Effect of Temperature on the Tensile Strength and Failure Modes of Angle Ply Aramid Fibre (KRP) Tubes Under Hoop Loading

A comprehensive study was undertaken to characterise Kevlar reinforced plastic (KRP) angle ply filament wound tubes at different temperatures. Quasi-static burst tests were performed on tubes of 25°, 55° and 75° winding angle. The tubes were burst under internal radial pressure with minimum end constraints. An experimental rig and two conditioning tanks were designed and built to test the specimens at three temperatures; –46°C (low temperature) and +20°C (room temperature) and +70°C (high temperature). For each test the internal pressure and the strains in both circumferential and longitudinal directions were recorded on suitable digital processing equipment.For a particular batch of tubes tested at three different temperatures, an increase in ultimate hoop strain and a decrease in hoop modulus of the 55° tubes with increasing temperatures was recorded; the temperature effect was less pronounced on the corresponding properties of 25° and 75° tubes. The use of a non-structural thin liner during the tests led to a higher ultimate strength of 55° tubes but had negligible effect on the behaviour of 25° and 75° tubes. The 75° tubes failed in a catastrophic fibre fracture under all test conditions. The mode of failure of 55° changed from weeping at 70°C to fibre fracture at –46°C. The 25° tubes failed by weeping with matrix cracking. The matrix cracking was particularly severe when a liner was used.     

Effect of Temperature on the Tensile Strength and Failure Modes of Angle Ply CFRP Tubes under Hoop Loading

A comprehensive study was undertaken to characterise carbon fibre reinforced plastic (CFRP) tubes at different temperatures. Quasi-static burst tests were performed on tubes of 25°, 55° and 75° winding angle. The tubes were burst under internal radial pressure with minimum end constraints. An experimental rig and two conditioning tanks were designed and built to test the specimens at three temperatures; -46°C (low temperature), +20°C (room temperature) and +70°C (high temperature). For each test the internal pressure and the strains in both circumferential and longitudinal directions were recorded using a digital processing equipment.For a particular batch of tubes, tested at three different temperatures, a decrease in hoop strength and modulus of the 55° tubes with increasing temperature was recorded; the effect was less pronounced on the properties of 25° and 75° tubes. The use of a non-structural liner during the tests led to higher ultimate strength and strain of 55° tubes but had negligible effects on the behaviour of 75° tubes. The use of a liner in 25° tubes altered the mode of failure, resulting in a very large tube deformation with no noticeable increase in burst pressure. Micrographic analysis was also undertaken to study the failure mechanisms during pressurisation of lined and unlined tubes.     

Effects of preheating temperature on cold cracks,microstructures and properties of high power laser hybrid welded 10Ni3CrMoV steel

Laser hybrid welding has become one of the most promising welding methods for high strength low alloy steels due to combining the advantage of the laser and arc. A novel Y-groove cold cracking test adapted to laser hybrid welding is designed to assess the weldability of 10Ni3CrMoV steels at room temperature and different preheating temperatures. The experimental results show that the orientation of the predominant root cracks generally follows the contour of the fusion line. As the temperature increases from 25 °C to 150 °C, at first the root crack rate decreases and then slightly increases at 150 °C. The root crack rate obtained at 120 °C is the lowest. The fracture model changes from a brittle cleavage fracture to a mixture fracture with quasi-cleavage facets and dimples. The thermal cycle curves of laser hybrid welding obtained by temperature measurement systems are used to evaluate the crack resistance and microstructure transformation. The microstructures of welded joints obtained at different temperatures are analyzed by optical microscope (OM). The results reveal that the microstructures of the coarse grained region and the fusion zone at 120 °C have higher cold crack resistance and good impact toughness. Mechanical properties of the welded joint obtained at 120 °C and 150 °C are comprehensively evaluated by microhardness test, uniaxial tensile test and charpy V-notch impact test with side notches. Fractographs of the impact specimens are studied by scanning electron microscopy (SEM). The test results show that the welded joints obtained at 120 °C have satisfactory mechanical properties that can meet the technical requirements for shipbuilding industry.     

The impact behavior of aluminum alloy 6061: Effects of notch severity

In this paper the influence of notch acuity and test temperature on the impact behavior of aluminum alloy 6061 is presented and discussed. Notch angles of 45°, 60°, 75° and 90° were chosen for a standard charpy impact test specimen containing two such notches positioned at right angles to the applied load. For a given angle of the notch the dynamic fracture toughness increased with an increase in test temperature. At a given test temperature, the impact toughness of a ductile microstructure decreased with an increase in notch severity. For the least severe notch dynamic fracture surfaces revealed the occurrence of localized mixed-mode deformation at the elevated temperature. An increase in notch severity resulted in essentially Mode-I dominated fracture at all test temperatures. The results are discussed in light of alloy microstructure, fracture mechanisms and deformation field ahead of the advancing crack tip.     

Temperature and Rate Effects on GRP Tubes Under Tensile Hoop Loading

A comprehensive study was undertaken to characterise glass fibre reinforced plastic (GRP) tubes at different temperatures and strain rates. The tests were performed on tubes of 25°, 55° and 75° winding angle. The tubes were burst under internal radial pressure with minimum end constraints. Two separate rigs were used, one for the static and the other for the dynamic tests. The tests were carried out at three temperatures; –46°C (low temperature), +20°C (room temperature) and +70°C (high temperature). For each test the internal pressure and the strains in both circumferential and longitudinal directions were recorded on suitable digital processing equipment. For a particular batch of tubes tested at three different temperatures, there is in general a decrease in hoop strength with increasing temperature during quasi-static tests. The use of a non-structural liner during such tests led to an increase in ultimate hoop strain of 55° tubes, especially at high temperature. The corresponding increase in ultimate hoop strain was markedly less in the case of 75° and almost negligible in the case of 25° tubes. Testing the tubes at high strain rates resulted in substantial increases in burst strength and ultimate hoop strain as compared with the quasi-static and low strain rate values. The mode of failure of 75° tube is a catastrophic fibre breakage under all test conditions. The mode of failure of 55° tube is a combination of weeping and fibre failure. The 25° tubes are characterised by matrix failure, which is very severe at high strain rates.     

Validation of pure shear test device using finite element method and experimental methods

In this paper, we will validate the Iosipescu shear test (IST) and the Hawong Iosipescu shear test (HIST) used for the pure shear test device; the HIST is modified from the IST. This validation uses finite element method and experimental method. In the IST the loads are applied on the outside edges of the specimen, while in the HIST the loads are applied on the neutral surface of the specimen. It has been certified that HIST is more effective than IST because of the simplicity of the loading device, loading method and the distribution of pure shear stress, etc. We know that the specimen with a 110° V-notched angle is more effective than the specimen with a 90° notched angle for a pure shear test device. In specimens with a 90° notched angle, the maximum shear stress occurs at the end of V-notch. While in specimens with a 110° notched angle, it is produced at the center of specimen. In both HIST and IST the most ideal ratio of a/b is 0.3 although the ratios of 0.3, 0.4, 0.5 of a/b are also useful, except for 0.2. When HIST or IST is under mode fracture, HIST or IST with β=90° is more effective than those with β=0°, as a pure shear test device.     

A combined cryostat/oven and specimen transfer device for tensile testing in the range 83 to 473° K

Design details and performance of a combined cryostat and oven for an Instron TT-CM universal testing machine are described. The cryostat is suitable for tensile testing in the range 83 to 473° K and has a test chamber 5.5 in. × 5.5 in. and 20 in. deep which could be used for testing specimens 7 in. wide. Special attention is drawn to the ease of specimen insertion which may be performed while the cryostat is cold. The temperature within the test chamber is controlled, by admitting dry air, to ± 1 ° C of any desired test temperature for periods of at least 20 min.A specimen transfer device is also described for transferring a pretreated specimen at –26° C to the cryostat with a temperature rise of less than 1 ° C. The transfer device provides a method of rapid specimen insertion once the cryostat is cold.     

An acoustic emission energy analysis and its use to study damage in laminated composites

A new technique which uses the output of a true RMS voltmeter to measure the acoustic emission energy output of a transducer is presented. To demonstrate its use in a typical case, this procedure is used to measure acoustic emission energy during tensile tests on [0°/±30°/90°]_s glass-epoxy laminate uniaxial and 10° off-axis tensile coupons. The test results were compared with numerical predictions of laminate response and acoustic emission energy. The experiments indicate that acoustic emission energy can be used to indicate the onset of ply and interlaminar failure.     

Characterization of the in-situ non-linear shear response of laminated fiber-reinforced composites

A simple procedure to determine the non-linear in-plane lamina shear response of laminated composites is presented. Using the ±45° symmetric laminate tensile test results, in conjunction with computational micromechanics, a method was developed and validated to characterize the lamina shear response and the in-situ matrix shear response. Load, and axial and transverse strains measured in the tests were used to calculate the non-linear shear stress–shear strain response of the composite. From this result, the in-situ matrix equivalent stress–strain response was obtained, with some simplifying assumptions, and subsequently used in a micromechanics-based representative finite element (FE) model of the ±45° symmetric laminate tensile test to determine the accuracy of the non-linear response of the in-situ matrix. Results from the FE model of a representative cell (RC) that depicts fiber diameter, fiber volume fraction (V_f) and angled fiber packing of the ±45° symmetric laminate were found to match the tests result well. Thus, the procedure to extract the non-linear lamina shear response and the non-linear in-situ matrix response from the ±45° symmetric laminate tensile test was validated.     

Fracture strength of melt-infiltrated SiC-mullite composite

The fracture strength of a melt-infiltrated SiC-mullite composite was measured from room temperature to 1500°C using a three-point bending test. The strength under argon at atmospheric pressure was not high. Mullite decomposition was found to be severe even at 1100°C in a reducing atmosphere, thus significantly degrading its strength. The strength in air, where the decomposition was suppressed, was moderately high and retained up to 1100°C. The composite revealed typical brittle failure up to the highest investigated temperature of 1500°C, with an indication of failure by slow crack growth at high temperature.     

Austenitizing treatment influence on the electrochemical corrosion behavior of 0.3C-14Cr-3Mo martensitic stainless steel

Effects of austenitizing treatment temperatures on aqueous corrosion properties of martensitic stainless steels were investigated by electrochemical tests (potentiodynamic test, potentiostatic test and electrochemical impedance spectroscopy), and surface analyses (optical microscopy and XRD). The results of potentiodynamic test revealed that the breakdown potential increased with the increased austenitizing temperature, indicating increased relative resistance to initiation of localized corrosion. EIS measurements showed that MSS3 (1030 °C) exhibits larger polarization resistance value than MSS1 (970 °C) and MSS2 (1000 °C) at passive and breakdown states. This was caused by decreasing the amount of Cr-rich M₂₃C₆ carbide which acts as preferential sites for pitting corrosion.     

Incipient melting of Al5Mg8Si6Cu2 and Al2Cu intermetallics in unmodified and strontium-modified Al–Si–Cu–Mg (319) alloys during solution heat treatment

The present work was performed on seven alloys containing in common Al–6.5 wt%Si–3.5 wt%Cu, with magnesium in the range 0.04–0.45 wt%, and strontium in the range 0–300 p.p.m. The alloys were cast in the form of tensile test bars, solution heat treated in the temperature range 480–540°C for times up to 24 h. Two types of solution heat treatment were applied: (i) single-stage, where the test bars were solution treated at a certain temperature for 12 h prior to quenching in hot water (60°C); (ii) two-stage, where the test bars were solution treated for 12 h/510°C+12 h/T°C (T=510, 520, 530, 540°C), followed by quenching in hot water. In the low-magnesium alloys (i.e. with Mg0.04 wt%), melting of the Al2Cu phase commenced at 540°C. Increasing the magnesium content to 0.5 wt% reduced the incipient melting temperature of the Al5Mg8Si6Cu2 phase to 505°C. The mechanism of incipient melting and its effect on the tensile properties have been discussed in detail. © 1998 Chapman & Hall     

Textile composite double dome stamping simulation using a non-orthogonal constitutive model

Stamping is one of the most effective ways to form textile composites in industry for providing high-strength, low-weight and cost-effective products. This paper presents a fully continuum mechanics-based approach for stamping simulation of textile fiber reinforced composites by using finite element (FE) method. A previously developed non-orthogonal constitutive model is used to represent the anisotropic mechanical behavior of textile composites under large deformation during stamping. Simulation are performed on a balanced plain weave composite with 0°/90° and ±45° as initial yarn orientation over a benchmark double dome device. Simulation results show good agreement with experimental output in terms of a number of parameters selected for comparison. The effects of meshing and shear moduli obtained from bias extension test and picture frame test on forming simulation results are also investigated.     

Porous ceramic lamellae for orthodontic ceramic brackets: Part II In vitro performance testing

This study was undertaken to test a new and original orthodontic bracket base, consisting of a porous lamella, which was designed to facilitate removal of ceramic brackets from the enamel surface after treatment. In the phase of the study presented here, two types of lamella and the adhesive resin used to bond them to brackets and teeth, were evaluated in vitro. Two types of test were carried out on bracketed teeth. The tensile bond strength was measured for specimens that had been either kept in water for 24 h at 37°C or subjected to 18000 cycles in water between 6°C and 55°C. The stress required to remove brackets with debracketing pliers was measured and the mode of failure recorded for specimens that had been kept in water for 24 h at 37°C. The results indicate that bracket/lamella assemblies can be bonded to enamel sufficiently strongly for clinical application and can be safely removed without damage to enamel.     

Mixed Bending-Tension (MBT) test for mode I interlaminar and intralaminar fracture

A new Mixed Bending-Tension (MBT) test is proposed for mode I fracture of laminated composites. The MBT specimen consists of a relatively small pre-cracked laminate adhesively bonded to pin-loaded steel beams. This design reduces significantly the bending stresses that prevent successful application of DCB tests to certain laminates. The MBT was here applied to carbon/epoxy unidirectional [0°]₂₆ and [90°]₂₆ laminates with starter delaminations. Interlaminar initiation G_IC values of [0°]₂₆ laminates agreed well with previous DCB test results, while [90°]₂₆ laminates exhibited 50% higher values. Significant lengths of fairly planar intralaminar crack propagation were seen in the latter laminates. The results showed a fibre bridging related R-curve, which was more pronounced in [0°]₂₆ laminates. The consistency of the present results indicates that the MBT opens new possibilities for the interlaminar and intralaminar mode I fracture.     

An experimental study on the effect of tow variations on compressive characteristics of plain weave carbon/epoxy composites under compressions

The effect of tow deformation on the static and fatigue characteristics of fabric composites under compression was investigated by experimental approach. Sheared specimens made of plain weave carbon/epoxy prepregs were prepared using a picture frame rig and the shear angles were 0°, 16°, 26°, 34°, 46°. To verify the effect of the tow variations of the fabric composites on compressive characteristics, the unidirectional composite specimens composed of the same fibre and matrix system with the same stacking sequences as the fabric composites were prepared for comparison. The static compressive test results showed that the static compressive strength of sheared fabric specimens was lower than that of the unidirectional specimens with the same stacking angle. On the other hand, the fatigue test results showed that fatigue life of sheared fabric specimens was higher than that of the unidirectional specimens for mild shear deformation cases. It was proved that these results were fully affected by the tow deformation caused by the shear deformation of the fabric specimens. The compression–compression fatigue behaviours of sheared fabric specimens were verified by appropriate unit-cell models.     

Short-term flexural creep deformation in synroc-C

The flexural creep behaviour of synroc-C in an inert atmosphere was studied at temperatures of 860°C, 900°C and 940°C under constant-load conditions in four-point bending. Applied stresses ranged from 100 to 160 MPa. Individual creep curves show primary and secondary creep but little or no tertiary creep stage. The log of the creep rate was found to increase linearly with log of the applied stress at each temperature over the entire stress range. Analysis of the creep data using the Norton power-law function revealed that the stress exponent decreased from 3.3 ± 0.6 for the 860°C and 900°C data to 2.0 ± 0.2 for the 940°C data, and an activation energy of 440 ± 40 kJ/mol was obtained over the entire temperature and stress range. Comparative analysis with the theta-projection equation was found to adequately represent the data yielding an activation energy of 464 kJ/mol while also showing a trend for the stress exponent to decrease with increasing temperature. Microstructural examination revealed extensive cavitation on the tensile surface of the creep specimens subjected to higher stresses at 900°C and 940°C. Dynamic high temperature X-ray diffraction analysis indicated little change in the phase assemblage apart from a slight reduction in the amount of the hollandite phase at higher temperatures which was attributed to a minor amount of oxidation. The possible creep damage mechanism was explored with reference to creep test results and microstructural modifications and the implications of the observations are discussed.     

Factors influencing softening temperature and hot-strength of geopolymers

This paper presents the effects of cation type, silicate concentration, compositions of low-calcium fly ash and test load on softening temperature and hot-strength (loaded while at high temperature) of fly ash-based geopolymers. It was found that softening temperature (T_s) of sodium (Na) based-geopolymer remained the same (610 °C ± 20 °C) regardless of the silicate concentration, fly ash composition, and test load. However, when the cation was changed from sodium to potassium (K), the T_s increased to 800 °C. Further, when Na/K is mixed, the T_s dropped to 570 °C.Significant increases in hot-strengths (at 530 °C and 730 °C) were found in all geopolymers. This increase in strength was observed to be in conjunction with heat release, indicating an exothermic reaction. Since the reaction between fly ash and activators is exothermic, this reaction is believed to be the reason for the strength gain at high temperatures.     

Low-velocity impact response of non-woven hemp fibre reinforced unsaturated polyester composites: Influence of impactor geometry and impact velocity

In this study, the influence of varying impactor geometries on the impact damage characteristics of hemp fibre reinforced unsaturated polyester composites were subjected to a low-velocity impact loading using an instrumented falling weight impact test setup. The three varying tup geometries: hemispherical, 30° and 90°, at four different impact velocity levels: 2.52 m/s, 2.71 m/s, 2.89 m/s and 2.97 m/s were assessed. The experimental results to investigate the influence of impactor geometry suggest that HFRUP composites were able to withstand higher loads when tested with hemispherical impactor and also absorbed more energy than that for 90° and 30° shaped tup geometry. The post impact damage patterns and failure mechanisms of impacted samples were further characterised by ultrasonic (UT) inspection. Impact induced damage characterised by scanning electron microscope (SEM) suggests that damage induced by the impact included a typical failure mechanisms showing matrix cracking, fibre breakage and fibre pullout. As the impact velocity increases the damage to back face of the laminate increased for laminates tested with a hemispherical impactor while it decreased to certain extent for laminates tested with 90° and 30° impactor geometries.     

Influence of recycled glass content and curing conditions on the properties of self-compacting concrete after exposure to elevated temperatures

The aim of this paper is to assess the performance of self-compacting glass concrete (SCGC) after exposure to four elevated temperatures of 300 °C, 500 °C, 600 °C and 800 °C. The influence of curing conditions on the high temperature performance of SCGC was also investigated. For each curing regime, five SCGC mixtures were prepared with recycled glass (RG) which was used to replace natural fine aggregate at the level of 0%, 25%, 50%, 75% and 100%. After exposure to the elevated temperatures, concrete mass loss, density, water porosity, ultrasonic pulse velocity (UPV) and water sorptivity were determined and then a compressive strength test was conducted. The test results indicate that regardless of the exposure temperature, all the water cured specimens had higher residual strengths and mass losses while the water porosity and water sorptivity values were lower as compared to the corresponding air cured specimens. The incorporation of RG in the concrete mixes helped to maintain the concrete properties after the high temperature exposure due to the melting and resolidification of the recycled glass in the concrete matrix.