A. Langella

Indentation and penetration of carbon fibre reinforced plastic laminates

Static tests were carried out on circular carbon fibre reinforced plastic plates of various thicknesses, which where loaded at the centre by a hemispherical steel indentor. The tests were stopped at predetermined values of the displacement, and the indentation after the loading stage was evaluated. Tests were also performed up to complete penetration, using different indentor diameters. The data generated were compared with similar results previously obtained under low-velocity impact conditions, and treated according to models developed for the dynamic case. Apparently, both the penetration energy and indentation were not affected by the loading speed. The new experimental results showed that an empirical law previously proposed by the authors, aiming to predict the indentation as a function of the absorbed energy, is inaccurate when high energy levels are imparted to the material. A new empirical law, more efficient than the earlier, was assessed. The data collected indicate that the constants appearing in the new model are negligibly influenced by the laminate type and thickness, and constraint conditions adopted.

Elastic behaviour of circular composite plates transversely loaded at the centre

Abstract Static tests were carried out on moderately anisotropic, simply supported circular plates made of graphite fibre reinforced plastic laminates of various thicknesses, loading them at the centre by a hemispherical tup. A non-linear solution available for large deflections of isotropic plates was suitably modified to account for the Hertzian contact phenomena, and adopted to model the plate behaviour in the elastic field. From the experimental results, an unacceptable error is made in predicting the force–deflection curve up to first failure, if the non-linear portion of the deflection is neglected. This error is the more evident when thin laminates are concerned. For thick laminates, the Hertzian contact plays a significant role in affecting the plate behaviour. Taking into account both the local deformation and non-linearity due to large deflections, a very accurate prediction of the load–deflection curve was obtained. Only in the case of the thinnest composites tested, a divergence of the theoretical curve from the experimental data was observed at sufficiently high loads. The analysis of the failure modes revealed that the discrepancy is seemingly attributable to internal damage not resulting in clearly discernible discontinuities in the load–deflection curve.

The Wear Behaviour of Composite Materials with Epoxy Matrix Filled with Hard Powder

The wear behaviour of composite materials, sliding under dry conditions against smooth steel counterface, has been investigated. The composite materials consisted of glass woven fabric reinforcing three different systems of matrix: epoxy resin, epoxy resin filled with powders of silica and epoxy resin filled with powders of tungsten carbide. The powders were mixed in a volumetric fraction of 6% with the epoxy resin. Three laminates were manufactured by hand lay up technology. The sliding tests have been conducted on the specimens, cut from the three laminates, with a pin on disk apparatus. The results put in evidence different wear behaviours of the composite materials observed at different values of sliding speed and pressure. The presence of different wear mechanisms has been appreciated by SEM-micrographic examinations.

Impact damage investigation on composite laminates: comparison among different NDT methods and numerical simulation

The aim of this paper is to investigate the ability of different NDT techniques to detect and evaluate barely visible and non-visible impact damage on composite laminates. Firstly, a conventional ultrasound technique was adopted to investigate the delamination in carbon fibre laminates after low velocity impact s. Then the results were compared with a thermographic and holographic analysis, as well as a theoretical simulation of the expected delamination. The results were compared and discussed. Overall a good agreement was found between the data obtained by the different techniques. Furthermore, the true values of the damage parameters were confirmed by DT performed on the samples.

Study of a three-point bending specimen for shear characterisation of sandwich cores

A sandwich beam loaded in three-point bending (TPB) was employed for the shear characterization of foam cores destined to structural sandwich application. In the design of the specimen, particular care was taken to avoid measurement errors deriving from the flexural component of the displacement and from the de Saint Venants effects, yet retaining the simplicity in the formulae for data reduction. Using the new method, experimental tests were carried out on a PVC foam 55 Kg/M3 in density. For comparison, shear characterization tests were also performed according to ISO 1922. The results obtained demonstrate that, when the core shear modulus is considered, TPB and ISO 1922 can provide practically coincident results. However, TPB yielded a shear strength about 20% higher than the ISO Standard, together with a shear strain at failure that is 10% lower. The failure modes observed suggest that the core shear behavior is better represented by TPB, whereas ISO 1922 is unsuitable to correctly measure the core shear strength.

Prediction of the first failure energy of circular carbon fibre reinforced plastic plates loaded at the centre

This work was devoted to the prediction of the elastic energy stored at first failure in a circular composite plate statically loaded at the centre. To describe the load‐ deflection curve, a previous model was further developed, to explicitly account for the tup diameter. The first failure load was calculated through a simple formula, available in the literature, which was suitably varied. An original expression was derived for the energy at first failure. The experimental tests were carried out on carbon fibre reinforced plastic laminates of various thicknesses, which were simply supported at the periphery and loaded using different support and indentor diameters. The results obtained show that the elastic model, which takes into account the non-linearity deriving from large displacements and local indentation, is very accurate in shaping the load ‐deflection curve up to the first failure point. In general, also the predicted load and energy at first failure are in good agreement with the corresponding measured values. Both theory and experiments demonstrate that the critical load is independent of the support diameter, whereas it increases with increasing the plate thickness and the indentor diameter. When the support diameter and thickness increase, the energy at first failure increases as well. A particular condition, resulting in the failure of the force model, is achieved when the curvature of the plate at first failure is considerable. In this case, critical forces notably higher than expected from theory are measured. A possible explanation for this behaviour is given. q 2003 Elsevier Science Ltd. All rights reserved.

An Intelligent Computation Approach to Process Planning in Multiple-Step Cold Forging

Abstract An intelligent computation approach to time and cost reduction in process planning of cold forging operations is illustrated. The problem taken into consideration is the generation of optimized working sequences in the fabrication of multi-diameter shafts through multiple-step cold forging. A supervised learning neural network paradigm was employed in order to identify the technologically feasible working sequences to be considered for process planning decision making. The process planner can then select the appropriate solution according to his experience or resort to further methods of detailed analysis (e.g. FEM analysis), with the advantage of applying time consuming numerical investigations only to a small number of cases suggested by the intelligent computing system. Neural network training and testing allowed to verify the system performance in classifying working sequence feasibility and its computational speed in providing technologically acceptable working sequences for process planner consideration.

Optimization of robotic arms made of composite materials for maximum fundamental frequency

Abstract The paper deals with the design of a composite arm, to be employed in the architecture of industrial, measuring robots. Based on the real working conditions, the arm is reduced to a cantilever beam, shaped as a thin walled tube, supporting a mass at the free end. An optimization study is carried out, aiming to determine the laminate properties capable of providing the maximum fundamental frequency (FF) in bending. The optimization relies on an approximate solution, obtained by modifying the Rayleigh energy method to account for the shear effect. It results in a closed-form formula, explicitly correlating FF with composite elastic properties. Two classes of laminates, namely (± θ) s and ( 0 ± 45 n ) s , are examined in order to assess their ability to fulfil the requirement of a maximum FF value. Moreover, the advantages and drawbacks of composites compared to metals are highlighted for the application under concern. Finally, the validity of the proposed solution is demonstrated by comparison with the results of a finite element analysis.

Automated Procedure for Roll Pass Design

The aim of this work has been to develop an automatic roll pass design method, capable of minimizing the number of roll passes. The adoption of artificial intelligence technologies, particularly expert systems, and a hybrid model for the surface profile evaluation of rolled bars, has allowed us to model the search for the minimal sequence with a tree path search. This approach permitted a geometrical optimization of roll passes while allowing automation of the roll pass design process. Moreover, the heuristic nature of the inferential engine contributes a great deal toward reducing search time, thus allowing such a system to be employed for industrial purposes. Finally, this new approach was compared with other recently developed automatic systems to validate and measure possible improvements among them.

Forces analysis in sheet incremental forming and comparison of experimental and simulation results

Publisher Summary This chapter characterizes innovative techniques, such as hydroforming and incremental forming by the possibility to be easily adapted to realize a small production lot with low tools cost. The chapter discusses grooves in sheets, which have been realized by means of the incremental forming technology. It presents the forces analysis in relation to the tool path and its diameter. FEM simulations are achieved with the purpose to carry out a comparison between the forces values experimentally pointed out and the ones by FEM. FE analysis also allows the individualization of the points where failure conditions take place by simple evaluation of the reach stress values. Therefore, the FE method can be used to determine the tool path in the design phase of the process cycle.