Papers by Keyword: Critical Distance

Abstract: Selective Laser Melting is an additive manufacturing practice that permits the production of metal alloy-based parts. While facilitating the design of complex geometry, SLM leads to the fabrication of a unique material structure that showcases distinct behavioural characteristics relative to their traditional methods of material manufacture. Defects that are innate to SLM inspire the presence of a compositional outlook that is inhomogeneous in nature and only serves to hinder part efficiency. Thus, the Theory of Critical Distances offers a refreshed proposal to evaluating notched Ti-6Al-4V material produced by additive manufacturing processes. Key principles of the theory’s working mechanisms are outlined. Subsequently, symmetrical notches of contrasting size are assessed. Findings reveal that the Theory of Critical Distances is adequately compatible with accurate fatigue prediction of SLM Ti-6Al-4V in its as-built state. Additionally, fracture surface analysis reveals that crack initiation is predominantly a surface-based phenomenon. Hereby, increased focus must be given to the quality of processed material that is located at the externalities of additively manufactured components, in order to enhance their service life capabilities. This will induce an increasingly uniform material structure that will allow for more predictable behavioural characteristics.

Abstract: There are more and more pit-in-pit excavations in cities, which include inner pit and outer pit. Owing to the inner pit excavation, pit-in-pit problem aroused and brought about accidents. For this reason, based on the co-construction, deep, and large pit-in-pit of Shanghai Museum of Natural History and Metro Line 13, the excavation influence between inner pit and outer pit was analyzed. The deformation of underground diaphragm wall under the condition of three different distances between outer pit and inner pit were compared through centrifuge model tests. Then, the effect of excavation width of outer pit on underground diaphragm walls was researched through numerical analysis. Results show that the deformation of outer underground diaphragm wall increased with the excavation width of outer pit, for the inner pit, the opposite was true. The critical influence distance between outer pit and inner pit was within 22 meter and 24 meter. According to the critical distance, the area adverse to excavation pit stability was identified.

Abstract: The work described below investigates, for the first time, the link between microstructural parameters such as grain size and the length constant L which is known as the critical distance. L is frequently used in the prediction of failure processes such as brittle fracture and fatigue, initiated at stress concentration features such as notches. Values of L were calculated using data from the literature on the effect of short cracks and notches in steels and ceramics. In some cases, simple relationships could be established between L and the grain size, or other microstructural features. Sometimes L was found to be much larger than anything in the microstructure and appeared to be related to the size of the damage zone at failure.

Abstract: A few years ago we showed that the Theory of Critical Distances (TCD) and the Crack Modelling Method (CMM) could be used to predict the behaviour of welded joints of various geometries, in both steel and aluminum alloys. However we found that there were certain kinds of joints for which our methods, and also other methods which are commonly used, consistently underpredicted the fatigue strengths. Some explanations are suggested for this problem. Finally, mention is made of some of failure investigations in which the author has been involved, to illustrate the complexities which arise in real-world situations.