Continuous resistance welding of thermoplastic composites: Modelling of heat generation and heat transfer

A process model composed of electrical and heat transfer models was developed to simulate continuous resistance welding of thermoplastic composites. Glass fabric reinforced polyphenylenesulfide welded in a lap-shear configuration with a stainless steel mesh as the heating element was considered for modelling and experimental validation of the numerical results. The welding temperatures predicted by the model showed good agreement with the experimental results. Welding input power and welding speed were found to be the two most important parameters influencing the welding temperature. The contact quality between the electrical connectors and the heating element was found to influence the distribution of the welding temperature transverse to the welding direction. Moreover, the size of the electrical connectors was found to influence the achievable welding speed and required power input for a certain welding temperature.     

Experimental assessment of dual-scale resin flow-deformation in composites processing

In this paper we are concerned with the assessment of sub-models within a two-phase continuum mechanical FE framework for process modeling of composites manufacturing. In particular, the framework considers the inclusion of two deformation dependent models describing resin flow related to: (1) meso-scale wetting and compaction of individual plies and (2) overall preform deformation and macroscopic Darcian flow. Using micro-mechanical modeling, we model the physics of these sub-processes in relation to the recently developed Out-Of-Autoclave (OOA) prepergs. The models are placed in context with a compression–relaxation experiment, employed to study the preform deformations considered separated from other sub-processes. Finally, calibrations and model validations are carried out against the relaxation experiment to relate the FE framework to the mechanical response of the preform. Therefore, using the above experiment, parameter values out of the literature and those estimated from micrographs gave a fair agreement between the simulation and experiments.     

Investigation of mechanical and tribological behaviors of multilayer graphene reinforced Ni3Al matrix composites

Multilayer graphene (MLG) shows an attractive prospect for the demanding engineering applications. This paper reports the mechanical and tribological properties of MLG reinforced Ni₃Al matrix composites (NMCs) under dry sliding at varying sliding speed. The hardness and elastic modulus of the NMCs are significantly influenced with MLG content. It is found that the hardness and elastic modulus of the NMCs are found to be increased by increasing MLG content up to 1.0 wt.%, while decreased when MLG content is above 1.0 wt.%. Tribological experiments suggest that MLG can dramatically improve the wear resistance and decrease the friction coefficient of the NMCs. Such marked improvement of wear resistance is attributed to the reinforcing mechanisms of MLG, such as crack deflection and pull-out, and reduction of friction coefficient is related to the formation of a tribofilm on the sliding contact surface.     

Dielectric relaxation and ionic conduction in 66%Silica/CW229-3/HW229-1 microcomposite polymer

Composites of epoxy resin with high percentage of silica fillers (66%) are designed to improve mechanical and electrical properties of transformers used in railway application. FTIR, (DRX and FE-SEM) and absorption/desorption phenomena are used to investigate the structure, the morphology and the diffusion of water in the microcomposites, respectively. Good dispersion of silica filler with size less than 10 μm was assessed by SEM, although some clustering (agglomerates) of greater than 1 μm was observed. The absorption water in the microcomposite obeys to the first Fickian law and shows saturation water of 0.6%. The calculation of the diffusion coefficient of water leads to a value of 2.9*10⁻¹² m² s⁻¹ in the studied system. Relaxation times of α-relaxation and ionic conduction relaxation processes are determined. A correlation is observed between the ionic conductivity and dielectric relaxation processes. The dc-current behavior shows a change in the conduction mechanism from electronic conduction below the T_g to ionic conduction above the T_g. Shallow traps of 0.54 eV and deep traps of 2.21 eV are determined below and above the T_g, respectively. The TSC analysis confirms the VFT behavior of the α-relaxation of the microcomposite as obtained by the dielectric spectroscopy.     

Improved fracture toughness and integrated damage sensing capability by spray coated CNTs on carbon fibre prepreg

The development of a hierarchically engineered micro-nano hybrid composite system is described. A spray coating technique has been utilized as an effective way to deposit carbon nanotubes (CNTs) onto carbon fibre prepregs with good control of network formation and the potential for localization. Compared to more traditional approaches of introducing CNTs into epoxy matrices for enhancing composite properties, this technique has benefits in terms of its simplicity and versatility, as well as the potential for industrial scale-up. The effectiveness of the technique is demonstrated by the extremely low CNT loading (0.047 wt.%) needed to significantly increase the Mode-I fracture toughness of the carbon fibre laminates by about 50%, which is so far the largest reported improvement for such extremely low concentrations of non-functionalized CNTs. In-situ damage sensing has also been presented for the monitoring of structural health of these nano-engineered composite laminates upon loading, and a systematic analysis of sensing signals is performed.     

The influence of paper type on the properties of structural paper – Polypropylene composites

In this work, different types of paper were used for producing cellulose reinforced polypropylene composites with MAPP as a coupling agent. The samples were prepared by a film stacking method of the polymer and paper layers, followed by hot pressing in order to fabricate structural composite laminates. Virgin copy, filter and newspaper were used as reinforcements for producing composites with varying paper content. The influence of paper type and content on the mechanical and physical properties of the laminates was investigated and discussed in detail. Remarkable results for tensile and bending test were obtained for copy and newspaper composites at a paper content of 30 and 40 vol.%, indicating a high potential for constructive and industrial applications of the laminates. Further characterization was carried out by Charpy impact test, water uptake study, TGA and light microscopic analysis. To summarize the characterization, structural paper reinforced composites with attractive properties were obtained.     

Mechanical and thermal properties of carbon fiber/polypropylene composite filled with nano-clay

The effect of organoclay on the mechanical and thermal properties of woven carbon fiber (CF)/compatibilized polypropylene (PPc) composites is investigated. Polypropylene–organoclay hybrids nanocomposites were prepared using a maleic anhydride-modified PP oligomer (PP-g-MA) as a compatibilizer. Different weight percentages of Nanomer® I-30E nanoclay were dispersed in PP/PP-g-MA (PPc) using a melt mixing method. The PPc/organoclay nanocomposite was then used to manufacture plain woven CF/PPc nanocomposites using molding compression process. CF/PPc/organoclay composites were characterized by different techniques, namely; dynamic mechanical analysis (DMA), fracture toughness and scanning electron microscope. The results revealed that at filler content 3% of organoclay, initiation and propagation interlaminar fracture toughness in mode I were improved significantly by 64% and 67% respectively, which could be explained by SEM at given weight as well; SEM images showed that in front of the tip, fibers pull out during initiation delamination accounting for fracture toughness improvement. Dynamic mechanical analysis showed enhancement in thermomechanical properties. With addition 3 wt.% of organoclay, the glass transition temperature increased by about 6 °C compared to neat CF/PPc composite indicating better heat resistance with addition of organoclay.     

An experimental investigation on the repeated impact response of glass/epoxy composites subjected to thermal ageing

In this study, the effect of thermal ageing on low velocity impact response of E-glass/epoxy composites was investigated. Together with single impact case, repeated impact response of the composite samples was also investigated. Impact energies were chosen as 20 J, 40 J, 60 J, 80 J and 100 J for single impact tests while 20 J was chosen for repeated impact tests. The test coupons were cut out from composite panels with stacking sequence of [0/90]_4S and the dimensions of the specimens were 100 mm × 100 mm, with the nominal thickness of 4.2 mm. The conditioning humidity and temperature were chosen respectively as 70% and 95 °C, considering the glass-transition temperature (T_g) of the intact composites which was determined as 78 °C. The samples were exposed to ageing durations of 100, 400, 700, 1000 and 1300 h by using a climatic test cabin. Along with images of damaged samples, variations of the impact characteristics such as absorbed energy, maximum contact force, maximum deflection and contact duration for successive impacts until perforation of the samples are provided. As a result of the study it is found that in addition to the mechanical properties, damage resistance of the E-glass/epoxy composites is significantly affected by the thermal ageing.     

Effect of fibre wrinkling to the spring-in behaviour of L-shaped composite materials

To determine the amount of deformation resulting from fibre wrinkling at corner regions, a set of experiments have been conducted. As known in the conventional lay-up method, the prepregs are laid sequentially layer by layer on the mould surface. At the corner region of a female tool the radius decreases at the inner surface and the amount of wrinkles increase towards the top layer as the layers are laid up. In order to determine how much these wrinkles influence the dimensional stability of the manufactured parts, an alternative lay-up method is used. The amount of the wrinkles can be increased for the parts of same geometry by first stacking prepregs on a flat plate and then bending the whole stack to conform to the surface of the L-shaped mould. In this method, more wrinkling occurs on the inner surface of the corner regions as compared to the conventional lay-up procedure. It was found that fibre wrinkling decreases the spring-in values. The mechanism behind that observation is discussed with the help of a heuristic Finite Element Analysis (FEA). The conformation of the stacked prepregs on the mould was simulated by using FEA.     

Scaling of fracture response in Over-height Compact Tension tests

An experimental investigation into in-plane scaled Over-height Compact Tension (OCT) [45/90/−45/0]_4s carbon/epoxy laminates was carried out to study the scaling of fracture response. The dimensions of the baseline specimens were scaled up and down by a factor of 2. Interrupted tests were carried out for specimens of each size in which the tests were stopped after certain load drops in order to study the failure mechanisms. X-ray Computed Tomography (CT) scanning was applied after the interrupted tests to examine the damage development and its effect on the fracture response. The test results showed that the scaling of the initial propagation of fracture follows Linear Elastic Fracture Mechanics (LEFM), but the development of the damage process zone differs with specimen sizes. The OCT specimens were found to be not large enough to generate a self-similar damage zone during propagation, and so no conclusions could be drawn regarding the R-curve effect.