Low Velocity Impact Research Articles

Response and damage mechanism of carbon/aramid intra-ply hybrid weft-knitted reinforced composites under low-velocity impact

Carbon and aramid fiber hybridization is an effective method to improve the impact toughness of composites, thus this paper attempts to develop carbon/aramid hybrid weft-knitted reinforced composites to improve the impact resistance of carbon fiber composites. Three hybrid and two non-hybrid weft-knitted reinforced composites employing carbon and aramid bundles were prepared. Low-velocity impact tests at different impact energies were performed, and the impacted samples were analyzed for visual and internal damages utilizing a three-dimensional optical microscope, ultrasonic C-scan, and micro-CT to explore the damage mechanisms. The results demonstrate that the knitted stitches and loop configuration affect the peak load, deflection, and damage crack initiation and expansion of the composites. The alternating configurations of carbon and aramid fiber in the in-plane and thickness directions incorporate the advantages of the high strength of carbon fibers and the toughness of aramid, exhibiting good impact mechanical properties and damage tolerance. The tight loop laminated structure had excellent impact resistance, with prominent peak loads and tiny damage volumes, but it encountered internal delamination and loop breakages.

Nonlinear low-velocity impact response of sandwich beams with FG porous aluminum core reinforced by GPLs

Sandwich beam structures facing low-velocity impact frequently throughout their life cycle, making it necessary to investigate the impact response of these structures to enhance their design and reliability in service. In this paper, sandwich beam structures subjected to nonlinear low-velocity impacts are investigated, comprising a functionally graded (FG) porous aluminum core reinforced by graphene platelets (GPLs) and two aluminum alloy face sheets. The mechanical properties of FG-GPLRC core are predicted by a generalized Halpin-Tsai model, which takes porosity into account, where the material properties of the closed-cell aluminum alloy foam are established on experimental data. The numerical investigations are conducted using the finite element method and apply the Hertz contact law. The simulation results indicate that the FG-X pattern, where the porosity coefficients are designed to have the maximum values at the top and bottom layers, while to have the minimum values at the mid-plane layers, exhibits the best impact resistance, and that the incorporation of GPLs enhances the impact response. Furthermore, the findings suggest that the thickness of the core has no impact on the duration of the initial impact. Moreover, an increase in impactor velocity, density and radius results in an increase in both deflection and contact force.

Investigation of low-velocity impact behavior of two-way RC slab strengthening with basalt TRM strips

Investigation of low-velocity impact behavior of two-way RC slab strengthening with basalt TRM strips

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.

Effect of ultraviolet radiation on the low‐velocity impact and compression after impact performances of aerospace composite laminates

AbstractThe low‐velocity impact (LVI) characteristics and compression after impact (CAI) properties of aircraft composite laminates under the influence of ultraviolet (UV) radiation were studied. Firstly, 0, 30, 60, 90 days of UV radiation experiments were carried out on the specimens to analyze the characteristics of the surface topography. Secondly, LVI experiments, the impact energies of 10, 17, and 25 J, were carried out on specimens to analyze the impact response laws and the characteristics of the impact instantaneous deformation. Finally, through CAI experiments and scanning electron microscope (SEM) techniques to clarify the influence mechanism of UV radiation on the residual compressive strength of specimens. The results showed that with the increase of UV radiation time, the shrinkage and erosion phenomena of the surface matrix and the exposure degree of the surface fibers were gradually increased, and the surface fibers were completely exposed after 90 days of radiation. At the same impact energy, with longer radiation time, the peak force gradually decreased (from 8673.86 to 7851.68 N at 17 J), the absorbed impact energy (from 9.48 to 11.13 J at 17 J) and maximum displacement (from 4.1 to 4.73 mm at 17 J) increased, the depth of pit on the impact surface decreased (from 0.213 to 0.14 mm at 17 J), and the internal damage projection area increased (from 906.68 to 1158.66 mm2 at 17 J). The compression damage of the specimens not exposed to/ exposed to UV radiation was mainly fiber cracking/interlayer delamination, respectively.Highlights Ultraviolet (UV) radiation makes the matrix of surface shrink, the fibers exposure increase. The Stage II has obvious oscillation phenomenon in four stages of the low‐velocity impact process. With prolonged UV radiation, the projected area of internal damage expands. The residual compressive load increases with the increase of UV radiation time.

Experimental and numerical investigation on low‐velocity impact response of sandwich structure with functionally graded core

AbstractThe present research investigates optimizing the impact resistance of functionally graded sandwich structures using experimental and numerical approaches. The low‐velocity impact (LVI) responses of functionally graded sandwich composite (FGSC) with different configurations with skin material jute/rubber/jute (JRJ) and core material having epoxy and sea sand by volume fraction of sea sand at 0%, 10%, 20%, and 30%. Sandwich structures were impacted with LVI (5.89, 10.92, and 15.18 m/s), with the impactor dropped from heights of 0.5, 1, and 1.5 m with precompressed spring loads. FGSC samples are considered a deformable body, and the impactor is modeled as a rigid body using commercially accessible dynamic explicit software. The burn‐out test and weight method were used to test the core's gradience; both methods' results substantially matched, and the variance in gradation could be observed. The proposed sandwich structure characteristics are examined by energy absorption, peak force, energy loss percentage, and coefficient of restitution. Results showed that SC30S provides greater energy absorption and superior damage resistance when tested on LVI. To evaluate the accuracy of experimental findings in predicting the indentation behavior of the sandwich structure, the finite element analysis was used to compare with the experimental results. According to the examination of these proposed FGSC overall performance, they could potentially be employed as sacrificial materials for LVI applications like claddings to shield major structural components. The systematic approach used in this work serves as a standard for choosing and using FGSC effectively for LVI applications.Highlights Low‐velocity impact behavior of sandwich structures was investigated. Combining flexible skin and epoxy core enhances energy absorption. Based on impact energy levels, impact damage areas were determined. Examined sandwich structure advantages in structural and aerospace uses. In terms of time and cost, the numerical analysis method would be useful.

Experimental and simulative investigation on the mechanical behavior of GFRP T‐joints subjected to low‐velocity‐impact and post‐impact tensile loading

AbstractTo investigate the failure mechanism of the composite T‐joints subjected to low‐velocity‐impact (LVI) loading varying impact locations, a methodology composed of improved conventional vacuum‐assisted resin infusion (VARI) and LVI testing based on ASTM D 7136 is developed and employed. Moreover, the simulation is conducted to mainly reveal the damage evolution of interlaminar delamination between web and web/skin laminate based on surface‐based cohesive behavior in the commercial software of Abaqus 2020. Further, the effect of LVI loading with various distances from the web laminate to the impact location on the mechanical property and failure mode of the composite T‐joints are presented and discussed as well. By comparison, larger vertical cracks and higher residual tensile strength are found in the T‐joints impacting the corner. However, the T‐joints with the impact point near the corner have lower residual tensile strength and suffer more interlaminar delamination in the interface between web and skin, which is the most critical position of failure.Highlights GFRP T‐joints are manufactured by the vacuum‐assisted resin infusion process with a newly designed mold. The damage evolution in low‐velocity‐impact tests is presented via the quasi‐static tests and finite element simulation. Larger vertical cracks and higher residual tensile strength are found in the T‐joints impacting the corner. The T‐joints with the impact point near the corner have lower residual tensile strength. Interlaminar delamination in the interface between web and skin is the most critical factor of tensile failure.

Interphase enhanced low-velocity impact energy absorption in liquid crystal elastomer-based woven composites

A reasonable approach to enhancing the energy absorption capability of composites is to incorporate elastomers that possess viscoelastic properties capable of enduring considerable elastic deformations and absorbing significant energy without fracturing. From this perspective, using liquid crystal elastomers (LCEs) as a matrix for fiber-reinforced composites could be an excellent option for developing impact-absorbing materials since LCEs possess an outstanding energy dissipation ability compared with amorphous elastomers. Herein, we report excellent energy-dependent impact properties of LCE composites reinforced with carbon fiber (CF) woven fabric. We discovered that the LCE/CF composite can effectively dissipate high amounts of low-velocity impact energy. The exceptional characteristics of LCE, which make it adaptable to impact energy absorption, combined with the presence of an interphase featuring a higher loss modulus compared to the individual composite components, were demonstrated to significantly enhance impact energy absorption of the composite. The developed LCE/CF composite panel is capable of absorbing up to 60 J of impact energy despite its thickness of only about 1 mm and has a substantial damping loss coefficient of about 0.1, which is two orders of magnitude higher than those of typical fiber-reinforced composites.

Assessment of low-velocity impact response of a hybrid carbon-aramid braided composite by algorithmic quantification of volumetric structures

This work investigates the impact response of a hybrid two-dimensional (2D) tubular braided composite through an ex-situ examination of its internal structure. An inter-ply hybrid laminate of biaxial braided carbon and aramid layers was manufactured. The sample underwent split Hopkinson pressure bar (SHPB) impact testing, where the applied energy induced barely visible impact damage (BVID). Volumetric representations of the sample were created before and after impact testing using micro-computed tomography (µCT). Novel algorithms were developed to assess properties of the braided composite sample. First, voids in the sample before and after impact were identified through a series of image processing techniques, after which various void properties were extracted. Each void was then matched between datasets to track property change caused by impact. Next, damage in the sample after impact was identified through another series of image processing techniques, then quantified and characterized in the context of the full sample. Statistical analyses in the form of paired-sample t-tests were performed for void properties and overall surface topologies. Additionally, measurement of 3D strain within selected regions of the sample was performed using digital volume correlation (DVC). Results showed that the impact damage did not cause significant void enlargement, but instead caused surface topology shifts, particularly at the inner surface, owing to plastic deformations caused by impact damage, which were primarily caused by delamination and developed from large voids at the site of impact. The hybrid material configuration exhibited a phenomenon where the inner and outer layers minimized cracking in the middle layer, causing plastic deformation to be the primary impact response of the middle layer. Through the analysis processes developed in this work, quantitative assessment of tubular braided composites was achieved by measuring changes in voids caused by impact at the individual level, and by examining the damage profile while accounting for the voids. The methodology can be applied to various material configurations to provide meaningful insight into the effects of hybridization in the impact response of braided composites.

Finite Element Analysis of the Effect for Different Thicknesses and Stitching Densities under the Low-Velocity Impact of Stitched Composite Laminates.

In this study, a progressive damage model was developed for the mechanical response and damage evolution of carbon fiber stitched composite laminates under low-velocity impact (LVI). The three-dimensional Hashin and Hou failure criteria were used to identify fiber and matrix damage. The cohesive zone model was adopted to simulate the delamination damage, combined with the linear degradation discounting of the equivalent displacement method to characterize the stiffness degradation of the material, and the corresponding user material subroutine VUMAT was coded. The finite element analysis of the LVI of stitched composite laminates under different energies was finished in Abaqus/Explicit. Furthermore, the simulation predictions matched well with the results of the experimental tests. Based on this, composite laminates' mechanical response and damage forms with different thicknesses and stitch densities were analyzed. The findings show that the main damages of composite laminates were matrix tensile damage and delamination. The stitching process could improve the impact tolerance of composite laminates, inhibiting delamination and reducing the area of the delamination damage. The higher the density of the stitching, the more noticeable its inhibition would be. The thickness of the laminate also had a more significant effect on the damage to the laminate. Thin plates were more prone to matrix tensile damage due to their lower flexural rigidity, whereas thick plates were more susceptible to delamination because of their higher flexural rigidity.

Experimental and simulation study on bonded repaired low-velocity impact of carbon fiber reinforced plastic laminates for rail vehicles

In this study, a high-strength carbon fiber reinforced composite laminate for rail vehicles was machined as a perforated sample and repaired by bonding a patch of the same material. The mechanical response of the repaired laminate to a low-velocity impact with energies of 25J and 30J was investigated through experiments and simulations with variations in patch thickness, size radius, and off-axis angle. The finite element simulation model was established in Abaqus/Explicit. The model integrated the progressive damage model based on the 3D-Hashin failure criterion, which can simulate the intralaminar damage of the fiber and the matrix. The cohesive zone model was used to simulate the delamination damage. According to the finite element analysis results, the mechanism and process of impact damage of the repaired laminates were analyzed. Based on the validated finite element model, the effect of patch size, thickness and off-axis angle on impact response was investigated. Patch radius reduced to 15 mm or thickness reduced to 2.1 mm can still resist low-velocity impacts with an energy of 30 J. Although the off-axis angle of the patch had little effect on the impact response of the repaired laminate, an off-axis angle of 90° was effective in suppressing delamination damage within the patch.

Theoretical Analysis of Composite RC Beams with Pultruded GFRP Beams subjected to Impact Loading

Glass Fiber Reinforced Polymer (GFRP) beams have gained attention due to their promising mechanical properties and potential for structural applications. Combining GFRP core and encasing materials creates a composite beam with superior mechanical properties. This paper describes the testing encased GFRP beams as composite Reinforced Concrete (RC) beams under low-velocity impact load. Theoretical analysis was used with practical results to simulate the tested beams' behavior and predict the generated energies during the impact loading. The impact response was investigated using repeated drops of 42.5 kg falling mass from various heights. An analysis was performed using accelerometer readings to calculate the generalized inertial load. The integrated acceleration record and the measured hammer load vs. time data were utilized to determine the generalized bending load and fracture energy. Four forms of energy were calculated at the maximum load. The total energy was calculated and divided into two parts: The first part was gained by the beam's rotational kinetic energy, the bending energy in the specimen, and the elastic strain energy. The second part was the hammer's kinetic energy before striking the beam. The analytical results showed that the bending energy was less than its rotational kinetic energy for the encased GFRP beams and the reference specimens. In contrast, the encased steel beams had high bending energy due to the higher impact load and deflection. Strain energy recorded lower energy values for all specimens with higher bending energy. There is a good agreement between the tested and the calculated inertial and bending force for all beams. The ratio of inertia force to the total impact load for the encased GFRP and encased steel beams to the reference beam is about 9% and 5%, respectively.

Experimental investigation on the dynamic response of half steel-concrete composite slabs under low-velocity impact

The current research on the dynamic response of half steel–concrete (HSC) composite slabs is not only limited but also primarily concentrated on high-velocity impacts. This study investigates the dynamic response of such structures by examining failure modes, impact resistance mechanisms, and energy dissipation under low-velocity impacts through drop hammer impact tests conducted on five HSC specimens. In addition, the variation of the out-of-plane residual bearing capacity with the damage degree of specimens and impact energy is analyzed using static loading tests. Finally, the dynamic response differences between half steel–concrete slabs and steel–concrete (SC) slabs are analyzed by comparing multiple indicators. The results indicate that HSC slabs exhibit five distinct failure modes when subjected to low-velocity impact within a range of 3.13–7.00 m/s. Additionally, five stages of the dynamic response process of the HSC slabs are proposed. Moreover, the bottom steel plate plays a crucial role in retaining structural out-of-plane residual bearing capacity. Furthermore, compared with the SC structure, the HSC slab is capable of absorbing input impact energy within a much smaller displacement.

Low-velocity impact-resistance of aramid fiber three-dimensional woven textile-reinforced thermoplastic-epoxy composites

The development of impact-resistant composite materials for protective applications such as helmet and body armor has attracted considerable attention. In this study, a novel aramid fiber-woven thermoplastic-epoxy composite was developed. Furthermore, three types of woven textiles, namely three-dimensional (3D) orthogonal-woven (3DOW), 3D angle-interlock woven (3DAIW), and two-dimensional plain-woven (2DPW) textiles, were used as reinforcement structures. To study the effect of the woven structure, impact energy, and damage repairment on impact-resistance performance of these composites, low-velocity drop-weight impact tests with various impact scenarios, such as single-impact, repeated-impact, as well as multiple-impact with hot-press damage repairment, were conducted. The results revealed that the woven structure exhibited an obvious effect on the composite impact-resistance performance and failure modes when subjected to specific impact scenarios. For the single-impact scenario, especially under high impact energy levels (10 and 20 J), the 3DOW structure exhibited superior impact-resistance performance as well as damage tolerance, followed by 3DAIW and 2DPW structures. Furthermore, 3DOW achieved superior impact-resistance to the other two structures for the 10-J repeated-impact scenario. The 3DAIW structure, in which debonding or delamination as well as severe resin cracks dominated, achieved superior impact-resistance to multiple impacts with damage repairment.

EFFECT OF LOW-VELOCITY IMPACT DAMAGE ON THE ELECTROMAGNETIC INTERFERENCE SHIELDING EFFECTIVENESS OF CFRP COMPOSITES

Carbon fiber reinforced polymer (CFRP) composites are widely used engineering materials in aerospace technologies. These electrically conductive carbon-based materials, due to the lightness advantages, are preferred as shields against electromagnetic radiation, especially in aircraft and satellites. However, the performance losses caused by damage because of flying object collision such as bird, hail, or projectile contain significant uncertainty. Herein, the CFRP composite material was structurally damaged by low velocity impact test set-up at various energy levels between 2.5 to 10 joules, and then its electromagnetic interference (EMI) shielding performance was investigated. In addition, the electrical properties of the material were also examined, and the occurred damage status was evaluated by microscopy studies. Intrinsically, the increase in impact energy increases the grade of damage on body of the material. This results in a drastic decrease in electrical conductivity and EMI performance. In experiments, where 5 joule energy is detected as a threshold level, it has been observed that irreparable damage occurs at energy levels above this value.

Influence of Cell Pore Configuration on Dynamic Mechanical Properties of Honeycomb Structures

With the rapid development of advanced manufacturing technologies such as additive manufacturing, which provides an effective means for processing and preparing a variety of structures with more complex geometrical configurations, the design and study of honeycomb structures have played an important role in promoting the design and study of honeycomb structures. At present, the study of such structures is mainly limited to hexagonal honeycombs, and relatively few studies have been conducted on other cell geometries. In this study, by using the finite element method, we have simulated and investigated the mechanical properties of typical honeycomb structures, in which these structures have different cellular pore configurations and arrangements that are subjected to in-plane low-velocity impact loading. We compared their dynamic load-carrying capacity and deformation patterns with the relative density and impact velocity which is kept constant. Our results show that different cell pore configurations lead to different cell wall stress states during the compression of the honeycomb structure, which affects the macroscopic mechanical properties of the overall structure. Honeycombs with predominantly cell-edge bending have lower stiffness, compressive strength and smoother platform stresses. Honeycombs with deformation modes dominated by cell-wall plastic buckling have the opposite properties. The design of protective structures through further combinatorial optimization of honeycomb structures provides more options to enhance their overall behavior and energy absorption properties.

Experimental studies of CFRP laminates under repetitive low-velocity impact loading

Due to their exceptional properties such as high strength-to-weight ratio and fatigue tolerance, laminated composites are widely used in aircraft structures. When subjected to impact loading, composite structures experience intra/inter-laminar damages, and it is crucial to investigate the effect of damages on the strength of the laminate. Single and multiple impact tests are performed on CFRP laminates with different stacking sequences. Cross-ply [0/90]4S and quasi-isotropic [45/90/-45/0]2S laminates are fabricated and tested. Damage size as a function of the number of impacts and impact energy for different stacking sequences are studied. The damage configuration of impacted specimens is studied using the immersion ultrasonic technique. Damage size and shape of multiple impacted specimens are compared with single impacted specimens.

Failure mechanism and impact resistance of a novel all-composite double-corrugated sandwich plate under low-velocity impact

A novel composite double trapezoidal corrugated sandwich plate (CDTCSP) was prepared by mold hot pressing and secondary bonding of carbon fiber reinforced polymer (CFRP) prepregs. The DIT302E drop hammer testing machine with a hammerhead of 5.5 kg was selected to realize the impact test of the new corrugated sandwich structure and the all-composite trapezoidal corrugated sandwich plate (CTCSP) with three different energies of 10 J,30 J, and 50 J by changing the height. The failure modes of the two samples were further studied by experimental investigation along with the finite element model established in Abaqus/Explicit. Based on the verified numerical model, the failure process of CDTCSP under 30 J and 50 J impact energy is analyzed. At the same time, the effects of different impact positions and layup angles on the impact resistance of CDTCSP at 10 J energy were evaluated. It can be observed that as the impact energy increases, the peak load of the composite corrugated sandwich plate decreases. Compared with the traditional ones, the impact position has no noticeable effect on the overall impact resistance of CDTCSP. Based on the analysis of CDTCSP with five different layup parameters, it is found that the matrix compression failure extends along the fiber direction, and the peak load of the sample with all the surfacing layup of ± 45° is 17% larger than that of the sample with 0°.

Dynamic behavior of one-dimensional foam disk chains during low-velocity impact

This study experimentally analyses the deformation and energy retention behavior of ten closed-cell PVC foam disks constituting a one-dimensional granular chain subjected to low-velocity impacts. A pressure-driven impactor loads disk chains of two densities, each at 1 and 10 m/s. The deformations of the disks are captured using high-speed cameras, and the chain's input and output forces are recorded during the impact. Energy retained by the chain and the disks is calculated using the deformations of the disks, input, output, and contact forces. The results show that the energy retained by the chain of H130 foam is 3 times greater than that of the H35 foam at 1 m/s and is about twice as high at 10 m/s. Normalized with respect to input energy, the relative energy retained by the chains of H35 foam is more than that of the H130 foam for the same impact velocity and is higher at lower impact velocities for both foams. In addition, the energy the disk chain retains decays along the chain, and the decay rate is higher for lower impact speeds, implying that the disk chain should be longer for higher impact speeds to mitigate the energy fully.

Experimental study on the impact resistance and damage tolerance of thermoplastic FMLs

This study aimed to enhance the impact resistance of fiber metal laminates (FMLs) and achieve lightweight optimization by incorporating a new thermoplastic resin, a titanium alloy and ultra-high-molecular-weight polyethylene (UHMWPE) fiber to produce a novel type of FMLs (PEFMLs). The impact resistance of PEFMLs was analyzed through low-velocity impact tests conducted at different energy levels. Subsequently, the residual compression-after-impact (CAI) strength of the PEFMLs was evaluated through compression tests on the impacted specimens. The experimental findings revealed that PEFMLs exhibited subcritical failure when subjected to impact energies less than 35 J, with a penetration energy threshold of 55 J. Higher impact energies resulted in larger damage areas and increased plate buckling of PEFMLs, consequently leading to reduced CAI strength. The presence of metal, thermoplastic resin and UHMWPE in the PEFMLs effectively dissipated a substantial amount of impact energy while maintaining their structural integrity during both the impact and compression processes.