experiments, the residual strength and damage of the joint under different impact conditions are investigated, and a three-parameter Gram-Charlier model is established. The results show that the model can fit the data points accurately with a coefficient of determination of error above 0.99. As impact energy increases, the residual strength of the joint decreases, especially the AV 138 joint is more sensitive. The residual strength on one side of the impact joint is approximately 20% higher compared to the middle of the impact joint. For the same energy, the residual strength of the secondary impact was about 13% higher than that of the single impact. The main failure mode is cohesive failure, which gradually changes to fiber tear. The numerical simulation matches the experimental results, which verifies the reliability of the simulation and analysis methods.