R.A. Govender

Determining the through-thickness properties of thick glass fiber reinforced polymers at high strain rates

The use of thick fiber reinforced polymer (FRP) laminates in composite armor and naval structures requires thorough characterization of the through-thickness properties of said laminates, both quasi-statically and at high strain rates. Specimens cut from an E-Glass/vinyl ester FRP were tested in compression both quasi-statically and dynamically using a split Hopkinson pressure bar (SHPB). The SHPB tests utilized a conical striker for pulse shaping, to reduce the variation in strain rate during the test. The quasi-static through-thickness compressive strength was 417 MPa, while the SHPB tests produced a strength of 462 MPa at an average strain rate of 5.1 × 102 s−1. A single HPB configured for spalling tests was used to determine the dynamic through-thickness tensile strength (interlaminar tension). The interlaminar tensile strength was 125 MPa at an average strain rate of 1.8 × 103 s−1.

The “Open” Hopkinson Pressure Bar: Towards Addressing Force Equilibrium in Specimens with Non-uniform Deformation

Conventional Split Hopkinson Pressure Bar (SHPB) testing requires the verification of force equilibrium in a specimen for the test data to be considered valid. For very low impedance materials the large impedance mismatch between input bar and specimens leads to significant uncertainty in the force measurement at the input face. This makes it difficult to fulfil the equilibrium requirement for conventional SHPB testing of very low impedance materials. Cellular materials further complicate matters, as non-uniform densification can lead to different stress states on either side of a densification front. A novel configuration, termed the Open Hopkinson Pressure Bar (OHPB), is proposed to address the difficulties in measuring small differences in forces on either side of the specimen. The specimen is placed on a HPB, and impacted directly by an instrumented striker (effectively another HPB). This arrangement only requires the processing of one wave in each bar, as opposed to the three waves required in a conventional SHPB. This technique allows significant improvements to be made in the resolution of the force measurements.

The influence of interfacial bonding on the response of lightweight aluminium and glass fibre metal laminate panels subjected to air-blast loading

This paper examines the effects of glass fibre configuration and epoxy resin type on the response of glass fibre epoxy-based fibre metal laminate panels. These lightweight materials are excellent candidates for use in transportation applications, where mass is a major factor in design and materials selection. Interfacial bond strength was characterised through single leg bend testing and revealed varying failure characteristics for different epoxy configurations and surface treatments. A combination of bead blasting and silane treatment provided the best surface treatment for the aluminium, while SE84 epoxy resin gave superior adhesion properties compared to Prime 20ULV. Blast tests were performed to investigate the effect of bond strength on panel response under localised and more uniformly distributed air-blast loading conditions. Dimensionless analysis and failure mode identification were used to show that both fibre configuration and bond strength played a role in blast response but the bond strength (and particularly resin type) was more prominent.

Endolaryngeal anterior commissure stent-Cheap and easy: Endolaryngeal Anterior Commissure Stent

INTRODUCTION Acquired anterior laryngeal webs arise from vocal fold trauma and are an important iatrogenic consequence in the setting of endoscopic organ preservation surgery. Injury to the vocal fold initiates a healing cascade characterized by inflammation, fibroplasia, and remodeling. This results in collagen deposition within the superficial and deep layers of the lamina propria, and scar formation is completed between 12 and 20 weeks after the initial insult. Multiple management options have been described and aim to restore the patient’s voice and improve the airway. These include both endolaryngeal and open approaches. Endolaryngeal procedures are preferred over open techniques because they are less invasive and associated with lower morbidity. However, resection of the web with repeated lysis of adhesions has largely been abandoned as a result of the high rate of scar formation and restenosis. The preferred method for managing laryngeal webs is endolaryngeal incision of the web, followed by placement of a plate, keel, or vocal cord lateralization. The primary purpose of a laryngeal keel is to separate the raw edges of the vocal folds until remodeling occurs. However, a silicone laryngeal anterior commissure stent costs

Impact Bend Tests Using Hopkinson Pressure Bars

246. Although a keel may be fashioned out of a silicone sheet by threading a suture through one edge, a 1-mm or 2-mm sheet of silicone costs

Impact delamination testing of fibre reinforced polymers using Hopkinson Pressure Bars

70, is time consuming, and is mechanically awkward to fashion intraoperatively. We explored the use of single-sided adhesive tape to fashion a keel. It can be purchased in any normal store, is cost effective, and is suitable to the developing world setting where resources are limited. Critical to its use is that the integrity of the material and its adhesive properties not be compromised by the humidity and temperature in the airway. We assessed and compared the adhesive integrity of two different, easily available adhesive materials after they had been incubated in saline at 368C. We also present two cases in which single-sided adhesive tape was successfully employed as a laryngeal keel.

Implementation of viscoelastic Hopkinson bars

Bend tests under impact loading have traditionally been conducted using drop weight testers. However, the force readings from drop weight testers suffer from increasing oscillation (due to load frame vibration and stress wave excitation) as the impact velocity is increased. Different configurations of Hopkinson Pressure Bars (HPB) were adapted to conduct bend tests at impact rates have been presented in the literature. HPB are a well understood tool for measuring impact forces and velocities, but are limited by the duration of the impact event which may be measured. Thus prior HPB based bend test rigs have been limited to very short duration tests, and hence to materials with small deflections to failure. Some of the HPB bend test rigs have struggled with capturing well resolved force measurements, particularly for less rigid specimens. This paper presents a novel configuration of a HPB based bend test that results in vastly improved resolution of force measurements and increases the permissible specimen deflection by an order of magnitude greater than presented in past literature. Some results are presented for tests on Glass Fibre Reinforced Polypropylene (Twintex).