Mohd Afendi

Effects of Winding Angles in Biaxial Ultimate Elastic Wall Stress (UEWS) Tests of Glass Gibre Reinforced Epoxy (GRE) Composite Pipes

This paper presents an experimental investigation into the influence of winding angles in multiaxial ultimate elastic wall stress (UEWS) tests of glass-fibre reinforced epoxy (GRE) composite pipes. Currently, UEWS test is one of the alternative methods used to the 1000-hour test procedure detailed in ASTM D2992 for the detection of manufacturing changes and reconfirmation of the design basis of composite pipes. A stress-strain response was obtained for each winding angle and the results then compared with those computed through conventional laminate theory. Experimental data showed that the UEWS point varies for each winding angle, and the difference becomes even more pronounced, especially when the angles deviated from the ideal ±55°. It is also concluded that the UEWS stresses, which represent the onset of non-linearity were very much dependent on the transverse and shear stress responses, and these values were found to be consistent with the predicted values from the commonly used Tsai Wu failure criterion.

Strain response and damage modelling of glass/epoxy pipes under various stress ratios

Abstract This paper presents the stress–strain response and general lifetime damage modelling of glass fibre reinforced epoxy (GRE) composite pipes subjected to multi-ratios stress loadings at room temperature (RT). This particular modelling work was developed to predict the non-linear stress–strain response caused by the fatigue static and cyclic loading in the multiaxial ultimate elastic wall stress (UEWS) tests by considering the effects of matrix cracking within the laminates. Although the UEWS procedure is not a standard protocol used for qualification of GRE pipes, it appears to offer an option to existing procedures delineated in ASTM D2992. The ply properties initially expressed as a function of crack density was computed as a function of increasing stress and strain using shear lag approximation. In general lifetime damage model, the effects of stress developed in each ply from ultimate elastic wall stress (UEWS) test were expressed in a single quadratic term of axial and hoop stress. The term then solved to produce limits with respect to axial and hoop stress, which represented in a graphical form of failure envelope. The predictions from both models are found to be in good agreement with the data from the multiaxial UEWS tests of ±55° filament wound GRE pipes. These models thus enable for the long term performance prediction of the pipes under combined loadings.

Acoustic emission monitoring of multiaxial ultimate elastic wall stress tests of glass fibre-reinforced epoxy composite pipes

This paper describes the acoustic emission (AE) monitoring of multiaxial ultimate elastic wall stress (UEWS) tests of filament wound glass fibre-reinforced epoxy composite pipes under hydrostatic, pure axial and pure hoop loadings at room temperature. The purpose of AE monitoring is to quantitatively identify and characterise damage inception and evolution, which leading to different failure mechanisms via an analysis of AE parameters. AE parameters such as counts and energy released were plotted against time, and changes of these AE activities were monitored. A 3D correlation plot between AE amplitude and duration against time for each loading condition was produced and analysed. The AE measurement of both hydrostatic and pure axial loading suggested that matrix cracks were initiated early in the tests and possible had progressed into delamination failure just before UEWS point was reached at 200 MPa of hoop stress and 63 MPa of axial stress, respectively. No clear damage initiation and progression was observed for pure hoop loading condition. Significant AE events were only noted when buckling induced delamination and debonding failure, which followed by fibre fracture at the outer surface of the pipe.

General Lifetime Damage Model for Glass Fibre Reinforced Epoxy (GRE) Composite Pipes under Multiaxial Loading

This paper presents the modelling of a general lifetime performance for glass fibre reinforced epoxy (GRE) composite pipes similar to the well-known Tsai-Hill interactive failure criterion. Tsai Hill criterion is based on the Von Misses distortional energy criterion which was modified to satisfy the orthotropic nature of GRE composite pipes. The effects of stress developed in each ply from ultimate elastic wall stress (UEWS) test were expressed in a single quadratic term of axial and hoop stress through laminate theory. The term then solved to produce limits with respect to axial and hoop stress, which represented in a graphical form of failure envelope. The modelled envelop shows a good agreement with experimental data from the multiaxial UEWS test of ±55° GRE composite pipes. This indicates that such model can be used to predict the long-term performance of GRE pipes under combine loadings.

Effects of Alkaline Treatments on the Tensile Strength of Napier Grass Fibres

This paper presents the experiment test of the Napier grass fibres to determine the tensile strength of the Napier grass fibre. . Napier grass fibre is a natural source of fibre which is extracted from the internodes of Napier grass stems. Napier grass fibres were extracted trough conventional water retting process. However, the main disadvantages of natural fibres in composites are the poor compatibility between fibre and matrix and the relative high moisture absorption. These Napier grass fibre then undergoes alkaline chemical treatment using sodium hydroxide (NaOH) to improve the surface roughness and to minimize the water absorption into the cellulose. The treatment is conducted with different concentration of NaOH at 5%, 10%, 15% and 20% respectively. The single fibre tensile test was conducted using Instron micro tester. Based on the tests conducted, the results show that the fibre treated 10% concentrations yield the strongest tensile test compared to untreated Napier grass fibre.

An automated portable multiaxial pressure test rig for qualifications of glass/epoxy composite pipes

Abstract An automated multiaxial cyclic loading pressure testing rig was developed as an alternative to the existing short-term test procedure specified by ISO 14692 and ASTM D2992. Conventionally, 14 months are required to estimate the residual properties at the end of expected life (20–50 years). The test periods and costs associated with this long-term test are high. To resolve this, a novel rig was developed based on the ultimate elastic wall stress (UEWS) algorithm, allowing five multiaxial stress ratios to be tested. The test involved the cyclic pressurizing of the pipe with 1-min of pressure and 1-min of zero pressure. The test rig was tested under five stress ratios using glass-epoxy composite pipes with winding angles of [±45°]4, [±55°]4 and [±63°]4. The rig is capable of testing both static and cyclic pressure loading, thereby reducing the test period and related costs. The results provide a more realistic failure envelope.

Strength and Fracture Characteristics of SUS304/AL-Alloy Scarf Adhesive Joint with Various Adhesive Thicknesses

In this study, strength and fracture toughness of epoxy adhesively bonded scarf joints of dissimilar adherends, namely SUS304 stainless steel and YH75 aluminium alloy are examined on several scarf angles and various bond thicknesses under uniaxial tensile loading. Scarf angles, θ = 45°, 60° and 75° are employed. The bond thickness, t between dissimilar metals is controlled to be ranged between 0.1 mm to 1.2 mm. Finite element (FE) analysis is also executed to investigate the stress distributions in the scarf joints by ANSYS 11 code. From analytical solutions, stress singularity exists most pronouncedly at the steel/adhesive interface corner of joints having 45° to 75° scarf angle. This is not only in agreement with the FE analyses results but also confirmed by fracture surfaces observation wherein the fracture has always been initiated at this point. The strength of scarf joints increases as the bond thickness decreases. Interface corner toughness, Hc approach can be applied when predicting the failure stress of scarf joints. Besides, for scarf joints with an interfacial crack, the fracture toughness, Jc values are independent of bond thickness and less sensitive to adherends. Moreover, Jc increases as mode mixity increases.

Effects of Alkaline Concentrations on the Tensile Properties of Napier Grass Fibre

This paper presents an experimental investigation of the effects of alkaline treatment on the tensile properties of Napier grass fibres. The effect of different concentrations of NaOH aqueous solutions on the morphology and structure of the fibres were studied. The fibres were treated with 5%, 10%, and 15% of Sodium hydroxide (NaOH) concentration for 24 hours of soaking time. The single fibre tests were then performed in accordance with ASTM D3822-07 standard. The morphology of the fibres before and after alkali treatment was observed with a Metallurgical Microscope MT8100. The results show that the physical properties were varied after the treatments and 10% concentration of NaOH treatment yield the maximum tensile strength and elongation of the fibre at 172 MPa and 5.7% respectively. Morphology observation found that the fibre became thinner, and the surface roughness of the fibres increased with the increment of NaOH concentration.

Tensile Strength of Untreated Napier Grass Fibre Reinforced Unsaturated Polyester Composites

This paper describes the experimental investigation of the tensile strength of untreated Napier grass fibre reinforced polyester composites. Napier grass fibres were extracted trough conventional water retting process and used as reinforcing materials in the polyester composite laminates. Tensile tests were then conducted for the composite specimens from the laminates at 25% fibre loading using the electronic extensometer setup to obtain the tensile properties. The results show significant differences in tensile strength between random short fibres laminates and random long fibre laminates with the long fibres yield almost 45 % higher in the strength. The laminates also show higher maximum strength compared to other commonly available natural fibre composites with over 70 % increase in the maximum strength compared to the short kenaf fibre reinforced composites.

Ageing Effects on Burst Pressure Test of Impacted Glass Fibre Reinforcement Epoxy (GRE) Pipes.

The main objective of this experimental study is to investigate the effects of hydrothermal ageing on the pressure bearing capacity of the E-glass/epoxy composite pipes subjected to impact loadings. The pipes were produced by the conventional filament winding technique comprises of six antisymmetric layers with (±55°)3 winding angles. The pipes were immersed in tab water for period of 500, 1000, and 1500 hours. The specimens were impacted at three different energy levels; 5 J, 7.5 J, and 10 J using an instrumented drop weight impact testing machine (IMATEK IM10). The samples were then subjected to pressure test until distinct leakage failure is observed. The results indicates that peak force and contact time increase with increasing impact energy. The tests results show that the burst pressure decreases with increase in energy levels during impact loading. During the burst tests, several damage types named leakage and eruption were observed.