EFFECT OF WIRE-EDM CUTTING ON FATIGUE STRENGTH OF AZ61 MAGNESIUM ALLOY
Effect of wire electrical discharge machining (wire-EDM) cutting on fatigue strength of an extruded AZ61 magnesium alloy at room temperature was investigated. The surface condition of the samples after the wire-EDM cutting process is compared to the samples which have undergone careful polishing on their surfaces. A series of high cycle fatigue tests are performed on both the wireEDM as-cut and polished samples with constant amplitude stress at the frequency of 10 Hz. Fractographic analyses were conducted on the tested samples to identify the mechanism of fatigue fracture. The finding show that the fatigue limit of wireEDM as-cut specimen is 20 MPa lower as compared to smoothly polished specimens. Fatigue cracks are found to initiate and propagate to final failure from a cutting pit on the wire-EDM as-cut specimens.
The effect of thermal cycling on the properties of a carbon fibre reinforced magnesium composite
Abstract Effects of thermal cycling on mechanical properties of two unidirectional ultra-high modulus carbon fibre reinforced magnesium composites (P100S/AZ91D) have been investigated. Composite specimens reinforced with ∼50% or 60% fibre volume fraction were thermally cycled between the temperatures of 100 °C and −100 °C, in a vacuum, for up to 100 cycles. Mechanical testing showed there was no change in the bending strength of samples or the associated failure mode during cycling. Composites did, however, exhibit a moderate reduction in bending modulus and interlaminar shear strength during the first few thermal cycles. Little further degradation was observed thereafter. Modifications to the matrix microstructure were examined and related to a change in matrix properties measured via microhardness testing. Composite property degradation was attributed to the formation of microvoids and interfacial sliding in the early stages of cycling. The implications these processes may have on composite application are discussed and it is concluded that based on the limited dependence of mechanical properties to thermal cycling carbon fibre reinforced magnesium shows potential for space applications operating under transient thermal conditions.
Timber, its nature and behaviour
Preface. Acknowledgements. Chapter 1 - Structure of Timber. Chapter 2 - Appearance of Timber in Relation to its Structure. Chapter 3 - Mass Volume Relationships. Chapter 4 - Movement in Timber. Chapter 5 - Flow in Timber. Chapter 6 - Deformation Under Load. Chapter 7 - Strength and Failure in Timber. Chapter 8 - Durability of Timber. Chapter 9 - Processing of Timber. Index.