Fatigue Behaviour of Connectors used in Cable Harnessing through Cavity Formation Related Microstructural Degradation: A Failure Investigation Perspective

Two separately failed electrical connector pieces during a vibration test were received for failure analysis. Chemical composition, hardness values and microstructures of the each of the connector material indicate that the material of construction is a die cast aluminium-silicon type of alloy, closely matching with the standard ANSI/AA B380 alloy. Intergranular and faceted fracture features are observed and failure mechanism is found to be fatigue dominated. The connectors failed by impact fatigue arising out of the loosening of the connector assembly. This has happened by cavity formation and/or growth related microstructural degradation processes. Initial casting pores as well as microstructural degradations such as interconnected pores have developed in service and their successive growth, decohesion and interconnection of each of primary Si particles and Al-Fe-Mn precipitates (along precipitate-matrix interface) have led the initiation of the crack under fatigue loading. Brittle as-cast microstructure (as typified by the precipitate-matrix interfacial cracking), existing vibratory loading and absence of any rise in temperature in the system have assisted the initial cavity (crack) formation and/or growth. Moreover, initial fitment related looseness is an additional factor in initiating and propagating this damaging mechanism.

Correlation Between Microstructure and Fracture Behavior in Thick HARDOX 450 Wear-Resistant Steel With TiN Inclusions

This work investigates the correlation between TiN inclusions and microstructural properties of HARDOX 450 steel using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron backscattered diffractometer (EBSD) methods. Some amount of microsized TiN inclusions were formed in the temperature range of the solid–liquid zone; however, they exhibited fracture features of deep dimples rather than a cleavage plane, which is closely related to the ability of the microstructure to arrest cracks. Upon tensile loading, a single microcrack first appeared inside the microsized TiN inclusions, and then, multiple microcracks formed, parts of which widened in the direction of tensile stress. A schematic mechanism map was plotted to reveal the propagation behavior and fracture mechanism of the microcracks in the TiN inclusions.

Microstructural Features of Freezing and Thawing-Creep Damages for Concrete Mixed with Fly Ash

The macroscopic morphology characteristics, pore structure characteristics, and microfracture morphology of concrete with fly ash subjected to the freeze-thaw-creep effect were analyzed via scanning electron microscopy (SEM). The results revealed that the macrosection of a specimen subjected to freeze-thaw cycling evolves from a regular to an irregular morphology in which the degree of fragmentation increases. Four specimen pore structure types characterized by single holes, nonconnected hole clusters, connected hole clusters, and fly ash holes, respectively, were identified. The microfracture morphology of the concrete was found to include five types of brittle fractures—river, step, cascade, hemispherical, and irregular patterns—and two types of ductile fractures—dimple and peak forest patterns. Two sets of experiments in which (1) the fly ash content ( m = 35 % ) was kept constant and the number of freeze-thaw cycles increased, and (2) the number of freeze-thaw cycles ( n = 120 ) was kept constant, and the fly ash content was increased were carried out. In both cases, the number of connected hole clusters increased and a surrounding skeleton structure with a needle filamentous or flaky appearance was produced. In addition, the degree of deterioration of the pore structure increased and the fracture features changed from brittle to ductile.

Chemical-heat treatment influence on thermal stability of microstructure, mechanical properties and fracture features of V-Cr-Ta-Zr alloy

A study of the features of structural-phase state, thermal stability, mechanical properties characteristics and fracture features of V-Cr-Ta-Zr alloy after chemical-heat treatment by the method of nonequilibrium internal oxidation has been carried out. It has been established that, in contrast to chemical-heat treatment in a defect state, the effect of oxygen when introduced into a material with a stabilized structure is observed only at high concentrations. At such oxygen concentrations, which ensure the maximum binding of Zr into particles based on ZrO2, the alloy under study demonstrates a high level of thermal stability and strength properties. These effects are associated with the implementation of disperse strengthening according to the Orowan mechanism by nanosized ZrO2 particles characterized by high thermal stability. The concentration and nature of the distribution of oxygen predetermine the spatial distribution of nanosized ZrO2 particles formed during chemical-heat treatment, which manifests itself in fracture features of the material at different temperatures.