Towards a process simulation tool for the laseer assisted tape placement process

A combined optical and thermal model for the laser assisted tape placement process is presented. The optical model adopts a ray tracing procedure, based on the Fresnel equations, to predict the incident heat flux on the tape and substrate near the nip-point. The heat flux distribution is subsequently used in a one-dimensional thermal model to predict the temperature distribution in the tape and substrate. The results demonstrate that for small incident laser angles a part of the laser light is reflected at the surface, which significantly influences the temperature distribution in the nip-point. The presented model allows, with a weld strength and consolidation model, optimization of the processing parameters

Impact damage in woven fabric reinforced composites

Very often, woven fabrics are used as the reinforcement in advanced composite materials. Although the resulting inplane stiffness is lower than of their unidirectional counterparts, the excellent drapability of these materials eases the production of more general doubly curved components. In addition, the inherently low out-of-plane strength of these layered materials improves due to the undulating yarns. This paper considers both the initiation and growth of defects in these woven fabric reinforced plastics. Ten Cate Advanced Composites’ 5H Satin carbon reinforced PPS is taken as the model system. A 5H satin fabric exhibits very good drapability and PPS has a low viscosity above its melting point, enabling good yarn impregnation. Apart from this PPS has approved solvent resistance for aerospace applications and good temperature resistance. For a thermoplastic matrix, however, the material is fairly brittle

Analysis of the mechanical properties of a reinforced thermoplastic pipe (RTP)

This paper describes the analysis of a long length reinforced thermoplastic pipe. For this new class of pipe, which is constructed of a polyethylene liner pipe over wrapped with two layers of non-impregnated twisted aramid cords, peculiar deformation behaviour was observed when a pipe was pressurised. This behaviour was found to be a result of a difference in cord-slack between the two reinforcement layers in conjunction with an unbalanced torsion moment generated by the two reinforcing layers. Cord slack is a certain surplus length of the reinforcing cords relative to the pipe geometry. The cord-slack is estimated for the two different layers and first incorporated into an earlier published model, based on a plane stress characterisation. As no substantial improvement has been achieved by this approach, a new model based on a plane strain characterisation is introduced. This model shows good agreement with the experimentally determined strains for the hydrostatic pressure load-case

Vibration based Structural Health Monitoring of a Composite Plate Structure with Multiple Stiffeners

A vibration based damage identification method is investigated experimentally.\ud The dynamic response of an intact and a locally damaged 16–layer unidirectional\ud carbon fibre PEKK reinforced plate structure with two stiffener sections is considered.\ud A forced–vibration set–up, including a laser vibrometer system, is employed\ud to measure the dynamic behaviour. The feasibility of the two–dimensional Modal\ud Strain Energy Damage Index algorithm to detect and localize impact induced defects\ud is demonstrated

Dynamic characterisation of a damaged composite structure with stiffeners employing fibre bragg gratings

One of the key issues in composite structures for aircraft applications is the early detection and localisation of damage. Often service induced damage does not involve visible plastic deformation, but internal matrix related damage, like transverse cracks and delaminations. Their detection imposes costly maintenance techniques. Vibration based damage identification methods are promising as an alternative for the time consuming and costly Non-Destructive Testing methods currently available. These methods also offer the potential to be used in a real-time health monitoring system. The measured change of the dynamic properties is employed to identify damage such as delaminations.\ud Earlier performed research [1] showed that the Modal Strain Energy Damage Index algorithm [2] is a suitable method to identify impact induced damage in a fibre reinforced composite plate structure with stiffeners using laser vibrometer measurements. The damage identification algorithm requires the computation of the second derivative of the displacement mode shapes.\ud The goal is to extent this research by applying fibre Bragg gratings since they can be valuable. Firstly, optical fibre sensors are suitable for integration, which is required in a Structural Health Monitoring environment. Secondly, measured strain mode shapes could be advantageous with respect to the numerical errors induced by the computation of second derivatives of the displacement mode shapes.\ud Before applying the damage identification algorithm, it is a challenge to accurately extract the dynamic properties. The dynamic properties of a damaged composite T-shaped stiffener section, shown in figure 1, are investigated in this work using fibre Bragg gratings

Modeling anisotropic friction in triaxial overbraiding simulations

Triaxial overbraiding is a highly intricate textile manufacturing process that involves interlacing yarns in three directions, enhancing reinforcement of the final composite compared to biaxial braids. Predictive process simulation is a cost-effective approach to optimizing the manufacturing process. Previous research on biaxial overbraiding simulations indicates that yarn-yarn friction has a significant effect on the braid angle and convergence zone length. This study presents an extended yarn interaction model; it utilizes a fast frontal approach and a Eulerian on Lagrangian method to simulate the complex interlacing of multiple yarns in triaxial overbraiding, including yarn-yarn and yarn-ring friction. Experiments were conducted to evaluate the effect of UD yarn tension on the convergence zone length and braid angle, and to validate the simulations. The model validation shows that a recently proposed anisotropic yarn-yarn friction model predicts braid angle more accurately than an isotropic friction model

Excellent impact performance of PVC pipeline materials in gas distribution networks after many years of service

It has been about fifty years ago since the first unplasticized poly(vinyl chloride) (uPVC) pipes were installed for use in gas distribution purposes. Currently, about 22,500 km of uPVC is still in use in the Dutch gas distribution network. The pipes were originally designed for a lifetime of 50 years, but due to positive experiences the question arises if (and how long) the lifetime can be extended without any concessions to safety. This is supported by the data of leak surveys presented in this paper. The amount of leaks per installed km of uPVC is even slightly lower than that of polyethylene or steel pipes. Only impact modified PVC has a better performance. The impact behaviour is presumed to be the limiting factor for the lifetime of uPVC. Therefore, the impact behaviour was studied as a function of the age. Two types of research have been carried out: instrumented falling weight tests were carried out on recently produced uPVC pipes (some of which were aged artificially) and tensile impact tests were carried out on excavated uPVC pipes which had been in service for 20 to 50 years. The overall conclusion that can be drawn from these experiments is that the most significant change in impact behaviour is likely to occur in the early stages, just after the production of the uPVC pipe. Physical ageing occurs on a logarithmic timescale, thus the changes occurring between the 20th and the 50th year of service are relatively small compared to the changes that occur in the first 20 years. This leads to the conclusion that uPVC pipes that currently show good impact behaviour, are expected to have good impact properties for many years to come