A flexible online apparatus for projectile launch experiments

In order to provide a more flexible learning environment in physics, the developed projectile launch apparatus enables students to determine the acceleration of gravity and the dependence of a set of parameters in the projectile movement. This apparatus is remotely operated and accessed via web, by first scheduling an access time slot. This machine has a number of configuration parameters that support different learning scenarios with different complexities

Dynamic qualitative bolt force measurements for investigating influence factors on the pushout effect of small calibre ammunition

A small calibre weapon system consists of the weapon and the ammunition. In the case of bolt action rifles during the process of firing, the breech is a rigid bearing which prevents the casing from being pushed out. However, not the whole pushout force is taken by the bolt. Due to friction forces at the casing boundary, the chamber of the weapon can absorb a significant part of the pushout force. The duration of the pushout force is in the order of milliseconds. Piezoelectric strain gauges are capable of recording such short time events qualitatively. To increase the measurability of force obtained from raw signal, is filtered using a bandpass filter and applying a signal envelope. The results from the strain gauges are verified by a piezoelectric force washer. In this paper, two different lubrication states and two different casing materials are analysed to evaluate their influences on the force absorbed by the bolt. The analysis indicated that lubricated casings lead to bolt forces which are more than three times higher when compared unlubricated casings. The unlubricated steel casing also showed a significant lower bolt force when compared with the regular brass casing. However, this effect is reversed, if the casing is lubricated. This work demonstrates how to measure highly dynamic events. The acquired results can be directly applied to 5.56x45 bolt action rifles. These measurements may also have a significant influence on self-loading rifles, since the process of reloading is also dependent on the pushout force. The general application area is target competitive shooting and military purposes

Characterization of the Shock Wave Structure in Water

The scientific community is interested in furthering the understanding of shock wave structures in water, given its implications in a wide range of applications; from researching how shock waves penetrate unwanted body tissues to studying how humans respond to blast waves. Shock wave research on water has existed for over five decades. Previous studies have investigated the shock response of water at pressures ranging from 1 to 70 GPa using flyer plate experiments. This report differs from previously published experiments in that the water was loaded to shock pressures ranging from 0.36 to 0.70 GPa. The experiment also utilized tap water rather than distilled water as the test sample. Flyer plate experiments were conducted in the Shock Physics Laboratory at Marquette University to determine the structure of shock waves within water. A 12.7 mm bore gas gun fired a projectile made of copper, PMMA, or aluminum at a stationary target filled with tap water. Graphite break pins in a circuit determined the initial projectile velocity prior to coming into contact with the target. A Piezoelectric timing pin (PZT pin) at the front surface of the water sample determined the arrival of the leading wave and a Photon Doppler Velocimeter (PDV) measured particle velocity from the rear surface of the water sample. The experimental results were compared to simulated data from a Eulerian Hydrocode called CTH [1]. The experimental results differed from the simulated results with deviations believed to be from experimental equipment malfunctions. The main hypothesis being that the PZT pin false triggered, resulting in measured lower than expected shock velocities. The simulated results were compared to published data from various authors and was within range

Piezo-driven clamp release for synchronisation and timing of combined direct-shear stress waves

We propose a novel double clamp Tension-Torsion Hopkinson bar (TTHB) technique for measuring material responses under combined direct-shear loading. The proposed method overcomes the limitations of the existing high rate loading techniques by allowing arbitrary loading paths of tension and torsion to be prescribed to the specimen. High speed piezo actuators were employed to enable the synchronisation of direct stress and shear stress waves. The system also allows flexibility of control on the arrival times of torsional and tensile waves, thus enabling the generation of different dynamic loading paths. Direct and shear stress pulses can be generated such a way to achieve synchronised loading, torsion loading followed by tensile loading, and vice versa. The stress pulse histories of three different loading paths are presented to illustrate and validate the technique

The optimisation of flexible impact-protection systems for varying strain rates and energies.

The need for smarter and active, energy absorbing systems designed especially for human protection applications has sparked interest in highly strain rate sensitive compounds. This thesis describes the iterative design, development and optimisation of a novel form of energy absorbing, body worn protection. The original contribution to knowledge is the development of a novel strain rate sensitive protection system incorporating synergetic internal architecture. Co-continuous blends of silicone based dilatant and thermoplastic elastomer have been developed through a recursive design process to develop a new material specifically optimised for body worn protection. Failure mechanisms were analysed, and from these results techniques have been developed to mitigate internal fracture mechanisms. This enabled the development of a strain rate sensitive material utilised with an internal architecture. The novel material properties were examined and developed using monolithic samples, tested at a variety of energies, speed and environmental conditions. Methods for designing and developing auxetic structures that work synergistically with the new material have been developed. The novel system has also been combined with textiles, and the merit of this combination explored. An improvement in performance has been validated, as well as a design improvement through being able to attach parts directly to garments. The resulting impact protectors are applicable over a range of strain rates. Systems have been designed to incorporate this novel technology in pre-production prototypes in three selected market areas, which typify low, medium and high impact speeds. The work also explores the systems ability to manage multiple impacts at the same location with a surprisingly low loss in performance, effectively making a protector that can withstand repeat impacts. This work has contributed to the methods previously used in testing personal protective equipment. The techniques developed in this work have enabled new revision of these PPE standards, as well as directly contributing to two new standards.Open Acces

Development and Characterization of Piezoresistive Nanocomposites for Sensing Applications

Carbonnanotube basedhybrid nanocomposites are known to exhibit remarkable electrical and mechanical properties with many potentials in strain and damage sensing applications. In this work, we fabricate hybrid nanocomposites with carbon nanotube (CNT) sheet and graphene nanoplatelets (GNP) as fillers with epoxy matrix. An improvement in both electrical conductivity and piezoresistivity is observed with the combination of CNTs and GNPs, indicating the formation of efficient hybrid conductive networks for strain and electrical transfer in the material. Different matrix materials have been compared to investigate the effect ofmatrixand to choose the one that yields increased strains, flexibility, and electromechanical response. The electromechanical behavior of the hybrid composites is investigated both under static and dynamic loading at various frequencies with induced levels of strains, and has shown positive response under all tested conditions. Digital image correlation has been used to investigate the strain variation within the specimen both during static and dynamic testing. As these sensors will be tested for damage sensing in space applications for inflatable habitat under Micrometeoroid and Orbital Debris (MMOD) impact, the sensitivity of the sensor with 3 mm impact holes is evaluated usingfour pointprobe electrical resistivity measurements. An array of these sensorswhen sandwiched between soft good layers in a space habitatcan act as a damage detection layer for inflatable structures. A computer program is developed to determine the event of impact, its severity and the location on the sensing layer for active health monitoring. Outgassing testing has been performed to evaluate the Total Mass Loss (TML) of the nanocomposite in space environment. Our results indicate that these hybrid nanocomposites exhibit a distinct piezo resistive response which can be beneficial for potential strain, vibration, and damage sensing applications

Coherence of structural visual cues and pictorial gravity paves the way for interceptive actions

Dealing with upside-down objects is difficult and takes time. Among the cues that are critical for defining object orientation, the visible influence of gravity on the object's motion has received limited attention. Here, we manipulated the alignment of visible gravity and structural visual cues between each other and relative to the orientation of the observer and physical gravity. Participants pressed a button triggering a hitter to intercept a target accelerated by a virtual gravity. A factorial design assessed the effects of scene orientation (normal or inverted) and target gravity (normal or inverted). We found that interception was significantly more successful when scene direction was concordant with target gravity direction, irrespective of whether both were upright or inverted. This was so independent of the hitter type and when performance feedback to the participants was either available (Experiment 1) or unavailable (Experiment 2). These results show that the combined influence of visible gravity and structural visual cues can outweigh both physical gravity and viewer-centered cues, leading to rely instead on the congruence of the apparent physical forces acting on people and objects in the scene

EXTREME DYNAMICS OF NANOMATERIALS UNDER HIGH-RATE MECHANICAL STIMULI

Nanomaterials demonstrate novel mechanical properties attributed to the extremely large interfacial area. At quasi-static rates, the interfacial interactions are crucial in mechanical behaviors, however, materials under extreme mechanical stimuli are rarely studied at nanoscale. With an advanced laser-induced projectile impact test, we perform supersonic impact of micro-projectiles on polymer films, multilayer graphene, carbon- based nanocomposites membranes as well as individual micro-fibers, to study the interface interactions in the high-rate regime, and develop a simplified model to characterize the ballistic performance of materials