Low-velocity Impact Response Research Articles

Investigating the low velocity impact response of additively manufactured tri-material composite structure with application on helmet

Additively manufactured composite structures can be utilized in the production of engineering materials with enhanced mechanical properties. In this work, mono-, bi-, and tri-material structures (MMS, BMS, and TMS, respectively) were fabricated using additively manufactured PLA (poly-lactic acid) lattice frames embedded with Polyurethane (PU) foam and milled glass fibers (MGFs). TMS samples were reinforced with MGFs at 1.25, 2.5, 3.75, and 5.0 vol%, indicated as TMS-1, TMS-2, TMS-3, and TMS-4, respectively. The mechanical response of these composite structures was tested by applying a low-velocity impact load. The effects of MGF content and variations in applied impact energy, and variation in microstructure on the composite samples were investigated. Results revealed an enhanced mechanical response of TMS samples compared to MMS and BMS. Additionally, with increasing applied impact energy, the TMS samples showed an improved corresponding response, with a peak absorbed energy of 96.03% of the applied 60 J energy. Furthermore, to study the applicability of the composite structures in real-life applications, helmet prototypes made of MMS, BMS, and TMS were designed and tested under the applied low-velocity load, showing an improved response of TMS helmet samples compared to the other composite structures.

Empirical and numerical analysis of damage tolerance in multifunctional hybrid sandwich fiber reinforced polymers composite structures for aerospace applications using compression after impact (CAI) testing

AbstractThis study presents a novel hybrid‐sandwich composite structure, customized for nose radomes applications, incorporating a foam core and distinct opposite face sheets composed of Kevlar and S‐Glass materials. Addressing in‐phase electromagnetic properties, UV protection and low velocity impact responses in our previously published work, this paper empirically and numerically investigates the damage tolerance response of the proposed structures through compression after impact (CAI) testing. The low velocity impacts (LVIs) on S‐Glass face sheets exhibited unique energy dispersion and absorption mechanisms, resulting in variations in indent damage depths and widths across all impact energy levels as compared with LVIs on Kevlar face sheets. After experimentally assessing the CAI behavior, a FE model is developed to predict CAI behavior, which closely aligned with experimental findings. This study, unprecedented in existing literature, proposes hybrid sandwich structures for nose radome aerospace applications, with superior specific impact and residual strength compared to various composite sandwich structures documented in the published literature expanding its utility beyond radomes.Highlights Innovative composites with superior low velocity impact response, tested for compression after impact performance. Designed for nose radomes found suitable for other impact prone applications. Experimental and numerical modeling showed comparable results. Major differences observed in damage mechanics, resistance, and tolerances.

Low‐velocity impact characterization of polyurethane rubber/nano‐clay enriched sustainable sandwich composites: Synergy of experimentation and simulations

AbstractThis research proposes a novel sustainable composite using basalt (B), hemp (H) and polyurethane rubber (Pu) reinforced in nano clay functionalised epoxy matrix for sacrificial structural applications prone to low‐velocity impact (LVI). To this end, symmetric and asymmetric laminates such as HHHH, BBBB, BHHB, BHPuHB, BBPuHH and BPuBPuHPuH are fabricated using compression molding techniques and subjected to LVI at three different impact energies of 19.66, 39.39, and 59.05 J. The hemp fibers were treated with NaOH solution before fabrication. Material characterization such as X‐ray diffraction, Raman spectroscopy and morphological studies has been carried out. The impact and post‐impact properties of the proposed composites are experimentally evaluated and validated with the finite element (FE) results. The effect on the residual tensile strength degradation of laminates at different interlayers and energy levels is also investigated using the Caprino analytical model. The barely visible impact damages (BVID) are investigated through non‐destructive dye‐penetration tests, which facilitate easy identification of the prominent LVI damages like “Plateau” and “Cliff‐drop” impressions. Based on the impact energy absorption and residual tensile strength, proposed laminates followed BHPuHB > BBBB > BHHB > HHHH. The experimentation suggests that Polyurethane core laminates support maximum impact energy absorption by favoring a structural change in interlayers. Also, the residual tensile strength decreases as impact velocity increases.Highlights Low‐velocity impact behavior of sustainable composites is experimented. Basalt, hemp and polyurethane rubber are reinforced in nano clay epoxy matrix. A FE framework to validate the experimentation is proposed. Dye penetrant NDT is adopted to investigate the damages. Morphological studies are conducted to understand LVI responses.

Analysis of low-velocity impact responses in bidirectional gradient double-arrow auxetic metamaterials

In this paper, we propose double-arrowed auxetic metamaterials (DAMs) featuring bidirectional wall thickness gradients. Their crushing behavior under low-velocity impact is systematically investigated using a validated finite element (FE) model. The results show that the bidirectional gradient design effectively improves the transverse necking effect observed in uniform DAMs. The bidirectional gradient configuration contributes to improved energy absorption and impact strength. Specifically, there is a 60.7% increase in specific energy absorption (SEA) and a 40.5% improvement in plateau stress, compared to uniform DAMs. Furthermore, the bidirectional gradient configuration reduces the initial peak stresses generated during the dynamic crushing process and exhibits higher crash load efficiency (CLE).

Low-velocity impact response optimization of the foam-cored sandwich panels with CFRP skins for electric aircraft fuselage skin application

Abstract Composite sandwich structures are widely used in the aerospace field due to their advantages of high strength, lightweight, and fatigue resistance. However, these structures are prone to damage with very-low-energy impacts. In order to improve the impact resistance of aircraft skin structure, a low-velocity impact resistance of sandwich structure specimens was tested by means of drop hammer impact, and the impact damage area was scanned by ultrasonic C-scan, and obtains the impact damage of specimens with different impact energies and different ply sequences. Combined with the Hashin failure criterion, the finite element equivalent model of composite sandwich structure under low-velocity impact was established. The errors between the simulation results and the C-scan results of the test piece were less than 10%, in which the experimental measurements and numerical predictions were in close agreement. Finally, the finite element equivalent model was applied to optimize the application of model sandwich, which was used for fuselage skin of a certain electric aircraft. The total thickness of the laminate structure remains unchanged before and after optimization, but the impact resistance was significantly enhanced. The ±45° lay-up was beneficial for the structure to absorb the impact energy.

Dynamic responses and damage/element composition analysis of thermoplastic polyamide reinforced epoxy composites exposed to HCI environment

AbstractThe present study aimed to examine how the corrosive environment affected the low‐velocity impact (LVI) characteristics and damage mechanisms of thermoplastic polyamide fiber‐reinforced polymer (PFRP) composites. In this regard, composite specimens were subjected to corrosive environment containing 10 wt.% diluted HCl for one week and one month before LVI tests. To investigate the hostile effects of the corrosive environment on the composites, scanning electron microscope (SEM) coupled with energy‐dispersive X‐ray system (EDX) analyses were carried out, and thus variations in the elemental composition and damage mechanisms for the composites were determined. According to the examinations, it was discovered that the degradation in LVI responses, such as contact stiffness, bending stiffness, and peak force, increased with longer aging time, as expected. Furthermore, when the aging effect was assessed based on absorbed energy, the specimens exposed to a corrosive environment for one month exhibited the highest energy absorption compared to the control and 1‐week‐immersed ones. The degrading effect of the HCI environment appeared as higher damage severity on the composites, which was also detected from the SEM images. According to the SEM analyses, matrix cracks, corrosion pits, and local surface imperfections caused by ion exchange are detected in 1‐week‐immersed specimens, while more serious damage mechanisms such as fiber breakage and fiber pull‐out are noted in specimens exposed to corrosive environment for 1 month. Furthermore, approximately 6.33 wt.% CI was identified in the composites after 1 month of aging, which was associated with the hydrolysis triggered by rise in the composite's damage severity.Highlights Aging effects in mechanical properties of PFRP composites were investigated LVI tests were conducted to determine dynamic responses of aged composites Longer aging time led to more severe damages such fiber rupture, delamination etc. PFRP composites absorbed at least 68% of impact energy.

On low velocity impact response of Sandwich composite with jute/epoxy facesheet and cenosphere reinforced functionally graded Core: Experimental and finite element approach

AbstractThe assessment of energy absorption behavior has a vital role in determining suitability of lightweight composites for impact protection applications. This study focuses on evaluating the energy absorption characteristics of cenosphere reinforced epoxy syntactic foam core and jute epoxy facesheet sandwich composite subjected to low velocity impact. The syntactic foam is composed of lightweight cenospheres embedded within an epoxy matrix, resulting in a high‐strength and lightweight composite material. Low velocity impact tests were conducted using a drop tower apparatus to simulate realistic impact conditions. The impact force, energy absorption and damage mitigation of the syntactic foam specimens with varied weight percentage of Cenosphere (0%, 10%, 20% and 30%) were measured and analyzed to assess the energy absorption behavior. The gradation revealed that the weight of top layer when compared to bottom layer is 50.49%, 70.23% and 95.74% less in syntactic foam core with 10, 20 and 30 wt% Cenosphere respectively, indicating gradation. The study demonstrates that the addition of Cenosphere up to 20 wt% enhances the energy absorption capacity of the sandwich composites by 59.37%–93.44% compared to sandwich without Cenosphere reinforced core. However, beyond this threshold, a decline in energy absorption is observed when subjected to low‐velocity impact (LVI). Fractography analysis demonstrates that the incorporation of Cenosphere induces a rough fracture surface with deep river‐like topography, indicative of greater energy absorption during impact loading. This substantiates the conclusion that Cenosphere‐reinforced syntactic foams exhibit enhanced impact resistance, making them promising materials for structures subjected to low‐velocity impact events.Highlights Development of functionally graded core sandwich composite for low velocity impact applications. Assessing the performance of developed composites under low velocity impact loading. Determining the optimal weight percentage of cenospshere in functionally graded core. Studying the fractography of developed sandwich composites. Corelation between experimental and finite element studies.

Low-velocity impact responses and failure of sandwich structure with carbon fiber composite honeycomb cores

The objective of this study is to examine the response and failure of honeycomb sandwich structures made of carbon fiber reinforced polymer (CFRP) composites under low-velocity impacts. Four impact tests with varying energies are performed to induce four distinct damage states in the sandwich structure: no discernible damage, damage to the top face sheet and a portion of the core, damage to the lower face sheet, and total penetration. The damage characteristics of the sandwich structures is analyzed by using industrial tomography technology (CT) without destroying them. A refined finite element model is established to further explain the deformation behavior and energy absorption mechanism of the structure, clarifying the effects of the honeycomb core's structural parameters, such as wall thickness, cell side length, and core height. To enhance the precision of simulation outcomes, a model for the onset and progression of damage in plain woven composites is incorporated into the user-defined material subroutine. The experiments and simulations demonstrate a high level of consistency in terms of peak loads, failure mode, and energy absorption.

A plate containing a central rectangular hole made of PMMA resin and reinforced with graphene particles: low-velocity impact analysis

Purpose Due to the important and extensive use of graphene in the engineering structures, the purpose of this paper is to investigate the low-velocity impact (LVI) response of a graphene-reinforced plate with a rectangular central hole. Design/methodology/approach In this paper, Halpin-Tsai theory is used to model the mechanical properties of the plate made of polymethyl methacrylate (PMMA) resin and graphene particles. First, the plate displacement field is presented, and then the strains and stresses are obtained. The motion equations are extracted using energy equations, Ritz method and generalized Lagrange equations. The verification of theoretical formulation shall be carried out using the ABAQUS finite element software suite. Findings The effects of graphene volume fraction, approaching the impact point to the corner of the rectangular plate, and different boundary conditions of the plate are studied for LVI of impactor with spherical tip on the rectangular central hole reinforced by graphene. Important responses of the impact, such as the contact force between the impactor and the plate as well as the displacement of the plate at the impact place, are investigated and analyzed in this research. Originality/value Considering the wide application of graphene in the engineering structures, the simulation of the LVI on the graphene-reinforced plate made of PMMA resin with a rectangular central hole is carried out in this paper using numerical and theoretical modeling.

Numerical investigation of the low-velocity impact response of 3D orthogonal woven composite plates with preloads

Three-dimensional orthogonal woven composites (3DOWCs) offer significant advantages in engineering applications due to their designability for spatial structures and ability to minimize delamination damage. As primary load-bearing structures, 3DOWCs are always in preloading conditions prior to potential low-velocity impact (LVI) events. This paper presents a macro-meso coupled finite element (FE) model for investigating the response of preloaded 3DOWCs subjected to LVI. The accuracy of the proposed numerical model is validated by a comparison with available experimental data in terms of impact performance and damage state. Furthermore, the influence of preload and impactor shape on the LVI performance of 3DOWCs is examined, and detailed analysis is provided regarding the associated damage mechanisms. This study offers a transferable numerical approach that can be applied to studying the coupling problems of LVI and preload in other textile composite structures.

On multiple low-velocity impact response and compression after impact of composite laminates

This paper aims to study the multiple low-velocity impact (LVI) response and compression after impact (CAI) performance of composite laminates subjected to different energy impacts. The study includes an analysis of the effect of the first impact with different energy on the second impact with the same energy at the same location. The results show that the first impact has a certain enhancement effect on the impact resistance of the laminates when the impact energy is very small. Overall, with the increase of the first impact energy, the impact resistance and the residual compressive strength of the laminate significantly reduce.

Experimental investigation on the low-velocity impact responses of fibre metal laminates with various internal and external factors

This paper aims to investigate the low-velocity impact (LVI) failure mechanism of fibre metal laminates (FMLs), and systematically explore the effects of internal factors (layup sequence and laminate configuration) and external factors (impact energy and environmental temperature) on the LVI responses. The drop-weight impact tester was utilised to conduct LVI tests at -30 °C, 25 °C, and 80 °C on FML-2/1 and FML-3/2 laminates. These laminates were made of S-class high-strength glass fibre and 2024 aluminium-alloy sheet with unidirectional, angle-ply, cross-ply and quasi-isotropic layup sequences. The characteristic curves including contact force-time, contact force-deflection, absorbed energy-time, and strain-time near the dent on the impacted and non-impacted specimen surfaces were obtained respectively. Furthermore, the dent depth of the impacted surface of the FMLs was measured. FML's damage was detected by ultrasonic C-scan, and its longitudinal and transverse sections were scanned by X-ray computed tomography (CT). The findings suggest that the layup sequence has a significant effect on the LVI response of FML-2/1, but has no obvious influence on FML-3/2. Moreover, FML-3/2 exhibits greater impact resistance compared to FML-2/1. The severity of LVI damage increases with the increase of impact energy. Notably, compared to the cases at 25 °C, the LVI failure mechanisms of FMLs undergo significant changes at -30 °C. The elevated temperature of 80 °C significantly affects the LVI damage of FML-2/1, while it has no significant effect on FML-3/2.

Low velocity impact response of Automated Fiber Placement Advanced Placed Ply composites

This study explores the influence of the internal architecture in the low-velocity impact response of Automated Fiber Placement Advanced Placed Ply laminates. AP-PLY laminates with different lay-up are subjected to low velocity impact and compression after impact experiments. Different performance in terms of damage tolerance is obtained as a function of their internal architecture. Triaxial and quasi-isotropic AP-PLY configurations presented a reduced extension of the delamination in comparison to cross-ply panels. As a result, the cross-ply configuration exhibited a drastic loss in residual strength of 49.1% when subjected to 50 J of impact energy. Numerical simulations were employed to provide insight into the deformation and failure mechanisms (e.g., matrix cracking of directly impacted yarns, delamination or tow debonding), and assess the performance of AP-PLY against conventional angle-ply laminates, predicting larger delamination for the latter, showing the potential of the AP-PLY architecture to produce laminates with improved low-velocity impact performance.

Experimental investigation on the effects of stainless-steel mesh reinforcing layers on low-velocity impact response of hybrid thermoplastic glass fiber composites

This study aims to assess the hybridization effect on the perforation threshold of Low-Velocity Impact (LVI) in thermoplastic glass composite laminates, incorporating layers of resin-impregnated stainless-steel mesh. Reinforcing methodologies such as hybridization are recently being adopted as a practical approach to increasing the energy-absorbing capacity of polymer composites. In the current paper, a multi-step hot press lamination method has been employed to fabricate the hybrid composite laminates strengthened with stainless-steel mesh layers. Several stacking sequences, metal mesh wire sizes, orientation and position relative to the impactor have been examined under various LVI energies. It was revealed that the LVI penetration energy was increased for the thermoplastic-based composite laminates reinforced with stainless-steel mesh layers. Furthermore, the LVI penetration energy threshold was significantly influenced by the metal mesh wire size, orientation and stacking sequence. Finally, the backlight method capability was assessed to detect the after-impact interlaminar damages.

A novel technique for low-velocity impact of shallow arches

In the current study, an analytical model to analyze the low-velocity impact (LVI) response of metamaterial shallow arches subjected to rigid body impact is presented. The presented nonlinear model considers transverse deformation of the cross-section and geometric nonlinearity based on the higher-order shear theory and von Kármán nonlinearity. The research delves into three key aspects. The first is concerned with the establishment of a contact model to capture the contact characteristics between the impactor and the arch. The second aspect deals with the design of the member with Negative Poisson’s Ratio (NPR). The third aspect is concerned with the asymptotic solution of dynamic equations by using a two-perturbation technique. The proposed model is used to analyze the effects of auxetic, initial deformation, and foundation on the impact response and post-impact vibration of the arch. The results show that the contact area between the sphere impactor and the arch is elliptical. It is also noted that the contact force and indentation are highly dependent on the laminated configuration and auxetic properties. The study reveals that the presented model is a valid technique to evaluate the impact characteristics of metamaterial arches along with optimal design impact resistance of arches.

A comprehensive analysis of low velocity impact response of [0/±45/90]s thin woven GFRP composites at room temperature

This study is motivated by the need to explore the low-velocity impact behavior of angle-ply thin woven GFRP composites with stacking sequence of [0/±45/90]s, especially the lack of literature concerning damage analysis correlation with a comprehensive range of measurements. The damage diameter, area, and perimeter length are characterized in this study by a novel AutoCAD image processing technique. The test results revealed that specimens subjected to impact energies in the range of 2–30 J are free from edge delamination compared to those tested at 40–50 J. Decreasing the contact duration at impact energy of 60 J is due to perforation accompanied with damage propagation toward the specimen edges and thus, the contact force is sharply dropped from its maximum value of about 4.48kN to 1.3kN. Consequently, both rebound speed and coefficient of restitution dropped to zero. The direct measurement of the energy threshold is increased in the following order: energy threshold at Fmax (2.3–14.9 J), first penetration (load drop) after peak load (23.9–25.6 J), penetration energy threshold (37.9 J), perforation energy threshold (31.1 J), and perforation and crack propagation energies (43.3 J). The perimeter length represents a novel damage parameter, exhibiting a strong correlation with impact energy, as evidenced by a high coefficient of determination of 0.97.

Experimental Investigation of the Effect of Core Structures on Low-Velocity Impact Response of PEEK Sandwich Panels Manufactured by FDM

Experimental Investigation of the Effect of Core Structures on Low-Velocity Impact Response of PEEK Sandwich Panels Manufactured by FDM

Low Velocity Impact Response of Kenaf/Epoxy Composites Exposed to Corrosive Solutions

Kenaf fibres are one of the natural fibres that have been widely explored since the fibres are low in cost, have excellent mechanical properties and biodegradability features. Recently, there have been numerous efforts to employ kenaf fibres reinforced composites in a wide range of applications. One of the concerns is that these composites may be exposed to several ranges of corrosive conditions during their in-service life and their durability performance is extremely necessary. Therefore, the aim of this work is to study the mechanical response subjected to flexural and low velocity impact tests of kenaf/epoxy composites with a variety of corrosive solutions, after being exposed to hydrochloric acid (HCl) and sodium hydroxide (NaOH) solutions for durations of 12, 24 and 36 days. The experiment result demonstrated that the corrosive solutions have a detrimental effect on the flexural properties and impact response of composites. The degradation effect on composites is also found to be dependent on the exposure period in the corrosive solutions. On the other hand, acidic environments have been shown to have a more aggressive effect on the performance of composites than an alkaline environment.

Study on the Low-Velocity Impact Response and Damage Mechanisms of Thermoplastic Composites.

A comparative experimental and numerical study of the impact behaviour of carbon-fiber-reinforced thermoplastic (TP) and thermoset (TS) composites has been carried out. On the one hand, low velocity impact (LVI) tests were performed on TP and TS composites with different lay-up sequences at different energy levels, and the damage modes and microscopic damage mechanisms after impact were investigated using macroscale inspection, C-scan inspection, and X-ray-computed tomography. The comparative results show that the initial damage valve force under LVI depends not only on the material, but also on the layup sequence. The initial valve force of the P2 soft layer with lower stiffness is about 11% lower than that of the P1 quasi-isotropic layer under the same material, while the initial valve force of thermoplastic composites is about 28% lower than that of thermoset composites under the same stacking order. Under the same stacking order and impact energy level, the damage area and depth of TP composites are smaller than those of TS composites; while under the same material and impact energy level, the indentation depth of P2 plies is greater than that of P1 plies, and the damage area of P2 plies is smaller than that of P1 plies, but the change of thermoplastic composites is not as obvious as that of thermoset composites. This indicates that TP composites have a higher initial damage threshold energy and impact resistance at the same lay-up order, while increasing the lay-up ratio of the same material by 45° improves the impact resistance of the structure. In addition, a damage model based on continuum damage mechanics (CDM) was developed to predict different damage modes of thermoplastic composites during low velocity impact, and the analytical results were compared with the experimental results. At an impact energy of 4.45 J/mm, the error of the initial damage valve force is 5.26% and the error of the maximum impact force is 4.36%. The simulated impact energy and impact velocity curves agree with the experimental results, indicating that the finite element model has good reliability.

Energy absorption and low-velocity impact responses of the sandwich panels with lattice truss core

This study investigates the dynamic energy absorption performance of composite sandwich panels with two different configurations of lattice truss core. Two types of core structures were designed and created using polyamide 12 through the selective laser sintering (SLS) additive manufacturing method. These structures, with uniform and graded cell topologies, were created by changing the geometry and layer density of the body-centered cubic (BCC) unit cell. The cores were used to fabricate composite sandwich panels, which were made with E-glass/epoxy face sheets. Then, their ability to absorb energy during low-velocity impact and quasi-static compressive strength was tested using both experimental and numerical methods. It was found that the graded structure absorbed 10, 5, and 3% more energy than the uniform structure for the energy levels of 12.4, 16.5, and 17.9 J, respectively. It was also found that both structures could absorb at least 90% of the impact energy. In terms of strength, the uniform structure was able to tolerate 1.15 times larger impact loads, indicating its higher strength than the graded structure. The uniform structure had 8% more compressive strength.