Topic
Fractography
About: Fractography is a research topic. Over the lifetime, 5043 publications have been published within this topic receiving 86068 citations.
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TL;DR: This guidance document will contribute to a more accurate use of fractography and help researchers to better identify, describe and understand the causes of failure, for both clinical and laboratory-scale situations.
122 citations
TL;DR: The structural fatigue of Ni-Ti wires was investigated using bending-rotation fatigue (BRF) tests, where a bent and otherwise unconstrained wire was forced to rotate at different rotational speeds as discussed by the authors.
Abstract: The structural fatigue of pseudoelastic Ni-Ti wires (50.9 at. pct Ni) was investigated using bending-rotation fatigue (BRF) tests, where a bent and otherwise unconstrained wire was forced to rotate at different rotational speeds. The number of cycles to failure (N
f
) was measured for different bending radii and wire thicknesses (1.0, 1.2, and 1.4 mm). The wires consisted of an alloy with a 50-nm grain size, no precipitates, and some TiC inclusions. In BRF tests, the surface of the wire is subjected to tension-compression cycles, and fatigue lives can be related to the maximum tension and compression strain amplitudes (ɛ
a
) in the wire surface. The resulting ɛ
a
-N
f
curves can be subdivided into three regimes. At ɛ
a
> 1 pct rupture occurs early (low N
f
) and the fatigue-rupture characteristics were strongly dependent on ɛ
a
and the rotational speed (regime 1). For 0.75 pct < ɛ
a
< 1 pct, fatigue lives strongly increase and are characterized by a significant statistical scatter (regime 2). For ɛ
a
< 0.75 pct, no fatigue rupture occurs up to cycle numbers of 106 (regime 3). Using scanning electron microscopy (SEM), it was shown that surface cracks formed in regions with local stress raisers (such as inclusions and/or scratches). The growth of surface cracks during fatigue loading produced striations on the rupture surface; during final rupture, ductile voids form. The microstructural details of fatigue-damage accumulation during BRF testing are described and discussed.
122 citations
TL;DR: In this article, the authors describe micromechanical research which has been undertaken to acquire a detailed understanding of the fracture behaviour of carbon fiber-reinforced plastics and to establish the expertise necessary to analyze successfully the fracture modes, failure sequence and hence the initial cause of breakdown of aerospace structures made from cfrp.
121 citations
TL;DR: In this paper, the effect of test environment and pre-conditioning on the fatigue behavior of CFRP/epoxy lap-strap joints was investigated and it was shown that the fatigue resistance of the lapstrap joints did not vary significantly until the glass transition temperature, Tg, was approached, at which point a considerable reduction in the fatigue threshold load was observed.
Abstract: In this work, the effect that test environment and pre-conditioning had on the fatigue behaviour of CFRP/epoxy lap–strap joints was investigated. It was shown that the fatigue resistance of the lap–strap joints did not vary significantly until the glass transition temperature, Tg, was approached, at which point a considerable reduction in the fatigue threshold load was observed. It was also noted that absorbed moisture resulted in a significant reduction in the Tg of the adhesive. This must be taken into account when selecting an adhesive to operate at elevated temperatures. The locus of failure of the joints was seen to be highly temperature dependent, transferring from primarily in the composite adherend at low temperatures to primarily in the adhesive at elevated temperatures. It was also seen that as the crack propagated along the lap–strap joint, the resolution of the forces at the crack tip tended to drive it into the strap adherend, which could result in complex mixed mode fracture surfaces.
120 citations
TL;DR: In this article, a full-coverage model is proposed to estimate the critical hydrogen content that makes ZIRCALOY-4 totally brittle, and the effect of microstructure on hydride embrittlement in different metallurgical states is explained according to the modeling.
Abstract: The hydride embrittlement in ZIRCALOY-4 was studied at room temperature and 350 °C. Sheet tensile specimens of two fabrication routes in the stress-relieved, recrystallized, andβ-treated states were hydrided with or without tensile stress. It was found generally that the effect on strength of increasing hydrogen content was not important. However, for the tensile tests at room temperature, there is a ductile-brittle transition when the hydrogen content is higher than a certain threshold. The prior thermomechanical treatment shifts this transition considerably.In situ scanning electron microscopy (SEM) tests, fractography, and fracture profile observations were carried out to determine the fracture micromechanisms and the microscopic processes. At 20 °C, the fracture surfaces are characterized by voids and secondary cracks for low and medium hydrogen contents and by intergranular cracks and decohesion through the continuous hydride network for high hydrogen contents. This phenomenon disappears at 350 °C, and the hydrogen seems to exert no more influence on the fracture micromechanism even for very high hydrogen contents (up to 1500 wt ppm). A full-coverage model is proposed to estimate the critical hydrogen content that makes ZIRCALOY-4 totally brittle. The effect of microstructure on hydride embrittlement in different metallurgical states is thus explained according to the modeling. Special attention is devoted to relating the micromechanisms and the modeling in order to propose the possible measures needed to limit the hydride embrittlement effect.
120 citations