Initial Impact Energy Research Articles

Delamination Resistance of Laminates with Various Stacking Sequences against Low Velocity Impacts

Effects of low-velocity-low-energy impacts on interlaminar damage extent in Glass/Epoxy laminate panels of [0°/90°]10, [0°10/90°10], [0°5/90°5]2, [0°5/-45°5/90°5/+45°5] layups were experimentally investigated. The tests were carried out at room temperature with the help of INSTRON CEAST9350 impact system. The initial impact energy was 18J, impactor mass equaled 4kg and the corresponding contact speed was 3 m/s. During the impacts panels were simply supported with a circular steel rings of inner diameters d=80mm. It was found that the amounts of dissipated energy substantially varied depending on the reinforcement sequence and that the lowest amount of energy was dissipated by the laminate panel of [0°/90°]10 reinforcement stacking sequence while the highest one by the panel of [0°10/90°10] reinforcement stacking sequence. Such results suggested that clustering reinforcement layers of the same reinforcement orientation produced negative effects with the regard to the resistance of laminates against impact induced damage.

Strength–Energy and Structural Effects of Dynamic Deformation of Aluminum Alloy

This paper presents the results of dynamic deformation tests performed on aluminum alloy PA4. The studiem was carried out by using rotary hammer, in the range of high rate of deformation: 400 – 2000 s-1. The test were carried using a rotary hammer of RSO type owned by Silesian Technical University in Institute of Technology Metals. Before the dynamic deformation, the heating treatment was carried out allowed for eliminating structural effects resulting from the previous technological treatments and for obtaining the homogenous grain structure. The tests were carried out with linear velocity in the range of 5 – 30 m/s. After deformation the following mechanical characteristics were determined: deformation limit εg, strain rate , tensile strength UTS, impact strength U. Independently of the dynamic deformation tests were carried out tensile test under static conditions. Moreover bending test were performed on Charpy type hammer with initial impact energy equal 300 J. The analysis of the microstructure was carried out using scanning electron microscopy Hitachi S–3400 N.

Impact strength of Hybrid Steel Mesh-and-Fiber Reinforced Cementitious Composites

Large volumes of concrete are produced for construction purposes which creates sustainability issues. Therefore, some of the alternatives to concrete that are being researched and implemented are Steel Mesh Reinforced Cementitious Composites (SMRCC) and Fiber Reinforced Cementitious Composites (FRCC). But due to limitations in element thickness and volume percentage of reinforcement in SMRCC and FRCC, this study has made an attempt to develop Hybrid Steel Mesh-and-Fiber Reinforced Cementitious Composites (HSMFRCC) and study its impact performance. Thus, in order to evaluate the energy absorption of HSMFRCC, 250 mm × 250 mm × 25 mm (thick) slab elements were cast with various combinations of 3–5 layers of steel weld mesh and SS fibers of 0.5–2.5% (of volume of specimens) and low velocity repeated drop weight impact test was administered. From the experimental results, it was found that the impact resistance of HSMFRCC (test specimens) is higher than SMRCC (control specimens using only steel mesh as reinforcement). Regression models have been developed in this study and validated using new hybrid mesh and fiber reinforcement mix. The predicted regression equations developed for initial and ultimate impact energy absorption of cementitious composites with hybrid steel mesh and fibers will be quite useful to the practitioners.

An empirical modified fatigue damage model for impacted GFRP laminates

The aim of the present paper is to evaluate the residual strength of GFRP laminates following a low-velocity impact event under cyclic loading. The residual strength is calculated using a linear fatigue damage model. According to an investigation into the effect of low-velocity impact on the fatigue behavior of laminates, it seems laminate fatigue life decreases after impact. By normalizing the fatigue stress against undamaged static strength, the Fatigue Damage parameter “FD” is presented with a linear relationship as its slope which is a linear function of the initial impact energy; meanwhile, the constants were attained from experimental data. FD is implemented into a plane-stress continuum damage mechanics based model for GFRP composite laminates, in order to predict damage threshold in composite structures. An S–N curve is implemented to indicate the fatigue behavior for 2mm thickness encompassing both undamaged and impacted samples. A decline in lifespan is evident when the impact energy level increases. Finally, the FD is intended to capture the unique GFRP composite characteristics.

Damage behaviors of woven basalt-unsaturated polyester laminates under low-velocity impact

This paper describes the damage behaviors of plain-woven basalt-unsaturated polyester laminates under low-velocity impact from experimental and finite-element approach. Experimental tests were carried out in an INSTRON® drop-weight machine with different initial impact energy levels varying from 15 J, 30 J, 50 J, and 70 J with specimen thicknesses of 4 mm. The results showed that as the impact energy increased, the peak force, the energy absorbed, i.e. area under the force–displacement curve, and the damage area increased. The damage mechanism included matrix crack, delamination with fiber bending, and breakage. Finite-element analyses were carried out to verify further the impact mechanism and correlation between these parameters with the induced damage by using software ABAQUS®. The finite-element method results were in good accord with the experimental results regarding peak force, maximum absorbed energy, and damage area.

Effect of preload on the impact response of curved composite panels

While in many structures, such as aircraft wings, curved laminates are widely utilized, researchers have mostly focused on flat ones. On the other hand, during their service these panels are under pre-stress which can affect their performance. This study therefore investigated the effect of preloading on the impact response of curved laminates. Low velocity impact tests were conducted on GFRP for three different initial impact energies and pre-loads in two different boundary conditions. The results showed that the damage mode is considerably different in these situations. For example, applying the compressive load on curved laminates, the upper and lower surfaces are under tension and compression stress. The compression stress reduces the propagation of cracks, while in a tension stress field cracks propagate easily. The influence on other impact parameters like maximum force and maximum displacement was also significant.

Impact Loading of Ductile Rectangular Plates

Abstract In many industries, rigid-plastic methods of analysis are a useful design aid for safety calculations, hazard assessments, security studies and forensic investigations of ductile structures, which are subjected to large dynamic loads producing an inelastic response. This paper examines the behaviour of a rectangular plate struck at the centre by a rigid mass impact loading. A theoretical method has been developed previously for arbitrarily shaped plates which retains the influence of finite transverse displacements, or geometry changes. It is used in this paper to predict the maximum permanent transverse displacements and response duration of plates having boundary conditions characterised by a resisting moment mM 0 around the entire boundary, where m =0 and 1 give the two extreme cases of simply supported and fully clamped supports, respectively. The theoretical predictions are compared with some experimental data recorded on fully clamped metal rectangular plates having a range of aspect ratios and struck by masses travelling with low impact velocities up to nearly 7 m/s and which produce large ductile deformations without failure. The theoretical analysis gives reasonable agreement with the corresponding experimental data for masses having blunt, conical and hemispherical impact faces. For sufficiently large initial impact energies, the projectile would perforate a plate and, for completeness, a useful design equation is presented which predicts perforation energies larger than all of the test data, as expected.

Low-velocity impact damage of woven fabric composites: Finite element simulation and experimental verification

This paper addresses the response of Glass Fiber Reinforced Plastic laminates (GFRPs) under low-velocity impact. Experimental tests were performed according to ASTM: D5628 for different initial impact energy levels ranging from 9.8J to 29.4J and specimen thicknesses of 2, 3 and 4mm. The impact damage process and contact stiffness were studied incrementally until a perforation phase of the layered compounds occurred, in line with a force–deflection diagram and imaging of impacted laminates. The influence that impact parameters such as velocity and initial energy had on deflection and damage of the test specimens was investigated. Finite Element Simulation (FES) was done using MSC. MARC® was additionally carried out to understand the impact mechanism and correlation between these parameters and the induced damage. The simulation and experimental results reached good accord regarding maximum contact force and contact time with insignificant amount of damage.

Design of Concrete-Filled Circular Steel Tubes under Lateral Impact

Infrastructures and key members are potentially exposed to accidental loads due to extreme situations such as collisions, impacts, and terrorist bombings. Consequently, the current design concept requires that the structures or key members possess adequate capacities to resist accidental loads. To understand the mechanical response of concrete-filled steel tube (CFT) beams subjected to impact loads, this paper presents numerical simulations on the CFT beam tests in an instrumented drop-weight impact facility using finite element code LS-DYNA. The adequacy of finite element modeling (FEM) has been validated against drop-hammer impact tests in the literature. Based on the dynamic increase factors (DIFs) derived from FEM, an algorithm based on theoretical sectional analysis (TSA) is introduced to evaluate the dynamic plastic moment capacity of CFT beams. A linear relationship between initial impact energies and absorbed energies by CFT beams is found using either FEM or TSA. To assist engineers in designing simply supported circular CFT beams subjected to lateral impact, an energy design procedure using TSA is proposed, along with the ranges of key parameters, and an example is presented to illustrate the design procedure.

Impact loading of ductile rectangular plates

In many industries, rigid-plastic methods of analysis are a useful design aid for safety calculations, hazard assessments, security studies and forensic investigations of ductile structures, which are subjected to large dynamic loads producing an inelastic response. This paper examines the behaviour of a rectangular plate struck at the centre by a rigid mass impact loading. A theoretical method has been developed previously for arbitrarily shaped plates which retains the influence of finite transverse displacements, or geometry changes. It is used in this paper to predict the maximum permanent transverse displacements and response duration of plates having boundary conditions characterised by a resisting moment mM 0 around the entire boundary, where m=0 and 1 give the two extreme cases of simply supported and fully clamped supports, respectively. The theoretical predictions are compared with some experimental data recorded on fully clamped metal rectangular plates having a range of aspect ratios and struck by masses travelling with low impact velocities up to nearly 7 m/s and which produce large ductile deformations without failure. The theoretical analysis gives reasonable agreement with the corresponding experimental data for masses having blunt, conical and hemispherical impact faces. For sufficiently large initial impact energies, the projectile would perforate a plate and, for completeness, a useful design equation is presented which predicts perforation energies larger than all of the test data, as expected.

Impact Model Tests and Simplified Analysis for Flexible Pile-Supported Protective Structures Withstanding Vessel Collisions

Flexible pile-supported protective structures have been used extensively in the protection of bridge piers against vessel collisions. Their success is dependent on their ability to absorb impact energy through large deflection and yielding. A large soil tank (15×5×6 m) was used to conduct large-scale model tests on protective structures in silt. A lateral static load test on a single pile was carried out to derive p-y curves for the piles on the basis of the measured bending moment of the pile shaft. Impact tests with different initial impact energies were then conducted on the protective structures and on a single pile to study the energy transfer mechanism during a collision. Soil damping and the inertia force of the pile shaft have obvious effects on the load-displacement curves of single piles, especially in the initial phase of impact. However, their influence on the maximum bending moment of the pile shaft was weak. Compared with protective structures that consist of free-standing piles or a pile row, a novel protective structure with two rows of piles has a relatively larger lateral stiffness and a much larger energy-absorbing capability. A simplified energy-based analysis method is proposed to estimate the lateral deflection of the flexible pile-supported protective structures that are subjected to a given impact energy. Comparison of the calculations with the test results shows that this simplified analysis method gives conservative results approximately 30% for the energy-absorbing capability.

Dynamic energy absorption and perforation of ductile structures

This article focuses on the energy absorption of structural systems and components subjected to extreme loadings which can arise from impact, explosion and various other dynamic events. The dynamic properties of high-strength steels are discussed briefly because they have been proposed for energy-absorbing systems and other components in place of the more common mild steel and aluminium alloys. An energy-absorbing effectiveness factor is proposed which compares the dynamic energy absorbed in a device with the energy consumed up to rupture in a uniaxial tensile test specimen, which is made from the same volume of the material. This dimensionless factor is examined for the axial impact loading of thin-walled tubes having several cross-sectional shapes and made from different materials. It transpires that the aluminium alloys are more effective than the mild and high-strength steels and that circular cylindrical shells are more effective than square tubes and thin-walled tubes having other cross-sectional shapes. The impact behaviour of pipelines, either empty or pressurised with a nitrogen gas, is studied when struck transversely by relatively large rigid masses travelling up to 10.4 m/s. The initial impact energy produces large inelastic ductile deformations of the pipeline, and, in some cases, failure. The results are compared with several empirical equations and comments are made on their accuracy. Some recent experimental test data are reported on the perforation of mild steel plates struck by relatively heavy masses travelling up to about 13 m/s. The projectiles have blunt, conical and hemispherical impact faces and strike initially flat plates clamped around circular, square and rectangular boundaries. The perforation energies are compared with empirical equations.

Low-velocity impact of pressurised pipelines

Experimental tests are reported on steel pipelines which have been struck by a relatively large rigid wedge-shaped mass travelling up to 10.4 m/s. A pipeline is supported across a span, is fully clamped at both ends and is struck at the mid-span and at the one-quarter span positions. Most of the pipelines are pressurised with a nitrogen gas. The initial impact energy produces large inelastic ductile deformations of the pipeline and, in some cases, failure. A method is introduced which idealises a deformed pipeline cross-section in order to estimate the local and global components of the total displacement from experimental measurements of the final cross-section. Comparisons are also made with several previously published experimental studies for which sufficient data are available to make the calculations. A clearer insight into pipeline behaviour is achieved than is possible only with values of the maximum permanent transverse displacements which have been reported in previous experimental studies. This information should assist with pipeline design, provide more rigorous validation for numerical schemes and contribute to a better understanding of pipeline failure. Recommendations are made on the accuracy and suitability of some well known empirical equations for predicting the permanent deformations of pressurised and empty pipelines caused by large rigid masses, relative to the pipeline mass, travelling with low initial impact velocities up to about 15 m/s.

Effect of lateral impact loads on failure of pressurized pipelines supported by foundation

The dynamic inelastic response and failure prediction of pipelines under lateral mass impact at the mid-span position are presented in this article. A total of 52 impact tests were carried out on seamless mild steel pipes with different internal pressure levels and foundation supports. Critical initial impact energies were obtained for each group of pipe specimens with different internal pressure levels and foundation supports. Numerical simulations of the experimental tests were carried out using three-dimensional dynamic non-linear finite element analysis, where both geometrical and material non-linearities were considered. Good agreements were achieved between the impact tests results and the numerical predictions. It has been found that the influences of the internal pressure and the foundation on the critical initial impact energy are significant. The critical initial impact energy is much less sensitive to internal pressure for the pipes with a foundation than those without a foundation.

Low-velocity impacts on preloaded GFRP specimens with various impactor shapes

The simultaneous effect of impactor shape and biaxial preload on the impact response of thin glass fibre reinforced polyester laminates is investigated herein. Using a specially designed drop weight test rig, specimens were impacted at initial impact energies of 4 J and 6 J using steel flat, hemispherical, ogival and conical impactors, all 12 mm in diameter. Biaxial tension of 500 and 1000 microstrain was applied to the specimens. The applied levels of preload were found to have little effect on the impact response of the GFRP specimens. Due to the stiffening effect of the biaxial tension, the contact duration and deflection were found to decrease with increasing preload. However, the peak force, absorbed energy and damage area were largely unaffected by the preload. The indentation depth produced by the conical impactor at 4 J increased significantly as preload was applied. However, this did not correspond to an increase in damage area.

The effect of impactor shape on the impact response of composite laminates

The effect of impactor shape on the impact response of thin woven carbon/epoxy laminates is investigated herein. Using a drop weight test rig, specimens were impacted at initial impact energies of 4 J and 6 J using steel hemispherical, ogival and conical impactors, all 12 mm in diameter. The specimens impacted by the conical impactor absorbed most energy as a result of local penetration. The hemispherical impactor produced the highest peak force and lowest contact duration as expected. Only the hemispherical impactor at an initial impact energy of 4 J produced barely visible impact damage (BVID) whereas the other impactor shapes produced permanent indentation and penetration. Destructive testing techniques are required to determine the internal damage mechanisms since non-destructive inspection (NDI) techniques provided similar damage areas for the three impactor shapes.

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Bowker's foot physiology

The computer simulation of the scattering of fullerenes from a graphite surface: Energy partitioning and vibrational spectra

Molecular dynamics computer simulation is used to investigate the scattering behaviour of C 60, C 76 and C 84 fullerene molecules from a graphite surface. In particular the energy partitioning into translational, vibrational and rotational motion is determined and the vibrational frequency spectra are calculated and the principal structure identified. At the glancing angle of incidence, studied here, it was found that the fraction of retained kinetic energy after impact increases to about 90% as the initial impact energy increases. The fraction of energy retained as translational motion remains constant as a function of impact energy. Only a small fraction (∼1%) of the energy goes into rotational motion. The rotational frequency remains constant regardless of impact energy ( ∼5×10 11 Hz ). A number of vibrational modes can be identified easily from the vibrational spectra. In particular the C–C and CC bonds and a “breathing” vibrational mode are seen.

Further experimental study on the failure of fully clamped steel pipes

In the present study experimental data recorded from 226 impact tests on seamless mild steel pipes are reported. The pipe specimens with different geometries were fully clamped at both ends, and impacted transversely by rigid wedge-shaped indenters at the positions of mid-span, one-quarter span and very close to a support, respectively. In order to model the fully clamped boundary conditions, a special clamping system was designed to hold the pipe specimens rigidly at each end to prevent any significant inward displacements from the supports. The impact velocities ranged up to 10.69 m/s and caused large inelastic indentations for the lower values and at higher values a loss of integrity near the supports. Particular attention was paid to obtaining the threshold value of initial impact energy that caused the onset of material rupture. Discussion is made for the influences of pipe geometry, impact position and internal pressure on the critical value of initial impact energy.

A study on impact properties of 3‐D composites by falling weight test method

Abstract Three‐dimensional carbon fiber/epoxy resin composites are prepared, which have either three‐axis or five‐axis fabrics (3D‐3A or 3D‐5A) in four woven gauges and four specimen thicknesses. The impact properties of these 3‐D composites are studied. The results show that when the woven gauge is decreased by 1mm, the impact perforation energies of 3D‐3A and 3D‐5A are increased by 12.6J and 5.4J, respectively, and the impact perforation energy is increased by 38J when the specimen thickness is increased by 1mm. The initial impact energy of 3D‐3A is higher than that of 3D‐5A, but the propagation energy and ductility index of 3D‐5A with a woven gauge larger than 3.75mm are higher than those of 3D‐3A. In addition, the impact properties, the impact damage area and the strength loss after impact test are better when the woven gauge is decreased.