A. Di Ilio

Laser cutting of fibre-reinforced polyesters

Abstract Composites of aramid, graphite and glass cloth-reinforced polyester have been cut by a laser and the morphology of the cut surfaces examined by scanning electron microscopy. The results are examined using a numerical thermal model and a mechanism for the laser-induced thermal changes observed in the composites is proposed. The thermal properties of the fibres and matrix are the principal factors which affect cutting performance. For the range of experimental parameters used in this study, the quality of the cut surfaces obtained depends on the type of composite being cut.

Cutting mechanisms in drilling of aramid composites

Abstract The results of an experimental research on the drilling of aramid fibre reinforced plastics are reported. A drilling machine has been instrumented in order to detect the thrust force and the torque as a function of the depth of the hole. The signals of the transducers were acquired by an analog to digital converter card inserted in a personal computer. The apparatus enabled analysis of the cutting mechanism of commercially available twist drills intended for the drilling of aramid fibre reinforced plastics. Relationships have been evidenced between the trends of the thrust force and the torque with regard to the tool bit geometry and the composite structure, for different feed rates and for different composite constructions. The thrust force shows irregular courses which are discussed in terms of non-uniform distribution of the thrust force along the tool cutting edges and of poor interlaminar strength of composites. A continuous decrease of the thrust force mean value has also been found which has been attributed to the heat build-up at the cutting front. The torque is strongly influenced by friction at the lands of the twist drill.

MACHINING PARAMETERS AND CUT QUALITY IN LASER CUTTING OF ARAMID FIBRE REINFORCED PLASTICS

ABSTRACT This paper deals with the quality evaluation in laser cutting of Aramid Fibre Reinforced Plastics. The typical features of cuts are described and the influence of the process parameters on cutting result is discussed. A new methodology based on a digital image processing technique for the evaluation of cut quality is presented.

Thermal damage in laser cutting of (0/90)2s aramid/epoxy laminates

Abstract The thermal damage caused during laser cutting of (0/90) 2s aramid fibre/epoxy laminates was investigated. Samples cut with a 500 W CO 2 cw laser using different parameters were examined by both optical and scanning electron microscopy. Thermal cracks were detected in plies with the fibre direction at 90° to the cutting direction. A model was developed to relate the material damage to the cutting parameters.

Composite materials response under low-velocity impact

Abstract A simple model, based on energy considerations, has been tested to predict the maximum contact force during a low-velocity impact between an impactor and a composite plate. Three different composites, i.e. glass cloth-polyester, carbon cloth-polyester and nylon cloth-polyester, were examined. The results reported here, obtained using an instrumented apparatus, show that the total energy applied during the impact is the governing parameter of the phenomenon, rather than the impactor speed or mass. All the composites under evaluation did not show any variation of elastic modulus with impact velocity. Moreover, the dynamic behaviour of carbon-polyester and nylon-polyester composites can be predicted by simple static tests, because of their insensitivity to rate-dependent phenomena; for these materials a simulation of impact tests by static tests is therefore suggested. Glass-polyester composites did show a rate-dependent behaviour, by an increase in strength of about 70% with respect to the static case; a small number of dynamic tests is, however, sufficient to characterise their behaviour under impact conditions.

From the experimental simulation to integrated non-destructive analysis by means of optical and infrared techniques: results compared

In this work the possibility of modeling manufacturing ceramic products is analyzed through the application of transient thermography, holographic interferometry and digital speckle photography, in order to identify the subsurface defects characteristics. This integrated method could be used to understand the nature of heterogeneous materials (such as plastic, sponge simulating a void, wood, aluminum) potentially contained within ceramic materials, as well as to predict crack formation due to them. The paper presents the analysis of green ceramic tile containing defects of different types and sizes located at different depths. The finite element method is used for solving the problem of transient heat transfer occurring in experimental conditions. Unknown parameters of the numerical model (such as convective heat transfer coefficients and sample surface emissivity) were adjusted to obtain numerical simulation results as close as possible to those obtained experimentally. Similarities and differences between experimental and simulated data are analyzed and discussed. Possibilities for improving the results and further developments are proposed.

An experimental study on grinding of silicon carbide reinforced aluminium alloys

This paper presents the results of an experimental research on the grinding of metal matrix composites. The aim of the investigation is to enhance the knowledge about the machinability of some aluminium alloys reinforced with SiC of different shape (powder or whiskers) and content. Investigations on chip morphology, ground surfaces and trend of forces acquired during the grinding process were carried out. The results show that the presence of the reinforcement enhances the machinability in terms of both surface roughness and lower tendency to clog the grinding wheel, when compared to a non-reinforced Al alloy. Particle-reinforced composites exhibit a linear relationship between the roughness of the ground surface and the average hardness of the material. Whisker-reinforced composites show higher roughness values than particulate composites. Data of grinding forces obtained under different machining conditions are reported which permit the evaluation of the specific cutting energy.

Elastic behaviour of composite structures under low velocity impact

Abstract The results of a study on the behaviour of glass cloth/polyester panels under low velocity impact are reported. The experimental load/time curve in the elastic region showed good agreement with that predicted by a simple analytical model, based on energy considerations, using elastic properties obtained by static tests. The structural rigidity of the panels was not significantly affected by premature local shear damage, due to the concentration of load, even after first fibre failure. The strength of the material was found to be strongly rate-dependent; as a consequence the response of the structure in the post-elastic region cannot be predicted from the results of static tests.

Experimental and Finite Element Investigation of Roll Drawing Process

In this research, the wire drawing process with flat roller dies is investigated. A prototypal apparatus is developed to conduct experimental tests on such a process and analyze the influence of main roll drawing parameters (e.g., incoming wire diameter, forming rolls diameter, thickness reduction, and friction conditions) on geometrical characteristics of flattened wires. A finite element model (FEM) is developed to simulate the deformation of the wire during the process. Within the entire range of experiments, a good agreement between experimental data and numerical results is found which allows validating the FE model. A further observation from the experimental program and numerical simulations is that a complicated dependence of the lateral spread of wire and width of contact area on process parameters exists during wire drawing with roller dies.

Laser Machining of Composite Materials

In this chapter the fundamental technological aspects of the laser machining of composite materials are reviewed, including: laser material interaction; laser cutting performances; maximum cutting speed evaluations; cut quality parameters; and, evaluation of damage.