Low Velocity Impact Studies Research Articles

Impact response of Shear Thickening Fluid (STF) treated ultra high molecular weight poly ethylene composites – study of the effect of STF treatment method

Shear thickening fluids (STFs) are a special class of field responsive non-Newtonian fluids which exhibit transition from low viscosity to high viscosity state when these are subjected to shear deformation, particularly when the shear rate exceeds a critical value termed as the critical shear rate (CSR). Due to this unique characteristic of STFs, these are generally used for vibration mitigation or shock absorbance such as in vibration dampeners, hip protection pads, in protective gear for athletes etc. From the last two decades, STFs have found application in the field of ballistics, particularly in the development of special class of STF-intercalated armours called Liquid Body Armours (LBAs). These new age armours are lighter in weight and more flexible as compared to conventional heavy armours, which, infact seriously affect the mobility and agility of the soldier, especially in combat situations. Although, exhaustive studies are available which show the improvement in impact resistance of STF-treated high performance fabrics, but there are limited studies which explore the efficacy of STF treatment method. In this study, an attempt is made to understand this aspect. The low velocity impact studies were conducted on drop tower machine, while high velocity impact studies were accomplished on in-house designed and fabricated Split Hopkinson Pressure Bar (SHPB) experimental set-up. It was observed that when STF was kept in liquid form between layers of ballistic fabrics, the composite exhibited reduced performance, whereas, STF-treated ballisic composites exhibited enhanced impact toughness at high strain rates in SHPB testing.

Impact Response of Shear Thickening Fluid (STF) Treated High Strength Polymer Composites – Effect of STF Intercalation Method

Modern and sophisticated ammunition systems have necessitated the development of advanced ballistic protection personal armour systems that are damage resistant, flexible, light-weight and possess high energy absorbing/dissipating capacity. Although, exhaustive studies are available which show the improvement in impact resistance of STF-treated high performance fabrics, but there are limited studies which explore the efficacy of STF impregnation method. In this study, an attempt is made to understand this aspect. The low velocity impact studies were conducted on drop tower machine, while high velocity impact studies were accomplished on Split Hopkinson Pressure Bar (SHPB). High impact Poly Propylene Co-polymer (CO15EG) and UHMWPE variants Gold Shield® and Spectra Shield® were chosen for this study. It was observed that when STF was kept in liquid form between layers of ballistic fabrics, the composite exhibited reduced performance, whereas, when STF was impregnated in a ballistic fabric it had a synergistic effect to enhance the impact toughness of ballistic composite.

A theoretical study of low-velocity impact of geometrically asymmetric sandwich beams

This paper uses the quasi-static method to investigate plastic behavior of fully clamped geometrical asymmetric sandwich beams with a metal foam core subjected to low-velocity impact. An analytical model is developed to predict the dynamic response of the geometrically asymmetric sandwich beams. Effects of local denting and core strength on the overall bending are considered. Good agreement is achieved between the analytical predictions and numerical results. It is demonstrated that the asymmetric sandwich beams with asymmetric factor α > 1 have the larger energy absorption than those with asymmetric factor 0 < α < 1.

Experimental Assessment of Single and Cumulative Impact Damage in Carbon Fiber Polymer Matrix Composites Using Electrical Resistance Measurements

In this work the impact damage sensing capabilities in AS4/3501-6 carbon fiber polymer matrix composites are investigated. A fully instrumented experimental setup for characterization of electrical properties has been developed. The one-dimensional electrical resistance method was employed for damage sensing. 16-ply [0/45/–45/90] 2s and 32-ply [0/45/–45/90] 4s laminates were tested. Single impact and cumulative low velocity impact studies were conducted and electrical resistance measurements were performed to assess damage. The results show that the one-dimensional electrical resistance technique had a limited success at sensing impact damage in AS4/3501-6 composites due to low initial resistances of the composites tested. doi:10.12783/issn. 2168-4286/2.2/Zhupanska

An Experimental and Numerical Study of Low Velocity Impact of Unsaturated Polyester/Glass Fibre Composite

In this paper validation of experimental and numerical results of low-velocity impact tests of unsaturated polyester/glass fibre composite laminate has been carried out. Impact response of composite laminates was experimentally studied with drop-tower Instron 9250HV determining impact force, energy absorption and deflection. In addition, quasi-static testing equipment Zwick Z100 has been used to determine material mechanical properties to ensure good input data for numerical predictions. Numerical model has been created with the finite element commercial code ANSYS/LS-DYNA to simulate impact response of composite laminate. Also non-destructive ultrasonic B- and C- scan imagining with USPC 3010 system has been used to identify the deformation regions in the specimens and compare to simulation results. During the impact test all samples were perforated, showing brittle response followed by matrix cracking and delamination. Overall good agreement between experimental and simulation results was achieved, comparing impact characterizing parameters as load, energy and deflection. Discrepancy has been observed between ultrasonic scanning and simulation code ANSYS/LS-DYNA results of rupture and delamination. Simulation shows less uniform and larger deformation than it was experimentally observed. http://dx.doi.org/10.5755/j01.ms.17.4.773

Fiber optic interrogation systems for hypervelocity and low velocity impact studies

The aim of this project was to develop non-contact fiber optic based displacement sensors to operate in the harsh environment of a “light gas gun” (LGG), which can “fire” small particles at velocities ranging from 1 km/s-8.4 km/s. The LGG is used extensively for research in aerospace to analyze the effects of high speed impacts on materials. Ideally the measurement should be made close to the center of the impact to minimize corruption of the data from edge effects and survive the impact. We chose to develop a non-contact “pseudo” confocal intensity sensor, which demonstrated resolution comparable with conventional polyvinylidene fluoride (PVDF) sensors combined with high survivability and low cost. A second sensor was developed based on “fiber Bragg gratings” (FBG) to enable a more detailed analysis of the effects of the impact, although requiring contact with the target the low weight and very small contact area of the FBG had minimal effect on the dynamics of the target. The FBG was mounted either on the surface of the target or tangentially between a fixed location. The output signals from the FBG were interrogated in time by a new method. Measurements were made on carbon fiber composite plates in the LGG and on low velocity impact tests. The particle momentum for the low velocity impact tests was chosen to be similar to that of the particles used in the LGG.

Acoustic Emission Analysis on Low Velocity Impact Damage of 2D C/SiC Composites

An experimental study of low velocity impact (LVI) was carried out on 2D carbon fabric reinforced silicon carbide (C/SiC) ceramic matrix composites. The C/SiC composite specimens were impacted by using a free-drop impact machine at different energy levels ranging from 1J to 9J and acoustic emission (AE) technique was used to detect the damage process. The results indicated that AE signals could evaluate the LVI damage behaviors of C/SiC composites from the different aspects. By comparing impact load process with AE hits and AE amplitude, the damage process could be determined. In the loading stage, matrix cracking mainly occurred in the composites; when impact load reached peak load, delamination and fiber fracture started to produce; in the unloading stage, the damage modes were mainly delamination and matrix cracking. AE event count fractions could quantify the main damage modes at different impact energy levels. At lower impact energy, matrix cracking was the main damage mode; when impact energy were between 3J and 6J, delamination and matrix cracking became the main damage modes; at higher impact energy, fiber fracture was the main damage mode.

Rubber Impact on 3D Textile Composites

A low velocity impact study of aircraft tire rubber on 3D textile-reinforced composite plates was performed experimentally and numerically. In contrast to regular unidirectional composite laminates, no delaminations occur in such a 3D textile composite. Yarn decohesions, matrix cracks and yarn ruptures have been identified as the major damage mechanisms under impact load. An increase in the number of 3D warp yarns is proposed to improve the impact damage resistance. The characteristic of a rubber impact is the high amount of elastic energy stored in the impactor during impact, which was more than 90% of the initial kinetic energy. This large geometrical deformation of the rubber during impact leads to a less localised loading of the target structure and poses great challenges for the numerical modelling. A hyperelastic Mooney-Rivlin constitutive law was used in Abaqus/Explicit based on a step-by-step validation with static rubber compression tests and low velocity impact tests on aluminium plates. Simulation models of the textile weave were developed on the meso- and macro-scale. The final correlation between impact simulation results on 3D textile-reinforced composite plates and impact test data was promising, highlighting the potential of such numerical simulation tools.

Ignition of a confined high explosive under low velocity impact

In the framework of low velocity impact studies, dedicated to safety analyses of plastic bonded explosives (PBX), we propose a new numerical tool, designed for restituting the ignition of a HMX (high melting point explosive) based composition. Major results are the use of a concrete-like constitutive law for the PBX and an efficient implementation of an ignition criterion. We also put forward two variants of classical Steven tests, which enable us to visualize either a dot ignition or an unusual ring-shaped ignition. It is shown that the calculation tool is able to restitute accurately both results.

Natural optima in human skull: a low-velocity impact study

Human skull bone is a three-layered structure with a compliant viscoelastic cancellous bone layer sandwiched between elastic compact layers. The objective of the work was to check whether the skull bone is innately optimized with respect to the various geometrical and material parameters and to find out the parameters with which they are optimized. The effect of varying the thickness of layers and short time modulus of the interlayer are studied for optimality using finite element analysis of the skull subjected to low-velocity impact. Results show that they are optimized to meet different objectives.

Low Velocity Impact Study of Laminate Composites with Mode I Crack Using Dynamic Optical Caustics

The dynamic evolutions of stress singularities at mode I crack tip in laminate composites are studied by combining optical caustic with high-speed schardin camera. Theoretical caustics and initial curve for two different fiber laminate composites are simulated. Some characteristics of stress singularity at crack tip are analyzed. On the other hand, the generation and the subsequent evolution of dynamic failure around the crack tip are visualized by the optical shadow spots. The characteristic sizes of local stress concentration are extracted and the stress intensity factors at crack tip are determined. The local response and failure evolution mechanism of laminated composite after impact are analyzed by means of a series of optical caustic image and the deformation of composites.

Transient Dynamic Analysis of Laminated Composite Plate Subjected to Low-Velocity Impact

This paper concerns with the transient response of composite laminates subjected to low-velocity impact. A drop weight impact tower is used for the low velocity impact study and the contact force during impact is measured with a piezoelectric force transducer. Composite laminates, made of E-glass/epoxy and having (0/90/0)s stacking sequence, are considered, Numerical results of E-glass/epoxy cross-ply laminates under three different impact velocities (l m/sec, 2 m/sec and 3 m/sec) and two different impactor masses (135 g and 2600 g) are investigated with 3DIMPACT computer code. Contact force between the impactor and composite laminate, maximum transverse displacement at the center are plotted as functions of time and predicted delamination shapes and sizes are found numerically. The resulting data from the drop-weight tests and computer code provide specific information about the effect of the impactor velocity and impactor mass, all of which have a great influence on the impact response of composite laminates.