Instrumented Drop Weight Impact Tester Research Articles

Modernization of the VK-350 Instrumented Drop Weight Impact Testing Machine for Impact Testing of Various Types

Modernization of the VK-350 Instrumented Drop Weight Impact Testing Machine for Impact Testing of Various Types

Fire reaction and post-fire impact properties of flax fibre reinforced composites containing intumescent flame retardants

The current research aims at investigating the fire reaction and post-fire impact characteristics of flax fibre reinforced composites based on different polymer matrices, such as epoxy resin and polypropylene (PP). The effects of stacking sequences of polymer sheets and flax fabrics within the composites are explored by a cone calorimeter. Heat release and smoke production results indicate that a top surface and number of flame-retardant polymer layers played significant roles in determining the fire reaction properties. Furthermore, post-fire impact properties of flax-epoxy and flax-PP composites depending on burning periods are analysed in this study at the first time. A fully instrumented drop-weight impact testing demonstrates that an increase in heat exposure time led a gradual decrease in impact properties of the composites due to fire-induced damages on fibres and polymers. However, pre-melting and re-consolidation of PP are beneficial to have higher impact energy and force of the flax-PP composite over those of the flax-epoxy counterpart. In addition, the char formation of composites due to intumescent flame retardant enhances the fire reaction properties of composites, whereas there is no significant influence on the post-fire impact characteristics due to highly brittle nature of carbonaceous char.

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.

Experimental and calculation investigations of deformation and fracture processes of various types of steels during impact shear tests

The paper proposes the experimental technique for investigating the deformation and fracture of the materials under dynamic shear. The authors have tested the specimens with two shear zones. A series of numerical calculations are performed using the finite element method. The variation of the shear zone length in such specimens allows one to change the strain rate in these zones at a constant loading rate. The specimens are made of the following steels: steel 20, Hardox 400 high strength steel, and ARMOX 500T armored steel. The tests are made on the instrumented drop-weight impact testing machine with a high-speed registration system. The obtained results make it possible to assess the influence of many factors (strain rate, specimen geometry, material, and direction of the specimen cutting) on the deformation and fracture of materials under dynamic shear conditions. It is employed to specify the parameters of the material models for the numerical simulation of complex loading processes, as well as to develop the experimental method for the mechanical characteristics determination considering fracture during dynamic shear.

Determination of fracture toughness for steel 22k from the results of tests of different types specimens

Nowadays, in various industries, in particular in nuclear energy, to determine the fracture toughness, along with standard tests of compact specimens, which are quite expensive and complex, methods are developed to determine these characteristics by impact tests of Charpy specimens using different correlations between Charpy impact fracture energy (CVN) and critical stress intensity factor (J-integral). The paper analyzes correlation and analytical methods, the authors of which consider them universal for a certain class of steels. Correlation methods are divided into one-stage and two-stage. One-stage methods allow to obtain the value of the critical stress intensity factor by the known fracture energy. Two-stage methods in the first stage offer the calculation of the dynamic critical stress intensity factor, in the second the temperature shift and obtaining a static critical stress intensity factor. Analytical methods according to the іmpact fracture diagram of the specimen allow to construct a J-R curve and calculate the value of the J-integral. A series of fracture tests of CT specimens made of heat-resistant steel 22K was carried out, the reference temperature T0 was determined according to the single-temperature method of the ASTM-1921 standard and the Master curve was constructed. A series of standard Charpy specimens impact tests in the temperature range -50…+100°С was performed using an instrumented drop-weight impact testing machine equipped with a high-speed registration system. According to the results of Charpy specimens impact tests, the fracture toughness were determined using different methods. It is established that both analytical and correlation methods cannot be universal and can be used to determine the fracture toughness of 22K steel. Therefore, a new exponential correlation was proposed between the fracture energy of the Charpy specimens and the critical stress intensity factor for heat-resistant steel 22K.

Low velocity impact (LVI) and flexure-after-impact (FAI) behaviours of rotationally moulded sandwich structures

There is limited academic knowledge and industrial understanding available on low velocity impact (LVI) properties, impact damage propagation mechanism and post impact residual strength of rotationally moulded skin-foam-skin sandwich structures. In this work, two roto-moulded sandwich structures (sandwich-1 and sandwich-2) were manufactured at the same thickness and skin layers configurations, with two different commercially available foam core material types and densities. They were tested using an instrumented drop weight impact tester at 25 J, 35 J and 45 J energy levels to analyse the force–time, force–deflections, and energy–time properties. The damage mechanism was investigated with a high-resolution X-ray micro Computed Tomography (μ-CT) technique which correlated the measured impact properties for both type of sandwich structures. Flexure-after-impact (FAI) test was carried out to characterise the effects of impact induced damage on the residual strength of impacted sandwich specimens for the first time in this study. In comparison of two sandwich structures, the lower density foam material manufactured sandwich structures (sandwich-2) showed a better impact property, damage resistance and FAI strength compared to higher density foam material sandwich structures (sandwich-1). This result was not industrially expected and could be related to the incomplete decomposition of blowing agents or forming of immature foam cells in the foaming process of higher density foam material in sandwich-1 leading to its less impact and FAI test load bearing capacities.

Impact response of steel-PU foam-steel-concrete-steel panel: Experimental, numerical and analytical studies

A new steel-polyurethane foam-steel-concrete-steel (SPUFSCS) panel, which consists of “soft” and “stiff” layers, was proposed and its impact resistant performance was experimentally, numerically and analytically studied. The front “soft” layer, including a steel plate and polyurethane foam (PUF), was designed for dissipating impact energy and reducing peak force transmitted to the rear “stiff” layer (i.e., SCS panel). The SCS panel with high strength and ductility was employed for resisting the transmitted impact force from PUF. Experimental studies on SPUFSCS panels under impact loading were first conducted by employing an instrumented drop weight impact test system to reveal their failure modes, impact force and displacement responses. The impact energy was found to be dissipated through local indentation and global deformation of the SPUFSCS panel. The Finite Element (FE) models of the tested SPUFSCS panels under impact loading were established and validated against the experimental results. Numerical results indicated that the impact energy dissipated by “soft” layer is higher than that of “stiff” layer, which demonstrated the benefits of employing “soft” layer on improving the impact resistance of the traditional SCS panel. In addition, an analytical model was also presented for predicting the displacement response of the SPUFSCS panel under impact loading. The analytical model was proven to be reasonable in predicting the displacement response by comparing with the experimental results.

Influence of Rubber Content on Failure Mode and Resistance Characteristics of PC/ABS Blends and their ABS Constituents under Impact

This present study has been re-established to investigate failure mode and resistance characteristics of the PC/ABS blends and their ABS constituents under impact for a range of rubber contents. This present study has still been experimentally performed under an instrumented-drop weight impact test (DWIT) at a room temperature. It has been finally revealed that with a particular size of rubber particle, content of rubber significantly influenced impact failure modes and impact resistances of the PC/ABS blends and their ABS constituents as well. The test results showed that impact strength of the blends was improved about 23.22% and 155.33% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. There was also found that an increase in impact toughness of the blends for 57.48% and 239.23% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. Whilst, impact strength of the ABS was improved about 392.98% and 190.12% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. An increase in impact toughness of the ABS for 308.20% and 172.56% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively.

A comprehensive review on drop weight impact characteristics of bast natural fiber reinforced polymer composites

The performance of fiber-reinforced composite laminates imitating the actual in-service impact loading conditions evaluated through an instrumented drop weight impact testing machine has been reviewed thoroughly. The study of the contact force response during impact is critical in determining the energy absorption capacity of the composites through force–displacement plots. Low-velocity impact (LVI) studies of synthetic fiber composites are extensively studied however, the natural fiber-based composites (NFC) are being studied for impact loading resistance that can offer competitive properties to some of the potential synthetic fiber-based composites (SFC). A comprehensive study on bast natural fiber-based composites is presented, discussing the impact resistance, failure modes, and residual properties towards use in automotive/aerospace applications.

Orthogonal optimum design of parameters of flux used for low carbon bainitic steel

L8 (27) orthogonal test table is applied to design eight kinds of flux, and arranged with SiO2, ZrO2 and TiO2 as three factors. The microstructure, morphology and mechanical properties of low carbon bainitic steels are investigated by means of optical microscope, scanning electron microscope, transmission electron microscope, tensile testing machine and instrumented drop weight impact tester with oscilloscope. The results indicate that the optimum composition rate is as follows: 20% SiO2, 10% ZrO2, and 6% TiO2, and the interaction between ZrO2 and TiO2 is obvious. The microstructure of deposited metal of low carbon bainitic steel is mainly formed by acicular ferrite and granular bainite. The acicular ferrite is paralleled distribution, and plenty of fine sheet Martensitic–Austenitic constituents are dispersing, which can hinder crack propagation and improve strength and toughness. The impact energy is up to 109.7 J at − 20 °C, and the ratio of brittle fracture termination load to maximum impact load is 0.378, ensuring excellent crack arrest toughness.

Drop-Weight Impact Behaviour of Hybrid Fiber/Epoxy Honeycomb Core Sandwich Composites under Hemi-Spherical Impactor

Low velocity impact test is conducted on hybrid fiber honeycomb core sandwich panels filled with different energy absorbing materials such as Rohacell, wheat husk and polyurethane foam (PUF) using an instrumented drop-weight impact testing machine as per ASTM D3763-93 standard. Low velocity impact characteristics such as peak load, absorbed energy and damage mechanisms of the sandwich panels are investigated at 17.16 J, 25.75 J, 34.33 J and 42.91 J energy levels by varying the height of the dropping weight. Image processing technique is performed to calculate the impact damage area of the specimens using MATLAB 2016 A. To observe the damage and failure mode in the failed specimen, optical microscopic observation method is used. As increasing the impact energy, fiber fracture at face sheets, core fractures, delamination between hybrid fabric-epoxy layers and indentations failures are perceived by the visual inspection. According to the obtained results, the low velocity properties such as energy absorption capacity, load at initial damage are significantly improved and impact damage area is decreased considerably by the PUF filled core sandwich panels. Thus, this analysis puts forward that PUF filled honeycomb core sandwich panel may be a preferable material in the field of composites to overcome delamination and impact damages and to reduce the weight especially for the applications of advanced aerospace structures.

Impact response and energy absorption of single phase syntactic foam

Abstract This study experimentally investigates the static and impact response of a new single phase syntactic foam which has been newly developed for impact energy absorption. The syntactic foam had different densities ranging from 172 kg/m3 to 366 kg/m3 depending on the thickness and composition of the coating layers. The impact response and impact energy absorption were investigated by using instrumented drop-weight impact tests. Under static loads, the mechanical properties of the syntactic foam including the compressive strength, the yield stress, and Young's modulus increased with the density but the rate of increment decreased at higher densities. There were two types of progressive failures of the syntactic foam under impact loads. The failure propagation was examined and found to be dependent on the material density and the impact velocity. Interestingly, the densification only occurred in the low-density specimens while this phenomenon was not observed for the specimens with the density greater than 288 kg/m3. The impact energy absorption capacity increased significantly with the density and the wall thickness of the macrospheres.

Impact Resistance of Bamboo Fabric Reinforced Polypropylene Composites and Their Hybrids

Bamboo in woven fabric form embedded in the polymer results in easier material handling during production and reduction in the manufacturing cost of the composites. In the current study, the effect of hybridization of bamboo fabric with glass fibres on the impact properties of the composites made from them has been studied. The composites were fabricated using a compression moulding method. Bamboo fibres were in the form of twill-weave fabric. Impact tests were conducted using an instrumented drop weight impact test system. It can be seen that the peak load and energy absorbed increase with the increase in the applied impact energy. For the BPP composites, the applied energy of the impact was increased until penetration was occurred at 55 J. While for the BGPP hybrid composites, they were penetrated at the applied energy of only 35 J. However, The hybrid composites exhibit a greater peak load resistance than the BPP composites. The crack damage in the composites was also reduced with the presence of fabric reinforcement. These preliminary results indicate that bamboo fabric is truly a new contender for developing excellent and balanced properties of composites such as for the interior components.

Response of E-glass/Epoxy and Dyneema® Composite Laminates Subjected to low and High Velocity Impact

Energy absorption of two different types of composite laminates i.e. glass composite (E-glass/epoxy) and ultra high molecular weight polyethylene (UHMWPE) (Dyneema®) laminates were studied under low and high velocity impact. Instrumented drop weight impact tester was used for low velocities and sub machine carbine (SMC) gun was used for high velocity impact. Failure behaviour of both E-glass/epoxy and dyneema laminates during impact was studied and results of the energy absorption of the tested composite laminates have been presented. Dyneema laminates showed 2 times higher energy absorption than E-glass/epoxy laminate under high velocity impact. However, both the laminates have showed higher energy absorption at high velocity impact as compared to low velocity impact. Failure analysis on impacted laminates reveals that the E-glass/epoxy laminate undergoes elastic deformation, delamination and brittle failure of fibres, whereas dyneema laminates undergo plastic deformation and associated tensile stretching of fibres. The results obtained from this study bear significance in the development of light weight add-on and structural composite armours for the real time applications.

Mechanical, Thermal and Instrumented Impact Properties of Bamboo Fabric-Reinforced Polypropylene Composites

Many automotive companies are experimenting with natural fibres as a substitute for glass fibres in polymer composites, especially polypropylene (PP) based composites. PP composites reinforced by plain woven bamboo fabric have recently been widely investigated. Bamboo in woven fabric form embedded in the polymer results in easier material handling during production and reduction in the manufacturing cost of the composites. In the current study, the performance of twill-weave bamboo fabric-reinforced PP composites, which were fabricated using a compression moulding method, was evaluated. The mechanical, thermal and impact performances of the bamboo fabric-reinforced PP (BPP) composites were evaluated in comparison to those of PP, at various bamboo contents and stacking sequences. The incorporation of bamboo fabric resulted in the improvement of tensile strength, tensile modulus, flexural strength, flexural modulus and Charpy impact strength of PP by 238%, 110%, 180%, 170% and 160%, respectively. The integration of bamboo fabric slightly increased the melting temperature and the degree of crystallinity of the composites. A 40% decrease in the heat of fusion of the composites was observed compared to that of PP. Impact tests were also conducted using an instrumented drop weight impact test system. The perforation impact energy, peak load and energy absorbed of the composites increased when the bamboo content was increased. The perforation impact energy was at 55 J for the BPP50% composite, compared to that of neat PP at 20 J. The crack damage in the composites was also reduced with the presence of fabric reinforcement. These results indicate that bamboo fabric is truly a new contender for developing excellent and economical light-weight composites as interior components in automobiles.

Low-velocity impact responses of Napier fibre/polyester composites

The low-velocity impact response of Napier grass fibre/polyester composites was investigated. Napier grass fibre was used as the reinforcing material in polyester composite laminates. Napier/polyester composites specimens of 10%, 15%, 20%, 25% and 30% fibre volume fraction were produced using a compression moulding machine. The specimens of the mentioned fractions were impacted with a 5 J energy level using an instrumented drop weight impact tester (IMATEK IM10). The fracture damage of the impacted specimen was analysed using a field-emission scanning electron microscope (FESEM). The experimental result shows the relationship between the volume fraction percentage of Napier fibres and the impact force, energy absorbed and stiffness of the composites. Pure polyester specimens displayed brittle behaviour with a lower peak force, lower energy absorption and less time to failure compared to Napier reinforced composites. The impacted Napier/polyester composites with fibre loading of 30% show higher absorbed energy, peak force and longer time to failure. Furthermore, the experiments on each fibre volume fraction revealed increasing load-bearing capability and energy absorption with an increase in the volume fraction of Napier fibre. The FESEM observation exhibits various failure mechanisms such as fibre breakage, fibre pull-out, matrix cracking and fibre splitting.

Burst Strength of Glass Fibre/Epoxy Composite Pipes Subjected to Impact Loading

The main objective of this experimental study was to investigate the effects of low velocity impact loading on the pressure bearing capacity of the E-glass/epoxy composite pipes. The pipes were produced by the conventional filament winding technique comprises of six axisymmetric layers with (±55°)3 winding angles. The specimens were impacted at three different energy levels which are 5 J, 7.5 J, and 10 J using an instrumented drop weight impact testing machine (IMATEK IM10). The samples were then filled with water and subjected to burst test until distinct leakage failure is observed. The results indicate that the peak force and contact time increases with increased of impact energy. For impacted samples, the pressure tests show that the burst strength of the pipes decreases with increase in energy levels during impact loading. During the burst tests, several damage types named leakage and eruption were observed.

Effect of temperature and hybridisation on the low velocity impact behavior of hemp-basalt/epoxy composites

This work focuses on the experimental investigation of the residual flexural strength of hemp/epoxy, basalt/epoxy and hybrid (hemp-basalt)/epoxy composite laminates subjected to low velocity impact damage at different temperatures. These specimens were subjected to a low velocity impact of 1.5 m/s with an incident impact energy of 2.17 J using an instrumented drop weight impact tester at three different temperatures of 30 °C, 50 °C and 65 °C. The residual flexural strength of the post impacted specimens were measured by the conduction of three point bending test in a 100 kN universal testing machine with acoustic emission monitoring. The effects of temperature and basalt fiber hybridisation on the damage initiation, propagation and onset of failure were investigated using the magnitude of AE cumulative counts at different stages of loading. The results show a reduction in impact strength and residual flexural strength after impact at elevated temperatures. Lower impact resistance shown in the impact test results for all three types of composites at elevated temperatures indicate the effect of temperature which leads to inferior impact properties. It was evidenced from the impact and dynamic mechanical analysis (DMA) carried out on the composites that hybrid composites have better residual flexural strength and impact properties compared to non-hybrid composites.

Experimental impact study on unidirectional glass-carbon hybrid composite laminates

Abstract In this experimental study, the impact response of unidirectional hybrid composite laminate was investigated. Hybrid laminates with different stacking sequences were fabricated, using unidirectional glass and carbon fiber as reinforcement and epoxy resin as matrix. ASTM standard D5628 was followed to conduct the experiment using the instrumented drop weight impact test apparatus. All the square specimens were tested at an impact velocity of 3.43 m/s and the time histories of force and energy absorbed were recorded. The impacted specimens and their X-ray images were visually inspected to understand the failure pattern. The experimental results showed that the addition of carbon fiber increases the impact strength by absorbing more force and energy. Furthermore, the laminate can be stiffened with the carbon fiber layers by interfacing glass fiber layers on either side.

The influence of low velocity repeated impacts on residual compressive properties of honeycomb sandwich structures

This paper describes the low velocity impact behavior of repeatedly impacted honeycomb sandwich structures which are used in aircraft interiors comprising of unidirectional glass fiber reinforced epoxy composite face sheets and aluminum honeycomb core. Impact energies, maximum loads and the permanent deflection of honeycomb sandwich structures were determined with instrumented drop weight impact test machine to evaluate the repeated impact performance and damage resistance. On the other hand, the preliminary single impact loading tests also performed in order to find the energy levels which were ranged fully elastic energy level to perforation energy level for sandwich composites. Impact test results obtained from repeatedly impacted honeycomb sandwich structures were correlated with a function of force–time, force–deflection and energy-number of impacts curves. This work is also focusing on the residual compressive properties of single and repeatedly impacted honeycomb sandwich structures. Shimadzu AG-X test machine with a load cell of 10kN was used for compression after impact tests (CAI). The values of residual compressive strength of the single and repeatedly impacted honeycomb samples were compared with the undamaged honeycomb samples according to compressive load–displacement curves.