Authors: Ivo Dlouhý, Zdeněk Chlup, Aldo Roberto Boccaccini
Abstract: A number of examples exist that indicate the potential for increasing the toughness of brittle matrices by dispersing different reinforcements. For further development of these advanced materials the actual material response during mechanical loading under presence of flaws appears to be important. Theoretical and experimental knowledge acquired on different kinds of brittle matrix composites is summarised in the paper. These include glass matrix composites with metallic particles, alumina platelets, continuous SiC (Nicalon®) fibres, and both chopped fibres and ZrO2particles (hybrid composites). The composites were tested in as-received state but also after different forms of thermomechanical loading, e.g. thermal shock, thermal cycling in air, which were investigated according to the envisaged composites application. Chevron notch technique was mainly used for fracture toughness evaluation. Microstructural damage is explained based on identified fracture micromechanisms.
Authors: Sabbah Ataya, Marcus Korthäuer, Essam El Magd
Abstract: Copper reinforced by tungsten particles has high potential applications in the fields of
electronics and electric contacts where high strength accompanied with good electrical conductivity is
required. The effects of different scaling parameters (deformed volume, tungsten volume fraction and
the tungsten particle size) affect the force needed for the machining of the W/Cu particle reinforced
W/Cu composites with different weight percentages of tungsten (80, 70 and 60 wt.%) were tested
under compression loading. Different sizes of the compression specimens were tested; the specimen
diameter DS was varied to be 1, 2, 4, 6 and 8 mm. The effect of the tungsten particle size was varied to
be 10 and 30-m. The compression tests were done at strain rates of 0.1s-1. The experiments were
carried out within a temperature range from 20 °C to 800°C. The mechanically tested specimens were
metallographically investigated to determine the degree of deformation of the tungsten particles in
different specimen geometries.
A clear dependence of the flow stress on the volume of the deformed specimens and the tungsten
volume fraction was found. This size effects were more obvious with increase of the tungsten volume
fraction at lower temperatures. The metallographic investigation was helped to understand the
observed size effect of the composites in relation to the volume fraction and the specimen size
Authors: Yan Jun Chang, Ke Shi Zhang, Hui Juan Hu, Gui Qiong Jiao
Abstract: The various damage mechanisms in 3D-C/SiC composites are identified using acoustic emission (AE) signal parameters, and the Felicity effect is studied on different unloading stress. As a result, the damage mechanisms in 3D-C/SiC composites can be identified successfully by the amplitude, average frequency and relative energy, and there are several damage modes together during uniaxial tensile process. The Kaiser effect is almost absent and the Felicity ratio fluctuates at 0.95 on lower stress stage and drops when the relative stress is above 65%.
Authors: Rupa Dasgupta, Satyabrata Das, Amol Kumar Jha
Abstract: Metal Matrix Composite made from Al-7075 based alloy dispersed with 10% SiC particles through the liquid metallurgy route were evaluated for their sliding wear properties under different loads and for a length of sliding distance. The volume loss and wear rate under different experimental conditions were compared between the following conditions for both the alloy and composite (i) cast (ii) aged (iii) extruded. Attempts have been made to arrest wear of the alloys that experience seizure under the mildest of experimental conditions through the above processing techniques and explain the experimental results through worn surface studies. The extent of success attained through each process has been discussed. It is felt that the cumulative effect of the different processing techniques including composite making, ageing and extrusion can open up new avenues for this alloy system, which in general is not used for wear resistant applications.
Abstract: In the present investigation, resin transfer molding has been used to produce high quality carbon fiber epoxy composites and nanotube-reinforced carbon fiber epoxy composites. To study the influence of carbon nanotubes (CNTs) on improving the mechanical properties and fatigue life, the tension-tension fatigue test has been carried out on those two kinds of material in the fiber direction. The damage mechanism in the fiber directions was analyzed by X-ray radiography and electron microscopy. The results show that CNTs pulled out, rapture and bridged cracks during the test, the results also show that CNTs possess an obvious potential on improving the property of carbon fiber epoxy composite, especially for properties that dominated by matrix.