Neal Murphy

Effect of an Atmospheric Pressure Plasma Treatment on the Mode I Fracture Toughness of a Co-cured Composite Joint

In this study, the surface of a composite prepreg was treated using an atmospheric pressure plasma in an attempt to improve the fracture toughness of a co-cured joint system. Three gas mixtures were investigated; helium, helium/nitrogen, and helium/oxygen. The processing parameters of the system were varied to obtain the maximum increase in surface energy of the prepreg. A He/O2 plasma was found to be the most efficient treatment, giving the largest increase in surface energy in the shortest time. Co-cured joints were then fabricated using prepreg that had been treated with various plasmas. A modest 15–18% increase in the Mode I fracture toughness was achieved. However, the locus of failure remained interfacial. It was also observed that a He/O2 plasma treatment could be detrimental to joint toughness for long treatment times.

Role of Rate and Temperature on Fracture and Mechanical Properties of PCD

Polycrystalline diamond compacts (PDC) cutters are widely used in oil and gas well drilling and a different format of the same material is also used in high speed turning. During the cutting process these tools experience very high temperatures and impact loads which lead to their sudden fracture. In this work the mechanical and fracture properties of two different grades of PCD test specimens, i.e. the Young’s modulus and fracture toughness, are measured under a range of test conditions such as temperature and loading rate, which correspond to the actual drilling conditions. The fracture is found to propagate in a highly dynamic manner, where the results show the examined properties of PCD specimens to vary with the loading rate and temperature. The study performed leads to a greater understanding of PCD behaviour, and aims to provide guidance for improved material design.

High rate and high temperature fracture behaviour of polycrystalline diamond

Polycrystalline diamond (PCD) materials have a variety of applications, mainly as cutting tools for machining non-ferrous metals and non-metallic materials. A significant application of PCD is in oil and gas industry for rock drilling operations. Other important areas, such as mining, have yet to reach their full potential. These cutters/tools are subjected to high operating temperatures, impact loads and abrasive wear during these operations, which may lead to their sudden failure. An advantage of these materials is that their structure and composition can be engineered to return properties required for specific applications and operations.

Fracture Properties of PCBN as a Function of Loading Rate and Temperature

Polycrystalline Cubic Boron Nitride (PCBN) is a super-hard material used in some of the most demanding material removal operations today. These include turning of hardened steels, as well as the machining of highly abrasive alloys. In these applications the tools are subjected to high operating temperatures, abrasive and impact loading. This can lead to the brittle fracture of the tool. Accurate determination of the fracture toughness and mechanical properties of PCBN under a wide range of operating conditions is therefore essential in order to evaluate the performance of the tool under these highly demanding conditions. For this study, a laboratory scale three point bend test rig has been used for the fracture tests. The fracture toughness of two different grades of PCBN are measured at a range of loading rates and temperatures corresponding to the actual in-service conditions. The results show the measured properties of these materials vary with both loading rate and temperature. The fracture surfaces of the specimens are examined using scanning electron microscopy to determine dominant fracture mechanisms.

Fracture Properties of PCBN as a Function of Loading Rate

Polycrystalline Cubic Boron Nitride (PCBN) is a superhard material which is used in machining of hardened steels and other abrasive and aerospace grade alloys. In these applications the tools are subjected to high operating temperatures, abrasive and impact loading. Impact loading can lead to the sudden fracture and hence failure of the tool. In this work the static and dynamic fracture toughness of PCBN is determined via a combined experimental-numerical approach. The results show that the fracture toughness of PCBN varies with loading rate.

Characterisation of the Fracture Energy and Toughening Mechanisms of a Nano-Toughened Epoxy Adhesive

In this study the adhesive joint fracture behaviour of a nano-toughened epoxy adhesive was investigated. Two experimental test methods were used; (i) the standard tapered double cantilever beam (TDCB) test to measure the mode I adhesive joint fracture energy, GIC, as a function of bond gap thickness and (ii) a circumferentially deep notched tensile test to determine the cohesive strength of the adhesive for a range of constraint levels. It was found that the fracture energy of the adhesive followed the well-known bond gap thickness dependency [1]. SEM analysis of the TDCB fracture surfaces revealed significant plastic void growth. Finally, numerical modelling of the experimental tests suggested that most of the fracture energy was dissipated via highly localised plasticity in the fracture process zone ahead of the crack tip.

Damage behaviour of nano-modified epoxy adhesives subject to high stress constraint

ABSTRACT This paper presents a combined experimental and numerical study on the damage behaviour of core–shell rubber (CSR)-modified epoxy adhesives subject to high stress constraints. The test method consists of a notched axisymmetric adhesive layer loaded in tension. The stress–displacement curves of the rubber-modified adhesives have been found to exhibit a sudden reduction in stiffness after an initial linear loading region. It has been demonstrated that this corresponds to the cavitation of the rubber particles. The stress of rubber cavitation remained essentially constant at a critical hydrostatic stress of approximately 21 MPa over different rubber contents and different stress constraints. It is important to note that the rubber cavitation stress is also dependent on the size of the rubber particles, and the diameter of the rubber core is approximately 170 nm in current work. The stress constraint had negligible effect on the failure strength of the adhesive joints for the studied systems.

The Role of Microstructure on the Fracture Behaviour and Statistics of Advanced Ceramics

Strength data of three advanced ceramics were fitted to the Weibull, normal and lognormal distributions. The three ceramics had similar grain size and varied in binder content. The role of microstructure in the failure mechanism of such ceramics was analysed in terms of the chosen strength distributions. The best-fit distributions were determined using the maximum log-likelihood criteria and a comparison between the best and worst fit was conducted using the Akaike Information Criteria (AIC). Both large and small samples were tested to investigate possible scaling effects for these ceramics. It was found that for two of the three ceramics tested that a lognormal distribution rather then the conventionally used Weibull distribution was preferable in characterising the strength data. A small drop in strength was noticed between large and small samples but this trend was not thought to be a result of scaling rather due to the decrease in binder content.

An Experimental and Numerical Investigation of the Mixed- mode Fracture Toughness and Lap Shear Strength of Aerospace Grade Composite Joints

In the present study, the mixed-mode fracture toughness of an adhesively bonded composite joint system was examined using a variety of linear elastic fracture mechanics (LEFM) based tests. These tests include the mode I double cantilever beam (DCB), mixed-mode asymmetrical DCB (ADCB) and mode II end load split (ELS) test. The joint system was also evaluated using the wide area lap shear (WALS) test that is often employed by the aerospace industry. While lap shear type tests are relatively simple to perform and post-process compared to their LEFM counterparts, the results can often be misleading and are greatly dependent on the overlap length, thickness of substrate and type of fillet. The experimental tests were also simulated using OpenFOAM, a finite volume based software package. Through this combined experimental-numerical approach, a greater understanding of the influence of the peel ply surface treatment and scrim cloth on the behaviour of the WALS test was achieved.

Optics education within engineering at University College Dublin

Undergraduate students within many of the departments which make up the Faculty of Engineering and Architecture at University College Dublin meet optics, optical inspection techniques and opto-electronics at various times during their standard four year undergraduate degree course. As well as optics fundamentals taught as part of their physics courses, engineering courses specifically concerning optics and opto-electronics are available. Furthermore many graduate students are involved in either projects, which are completely optics based, or carry out research projects involving the use or development of specific optical instruments. These projects include the development of image processing capture and processing software, high power laser machining of materials, design and testing of lasers for fiber optic telecommunication and sensing applications and photochemistry. In this paper we offer a brief review of some of the main optical educational themes covered within our faculty and present some details regarding a few optics based postgraduate research projects.