Quasi-static Indentation Tests Research Articles

Comparison and identification of efficient nanoparticles to improve the impact resistance of glass/epoxy laminates: Experimental and numerical approaches

This research has studied the low-velocity impact (LVI) response of glass-epoxy composite laminates reinforced with different percentage of carbon nanotube (CNT) and nanoclay particles. The obtained results facilitate industrialists’ decision-making on selection of high-performance and cost-effective nanoparticles. Through quasi-static indentation (QSI) tests, the optimal percentages of nanoclay, and CNT were identified, and the impact test was performed on them at wide range of energies. Three key indexes were presented to evaluate the composite resistance against impact loads. The results indicate that both types of nanoparticles have contributed to an improvement in impact resistance. Moreover, a finite element analysis was performed using Abaqus/Explicit package, in which the results were in good agreement with experimental values.

Energy absorption and damage characterization of GFRP laminated and PVC-foam sandwich composites under repeated impacts with reduced energies and quasi-static indentation

During service conditions, composite materials used in naval applications are subjected to repeated impact, the resultant damage can seriously affect their mechanical performance. Therefore, the knowledge of impact energy absorption is important to improve the impact damage tolerance of those materials under the multiple impacts. The main purpose of this original study is to investigate and compare the energy-absorbing capability, and the damage response of GFRP laminated and PVC-foam sandwich composite panels used in real naval and aeronautical structures, under repeated low-velocity impact with reduced energies and quasi-static indentation. To do so, a series of repeated impacts tests were performed until complete absorption of the imposed energy, and quasi-static indentation tests were conducted. Furthermore, the cumulative energy absorbed and inelastic restitution (IRI) indexes were proposed to evaluate energy-absorbing capacity, and the necessary allowable shear stress to initiate damage in the laminated composite was determined. The results of the repeated impact revealed that 80% of the initial energy was absorbed by the sandwich composite which is composed of two 4 mm laminated skin compared to about 60% for 8 mm laminate composite just after the first impact due to the damping power of the core. However, the indentation energy absorbed and the damage configuration for 8 mm laminates are almost the same for sandwiches. This result proves that the core does not have a significant effect on the quasi-static response of the PVC-foam sandwich due to its low perforation resistance.

A methodological approach to model composite overwrapped pressure vessels under impact conditions

A combined experimental-numerical method is proposed to predict the mechanical behavior of composite overwrapped pressure vessels under impact conditions. Material characterization tests are conducted on filament-wound samples to determine the key material parameters, whilst taking into account manufacturing defects due to the production process. These material parameters serve as input for the numerical model. The model captures the cylindrical area of a pressure vessel with diminishing levels of detail away from the impactor. The performance of the model is optimized using a comparison with quasi-static indentation tests on cylinders with different thicknesses and lengths. It is shown that the mechanical behavior of a pressure vessel can be predicted accurately both under quasi-static indentation loads as well as under impact loads.

Optimization of Cellular Concrete Microstructure for Improved Impact Resistance

Engineered material arresting system (EMAS) is a cellular concrete material currently used as passive aircraft arresting system at airports around the U.S.A. and abroad. Its cellular structure crushes on impact, helping to absorb energy and create drag resistance. Energy absorbed during crushing is defined by the load–deformation response curve, in which a plateau is indicative of crushing behavior at a near-constant load. At the microstructural level, the energy absorbed from crushing is a combination of elastic buckling, plastic yield, and brittle fracture of the cellular microstructure. Therefore, optimization of the cellular structure (e.g., bubble size and distribution) is paramount to the overall performance of these systems. This study makes use of microstructural investigations, quasi-static indentation, and drop weight testing to investigate the performance of cellular concrete with varied microstructures. The results show that, while density (air content) has been considered the main predictor of overall performance, the nature of the cellular structure created by the use of different foaming agents can be a useful design tool. This adds another critical consideration in the design of impact-resistant infrastructure. Given this finding, a new set of design guidelines are presented in this paper. This work aims to inform better design of impact-resistant infrastructure by identifying cellular concrete microstructures that lead to optimal energy absorption in low-velocity impact events, such as aircraft overruns.

An experimental study on quasi-static indentation, low-velocity impact and damage behaviors of laminated composites at high temperatures

Nowadays, fiber reinforced laminated composites are widely used in many applications due to their high strength/weight ratio. However, these materials are very sensitive to transverse loading. The low-velocity impact test has been widely used by researchers to simulate the transverse loading. However, the low-velocity impact tests are highly toilsome, and this test requires expensive hardware and software systems. To reduce the experimental costs of the low-velocity impact test, it will be more attractive, much simpler, cheaper and more widely available to achieve impact behavior using quasi-static tests. Thus, to compare both tests, in this work the absorbed energy and force-deflection curves obtained by low-velocity impact and quasi-static indentation loading in two different fiber reinforced epoxy composites have been investigated. The Carbon-Kevlar hybrid fabrics and S2 glass fabrics were used as reinforcements. For low-velocity impact tests, a range of energies was used between 20 and 80 J. For quasi-static indentation test, the crosshead speeds were increased gradually from 1 mm/min to 60 mm/min. In addition, tests at 23°C, 40°C, 60°C and 80°C were made to examine the effect of temperature on these tests. As a result of the quasi-static tests performed, the amount of energy required to perforate the samples at a certain test speed is at the same level as the low-velocity impact test. Thus, the required energy amount for the perforation of the materials can be found by performing a quasi-static test at an appropriate speed, rather than the low-velocity impact test.

Are there similarities between quasi-static indentation and low velocity impact tests for flax-fibre composites?

Flax-fibre composites are increasingly used as a replacement of classical synthetic composite materials. Due to the good energy absorption properties of flax fibres, they represent a promising alternative in structures susceptible to low velocity impact (LVI) damage. However, this type of dynamic loading is complex, expensive to perform and not necessarily easy to fully investigate. A simpler way to tackle this problem consists in investigating quasi-static indentation (QSI) tests, but this alternative remains relatively under-researched for natural fibre composites. Thus, this paper aims at providing a comparison between both types of loading to facilitate the later analysis and modelling of flax fabric laminates submitted to LVI. Six layers of a flax 2/2 twill fabric were used as reinforcement for epoxy laminates made through vacuum infusion. Specimens were then submitted to instrumented LVI and QSI tests at comparable energy levels, with a 1.5 %–3.9 % difference only. Load-displacement curves and visible damage were first analysed and compared between both test types. Then, the internal damage within QSI specimens were investigated using acoustic emission (AE). Our findings showed good analogies between both testing methods in all the stages of damage development. Great similarities were found in load-displacement curves (in shape, stiffness and peak load), in energy absorption capacity (at 5 and 10 J) and in visible damage. Actually, the differences between QSI and LVI remain low, i.e. 2.1 % for linear stiffness, from 0.2 to 5.6 % for peak load and less than 7% for the proportions of absorbed energy. Comparison of the QSI damage analysed from the AE data with LVI results from literature suggested similar mechanisms and onset sequences. These results revealed that QSI monitoring could provide characteristic indications on the damage evolution of flax-fibre woven composites during an LVI test.

A study on ballistic performance of origami sandwich panels

Sandwich structures with origami cores have shown great potential for engineering applications. However, few studies have been performed on the ballistic performance of origami sandwich panels, particularly on their plastic deformation and ballistic resistance. In this study, rectangular metallic sandwich panels with aluminium origami cores were manufactured. Quasi-static indentation and ballistic impact tests were conducted to explore their ballistic performance. Three different shapes of indenters were considered: flat-ended, hemispherical-nosed and conical-nosed. Plastic deformation and energy absorption capacities were observed and analysed. Subsequently, finite element (FE) simulations using Ansys/Ls-dyna were executed to compare the ballistic performance of sandwich panels with origami cores and honeycomb cores. Parametric studies were also conducted to examine the effect of wall thickness, cell edge length and cell number of origami cores on the ballistic performance of origami sandwich panels.

Improving the impact resistance of the multilayer composites using nanoparticles

The application of composites in various industries has grown considerably. The relatively high cost of Low-Velocity Impact (LVI) tests and the limitation in data collection due to the short time of this test, on one hand, and previous reports of the conformity of Quasi-Static Indentation (QSI) test results to LVI test results, on the other hand, have convinced researchers to use QSI instead of LVI. The present research investigates the effect of various percentages of nanoclay (because of their cost-effectiveness) on the impact properties of glass-epoxy composite and has used the QSI test to predict the behavior of this nano-composite. For the homogeneous distribution of nanoclay in the resin, a mechanical and an ultrasonic stirrer were used, and the EDAX image of the nano-resin cross-section confirms the success of this process. The QSI test results showed that adding 3% nanoclay to the glass-epoxy composite improves energy absorption by 18%. Moreover, the SEM images indicated that the samples containing 7% nanoclay had deteriorated mechanical properties due to nanoparticle agglomeration. In the end, experimental and numerical LVI tests were performed on the samples containing zero and 3% nanoclay to evaluate the agreement between QSI and LVI test results. The increase in the maximum force and elastic energy and the decrease in the damping ratio and residual deflection all indicate the positive effect of clay nanoparticles on impact-resistance. Numerical results were also very well matched with experimental ones.

E-Glass/phenolic matrix/APP laminate as a potential candidate for battery casing of e-vehicle - experimental investigations

The prime purpose of the current research is to investigate the influence of Intumescent flame retardant (IFR)-Ammonium polyphosphate (APP) on the mechanical properties of Phenolic resin/E-Glass hybrid configurations and suitability of hybrid configuration for battery casing in E-vehicle. Varying weight fractions viz. 2, 4, 6, 8, 10 wt% of APP were used to fabricate -Phenolic resin/E-Glass/APP polymer composites. Tensile, flexural, low velocity impact, and quasi static indentation tests were conducted and analyzed. Among the developed hybrid configurations 6 wt% APP filled laminate shows the better tensile and flexural properties than other configurations. It is understood from low velocity Izod impact test, falling weight impact test and quasi static indentation tests that APP filled hybrid configurations have more energy absorption. 6 wt% APP filled laminate has high deformation in elastic phase and low deformation in plastic phase. Morphology and fracture mechanism of polymer laminates are also presented and discussed. It is concluded from the investigations that E-Glass/Phenolic matrix/APP laminate is found as a potential candidate for battery casings of E-vehicle.

Experimental investigation of quasi-static behavior of composite and fiber metal laminate panels modified by graphene nanoplatelets

The current study investigated the influence of incorporation of graphene nanoplatelets (GNPs) on quasi-static behavior of composite and fiber metal laminate (FML) panels. The unmodified and modified composite specimens and FML panels with 2/1 configuration were fabricated using a hand lay-up method and investigated through a quasi-static punch and indentation testing. The two sets of tests were conducted with a flat-ended indenter and the loading conditions were the same for all samples, except support spans which were varied. Following experimental testing, possible damages at the punch region were closely investigated and localized and global damages were observed. The results revealed that adding 0.2 wt% GNPs improved the strength and fracture toughness of specimens by delaying the failure modes. On the contrary, GNPs made the bonding between the aluminum and composite interface to weaken.

Simultaneous reinforcement of both rigidity and energy absorption of polyamide-based composites with hybrid continuous fibers by 3D printing

The use of continuous fiber as reinforcement is well known to improve the mechanical performance of thermoplastic printed laminated composites. However, it is difficult to optimize the rigidity and energy absorption of continuous fiber reinforced composite components, since the inherent conflict between strength and ductility. For this purpose, this study focused on the design and characterization of continuous fibers reinforced polyamide (PA)-based composites, prepared via 3D printing, with synergistic enhancement of the strength and ductility. Continuous carbon and Kevlar fibers were used as reinforcements for production of printed non-hybrid and hybrid composites. The quasi-static indentation (QSI) test and structural evolutions analysis of composites were conducted to evaluate the mechanical properties and reveal the deformation and failure mechanisms. A Volume Average Stiffness (VAS) model and a hybrid effect model were introduced to predict the effective stiffness and to analyze the hybrid effect on the energy absorption capabilities of the printed hybrid composites, respectively. The results showed that the addition of the continuous carbon and Kevlar fibers with a certain designed improved toughness of the composite, which led to an enhancement of the energy absorption properties. The deformation and failure mechanisms of hybrid continuous fiber reinforced composites highly depended on the designed position of fibers. For the printed hybrid composites, the highest indentation force could be achieved when continuous Kevlar fiber layers were placed at the rear side. While the highest energy absorption capability of the printed composites was captured when continuous carbon fiber layers were positioned at the rear side.

Finite element analysis of porous polymer coated pipelines subjected to impact

Subsea steel pipelines are often coated with external polymer coatings. While primarily applied for corrosion protection and thermal insulation, such coatings have been shown to contribute significantly to the energy absorption during impact events. However, due to the lack of reliable models accounting for the complex coating features, positive contributions from the coating to the mechanical response of the pipeline are often omitted in design. In a previous study, samples of a typical polymer coating were scanned using X-ray micro computed tomography (XRMCT) and the density mappings were applied to build finite element (FE) models of the porous morphology. These FE models were then used to calibrate a constitutive material model, which takes the porosity of the coating into account. It was concluded that the constitutive model may be applied in large-scale FE simulations of coated pipelines. In this work, the calibrated constitutive model is used to simulate the response of quasi-static indentation and impact tests performed on full-scale offshore pipeline components with and without multi-layered polymeric coating. The objectives of the work are to evaluate the performance of the originally presented model and to implement modifications essential in capturing the physical phenomena of the problem. The original model is seen to describe the early parts of the deformation very well. However, some deviations are seen as the coating becomes severely compressed between the indenter and the steel pipe. A strain- and porosity-based fracture criterion is therefore implemented, which alleviates the problem and produces a good correspondence between simulations and experiments. Modifications are also made to the coating model to include dependencies of strain-rate and temperature in the coating material response. The modified model is calibrated to strain-rate and temperature data retrieved from a similar polymer material found in the literature. Case studies with simulations of impact events under various strain-rate and temperature conditions are performed. The simulation results are compared to quasi-static indentation and impact tests presented in previous works. These results give indications that the strain-rate and thermal sensitivity of the coating material should be further explored.

Investigation on the indentation mechanical performance of aluminum honeycombs

Quasi-static indentation tests were conducted to characterize the mechanical behavior of honeycombs. The local failure mechanisms of honeycombs with different relative density were discussed in detail. Results showed that the spread area of tearing deformations increases with increasing relative density and that difference in the neatness of tearing edges are obvious under different indenter shapes and sizes. The effects of indenter geometry on the plateau force and energy absorption of the honeycombs were analyzed. The tear energy of the specimens was determined, and an empirical formula was proposed to describe the relationship of energy absorption with indenter geometry.

Ductile and brittle behavior during deformation and fracture for pure ice detected by quasi-static indentation test

Ductile and brittle behavior during deformation and fracture for pure ice detected by quasi-static indentation test

Retracted] Effect of the Reinforcement Phase on Indentation Resistance and Damage Characterization of Glass/Epoxy Laminates Using Acoustic Emission Monitoring

The effect of reinforcement phases on indentation resistance and damage behavior of glass/epoxy laminates was investigated in this research work. Woven glass fiber mat and nonwoven chopped glass fiber mat were used as fiber reinforcement phases for fabricating the laminates. Low‐velocity impact and quasi‐static indentation tests were performed on both laminates to investigate the contact behavior and energy‐absorbing capability. Moreover, the acoustic emission (AE) technique was employed to monitor the indentation damage resistance. AE parameters including normalized cumulative counts (NCC), normalized cumulative energy (NCE), rise angle (RA), and felicity ratio (FR) were analyzed. The bidirectional laminates showed premature load drops and drastic changes in the normalized cumulative counts/energy profile in the beginning of loading cycles, indicating the development of macrodamage such as debonding/delamination. AE sentry function results of bidirectional laminates show longer PII function at the earlier stages, associated with minor PIII function and greater PIV function, indicating the continuous degradation and progression of damage. In contrast, the chopped laminates exhibited superior postimpact performance than the bidirectional laminates. The presence of randomly oriented fibres prevents the delamination crack propagation during compression loading, which was attributed with the increased residual compressive strength.

Deformation and fracture properties of pure ice through impact indentation testing

The deformation and fracture properties of ice have attracted considerable research interest. The tip shape of an object that comes into contact with the ice may affect the fracture phenomenon of ice, but these mechanisms have not been elucidated. In previous study, we experimentally showed that the shape of the indenter has a significant effect on pure ice deformation and fracture properties by quasi-static indentation testing. In this study, we focus on the impact fracture of pure ice to clarify the effect of strain rate on deformation and fracture phenomena. The impact indentation test was conducted using direct impact Hopkinson bar method, and a spherical indenter with a diameter of 9 mm was attached to the tip of the striking bar. The indentation rate was approximately 2.3 m/s, and the test temperature was approximately -10°C. It was clear that the maximum load of the load–displacement relationship was larger than that of the quasi-static indentation testing. This tendency was qualitatively consistent with the compressive strength of the uniaxial compression testing.

Quasi-Static Indentation test Analyses of CFRP laminate using quasi three-dimensional XFEM

Quasi-Static Indentation test Analyses of CFRP laminate using quasi three-dimensional XFEM

Evaluation of quasi-static indentation response of superelastic shape memory alloy embedded GFRP laminates using AE monitoring

In this paper, the potential of superelastic shape memory alloy (SE-SMA) wire embedded architectures to increase the quasi-static indentation properties of a laminated glass/epoxy composite material was evaluated. Three types of SE-SMA configurations namely straight independent, meshed and anchored wires were embedded in the glass/epoxy composite laminates via a vacuum bag resin infusion technique. Throughout this investigation, the changes in the quasi-static indentation behavior and allied damage mechanisms due to these embedments were compared with the homogenous glass/epoxy laminates. Real time acoustic emission (AE) monitoring technique was employed to characterize the damage profile of the different glass/epoxy specimens during the quasi-static indentation tests. The experimental results showed that SE-SMA embedments play a vital role in increasing the penetration resistance by enhancing redistribution of the indentation load all across the laminates. In particular, the meshed specimens restricted penetration of an indenter and delayed the critical fiber fracture unlike homogeneous and straight wired ones, whereas the anchored specimens further restricted extensive SMA/matrix pull-out, unlike meshed ones and provided the most excellent balance among rigidity, rear face fiber breakage, and SMA/matrix pull-out. Straight, meshed and anchored SE-SMA wires increased the load-carrying capacity approximately by 31%, 79%, and 100%, respectively, in comparison to the homogeneous ones.

Multiaxial stress and strain analysis on laminated plates under different flexural loading rates

The occurrence of events associated with Low-Velocity Impacts (LVI) is analysed by drop-weight impact tests on carbon fibre reinforced polymer laminates, comparing the response in these tests with Quasi-Static Indentation (QSI). A laminate sequence of interest, the angle-ply [±45]4S, is tested in both testing procedures with a simply supported configuration on a circular fixture. Both methodologies show similarities in the critical points for change of behaviour in terms of energy, while the strain rate effect is verified to influence the higher apparent stiffness of the laminate submitted to the LVI test compared with the QSI test. The effect of multiaxiality in loads existing in these tests is addressed in the quasi-static experiment by applying Digital Image Correlation (DIC), comparing the results with numerical simulations using the Finite Element Method (FEM). The orthotropy of the material generates strain and displacement fields which allow understanding the dissimilar response of the laminate in the different radial directions, also giving explanation to the initiation and evolution of different damage mechanisms.

Three-dimensional damage quantification of low velocity impact damage in thin composite plates using phased-array ultrasound

The evaluation of internal damage in multilayered composite materials is of great importance for high reliability-demanding applications, and remains a challenge due to the complex failure modes and mechanism of composite materials. This study presents a volumetric method of three-dimensional size quantification and prediction for low velocity impact damage in thin composite plates using phased-array ultrasound. A set of low velocity impact damages are induced in thin carbon fiber/epoxy resin matrix composite plates using quasi-static indentation tests. A volumetric reconstruction method is proposed to reconstruct a three-dimensional volume from the raw data, allowing for direct damage identification, localization, and quantification. Using the echo amplitude feature of the reconstructed volume, the 6 dB-drop method is employed to characterize the damage size in terms of volumes and areas. An impact size prediction model is established to correlate the impact energy and the damage volume/area. Comparisons are made between the microscopy measurement of the damage cross-section and results obtained using the developed method.