Papers by Keyword: Internal Defects

Abstract: The mechanical and fatigue behavior of a reactively modified Inconel 625 alloy (IN625-RAM2) produced by Laser Powder Bed Fusion (PBF-LB) was investigated. The alloy achieved near-full density (≈8.30 g/cm³) and exhibited a refined, irregular grain structure with localized equiaxed regions from ceramic-induced nucleation and Zener pinning. It showed high tensile strength (YS 680–770 MPa, UTS 1170–1250 MPa) with modest anisotropy. Under fully reversed loading (R = –1), fatigue limits at 2×10⁶ cycles were 110–122 MPa in the as-built condition and 180–187 MPa after electropolishing, improving fatigue efficiency from ~10% to ~15% of UTS. Compared with reference alloys (AISI 316L, Ti6Al4V, IN718), IN625-RAM2 combined high strength with moderate fatigue resistance, emphasizing the critical role of surface quality in optimizing PBF-LB nickel alloys.

Abstract: Cold metal transfer (CMT) based wire-arc additive manufacturing (WAAM) is increasingly popular for the production of large and complex metallic parts because of its high efficiency and low cost. The presence of internal defects in fabricated parts is a common and critical issue to the process, which degrades parts’ mechanical properties. However, the in-situ monitoring of internal defects can hardly be implemented through traditional inspection techniques due to the surface waviness and the high interlayer temperature of parts. In this study, based on the scan of each deposited layer by a laser sensor and the geometric criteria proposed, an in-situ monitoring method is developed for identifying internal defects, which can be easily applied in an automated WAAM system. Experimental results show that the developed in-situ monitoring identifies 100% accurately the parts without internal defects, and in the cases of parts with internal defects, defective layers can be identified with an accuracy of 93.2%. The effects of process parameters on internal defects have also been investigated.

Abstract: The objective of this paper is to quantify the influence of internal defect on the multiaxial strength. Numerical analyses are performed for the second and third axial strength of the concrete. The analysis result indicated the existence of defects not only decreases the strength of materials, but also changed the stress state of the specimen.

Abstract: Numerical analysis was performed for compressive strength of the concrete. Internal defects of the concrete specimen were simulated and compressive strength reduction mechanism was studied. The defects inside of the specimen are stochastic; therefore it is impossible to study the subject with physical material testing. From this study, it is shown that numerical analysis can effectively simulate internal defects and provide an efficient way to study compressive strength reduction.

Abstract: Numerical analysis was performed for compressive strength of the concrete. Internal defects of the concrete specimen were simulated and compressive strength reduction mechanism was studied. The defects inside of the specimen are stochastic; therefore it is impossible to study the subject with physical material testing. From this study, it is shown that numerical analysis can effectively simulate internal defects and provide an efficient way to study compressive strength reduction.

Abstract: Numerical analysis was performed for compressive strength of the concrete. Internal defects of the concrete specimen were simulated and compressive strength reduction mechanism was studied because of angle..

Abstract: The article presents the application of computed tomography (CT) for the detection of internal material defects in roller bearing rings made of steel. The tests were conducted using a set of four rings with different defects created artificially by means of electric discharge machining. In each test ring, several defects of the same type could be observed; however, they differed in terms of their size and geometry. The defects analysed had the form of internal blind holes with axes transverse or parallel to the surface of the track of the bearing – internal blind rectangular holes, and through slits in the inner cylindrical surface. The tests were conducted using a “V|tome|x s” X-ray CT scanner (tomograph) by GE. The roentgenograms of test objects were taken and then reconstructed in 3D. Each defect was visualised in different section planes of a reconstructed ring. Selected defects were represented in a solid form, and the measurements were taken in order to determine their geometry and volume. The tests confirmed that CT can be used in studies on such internal material defects in roller bearing rings as subsurface voids. All artificially made model defects were detected.

Abstract: In the low pressure casting process of A356 aluminum alloy wheel hub, casting defects including shrinkage cavity, shrinkage porosity, impurity and pore usually occur inside the casting. These defects affect the mechanical properties of the casting. To solve this problem, we conducted a study based on a cooperation project with a well-known domestic automobile wheel manufacturer. In the present study, uniaxial tensile test of aluminum alloy casting containing defects was simulated and analysed, and the effect of types and number of defects on mechanical properties was studied by finite element analysis software. Statistical analysis of the data was provided by the manufacturer. It has been found that the degassing technology is effective by the quantitative analysis method. Based on the analyses of experimental data and the numerical simulation it is deduced that the tensile strength of casting increases with the increase of the defects due to the presence of impurity. This was confirmed in this research project, it has been observed that the defect rate of the casting sample is reduced from 5%-6% to less than 1%.