Strength Of Composite Samples Research Articles

Mechanical properties of oil shale-coal composite samples

In this study, uniaxial compression tests were conducted on the composite samples of coal and oil shale characterised by high strength and low elastic modulus. Their fracturing and failure propagation processes were monitored by an acoustic emission (AE) device and a digital video camera. The strength, macro-failure initiation (MFI) and failure characteristics of composite samples are analysed. Differences in mechanical properties between the coal and oil shale influence the stress states near the interface area, resulting in strength increasing in the coal and strength decreasing in the oil shale. Strength characteristics of composite samples mainly depend on the strength σC of the coal far away from the interface, which is influenced by the coal's original defects and interactions with the oil shale. The large deformation of oil shale reduces the damage accumulation in the coal and the strengths of relatively intact composite samples are greater than σC; in contrast, the strengths of composite samples with more coal's original defects are low and less than σC. MFI occurs within the coal, causing a step-wise stress change accompanying the peak signal of the energy index and representing the beginning of macro-failure in composite samples. MFI models include the tensile fractures of coal near the interface, initiation and propagation of coal's original cracks, and surface spalling between coal's original cracks. The local ejection or surface spalling failure in the coal induces the chain destruction of its peripheral parts to form a large ejection or surface spalling failure zone. Finally, the coal displays the splitting ejection failure or shear failure along the original crack surface. The oil shale is destroyed through the tensile failure or mixed failure by crack propagation in the coal.

Stabilization treatment of a dispersive clayey soil using granulated blast furnace slag and basic oxygen furnace slag

Dispersive clays may pose considerable distress if not adequately taken care of. On the other hand, the treatment of problematic soils with waste materials has been recently proved to be a useful option from economic and environmental view point. Hence, in this research, the potential use and effectiveness of dispersive soil stabilization using two types of industrial by-product, including granulated blast furnace slag (GBFS) and basic oxygen furnace slag (BOFS) were investigated. The slags were separately added (ranging from 2.5 to 30%) to a laboratory dispersed sample and a set of experiments were performed to study the physicochemical, mechanical and microstructural changes of the stabilized soil. The results indicate that the soil dispersion can be eliminated upon adding 10% BOFS. This is attributed to the exchange of interlayer sodium ions on the clay surfaces by multivalent cations from the agent. Besides, an increase in the ion concentration of soil-additive mixtures induces a more depression of the diffuse double layer that decreases the soil dispersivity potential. With increasing the curing time, an improvement in the strength of composite samples is observed. The formation of cementitious compounds due to the pozzolanic reactions is responsible for such a treatment, as confirmed by the XRD analyses and SEM micrographs. It appears that the GBFS has a lower activity as compared to BOFS, therefore causes less influence on the soil engineering parameters and a higher percentage (20–25%) of GBFS is required to govern soil dispersion. Overall, utilization of the studied slags particularly of BOFS is very effective to overcome the problems associated with dispersive soils.

Fracture behaviour of SiC monofilament reinforced copper – an acoustic emission study

SiC monofilament-reinforced copper is a potential heat sink material for the divertor of future fusion reactors, where heat loads up to 15 MW/m2 must be removed. The composite combines high mechanical strength (300 MPa at 300℃) with sufficient thermal conductivity (at least 200 W/mK) at temperatures up to 550℃. The bonding between fibres and matrix is essential for the mechanical behaviour. We investigated two different fibre types (SCS0 and SCS6, Specialty Materials Inc.) with different interlayers in a galvanic copper matrix. Tensile tests in combination with acoustic emission analysis showed the dependence of fracture behaviour of the composite material on the fibre type. The average ultimate tensile strength of composite samples with 20% fibre reinforcement was in the range of 600 MPa, with a Young's modulus of 160 GPa. The tensile tested composite with SCS6 fibres generated roughly twenty times the number of acoustic emission events in comparison with the SCS0 fibres composite. Acoustic emission events in tensile test specimens with SCS6 fibres are correlated with the failure of the carbon-enriched surface layer of the fibre. In the case of SCS0 fibre-reinforced specimens, acoustic emission events were only caused by fibre failure. Fracture area analysis after tensile tests showed the failure of the SCS6 fibres at the interface between the two outer carbon layers and no interface failure for the composite with SCS0 fibres.

Effects of Accelerated Aging Period of Time at 180°C on Tensile Property of Plain Woven Fabric/Epoxy Resin Laminated Composites

In this paper, carbon fiber reinforced resin matrix composites were produced by stacking eight pieces of carbon fiber woven plain fabric and subjected to accelerated ageing. Accelerated ageing was carried out in oven at 180°C for three different time intervals (60 hours, 120 hours and 180 hours). The influence of different ageing time intervals at 180°C on tensile properties of laminated composites was examined, compared with the composites without aging. The appearance and damage forms of these laminated composites were investigated. The results revealed that the tensile strength of the laminates declined significantly after long term accelerated aging at 180°C. The average tensile strengths of composite samples aged 60 hours, 120 hours, and 180 hours period of time at 180°C are 80.36%, 79.82%, 76.57% of average tensile strength of composite samples without aging, respectively. The high temperature accelerated aging makes the resin macromolecular structure in the composites changed, and then the adhesive force between fiber bundles and resin declines rapidly which result in the tensile strength of composites aged decrease. This research provides a useful reference for long term durability of laminated/epoxy resin composites.

Effects of Accelerated Aging Period of Time at 150°C on Tensile Strength of 3-Dimension-4-Direction Braided/Epoxy Resin Composites

In this paper, the tensile strength of 3-dimension-4-direction braided/epoxy resin composites after accelerated aging for different period of time at 150°C was investigated. The tensile tests of 3-dimension-4-direction braided/epoxy resin composite samples without aging and aged 60 hours, 120 hours, 180 hours, at 150°C were carried out. The damage forms of braided composite samples tested were investigated. The experiment result indicates that the accelerated aging process at 150°C has some effect on the tensile strength of braided composite samples. The average tensile strengths of composite samples aged 60 hours, 120 hours, and 180 hours period of time at 150°C are 92.44%, 91.62% and 84.91% of average tensile strength of braided composite samples without aging, respectively. This means that the tensile strength will be decreased when the aging period of time increases at 150°C. The damage form of samples tested shows that when accelerated aging, the resin in the composite samples is damaged, which makes the adhesive force between fiber bundles and epoxy resin decline, so that the ability of fiber and resin bearing the tensile load together decreases.

Effects of Accelerated Aging Period of Time at 180°C on Tensile Strength of 3-Dimension-4-Direction Braided/Epoxy Resin Composites

The tensile strength of 3-dimension-4-direction braided/epoxy resin composites after accelerated aging for different period of time at 180°C was investigated. The tensile tests of 3-dimension-4-direction braided/epoxy resin composite samples without aging and aged 60 hours, 120 hours, 180 hours, at 180°C were carried out. The damage forms of braided composite samples tested were investigated. The experiment result indicates that the accelerated aging process at 180°C has obvious effect on the tensile strength of braided composite samples. The average tensile strengths of composite samples aged 60 hours, 120 hours, and 180 hours period of time at 180°C are 86.29%, 88.59% and 84.12% of average tensile strength of braided composite samples without aging, respectively. This means that the tensile strength of aged braided composites will be decreased. The damage form of samples tested shows that after aging for a long time at 180°C, the resin is damaged badly and becomes brittle which make the bonding force between fiber and resin decrease. This is the reason of the decrease of tensile strength of composites after accelerated aging at 180°C.

Effects of Accelerated Aging Period of Time at 150°C on Tensile Property of Plain Woven Fabric/Epoxy Resin Laminated Composites

The purpose of this paper is to investigate the tensile property of laminated epoxy resin composites reinforced by carbon fiber plain woven fabric after accelerated aging for different period of time at 150°C. For this purpose, the tensile tests of laminated resin composite samples without aging and aged 60 hours, 120 hours, 180 hours, at 150°C were carried out. The damage forms of composite samples tested were investigated. The experiment result indicates that the accelerated aging process has an obvious effect on the tensile strength of composite samples. The average tensile strengths of composite samples aged 60 hours, 120 hours, and 180 hours period of time at 150°C are 87.31%, 88.61%, 79.05% of average tensile strength of composite samples without aging, respectively. The observation of the damage form of samples tested shows that when accelerated aging, the resin in the composite samples is damaged and the adhesive force between fiber bundles and epoxy resin decline, which makes the ability of fiber and resin bearing the tensile load together decreases.

Composites consisting of poly(ε-caprolactone) and cellulose fibers directly molded during polymerization by yttrium triflate

Composite samples consisting of poly(e-caprolactone) (PCL) and cellulose fibers (CF) were prepared by the direct molding method during polymerization from e-caprolactone (CL) monomers. CL liquid was mixed with yttrium triflate as a catalyst and 2-propanol as an initiator. CF was easily added to CL liquid and was homogeneously mixed with CL liquid by this method. The mixture was put into a plastic tube. Heating temperature varied from 60 to 120 °C and heating time varied from 6 to 48 h. CF content varied from 0 to 30 wt%. After cooling, the sample was removed from the tube and cut into a column shaped specimen. PCL composites with CF dispersed homogeneously were obtained. The mechanical properties such as elastic modulus and strength of these PCL composites with CF were measured by compression test using the above specimen. The maximum values of modulus and strength of composite samples are the maximum values 654 and 13 MPa, when fiber content was 34% and these values are greater than those of PCL samples without CF. The biodegradability of PCL composites in an aqueous medium with commercial compost was evaluated measuring the biochemical oxygen demand (BOD). The biodegradability of composite samples was not affected by the presence of CF.