Drop Weight Impact Test Research Articles

Experimental investigation of hybridization effect of Kevlar and Glass fibers on CFRP composite under low velocity impact

This paper experimentally investigates the effect of Kevlar and glass fibers on carbon fibers epoxy composite to enhance the impact strength under low velocity impact (LVI). Experiments were conducted on various combinations of Kevlar, glass, and carbon FRP composites to study the dynamic impact behavior using a drop-weight impact tester. Five varieties of the hybrid composite were selected for experimentation using a drop-weight impact tower Instron, CEAST 9340. Out of five combinations, the first sample contains only carbon fiber with a different orientation, and the other four contain interplay hybrid fibers (Kevlar-carbon-Kevlar, Glass-carbon-Glass, Kevlar-carbon-glass, and glass-carbon-kevlar) 8-ply composite. The carbon fiber layers are inserted within each hybrid composites to investigate how the Kevlar and glass fiber qualities affect the impact resistance of CFRP composite. The analytical modeling results were compared with experimental results, which are in good agreement. The delamination and damage location were detected using an advanced ultrasonic C-scan. The damage area of laminates is measured using ImageJ software. The analysis shows that the amount of absorbed energy increased in a hybrid laminate having Kevlar at outer surface locations.

Effect of aramid core-spun yarn on impact resistance of aramid/epoxy composite

Introduction: The surface of aramid filament is smooth, which is a great defect for impact resistance and composite molding of aramid/epoxy composite. In this study, a new type of yarn—aramid core-spun yarn is introduced to the fabrication of compositematerials. It increases the friction among yarns and optimizes the performance of yarns.Methods: To verify the improvement of yarn in the composite material, the hand lay-up process is used, and the first layer and the fourth layer are replaced by core-spun yarns in a four-layer composite configuration.Results and Discussion: The energy absorption, and the damage of the impacted surface and the back surface are evaluated through the drop weight impact test. The yarn pull-out test can reflect the internal friction of fabric. The results show that the average energy absorption of new yarn in the first layer is 10 J cm2/g more than that in the fourth layer at a 90°/45°/-45°/0° configuration after the normalization, but the conclusion is contrary when the structure is -45°/0°/90°/45°. Under the structure of 90°/45°/-45°/0°, the damaged area of the fabric is larger when the aramid core-spun yarn is laid on the first layer, while a contrary result can be found for the structure of -45°/0°/90°/45°. The fundamental research will provide design ideas and supports for aramid composite.

Experimental Study of Glass Fiber Reinforced Concrete Incorporating Micro Silica

The most common building material utilized worldwide is concrete. Concrete with higher compressive strength is becoming more and more in demand as the trend toward using it more widely for high rise buildings. Experimental study of glass fiber (GF) reinforced concrete incorporating micro silica was investigated in this study. The concrete is prepared by using M40 mix. GF with 12 mm length with aspect ratio of 857 is used. Four volume fractions of 0%, 0.4%, 0.8% and 1.2% by weight of cement and micro silica with 5% by weight of cement are used. The fiber is distributed randomly in all directions. The mixes were cast and tested for workability, compressive strength, flexural strength, water permeability test, drop weight Impact test, bond strength test and residual compressive strength at elevated temperature. Micro structural study is done with SEM analysis. Workability of glass fiber reinforced concrete decreased with increase in GF. Compressive strength show 12% increment whereas Flexure strength is increases 35% compare to normal concrete. Different percentages of glass fibres and micro silica have lower water penetration depths. With regard to the fire resistance test the compressive strength at elevated temperature decreases significantly. Impact resistance and bond strength of glass fiber reinforced concrete with micro silica increases with increase in fiber content. Hence, it's suggested to use glass fiber in the concrete according to use of concrete.

Experimental study on a novel steel-PU foam-concrete-tube multilayer energy absorbing panel under impact loading

In this paper, a novel steel-polyurethane foam-concrete-tube multilayer energy absorbing panel (SFCTMEAP) was proposed to enhance the impact resistance and energy absorbing capacity of infrastructures and buildings. The dynamic responses of the SFCTMEAP were studied and presented. The impact tests on the SFCTMEAP were first conducted to obtain their failure modes, impact forces and displacement responses. Two response stages were identified based on the impact force and displacement responses during the impact process, two failure modes were observed from the tests. The varying parameters considered in the drop weight impact tests included the width and thickness of the steel tube as well as the thickness of the concrete core. Moreover, the displacement, mean force and energy absorbing performance of the SFCTMEAP were discussed in detail.

Repeated impact resistance of steel fibre-reinforced dry UHPC: Effects of fibre length, mixing method, fly ash content and crumb rubber

Dry concrete exhibits significantly different mechanical properties and failure patterns under dynamic loads from those under static conditions. Considering the practical applications of dry concrete, the flexural impact load renders its units/structures susceptible to unpredictable damage or even failure. In this study, the modified low-velocity drop-weight impact test was conducted on steel fibre-reinforced dry UHPC (FR-DUHPC) beam samples to simulate the frequent and multiple impact loads. The effects of steel fibre length, mixing method, fly ash content and crumb rubber addition on the impact resistance of FR-DUHPC were evaluated based on dynamic responses. Weibull distribution was then conducted to analyse the failure hit number of concrete samples in consideration of the large value variation. Test results indicated that the flexural impact performance was markedly improved with longer steel fibres, but deteriorated with increased fly ash content (especially at early ages) and considerably degraded with the inclusion of rubber aggregate. Hybrid medium/long fibre reinforcement was proposed for DUHPC that were mainly subjected to impact loads during service, while the fly ash content utilized to partially replace cement was not recommended to exceed 40%. Rubber aggregate was not proposed to be added to dry concrete mixtures since the impact load would greatly accentuate the initial matrix defects caused by the weak bonding. Additionally, the two-parameter Weibull distribution was verified to be a desirable statistical method for analysing the failure blow number of FR-DUHPC under repeated low-speed drop-weight impacts. The impact energy for the practical structural design could be preliminarily computed utilizing the derived Weibull parameters at different levels of reliability.

Improved double impact and flexural performance of hybridized glass basalt fiber reinforced composite with graphene nanofiller for lighter aerostructures

The growing demand for sustainable, lightweight yet rigid and cost-effective materials for airplane construction served as the impetus for this work. An E-glass fiber (400 GSM) is layered in a 6:2 ratio with natural basalt fiber and infused with graphene nanoparticles to produce a more appealing 40% lighter hybrid composite of 1.1 mm thickness for the aviation industry. Samples of hybrid composites with 1% and 2% graphene-to-fiber filler weight ratios are used. Then, using ASTM standard analysis tools, the damage that is caused on toughened laminates during low-velocity drop weight impact tests, tensile, 3-point bending, and Compression After Impact(CAI) is evaluated. The composites' tensile strength, flexural strength, low-velocity double impact, and compression impact strength all significantly improved at 2 wt% graphene, increasing by 37%, 55%, 56%, and 78%, respectively. Scanning Electron Microscope analysis of the damaged area demonstrated the presence of important toughening mechanisms, such as damage confinement through microcracks and improved fiber-matrix bonding. It has been established that adding an optimum blend of graphene and basalt to Glass Fiber Reinforced Polymer(GFRP) results in an unprecedented increase in effective strength with reduced weight.

Analyzing Impact Behaviour of Glass Fiber Epoxy Composites for Higher Safety Systems

Abstract This study investigates the impact behaviour of glass fiber epoxy composites with a focus on achieving enhanced safety. A drop weight impact test machine was used to perform a series of impact tests on the composite samples. Two different impactors as dimensions and three velocities were used to investigate the impact behavior of glass fiber epoxy composites. The study’s goal is to investigate the impact response of these composites and their potential for usage in impact protection applications. The study findings show that glass fiber epoxy composites have outstanding impact resistance properties, as well as high levels of the ability to absorb energy and withstand the initiation of damage. The findings suggest that both the impactor (as shape and dimensions) and the velocity of impact have a notable influence impact on the damage mechanisms and energy absorption capacity of the composite materials. The failure mechanisms detected in the composites were mostly delamination and fibre breakage.

Exploring the flexural and impact properties of pure flax/epoxy and Kevlar/flax/epoxy composites through experimental and numerical analysis

Hybrid composites offer a viable alternative to conventional composites in terms of reduced cost and environmental impact. This study investigated the effect of hybridizing flax with Kevlar on the flexural and impact properties of Kevlar/flax/epoxy composites using three-point bending, drop-weight, and Charpy impact tests. The tested specimens were made of unidirectional flax fibers (F) and woven Kevlar fibers (K) in four configurations: unidirectional flax/epoxy [016F] (UFE), angle-ply flax/epoxy [±454F]S (AFE), woven Kevlar/unidirectional flax/epoxy [0–902K/06F]S (UKFE), and woven Kevlar/angle-ply flax/epoxy [0–902K/±453F]S (AKFE). The three-point bending test results showed that the ultimate strength and the flexural modulus of the UKFE increased by 15% compared to pure UFE and by more than threefold for AKFE compared to AFE laminates. Additionally, the results of the drop-weight test revealed a significant increase in the impact force by 30% for both unidirectional and angle-ply laminate configurations. Similarly, Charpy test results indicated a 60% improvement in the impact energies of the flax laminates. The predictions of the proposed finite element model agreed very well with the experimental results. These findings demonstrate the effectiveness of hybridizing two layers of Kevlar onto flax/epoxy composites in enhancing the composite's impact and flexural properties.

Effects of woven structure and impact mode on the low-velocity impact properties and fractography of bamboo-textile-reinforced polymer composites

Bamboo-fiber-reinforced polymers have gained popularity in numerous industries because of their mechanical properties, lightweight, and ecological benefits. In this study, to determine the effects of textile structure on the impact resistance performance of bamboo-textile-reinforced polymers (BTRPs), we evaluated three impact modes: simple support beam (SSB), drop weight, and Charpy impact. We then used 3D X-ray scanning to determine the effects of the textile structure and impact modes on the microscopic fracture and crack development. The results indicated that the woven structure allowed for energy transmission in all directions during the drop weight impact test. During the SSB impact test, the large quantity of bamboo tows parallel to the major axis of the specimen increased the absorbed energy. When additional layers were added in the loading direction, the deflection of the entire specimen decreased, thus leading to lower absorbed energy. According to 3D X-ray images and quasi-static bending fracture results, similar fracture patterns appeared on dynamic and static loaded specimens. Consequently, the energy required for internal fracture and the strain energy of deflection are the two significant reasons that enable the excellent impact resistance performance of BTRPs.

High-strength steel beams with hexagonal web openings under impact load

A drop-weight impact testing machine was used to conduct an impact test on 15 specimens in order to examine the impact resistance of high-strength (HS) steel beams with hexagonal web openings (SBHWO). The test findings demonstrate that as steel strength increases, maximal impact force and impact platform value rise, while maximum displacement, residual displacement, beam-end rotation, reduction ratio of opening area, and energy absorption ratio decrease. The use of high-strength steel can significantly improve the impact resistance of the SBHWO. When steel Q235 was lifted to steel Q550, the average increase of impact peak and impact platform value was 17.94% and 90.80%, respectively, and the average reduction range of maximum displacement and residual displacement in the span was 45.36% and 55.30%, respectively. After steel Q550 was upgraded to steel Q690, the improvement effect of impact resistance is small. Empirical equations of the relationship between impact energy，steel strength and dynamic responses were established.

Micro-macro fracture mechanism of heterogeneous granite in percussive drilling

The conventional rotary rock breaking method faces a technical bottleneck in improving the rate of penetration (ROP) in deep hard formations. Percussive drilling is the most potential approach to increase rock-breaking efficiency and ROP. However, the rock-breaking mechanism of percussive drilling is still unclear enough, especially the micro-fracture mechanism of rock under confining pressure (under lateral pressure and hydraulic pressure). In this paper, the impact rock breaking experiments by four kinds of Polycrystalline Diamond Compact (PDC) cutters are carried out using a drop-weight impact testing machine and an acoustic emission (AE) recording system, the influence of parameters such as cutter shape, rake angle, and impact energy on rock-breaking are systematically analyzed. This study includes a numerical simulation to examine the process of crack initiation, propagation, and cuttings formation during the impact process with the consideration of confining pressure. The results show the conical-shaped cutter is the most aggressive with high breaking efficiency. The penetration depth of the cutter is mainly influenced by the impact energy and cutter shape than the rake angle of the cutter. There exists critical impact energy makes the rock breaking efficiency the highest. The critical impact energy is about 40 J when using the conical-shaped cutter with a rake angle of 15°. The rock mainly failed in tensile mode, and the inter-grain crack is the main crack. Hydraulic pressure can inhibit the formation of horizontal cracks, while lateral pressure can inhibit the formation of vertical cracks and reduce the proportion of tensile cracks. The research results can provide some reference and basis for improving the rock-breaking efficiency in deep hard formations.

Multi-objective crashworthiness optimization of energy-absorbing box with gradient lattice structure

To improve the lightweight and crashworthiness of energy-absorbing box, an energy-absorbing box with spatial lattice structure and multi-objective optimization method are proposed. First, a novel single-cell structure is proposed, which is replicated and arranged to form the spatial lattice structure. Then, the mechanical properties of the material are tested by quasi-static and high-speed tensile tests. The finite element model of the spatial lattice structure is established, and the numerical results are verified by the drop weight impact test. Finally, four different types of approximate models are used to fit different responses, and the combination of approximate models with higher accuracy is obtained. And the multi-objective optimization of our model is carried out. The optimal design of our model is obtained based on the grey relational analysis coupling entropy weight method. Compared with the energy-absorbing box with initial lattice, the specific energy absorption of the optimal design of our model is increased from 6.23kJ/kg to 8.91kJ/kg, an increase of 43.0%, and the mass is reduced from 1.1kg to 0.798kg, a reduction of 27.4%. The results show that the optimal design of our model has the advantages of lightweight and energy absorption.

Modelling low-velocity impact damage and compression after impact of 3D woven structures considering compaction

A novel finite element modelling approach is presented which incorporates representative binder yarn compaction, for simulating the low-velocity impact (LVI) and compression after impact (CAI) response of 3D woven layer-to-layer carbon/epoxy composite architectures. Simulations of out-of-plane drop-weight impact tests were performed at energies of 32 J and 42 J. Warp and weft layers were modelled as continuous plies and three different approaches were explored to model the binder reinforcement; (i) with a rectangular cross-section and non-compacted, (ii) with an elliptical cross-section and non-compacted, and (iii) an elliptical cross-section which accounts for compaction. Predictions were compared with experimental results from literature and it is shown that modelling the binder reinforcement as an elliptical cross-section with compaction leads to a predicted damage area, on the impacted side, which is within 2%, and the non-impacted side within 6% of experimental measurements. The predicted CAI strength is within 11% of the experimental values.

Experimental Research on Dynamic Behavior of Stiffened Plates under Drop-Weight Impacts of a Wedge Impactor.

Deck structures subjected to drop-weight low-velocity impact are critical safety elements for ships and offshore structures. Therefore, the aim of the present study is to propose experimental research on dynamic responses of deck structures composed of stiffened plates subjected to drop-weight impact of a wedge impactor. The first step was to fabricate a conventional stiffened plate specimen and a strengthened stiffened plate specimen, as well as a drop-weight impact tower. Then, drop-weight impact tests were carried out. Test results show that local deformation and fracture occurred in the impact area. A sharp wedge impactor caused premature fracture, even under relative low impact energy; the permanent lateral deformation of the stiffened plate was reduced by 20-26% by the strengthening effect of a strengthening stiffer; residual stress and the stress concentration of the cross-joint caused by welding may cause undesired brittle fracture. The present investigation provides useful insight for improving the crashworthiness design of the deck structure of ships and offshore structures.

Effect of thickness on mechanical properties of modified 9Cr 1Mo steel welds made by narrow gap hot wire gas tungsten arc welding process

Hot wire Gas Tungsten Arc Welding (GTAW) process is selected for fabrication of thick section modified 9Cr 1Mo steel components of Steam Generators (SGs) for 500MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, India. During the welding procedure qualification for fabrication of SGs, the 30 mm and 62 mm thick modified 9Cr 1Mo steel welds were subjected to chemical analysis, visual examination, liquid penetrant examination, radiography examination, micro-hardness tests, longitudinal and transverse tensile tests (at ambient temperature and 525 °C), bend tests, drop weight tests and impact tests (at 0 °C and +18 °C). Literature reveals both positive and negative view on the welding of thick section steel components. Limited information is available in open literature on the effect of thickness on material properties of modified 9Cr 1Mo steel welds made by hot wire GTAW method. In view of the above, authors attempted to systematically investigate the influence of thickness on mechanical properties of modified 9Cr 1Mo steel welds made by hot wire GTAW process. In this paper, the chemical compositions, hardness, tensile strength, bending strength and impact properties of 30 mm and 62 mm thick welds produced by narrow gap hot wire GTAW process are characterized and compared. It is found that the mechanical properties of 30 mm and 62 mm thick welds are comparable except the impact properties at 0 °C. The impact strength at 0 °C for 62 mm thick weld was found inferior in comparison with 30 mm thick weld.

Impact Response of RC Beams Coated with Polyurea Layers

During the service life of reinforced concrete beams (RC beams), they may experience impact loadings induced by various falling objects, such as falling rocks and fragments of upper floors. Therefore, the RC beam’s impact resistance is important to its application in structures. This paper investigated the impact mitigation performance of polyurea coatings on RC beams by drop weight impact tests with different impact velocities and hammer shapes. According to the test results, the polyurea coatings can significantly reduce the RC beams’ local damage and midspan displacement. Moreover, it was found that the RC beams’ plateau impact forces were notably increased by the polyurea coatings. Besides, comparisons between impact tests with different impact loads indicated that the polyurea coatings’ protection effect was not noticeably influenced by the hammer shape or impact velocity. Based on the test results, a numerical model was established and validated, and the model was used to study the mechanism and the parameter influence of polyurea coatings. By simulating the response of upper- and lower-side coated beams, it was revealed that the polyurea coating reduced the RC beam’s overall damage by reducing its local damage and increasing its bending moment. Parametric studies showed that the mitigation effect increased with coating thickness and the increase rate decreased with the thickness. In addition, the effect of longitudinal coating length was also studied via numerical simulation, and it was found that the mitigation effect increased with coating length, and it became nearly identical to that of the fully coated beam when the coating length exceeded 60[Formula: see text]cm.

Experimental study and machine learning algorithms for evaluating the performance of U-shaped ultra-high performance reinforced fiber concrete under static and impact loads

The inherent brittle nature of ultra-high performance concrete (UHPC) increased with strength and is considered its shortcoming in structural applications. This study investigated the impact strength of U-shaped UHPFRC mixtures involving different fiber volume fractions (Vf) under drop-weight impact loads. A U-shaped configuration was introduced in this research to modify the testing procedure of the ACI 544-2R committee for the drop-weight impact test aiming to minimize the scatter result of this testing method. The micro steel fiber (MSF) was incorporated into the UHPFRC mixes at 0–3% Vf (interval of 1%). Moreover, artificial intelligence (AI)-based techniques, including artificial neural network (ANN) and multilinear regression (MLR) model, were employed to train and test the experimental dataset for the prediction of energy absorption capacity (EI2) at the failure crack stage. The results indicated that micro steel has remarkably improved the absorbed energy absorption of the U-shaped UHPFRC mixtures. The U-shaped configuration controls the crack formation. The impact strength at the two cracking stages increased with micro steel fiber content. At the first crack stage, the impact strength of UHPFRC-2 and UHPFRC-3 is 100% and 408% higher than that of UHPFRC-1. The average ductility index value first increased and then decreased with high fiber content. The AI-based technique accurately predicts the energy absorption capacity of a U-shaped UHPFRC mixture at failure crack strength. The ANN and MLR model had an overall R2 value of 0.8231 and 0.9502, respectively.

Scrutiny of freeze-thaw cycles effect on physical and dynamic fracture characteristics of cracked sandstone

A series of freeze-thaw (FT) cycle experiments and drop-weight impact tests are performed to explore the dynamic fracture characteristics of fractured sandstone acted upon by FT cycles. To this end, an innovatively cracked sample, a tunnel with a single radial crack (TSRC), made from an intact sandstone rock is implemented. The experimental results reveal that for FT cycles 10, the dynamic elastic modulus and P/S wave velocities of sandstone exhibit the most drastically descending trend. In such a case, the decreasing percentage of the dynamic elastic modulus, P wave velocity, and S wave velocity reach 16.4%, 7.2%, and 8.3%, respectively. The percentage reduction of these three physical parameters is also tapered off as the number of FT cycles reaches 30 and 40. While the porosity of sandstone grows by 1%, the pore distribution substantially alters for the case of 10 cycles of FT. For the number of FT cycles greater than 30, the porosity of sandstone slightly increases. Further, the crack growth velocity generally grows with the number of FT cycles such that the highest crack growth velocity is detected for 40 cycles FT, and the corresponding velocity touches 427.6 m/s. The obtained results demonstrate that the dynamic fracture toughness lessens as the number of FT cycles increases, and the dynamic initiation toughness is less than the average dynamic propagation toughness in sandstone samples subjected to impact loads. The dynamic loading rate calculated from dynamic initiation toughness reduces with the number of FT cycles when the sandstone specimen experiences the same dynamic loading.

Hybridization effect of Kevlar and glass fibers on CFRP composite under low velocity impact: Numerical simulations

Present work aimed to investigate the hybridization effect of Kevlar and glass fibers to enhance the impact performance of CFRP composites under low velocity by numerical analysis. Analyzing the stack sequencing of Kevlar and glass fibers becomes essential to improve the impact resistance of CFRP composite structures. It is important to know the dynamic behavior of hybrid composites under LVI. To get the best possible stack sequence, numerical simulations were carried out on different stacking sequence combinations of Kevlar and glass with carbon fiber epoxy composites for 25 J energy levels. A virtual drop weight impact test conditioned numerical model created in Abaqus software mimics the actual intralaminar and interlaminar failure. Intralaminar models based on continuum damage mechanics and interlaminar, that is, delamination failure based on cohesive modeling used to evaluate the damage development and material behavior. From the obtained simulation results, the hybrid composites having Kevlar fibers exhibited superior impact resistance.

Residual Performance of Reinforced Concrete Beams Damaged by Low-Velocity Impact Loading

With the advancement of material science and infrastructure design technology, there is an increased need to reflect various loading scenarios in the design of civil infrastructures, including extreme loads such as impact and blast. However, structural behavior under extreme loads has been observed to be very different from that under static loads due to the high-rate loading condition. Therefore, extensive experimental and analytical studies have been conducted to explain the structural behavior under impact loading. From these efforts, various discussions have been presented on the impact behavior and the evaluation of the impact resistance of structures. However, despite the fact that the repair or reinforcement of structures damaged by impact loads is a critical issue, studies of the residual performance of impact-damaged structures are insufficient. This paper presents an experimental study to improve the understanding of the residual performance of impact-damaged structures. A total of 29 RC beams were tested under static loads to examine the effect of impact-damage on the residual behavior of RC beams. Of these, 8 RC beams were intact, and the other 21 RC beams suffered impact loading through drop weight impact tests and were damaged prior to the static flexural tests. The residual performance was evaluated by comparing the maximum load capacity, flexural stiffness, and displacement ductility of impact-damaged beams and intact beams. The comparison indicated that the flexural stiffness and displacement ductility of the impact-damaged RC beams decreased significantly, whereas their flexural strengths did not exhibit a significant difference. Predictive models for flexural stiffness and displacement ductility of the impact-damaged beams were suggested from the test results, and through these, the residual performance of the impact-damaged structure could be evaluated.