M.O.W. Richardson

Effect of Interlayer Delamination on Mechanical Behavior of Carbon/Epoxy Laminates

This article presents the results of a current study on the influence of interlayer delaminations on the static and fatigue behavior of composite laminates. The composite was manufactured by a vacuum molding method using 12 balanced bi-directional carbon fiber layers and epoxy resin. Delaminations with different length were artificially introduced. The specimens with dog bone shape were cut from the original plates having 3 mm thickness and fiber weight fraction of 0.66. Static tests were performed in order to study the influence of delamination size on the laminate stiffness and strength. Complementary finite element analysis was carried out showing the influence of angular misalignments of fiber/matrix delaminations on the laminate stiffness. Fatigue tests were performed in load control for R = 0.05 and R = —1, with a loading frequency of 10 Hz, at room temperature. The artificial interlayer delaminations have a negligible influence on the fatigue strength for tensile cycle loadings, but produce significant decreases in strength for R = —1 fatigue loadings.

Impact response of sandwich composites with nano-enhanced epoxy resin

Present work intends to study the improvement of impact performance on sandwich composites by the addition of nanoclays. For this purpose, nanoclays Cloisite 30B were previously subjected to a silane treatment in order to improve their dispersion and interface adhesion. Different incident impact energy levels were used and, for both sandwiches, the maximum load, displacement or elastic recuperation shows to be very dependent of the impact energy. Mathematical relationships are proposed to estimate the maximum impact force and displacement, based on the total impact energy and impact bending stiffness. Finally, sandwiches enhanced by nanoclays presented higher maximum impact loads, lower displacements, the best performance in terms of elastic recuperation and maximum residual flexural strength.

Effect of the Surface Preparation on PP Reinforced Glass Fiber Adhesive Lap Joints Strength

This article is concerned with the influence of surface treatment on the strength of single lap joints. The tensile tests were carried out in order to find the surface treatments which maximize joint strength using polypropylene reinforced glass fiber as adherents. The maximum shear strength was obtained with the trichlorethylene plus primer treatment when using a cyanoacrylate adhesive. The pretreatment effectiveness was evaluated in terms of environmental durability and an important decrease in static strength of adhesive joints occurred when they were immersed in water.

A study of the mechanical behaviour on injection moulded nanoclay enhanced polypropylene composites

This paper presents the results of a current study on the mechanical properties of a polypropylene matrix resin, enhanced using nanoclay filler with a special silane treatment. The study was centred on the effect of adding nanoclay and of water immersion on static and fatigue behaviour. Specimens filled up to 3% in weight were produced by an injection moulding process. The filler improved significantly bending quasi static and dynamic stiffness, and also marginally the bending strength. Surprisingly, the immersion in water for 40 days increases the bending stiffness and the bending strength. The addition of 3% w/w nanoclay promoted a negative effect in Gc. All material configurations exhibited a faster and intense stress release from the first cycles of fatigue. The 3% nano-enhanced composites exhibited higher fatigue strength than unfilled materials.

Nanomechanical behaviour and thermal degradation of nanoclays and supernanoclays enhanced marine gelcoat system

Novel nanoclay reinforced unsaturated polyester gelcoats for marine vessels are evaluated in terms of their thermal and mechanical performance. In this study, mechanical and thermal tests have been employed to characterise different gelcoat systems with various loading levels of nanoclays with and without X-treatment. Differences in mechanical properties were determined by using nano-indentation testing which shown an increase in hardness compared to the control system. Thermal degradation characteristics were determined using a thermogravimetric analyser (TGA). An increase in thermal stability was observed for all nanocomposites compared to the control system. Additionally, differential scanning calorimetry (DSC) showed that the effect of inclusion of nanoclays is to hinder the structure of unsaturated polyester gelcoats and hence increase glass transition temperatures. Furthermore, X-treated supernanoclay is shown to be significantly more effective than untreated nanoclay. Enhancement of mechanical property and thermal degradation could be attributed to the grafting of hydroxyl groups (?OH) in the nanoclays with polymer chains.

Creep behaviour of adhesive lap joints in thermoplastics composites

Environmental factors, most of which are of a non-mechanical nature, have an influence on the properties of materials. A typical case is the temperature, which associated with load affects the performance of any structure in service. To study the effect of temperature in polypropylene-glass fibre composite adhesive lap joints, tests within the temperature range from 20 to 50 °C were carried out, and the results were plotted in terms of the deformation and strain rate versus time. The failure surfaces were also observed by the scanning microscopy technique to obtain the failure mechanisms. Creep parameters were correlated using the Manson-Haferd parameter, the Findley et al. equation and the Little et al. equation, the best agreement being with experimental results obtained with the last model.

The high velocity impact loading on symmetrical and woven hybrid composite laminates

Space structures use fibre composite materials, due to their lightweight. This paper examines the impact response of symmetrical and hybrid composite laminates. Special attention is given to the stacking sequences used. The experimental study of structures has always provided a major contribution to our understanding. Even with the formidable growth in the use and capacity of computing power the need for experimental measurement is as compelling as ever. The design of hybrid composite structures is complicated by the number of design variables and the interaction of the constituents is the composite system. Since it is desirable to experimentally test the design and it is not practical to test a full scale model, the structural/material similitude concept is used to create a small scale model with a similar structural response. In the current study, experimental investigations were carried out to determine the response of four different combinations of hybrid laminates to low-velocity impact loading using an instrumented impact testing machine. Hybrid laminates were fabricated with twill weave carbon fabric and plain weave S2-glass fabric using vacuum assisted resin molding process with SC-15 epoxy resin system. Response of carbon/epoxy and glass/epoxy laminates was also investigated to compare with that of hybrid samples. Square laminates of size 100 mm and nominal thickness of 3 mm were subjected to low-velocity impact loading at four energy levels of 10, 20, 30 and 40 J. Results of the study indicate that there is considerable improvement in the load carrying capability of hybrid composites as compared to carbon/epoxy laminates with slight reduction in stiffness.