Low Velocity Impact Behavior Research Articles

Nonlinear low-velocity impact response of GRC beam with geometric imperfection under thermo-electro-mechanical loads

This paper presents an investigation on thermo-electro-mechanical nonlinear low-velocity impact behaviors of the geometrically imperfect functionally graded (FG) graphene-reinforced composite (GRC) beam with surface-bonded piezoelectric layers. Both uniformly distributed and FG patterns of graphene nanoplatelets (GPLs) are considered along the thickness of the GRC host beam. The effective Young’s modulus is calculated by the Halpin–Tsai model. The Poisson ratio and mass density are calculated by the rule of mixture. The modified nonlinear Hertz contact law is employed to predict the impact force between the spherical impactor and the geometrically imperfect GRC piezoelectric beam during impacting. By considering the first-order shear deformation theory and von Kármán nonlinear displacement–strain relationship, the nonlinear governing equations are obtained by Hamilton principle and dispersed by differential quadrature (DQ) method. The Newmark-β method associated with Newton–Raphson iterative process is adopted to parametrically identify the impact force and the dynamic response of the system. The effects of geometric imperfection, weight fraction and distribution pattern of GPLs, temperature variation, thickness of piezoelectric layer and impactor’s initial velocity on nonlinear low-velocity impact behaviors of geometrically imperfect GRC beams are discussed in detail. Our results illustrate that the coupling effect of geometric imperfection and thermo-electro-mechanical load has a significant effect on the nonlinear low-velocity impact behavior of GRC beam, and GPLs distributing into the piezoelectric layers is better for reducing the impact response of geometrically imperfect GRC piezoelectric beam.

An experimental study on the effects of introducing carbon nanotube on low velocity impact behavior of carbon/aramid fiber reinforced intra-ply hybrid composites

In this research, the addition effects of Multi Wall Carbon Nanotube (MWCNT) on low velocity impact behavior of Carbon/Aramid Fiber Reinforced (CAFRP) intra-ply hybrid composites were studied. In this regard, three types of pure, 0.1 wt.% and 0.5 wt.% introduced CAFRP intra-ply hybrid composites were fabricated by Vacuum Assisted Resin Infusion Molding (VARIM) method. The profile energy method was used to determine the penetration and perforation threshold. The main purpose of this research was to improve the impact behavior of CAFRP by addition of MWCNT to the matrix of these composites. The low velocity impact test was also carried out in 30, 50, 80 and 120 J energy values. The effect of addition MWCNTs in the matrix of composite was investigated by plotting force, absorbed energy and deflection vs. time and the key parameters of impact test such as maximum contact force, absorbed energy, deflection and duration time were compared for pure and multi scale CAFRP composited. According to the results, the addition of MWCNT improved the low velocity impact behavior of CAFRP intra-ply hybrid composites by not only increasing the toughness of epoxy matrix but also upgrade the adhesion of carbon fibers to the epoxy matrix. It was also found that fiber breakage, fiber pull out, matrix cracking, delamination and fiber matrix debonding were the most important failure modes in these types of tested composites.

Experimental study of low-velocity impact behavior and damage characteristics of flat-knitted spacer fabrics reinforced composites

Flat-knitted spacer fabrics are three-dimensional fabrics with good formability and impact resistance, which can be rapidly produced complicated shape preforms. In this work, low-velocity impact behavior and damage characteristics of flat-knitted spacer fabrics reinforced composites were studied and the mechanism of the effects of spacer yarn structure on the impact properties of the composites were explored. Flat-knitted spacer fabrics with three spacer structures were produced using ultrahigh molecular weight polyethylene (UHMWPE) filaments, and composite plates were prepared by vacuum-assisted resin infusion. Low-velocity impact tests were carried out using a drop-weight impact testing machine equipped with a hemispherical impactor. It was revealed that the impact process of the flat-knitted spacer fabrics reinforced composites could be divided into three areas. The effect of initial impact energy on the impact properties of the sample was mainly reflected in the damage speed and initial damage threshold in the first areas. With the increase of spacer yarn span, the damage tolerance, stiffness, and impact resistance of the composite were also increased. Besides, the main damage mechanism of flat-knitted spacer fabric reinforced composites was plastic deformation, matrix fracture, fiber-matrix debonding, and tow splitting.

Solidification of a shear thickening fluid in a finite volume under low-velocity impact

Shear thickening fluids show a reversible viscosity increase and even a transient solid-like behaviour when the shear rate is above a critical value, hence they are widely used as an impact energy absorber. This work aims to characterise the low-velocity impact behaviour of an STF in a finite volume in a container − a situation where the material is normally used in a real-life application. The STF contains 58 vol% styrene/acrylate particles dispersed in ethylene glycol. Instrumented drop-weight impact tests are carried out, with transducers attached on the striker, the bottom and the side wall of the container, to characterise the low velocity impact-activated solidification behaviour of STF, addressing the effect of the finite volume. A new two-dimensional mechanistic model is proposed to describe the evolution of the solidification of the STF with a finite volume under the low-velocity impact. It was found that the impact-activated solidification of the STF is clearly dependent on not only the depth of the STF, as reported in previous studies, but also the radial dimension of the STF. In addition, the propagation velocities of the solidification front, in both the depth and radial directions, are found to be linearly proportional to the impact velocity.

On low-velocity impact behavior of sandwich composites with negative Poisson’s ratio lattice cores

In order to investigate the low-velocity impact performance of a new type of sandwich composite structure with negative Poisson’s ratio lattice cores, low-velocity impact tests were carried out using the sandwich composite specimens, which were prepared by 3D printing lattice cores and glass/epoxy composite sheets. A finite element dynamic analysis strategy was also employed to investigate the mechanical response, the total energy absorption, and energy absorptivity of the sandwich panel at impact energies of 5 J, 10 J, 15 J, 20 J, 30 J and 40 J, respectively. Results show that the new sandwich structure can better disperse the concentrated impact load received by the upper sheet and dissipate most of the impact energy in the process of transferring the loads during cushioning. The negative Poisson’s ratio lattice structure can guide damages, and it is found that the position of the impact point will affect the impact mechanical response and energy absorption ability of the sandwich panel.

Impact behaviors and damage mechanisms of 2.5D woven composites: Experiment and simulation

2.5D structures have received attention because of their excellent interlaminar mechanical properties. However, there is a lack of research on impact progressive damage, damage mechanisms and internal damage morphology. This paper investigated the low-velocity impact behavior and damage mechanisms of 2.5D woven carbon/epoxy composites through a couple of numerical-experimental approach. Two different impact energy levels, 15 J/mm and 20 J/mm, were designed for all the samples using drop weight impact equipment. Then Micro-CT was employed to identify the impact damage volumes and damage distribution of 2.5D woven composites. A novel whole-local finite element model was proposed based on the tests results and Micro-CT images. The experimental results indicated that the impact energy has a significant effect on the damage modes of 2.5D woven composite. Moreover, the numerically predicted mechanical curves and damage modes exhibit good consistency with the experimental results. Importantly, the numerical simulation results showed that the damage mode of 2.5D woven composites under impact energies of 15 J/mm was mainly controlled by yarn-matrix debonding. With the increase of impact energy per unit thickness, the dominated failure mode of 2.5D woven carbon/epoxy composites changes from yarn-matrix debonding to delamination and eventually to yarn breakage.

Theoretical modeling of low-velocity impact behavior of sandwich-structured composites reinforced with weft-knitted spacer fabric

The aim of this paper is to develop an analytical model to predict indentations of the impactor on the composites reinforced with weft-knitted spacer fabric using Hertz contact law. For this purpose, simply supported rectangular plate with partially load developed by Timoshenko was applied to analyze the deflection of top face, and the concepts of the buckling of initially curved struts were used to find the buckling of Z-fibers. To evaluate the accuracy of the model, the effect of the number of Z-fiber per unit area and elastic modulus of Z-fiber were investigated. The results showed that in the outside the contact area, the impact force bends the layer and causes the Z-fibers to buckle, but no indentation occurs. Inside the contact zone, the indentation has occurred, in addition to the layer deflection and Z-fiber buckling. Also, indentations in both X and Y directions decrease by increasing the Z-fiber density. In addition, the higher the z-fiber modulus leads to fewer indentations. Decreasing the angle coefficient of Z-fibers leads to increase their buckling resistance. Moreover, a reasonable agreement was observed between theoretical and experimental results; so that the maximum error of prediction was less than 20%. Furthermore, the proposed model can give the indentation of different points of sandwich-structured composites according to their coordinates.

Foam-filling technique to improve low-velocity impact behaviors of woven lattice truss sandwich panels

In this paper foam-filling technique was applied to strengthen woven lattice truss sandwich panels (WLTSPs). The foam-filling effects in enhancing impact resistances of WLTSPs under low-velocity perforation and three-point-bending were investigated by experiments. In local perforation testing, the foam filling effectively improves the penetration force and greatly reduces the penetration depth. Adopting the foam-filling technique, the back skin is seldom damaged. The foam-filling approach can effectively prevent the ‘pierce’ of the WLTSP and the anti-penetration ability is doubled. Under dynamic three-point bending, the impact force is doubled while the mid-span deflection is reduced by half. The back skin is undamaged. The foam-filling technique can reduce the structural damage factor from 0.8 to 0.3 in this research.

Oblique Low-Velocity Impact Response and Damage Behavior of Carbon-Epoxy Composite Laminates.

The low-velocity impact behavior of carbon-epoxy cross-ply composites was numerically investigated, examining the effect of impact angle. A plastic continuum damage model, introducing the cohesive interface to describe delamination damage, was established and was validated by available experimental data. Impact histories, progressive deformation, stress transfer, and impact damage are respectively discussed. The results show that an increase in impact angle intensifies the action of tangential force, and gradually transfers energy absorption from normal plastic deformation to tangential deformation and friction, which dissipates more energy through relatively longer contact duration and larger impactor displacement. The delamination damage to upper layers is more affected by tangential loads, intensifying with the increase of the impact angle, and the damage area to the top interface is increased by 132.1% from 0° impact to 60° impact. Meanwhile, the delamination damage to lower layers is mainly determined by normal loads, weakening with the increasing impact angle overall, and the damage area of the lowest interface decreases by 36.6% from 0° impact to 60° impact.

On impact behaviors of 3D concave structures with negative Poisson’s ratio

Lattice structures with high mechanical properties and lightweight performance attracted increasing attention to the application of automotive, railway vehicle, and aerospace industries. This work developed a novel three-dimensional concave lattice structure using a hyper-elastic soft photopolymer via the digital light processing technique. The axial low-velocity impact behaviors of the proposed structures were investigated by a drop hammer machine and numerical simulation. The results showed that the novel 3D concave structures could present continuous auxetic behaviors with large negative Poisson’s ratios. The structural design parameters such as concave angle and thickness had significant effects on Poisson’s ratio and energy absorption. Specifically, the structures with concave angles from 10° to 20° and with thicknesses from 0.5 mm to 1.0 mm presented the higher negative Poisson’s ratio. The highest negative Poisson’s ratio of −0.86 was obtained. This work offered a new insight into designing novel meta-lattice structures with improved impact resistance.

Low-Velocity Impact Behavior of Sandwich Plates with FG-CNTRC Face Sheets and Negative Poisson’s Ratio Auxetic Honeycombs Core

The combination of auxetic honeycomb and CNT reinforcement composite is expected to further improve the impact protection performance of sandwich structures. This paper studies the low-velocity impact response of sandwich plates with functionally graded carbon nanotubes reinforced composite (FG-CNTRC) face sheets and negative Poisson’s ratio (NPR) auxetic honeycomb core. The material properties of FG-CNTRC were obtained by the rule of mixture theory. The auxetic honeycomb core is made of Ti-6Al-4V. The governing equations are derived based on the first-order shear deformation theory and Hamilton’s principle. The nonlinear Hertz contact law is used to calculate the impact parameters. The Ritz method with Newmark’s time integration schemes is used to solve the response of the sandwich plates. The (20/−20/20)s, (45/−45/45)s and (70/−70/70)s stacking sequences of FG-CNTRC are considered. The effects of the gradient forms of FG-CNTRC surfaces, volume fractions of CNTs, impact velocities, temperatures, ratio of plate length, width and thickness of surface layers on the value of the plate center displacement, the recovery time of deformation, contact force and contact time of low-velocity impact were analyzed in detail.

Low velocity impact behavior of sandwich composites with different structural configurations of foam core: An experimental study

In this study, various structural configurations such plain core, two-core, epoxy columns in the core, core stitched, and facesheet stitched were designed in the foam core sandwich composite with the aim to increase the absorbed energy and to decrease core/facesheet debonding area due to low-velocity impact. Glass fiber/epoxy and PVC foam were used as a facesheet material and a core material, respectively. The impact energy values were selected considering to penetration and perforation cases. The core stitching effect on low velocity impact behavior of sandwich composites were compared to facesheet stitching and it has been determined that the core stitching process can be an alternative to the facesheet stitching process in terms of the absorbed energy value. Impacted sandwich composites are investigated for core/facesheet debonding; the modifications through the thickness increased the failure path for core/facesheet debonding initiation and the results show that a significant decrease in the core/facesheet debonding area has been achieved.

Low-velocity impact behavior of carbon woven laminates after exposure to varying temperatures

The present study reports the low-velocity impact (LVI) performance of carbon woven reinforced polymer (CWRP) composites with varying temperatures. The fabrication of carbon woven lamina and carbon woven reinforced two-layered laminate (named CWRP-1 and CWRP-2) was done using a vacuum-assisted resin transfer molding (VARTM) process. CWRP-1 samples were tested at varying impact velocities of 1, 2, 3, and 4 m/s at −25, 25, and 50 °C for each incident velocity. CWRP-2 samples were tested at room temperature at varying incident velocities to determine the effect of multiple woven layers. The impact resistance of the first-crack load, peak impact load, and absorbed energies were recorded and evaluated under different loading conditions. In addition, the Weibull probability method is adapted to forecast failure behavior as a function of load. Visual inspection, optical microscopy, and scanning electron microscope (SEM) images were used to assess the damage pattern and failure morphologies in forecasting the failure phases during LVI. The low-velocity impact behavior of CWRP-1 at −25 °C with various velocities was shown to be random due to the polymer matrix freezing condition. The softening of the resin matrix at 50 °C is responsible for the difference in damage tolerance. The relevance of multiple layered composites for better impact resistance characteristics was demonstrated during testing of CWRP-2 at room temperature. Overall, the results of this experiment showed that CWRP lamina and laminates are highly sensitive to the impact velocities and external temperatures.

Symmetric and asymmetric intercalation effect on the low-velocity impact behavior of carbon/Kevlar hybrid woven laminates

Hybrid fiber composite laminates with the same materials, manufacturing methods and molding processes may present different mechanical behaviors. In this paper, the effect of intercalation sequence on the mechanical performance of carbon/Kevlar plain laminates were studied. According to different intercalation methods, the hybrid layout was divided into symmetric and asymmetric configurations. It is found that the symmetric intercalation structures (KCCK and CKKC) possess better load-bearing and resilience capacity compared with asymmetric structures (CCKK and CKCK), even better than pure carbon structure (CCCC) under high energy impact. The impact damage volume of symmetric specimens was significantly smaller than that of asymmetric specimens by quantitative micro-CT analysis. The apparent damage index (df and dr) can be used to estimate the internal damage data (dCT, H and V). KCCK, a typical symmetric sandwich-like structure, presented the most slight damage among all symmetric and asymmetric configurations, with shear cracks observed at the brittle carbon fiber core layers, while the delamination cracks between Kevlar-carbon interlayers were away from the central damaged region. In CKCK, interlaminar cracks were formed at each carbon-Kevlar interlayers, which shared and relieved the primary interlaminar crack at the core layers compared with CCKK.

Mechanical characterization and low-velocity impact behavior of flax woven fabric-reinforced polymer composites

Man–made fibers like carbon or glass are main components for fiber-reinforced polymer composites thanks to their high strength and stiffness values. However, man-made fibers are not eco-friendly and can hardly be recycled in the nature. Using a high amount of man-made fibers threatens our nature and poses a significant risk for the future of world. Natural fiber reinforced composite (NFRC) is considered as a good alternative for traditional composites. Therefore, NFRC has been examined to develop materials, which have comparable mechanical properties with the man-made fiber reinforced composites, for last decades. Although lots of studies were carried out on the mechanics of NFRC, a few of them focused on the structural design of reinforcement and their effects on composites performance. In this study, the number of weft densities of reinforcements were differentiated and their effects on the mechanical properties of composites were investigated. Fabrics were produced from flax yarns and composites were manufactured by vacuum assisted resin infusion molding method. The tensile, compression, shear and impact tests were carried out to characterize the manufactured composites. Results show that while increasing number of weft density of reinforcement improves the tensile and compressive strength of NFRC in the weft direction, the tensile strength and elastic modulus of composites in the warp direction were characterized by the crimp percentage values of warp yarns. Moreover, it was determined that the number of weft density in the reinforcement affect the contact force and energy absorption capacity of NFRC.

Experimental studies of low-velocity impact behavior on hybrid metal wire net/woven carbon-fiber reinforced composite laminates

Due to its excellent ductility property, metal laminates have been inserted in fiber reinforced polymer to improve impact resistance. In this paper, two woven carbon layers, stainless steel and aluminum alloy wire net are inserted into the middle of 14 woven carbon layers with the same increment in thickness to enhance the laminates. Low-velocity impact tests and damage inspections are conducted to analyze the strengthening mechanisms. After comparing the response history and damage morphology of various panels, it is found that the additional metal wire net could improve the ductility of panels, and then promote the performance in the low-velocity impact events. This is because the ductility metal wire net could absorb and transfer more impact energy to the area around the impact point.

Low‐velocity impact response and inspection of damage propagation for basalt fiber reinforced filament wound pipes

AbstractIn many industrial applications, filament‐wound composite pipes are utilized to transmit the liquefied natural gas, chemical liquids, and waste hazardous liquids. This reveals the importance of the energy absorption capacity because the pipes in question are placed underground and occasionally exposed to impact loads. However, the high cost of carbon fibers and partially inadequate mechanical features of glass fibers have led to the search for alternative fibers. Some studies show that basalt fiber is likely to be an alternative and practical solution. In this study, it is purposed to define the low velocity impact (LVI) behaviors and damage development of basalt fiber reinforced (BFR)/Epoxy composite pipes with various winding angles. LVI tests were performed on the [±90°]6, [±75°]6, and [±55°/75°]6BFR pipes at energy levels of 15, 20, and 25 J. The impact responses of the composite samples were compared with respect to values of force, time, displacement and absorbed energy. In order to determine the dominant damage types and their progression, microscopic examinations were carried out by taking sections in the impact area in the radial and axial directions. It has been revealed in this study that it is significant to examine the dominant damage of filament‐winding composites, especially by taking cross‐sections from two axes. It was determined that there are damage changes in the layers where compressive and tensile stresses occur in the impact region. It has been observed that the winding angle has a great importance on the LVI responses and damages.

Effect of stacking sequence of glass and jute fiber reinforced polymer composites on their low velocity impact properties

This paper investigated the effect of stacking sequence on the low velocity impact behavior of glass and jute fiber reinforced hybrid composites. The hand layup method is used to fabricate the composites with various stacking sequences. The low velocity impact analysis was carried out at various impact energies, namely 5 J, 10 J and 15 J. Dye penetrant inspection (liquid penetrate inspection) was performed to analyses the damage area in the composites. Compression after impact (CAI) testing was conducted to study the compression strength of the composites after the impact. The study revealed that the jute fiber composites exhibited better results in terms of energy absorption, but the damage area of the composites was higher, compared to the other specimens fabricated. Meanwhile, hybrid composite S7 presented high energy absorption and the minimum damage area. To conclude, the hybrid composite S7 appeared to have the optimum formulation, showing better results in energy absorption, with lower damage and higher compression strength.

Comparison of off-axis angle on the low velocity impact behaviors for carbon-fiber-reinforced polymer laminates

Three types of composite specimens with different off-axis angles after indentation were subjected to progressive tensile loading, and the results showed that although the tensile strength is reduced with an increase in off-axis fiber orientation angle, such off-axial structure can enhance the impact-resistance capacity. An acoustic emission (AE) signals analysis showed that data can be divided into categories that correlate with three damage modes. The AE peak frequency characteristics of each damage mode were also identified for both specimens with and without indentation, and the results also showed that indentation can change the order of appearance of different damage modes during loading. Additional characterization was provided by using Micro-computed tomography (Micro-CT) during a progressive tensile loading process, and the CT images provided visualization of damage location and evolution in the composites, with the data exhibiting good correlations with the AE data for defect prediction. The use of AE and Micro-CT technology was shown to effectively characterize composite damage evolution, and such data can potentially serve as a reference for the structural health monitoring (SHM) of such composites when used in structures.

Low-Velocity Impact and Compression after Impact Properties of Hemp and Jute Fiber Reinforced Epoxy Composites

ABSTRACT This paper presents an experimental study on the low-velocity impact behavior of hemp and jute fiber-reinforced epoxy composite. The Compressive After Impact (CAI) properties of composites post-impact are used for analysis. The type of damage and area of damage is used to analyze the effectiveness of composites for variation in impact energy. The impacted composite specimens were subjected to Compression After the Impact (CAI) test. A two-factor, five-level Central Composite Design (CCD) model of response surface methodology (RSM) is used to analyze the effect of input variables on ultimate load and thereby obtain the optimized input conditions for damage. The experimental results were optimized using Derringer’s Desirability function. The results indicate that jute laminates show a better impact energy absorption capability than hemp laminate composites. From the study, it was observed that the CAI strength of jute/epoxy composite was high compared to hemp/epoxy composite and the jute/epoxy composite exhibited enhanced CAI properties of the composite. From the regression equations and the three-dimensional response surface plots obtained from CCD, optimized ramp values were obtained. The optimized ultimate load of hemp and jute fiber laminate was 5.90 MPa and 10.68 MPa, respectively.