Thermal and Principal Ablation Properties of Carbon-Fibre-Reinforced Polymers with Out-of-Plane Fibre Orientation

This work characterises thermal properties of a typical epoxy-based carbon-fibre-reinforced polymer used in aircraft construction, but with an out-of-plane fibre orientation, and assesses its potential as a structural ablative material. Samples of the commercially available Hexply® 8552/IM7 are prepared with out-of-plane angles up to 90°, with a focus on 0° to 15°, enhancing thermal conductivity through the thickness of the panel. Ablation processes are simulated by a hot-air blower at 580 °C, and examined in detail by ultrasonic testing and microfocused computed X-ray tomography afterwards. Matrix degradation is characterised by infrared spectroscopy and mass loss. To assess structural properties, tensile, compression, and bending tests are performed. The results show a loss in mechanical performance with an increasing fibre angle, which may be negligible for angles lower than ~5° in the initial state. Composite material with an out-of-plane fibre orientation is deeply penetrated concerning matrix degradation by thermal loading, but it is held together by the fibres fixed in the intact matrix underneath. This type of material shows a high potential for structural components in single-use, high-temperature, ablative applications with a focus on saving weight.

Strength grading of hardwoods using transversal ultrasound

Detection of local wood inhomogeneities is important for accurate strength and stiffness prediction. In hardwood specimens, visual characteristics (e.g. knots or fibre deviation) are difficult to detect, either with a visual surface inspection or by the machine. Transversal ultrasound scan (TUS) is a non-destructive evaluation method with high potential for hardwoods. The method relies on differences in ultrasound wave propagation in perpendicular to the grain direction. The aim of this study is to estimate and analyse the capabilities of TUS for defect detection in hardwoods and prediction of mechanical property values. In the current paper, the TUS was applied to the hardwood species European ash (Fraxinus excelsior L.), Norway maple (Acer platanoides L.) and sycamore maple (Acer pseudoplatanus L.). In total, 16 boards of both specimens were completely scanned perpendicular to the grain using a laboratory scanner with dry-coupled transducers. The measurements were processed to 2D scan images of the boards, and image processing routines were applied to further feature extraction, defect detection and grading criteria calculation. In addition, as a reference for each board, all relevant visual characteristics and mechanical properties from the tensile test were measured. Using the TUS global fibre deviation, the size and the position of the knots can be detected. Knottiness correlates to the strength properties similarly or even better compared to the manual knottiness measurement. Between the global fibre angle measured using TUS and measured on the failure pattern, no correlation could be found. The ultrasound modulus of elasticity perpendicular to the grain does not show any meaningful correlation to the elastic properties parallel to the grain. In overall, TUS shows high potential for the strength grading of hardwoods.

The response of pin-clamped carbon fibre-reinforced plastics composite sandwich beams with polyvinylchloride foam core under bending impact

The dynamic response of pin-clamped composite sandwich beam in terms of face-sheet effect with polyvinylchloride foam core subjected to bending impact loading was investigated in this paper. Composite sandwich beams with three different unidirectional skin layups of [0]4, [45]4 and [90]4 and two types of face-sheet thickness of 1 ([0]4) and 2 ([0]8) mm were fabricated. An explicit code, VUMAT, is written and implemented in ABAQUS/Explicit. The micro-computerised tomography scanning was used to detect adhesive layer failure. The ply angle orientation of face sheets plays an important role in the failure mechanism of the sandwich beam under bending loads. Although it is known that the fibre angle in the direction perpendicular to the bending direction is more stiff and strength, damage tolerances under bending impact loads of beams with other fibre angles were determined. In addition, as the number of layers increased, failure mechanism and load-carrying capacity of composite face sheets changed completely for increasing bending stiffness. This research provides fundamental information about the change of the failure mechanisms as the fibre angle and thickness of the face sheet were changed and in terms of interpretation with the help of finite elements using different failure criteria.

Design of a High-Performance Composite Triple Clamp of Motorbike

A simple and novel design concept for a CFRP composite triple clamp of a motorbike is brought out for low mass that fulfills the stiffness and strength requirement when compared to an existing steel triple clamp. In general, for any triple clamp configuration, the ideal fibre angle is chosen as the angle that subtends in the arm of the clamp with respect to the longitudinal direction (a line connecting the two fork holes). The initial design configuration is fabricated using a commercially available low modulus bi- directional carbon–epoxy laminate and tested for the evaluation of axial and transverse stiffnesses. Finite element model is then verified through the test data. Using the validated FE model, a new design with the high modulus carbon-fiber is arrived at. The proposed composite design suitable for high performance motorbike that possesses, high margin over critical load case with low mass when compared to steel clamp is provided.

Effect of Intra-Ply Hybridization of Carbon-Aramid/Epoxy Laminates under Tension-Tension Fatigue Loading

The objective of the research is to investigate the fatigue life of intra-ply hybrid Carbon-Aramid laminate with Epoxy resin in on-axis and off-axis directions. Three different off-axis angles of 15, 30 and 45 degrees were considered for the present work. The intra-ply hybridization is used to combine the superior mechanical properties of Carbon fibre with excellent elongation-to-failure property of Aramid fibre in the same lamina. The fatigue test was performed using load control using a frequency of 5Hz. The fatigue behaviour was studied for Carbon/Epoxy, Aramid/Epoxy, Carbon-Aramid/Epoxy, Carbon-Aramid/Epoxy - 15, Carbon-Aramid/Epoxy - 30 and Carbon-Aramid/Epoxy - 45 with the stress ratio of R = 0.1. The ultimate tensile strength decreases progressively for Carbon/Epoxy, Carbon-Aramid/Epoxy, Aramid/Epoxy, Carbon-Aramid/Epoxy - 15, Carbon-Aramid/Epoxy - 30 and Carbon-Aramid/Epoxy - 45. The effect of off-axis loading indicates that the increase of fibre angle influences the decrease in tensile strength and fatigue life.

Tensile Strength and Density of Teki Grass (Cyperus Rotundus) Used as Materials for Fibre Composites with Fibre Angle Variation

The primary purpose of this study is to determine the tensile strength and density) of the Indonesian term teki grass (Cyperus rotundus) in which this teki grass is used as the reinforcement materials for the production of fibre composite. The production process is carried out by using varieties of fiber directions ranging from 0°, 45°, 90°,and random.The methods in use is hand lay-up with 3 repetitions. Teki grass is chosen because it is easily found and has the following significances: biodegradable, harmless to health, available in nature in large quantities, and cost-efficient. Another reason because this plant is also an agricultural weed that is difficult to eradicate, not fully utilized, and often found in open field. While a matrix for fiber binder selected from epoxy resin material. From the test results it can be concluded that the variations in the direction of fibers effect on the tensile strenght of the composite. Average tensile strength of specimens with fibre directions of 0°, 45°, 90°, and random are 15.60 MPa, 18,69MPa, 30.11 MPa, and 22.79 MPa. In contrast, variations of fibre directions do not affect the density.