Advanced Materials Research Vols. 891-892

Abstract: Ferrite-pearlite steel is the most widely used material for railway wheel. However, such wheel steel can not meet the strict demands for rolling contact wear and fatigue resistance with the rising speed and weight of traffic. The aim of this paper is to improve the rolling contact wear and fatigue resistance of wheel steel by laser dispersed treatment. Such treatment creates isolated glazed regions on the surface layer of wheel steel, which are composed of fine martensite and retained autensite and have an avera0ge hardness of 762HV_0.3. Compared with the conventional laser surface treatment technologies, such as laser hardening, laser melting, or laser cladding, which have been applied for improving rolling contact wear and fatigue resistance of wheel/rail, the multiple overlapping laser tracks that cause the premature failure are avoided by laser dispersed treatment. The wear rate and rolling contact fatigue life of treated and untreated wheel steel were evaluated and compared by Amsler twin-disc testing machines in dry and lubricated condition, respectively. The test results show that laser dispersed treatment improves the rolling contact wear and fatigue resistance of wheel steel. The stable wear rate of the laser treated wheel steel is about 0.3 times that of untreated wheel disc and the average rolling contact life of treated wheel steel is about double that of the untreated steel. Further investigations show that the glazed regions suppress the plastic deformation of wheel steel. This inhibits the treated wheel steel from delamination wear and delays the formation of fatigue crack initiation.

Abstract: Aircraft structural design and manufacture is moving towards lighter structures that have extended lives and improved damage tolerance. Hybrid structures are a possible solution to improve damage tolerance. They are a combination of metallic structure locally reinforced with adhesively bonded damage tolerant straps. In the present study a 3D finite element model has been developed with a bond line delamination growing under a fatigue law. A series of fatigue delamination tests on bonded aluminium were performed to provide input data. An iterative model for crack and debonding growth was developed to describe how debonding influence crack stress intensity and crack profile, which in turn influence debonding. The model predicts decrease in stress intensity on the bonded face and an overall retardation of fatigue crack growth rates. The stress intensity factor was predicted to vary through the thickness of the substrate due to the phenomenon of secondary bending and also the bridging effect caused by the presence of the reinforcing strap.

Abstract: This paper presents a preliminary investigation into the effect of incipient heat damage on the mechanical properties of a carbon-epoxy composite. Specimens were exposed to a range of temperatures varying from 0°C to 280°C for one hour and then tested to quantify the effects of this high temperature exposure on the short-beam shear, Mode I and II interlaminar fracture toughness, and the Mode I fatigue properties. The results showed that as the exposure temperature increased, the short-beam shear suffered a reduction, whereas the Mode I and Mode II fracture toughness increased after an initial reduction. The fatigue disbond growth rates were largely un-affected under heat exposure below 280°C. This complex behaviour in the degradation in fracture toughness is likely due to the increased fibre bridging brought about by the reduction in matrix strength.

Abstract: The AA7050 aluminum alloy is widely used due to its low specific combined with high strength and toughness obtained from the heat treatment which involves solution treatment and ageing. It produces the mechanism of precipitation hardening of a thin phase and disperses. In this context, the present study to investigated three ageing treatments, their influence on fatigue crack growth. In order to find a better condition of precipitation of η' phase, which may increase resistance to fatigue crack growth of AA7050 aluminum alloy. The T614-65 condition was chosen as an alternative treatment in relation to T7451 and T6 conditions of current use in the industry. The fatigue crack growth rate results have shown that T614-65 fatigue strength were up to 14% higher than the shown for T7451 temper.