Elias Siores

Compressive behaviour of aluminium foams at low and medium strain rates

Abstract Compressive behaviour of CYMAT aluminium foams with relative densities ranged from 5% to 20% has been studied experimentally in this paper. An MTS machine is employed to apply a compressive load at strain rates of 10 −3 –10 +1 s −1 to these closed-cell aluminium foams. It has been found that the plateau stress is insensitive to the strain rate and is related to the relative density by a power law. Deformation is not uniform over the whole sample: it first occurs in the weakest band, followed by the next weakest bands after the first one has been completely crushed.

Optimising the AWJ cutting process of ductile materials using nozzle oscillation technique

Striations and roughness on workpiece surfaces produced by abrasive waterjet (AWJ) have been the most persistent problems that stand in the way of wider applications of the technology in industry. This paper presents the experimental investigation on the impact of using nozzle oscillation cutting technique in minimising or reducing these AWJ cut surface irregularities. The technique was used for cutting ductile materials, i.e. mild steel and aluminium, at various traverse speeds, oscillation angles and frequencies of oscillation. The results show that by oscillating the nozzle during cutting, the improvement in surface finish as measured by centre-line average Ra can be obtained by as much as 30%.

Kerf characteristics in abrasive waterjet cutting of ceramic materials

An abrasive water jet (AWJ) can provide a more effective means for precision cutting of ceramic materials as compared with conventional machining methods, but many aspects about this cutting technology are still under flux and development. In this study, experimental techniques based on statistical experimental design principles and theoretical investigations were conducted to study AWJ cutting of alumina-based ceramics. Semi-empirical cutting depth equations are determined for the prediction and optimization of the AWJ cutting performance. Topographical characteristics of uncut-through kerf and the effects of various parameters are discussed. In addition, visualization studies are conducted to develop further understanding of the macromechanics of the AWJ cutting process.

Comparative study of jetting machining technologies over laser machining technology for cutting composite materials

Abstract There has been a great interest for improving the machining of composite materials in the aerospace and other industries. This paper focuses on the comparative study of jetting techniques and laser machining technics. This paper concentrates on the machining of composite materials like epoxy pre-impregnated graphite woven fabric and fibre reinforced plastic materials that are used in aerospace industries. While considering machining these materials with the traditional machining there are many disadvantages projected. One of these advantages is that all the traditional machining processes involve the dissipation of heat into the workpiece. This serious shortcoming has been dealt by the jetting technologies, which, contrary to the traditional machining, operate under cold conditions. The two methods in the jetting technologies used for processing materials are water jet machining and abrasive water jet machining. The first of these, water jet machining, has been around for the past 20 years and has paved the way for abrasive water jet technology. Water jet machining and abrasive water jet machining have been used for processing composite materials because of the advantages offered by this technologies as compared to traditional techniques of processing. The high surface and structural integrity required of any technique used for processing composite materials has created an opportunity for abrasive water jet machining. Cutting of composites using laser is also an option, and experiments were also conducted to reveal the extent of using laser technique.

Productivity improvement through the use of industrial microwave technologies

Microwave processing of materials is a relatively new technology advancement alternative that provides new approaches for enhancing material properties as well as economic advantages through energy savings and accelerated product development. This paper presents a state-of-the-art review of microwave technologies, processing methods and industrial applications. The characteristics of microwave interactions with materials are outlined together with the challenges that are difficult to process the materials present. To fully realise the potential benefits of microwave and hybrid processes, it is essential to scale-up process and system designs to large batch or continuous processes. This necessitates computational modelling and simulation, system design and integration and a critical assessment of the costs and benefit analysis. Impediments to industrial applications are identified and development opportunities that take advantage of unique performance characteristics of microwaves are discussed. Clearly, advantages in utilising microwave technologies for processing materials include penetrating radiation, controlled electric field distribution and selective and volumetric heating.The aim of the work presented in this paper is to help guide those interested in using microwaves to improve current materials processing. Microwave fundamentals are described to provide a brief awareness of the advantages and limitations of microwaves in the processing of materials. Furthermore, the limitations in current understanding are included as a guide for potential users and for future research and development activities. Examples of successful applications are given to illustrate the characteristics of materials, equipment and processing methods applicable to industrial microwaves. Economic considerations are described and costs are provided as guidelines in determining the viability of using microwaves for processing materials.

An intelligent system for plastic injection molding process design

Abstract An AI System for obtaining the magnitude of process parameters in plastic injection molding operation has been developed. The system is user interactive and can be used at shop floor. This system applies two techniques, Rule-Based and Case-Based Reasoning. Case-Based Reasoning is used to derived the first trial setting of processing parameters, while the Rule-Based sub-system suggests a set of corrective actions to deal with possible corresponding variations in molding. The system reduces optimization time and human expert dependency.

Striation formation mechanisms on the jet cutting surface

An understanding of the mechanisms of striation formation on the surfaces produced by abrasive water jet (AWJ) cutting is a crucial step in reducing or eliminating the striations. Various reported investigations and findings in this regard are reviewed and discussed. The sources of striation formation are classified into three groups; namely the nature of the step formation inherent to a jet cutting process, the dynamic characteristics of the water jet, and the vibration of the machining system. It is believed that all these sources contribute to the formation of striations although it is difficult to separate their effects in practice. Recommendations are finally made on the future work and the approaches to reducing or eliminating striations on the AWJ cut surfaces.

The effect of cutting jet variation on surface striation formation in abrasive water jet cutting

Abstract Abrasive water jet machining is an emerging technology which can shape almost all engineering materials, but also produces a characteristic striated surface finish which limits its potential applications. In this study, the characterisation of different materials’ cut surfaces is investigated using a scanning electron microscope. The effect of abrasive particle distribution in the jet on striation formation is detailed. A non-invasive technique: laser Doppler anemometry is used to analyse the abrasive particle distribution in the jet. Furthermore, the mechanisms of striation formation are discussed in detail and an effective striation minimisation technique applied to the cutting process is outlined.

Applications of fixed and variable frequency microwave (VFM) facilities in polymeric materials processing and joining

Microwave processing of materials is a relatively new technology advancement alternative that provides new approaches for enhancing material properties as well as economic advantages through energy savings and accelerated product development. Factors that hinder the use of microwaves in materials processing are declining, so that prospect for the development of this technology seem to be very promising [Ceram. Bull. 68 (2) (1989) 376]. The two mechanisms of orientation polarisation and interfacial space charge polarisation, together with DC conductivity, form the basis of high frequency heating. Clearly, advantages in utilising microwave technologies for processing materials include penetrating radiation, controlled electric field distribution and selective and volumetric heating. However, the most commonly used facilities for microwave processing materials are of fixed frequency, e.g. 2.45 GHz. This paper presents a state-of-the-art review of microwave technologies, processing methods and industrial applications, using variable frequency microwave (VFM) facilities. This is a new alternative for microwave processing. The technique is geared towards advanced materials processing and chemical synthesis. It offers rapid, uniform and selective heating over a large volume at a high energy coupling efficiency. This is accomplished using a preselected bandwidth sweeping around a central frequency employing frequency agile sources such as travelling wave tubes as the microwave power amplifier. Selective heating of complex samples and industrial scale-up are now viable. During VFM processing, a given frequency of microwaves would only be launched for less than 1 ms.

Study of cutting fiber-reinforced composites by using abrasive water-jet with cutting head oscillation

Abstract An experimental and theoretical research work on abrasive water-jet (AWJ) oscillation cutting of glass fiber reinforced polymer (GFRP) composite materials was conducted at the Water-jet Laboratory of the Industrial Research Institute of Swinburne (IRIS). The objective of this research work was to conduct a comparative study of the oscillation and normal (without head oscillation) cutting of GFRP composite materials and compare the performances the two processes. This new technique which is a variant of the traditional AWJ cutting technique, makes use of a back and forth motion of the cutting head which is superimposed on the normal linear motion to effect optimum loading of the cutting forces on the workpiece material and scan the cut-wall surface to also improve surface finish. The technique was used for cutting GFRP composites materials and the qualities of resulting surfaces were measured using stylus type equipment. A comparison of the results indicates that there is significant improvement in the quality of surfaces produced by head oscillation technique than normal AWJ cutting. In some of the samples, an improvement, in surface quality, as measured by R a values, up to 20% was found.