M.S. Abdul Majid

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.

Mechanical, thermal and morphological characterisation of 3D porous Pennisetum purpureum/PLA biocomposites scaffold

The mechanical, thermal, and morphological properties of a 3D porous Pennisetum purpureum (PP)/polylactic acid (PLA) based scaffold were investigated. In this study, a scaffold containing P. purpureum and PLA was produced using the solvent casting and particulate leaching method. P. purpureum fibre, also locally known as Napier grass, is composed of 46% cellulose, 34% hemicellulose, and 20% lignin. PLA composites with various P. purpureum contents (10%, 20%, and 30%) were prepared and subsequently characterised. The morphologies, structures and thermal behaviours of the prepared composite scaffolds were characterised using field-emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The morphology was studied using FESEM; the scaffold possessed 70-200μm-sized pores with a high level of interconnectivity. The moisture content and mechanical properties of the developed porous scaffolds were further characterised. The P. purpureum/PLA scaffold had a greater porosity factor (99%) and compression modulus (5.25MPa) than those of the pure PLA scaffold (1.73MPa). From the results, it can be concluded that the properties of the highly porous P. purpureum/PLA scaffold developed in this study can be controlled and optimised. This can be used to facilitate the construction of implantable tissue-engineered cartilage.

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.

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.

Qualification and lifetime modelling of fibreglass pipe

Abstract Procedures for qualifying fibreglass pipes are discussed here in relation to industry needs. The ultimate elastic wall stress (UEWS) test appears to provide an efficient means of rating pressure pipe, and indeed vessels, for the case where weepage failure occurs resulting from the accumulation of matrix cracks. The principle behind the UEWS test is to identify, from the pressure–strain response, a pressure level below which damage growth is either negligible or at least sufficiently low to avoid failure within the design life. The version of the UEWS test most often used involves the application of groups of 10 one‐minute pressure cycles at increasing pressure values, recording the hoop or axial strain. The onset of non‐linearity in the pressure–strain relationship can be accurately determined and enables a safe long term pressure level to be identified. The UEWS test appears to provide a desirable alternative to the currently used procedure laid down in ISO 14692, which involves an expensive series of long term constant pressure tests, as described in ASTM 2992, running for a period in excess of 10 000 h. It is shown here that the UEWS test reflects the cyclic fatigue behaviour of fibreglass pipe, but further work on the relationship between cyclic and static behaviour would be desirable. It has been shown that a Miners law approach is effective in modelling damage due to combined static and cyclic effects, and that damage can be directly related to matrix crack growth. This approach could form the basis of a future procedure for describing lifetime behaviour of glass reinforced epoxy pipes under any required combination of static, fatigue, hydrostatic and non‐hydrostatic (multiaxial) loading.

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.

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.

Strength of Adhesive T-Joint in Granulator Fluidization Bed at Elevated Temperature

This paper presents the results of an experimental investigation on mechanical characterization of adhesive T-joint in granulator fluidization bed at elevated temperature. This research aims to explore the suitability of adhesive bonding between stainless steel plate and perforated plate to replace plug weld in granulator fluidization bed. For this purpose, T-joint and bulk specimens were prepared for tensile loading tests, at different temperature. Measurement of the temperature-dependent of the tensile strength was conducted using thermostatic chamber attached to a universal testing machine for a range from room temperature to 100°C. The strength of adhesive T-joint decreases for temperatures over than 35°C. This is because at high temperature, the failure is determined by the changes of mechanical properties of adhesive. The results have shown that the strength of adhesive T-joint was affected by both temperature and bondline thickness. The objective of the present study was to examine a series of adhesively-bonded T-joints in tension at elevated temperatures between room temperature and 100°C having various bond thicknesses.