Abstract: Drilling holes in the vicinity of the crack tip turns the crack into a notch and reduces the crack tip stress intensity factor. In this paper, a new idea is used in which instead of a single hole, two symmetric and interconnected holes are drilled at the crack tip. The main concept of double stop-hole method is to reduce the stress concentration at the edge of stop-holes in the cracked structural elements. The double stop drill hole method can be used to increase the fatigue life of the cracked components. The fatigue crack growth retardation is examined using an experimental investigation coupled with a stress analysis on the efficiency of proposed double stop-holes. The distance between the hole centers is considered as the main parameter affecting the efficiency of this method. The results show that the fatigue life extension caused by the double stop-hole method is significantly more than the conventional single stop-hole method.
Abstract: Al containing intermetallic phases have been evaluated in various bcc and fcc steels. Attractive application options have been derived for hot working tools steels with respect to a reduction of resource critical alloying elements and in cold formable steels by the combined density reduction and strength increase.
Abstract: “Art is everywhere” to quote Ben, a renowned French contemporary artist. However, there are some areas in which art is more prevalent. Thermal spray is one of them, as this presentation seeks to demonstrate. For this, each of the arts (according to their official classification) is shown to correspond to a specific key point of the thermal spray process for coating: e.g., coating build-up, additive manufacturing, deposition onto brittle and/or temperature sensitive materials (glass, wood, fabrics, polymers), powder optimization, and adhesion. Both modeling and experimental aspects are discussed, focusing on the study of particle-to-particle or particle-to-substrate interfaces, shock phenomena and advanced investigation techniques such as X-ray microtomography or high-speed instrumentation. Plasma spray and cold spray provide the relevant examples that this contribution elaborates. They relate to different industrial sectors such as aircraft-aerospace, luxury, biomedical and the automotive industry. Beyond anecdotal evidence, the discussion aims to show that an artistic approach to thermal spray does help to understand better this powerful coating process.
Abstract: Torsion simulations were carried out of both plate (long interpass times) and strip (short interpass times) rolling. Both isothermal and continuous cooling conditions were employed. The dynamic transformation of austenite to ferrite was observed under all conditions and at all temperatures within the austenite phase field. About 8 to 10 volume percent ferrite was formed in a given pass, leading to about 50 - 70 % ferrite at the end of selected simulations. During the interpass intervals, some retransformation to austenite took place, the amount of which increased with holding time and temperature and decreased with the addition of alloying elements. It is shown that the driving force for the transformation is the softening associated with the replacement of work-hardened austenite grains by the softer alpha phase. The implications with respect to rolling load (i.e. mean flow stress) are also discussed.
Abstract: Tempered martensite lath structure (TMLS) plays a vital role in creep resistance of high chromium martensitic steels. Under creep conditions the TMLS could be stabilized by three agents: (i) a dispersion of boundary M23C6 carbides and Laves phase; (ii) a dispersion of M(C,N) carbonitrides, which are homogeneously distributed within ferritic matrix; (iii) substitutional alloying element within ferritic matrix. The boundary particles exert a large Zener drag force which effectively hinders migration of low-and high-angle boundaries. A dispersion of M(C,N) carbonitrides both within ferritic matrix and lath boundaries provides the pinning of mobile dislocations. This process is responsible for reliving long-range elastic stress field originated from lath boundaries. In addition, M(C,N) carbonitrides provide high threshold stress. Substitutional elements as W and Mo effectively slowing down diffusion in ferritic matrix retard climb of lattice dislocation that also prevents the aforementioned knitting reaction. The suppression of knitting reaction between lattice dislocation and low-angle boundaries prevents their transformation to subboundaries by concurrent operation of all three agent types.
Depletion of W and Mo from solid solution leads to the occurrence of static recovery and precipitation of Laves phase at boundaries under long-term aging. This process is responsible for creep strength breakdown. The strain-induced formation of Z-phase at the expense of V-rich M(C,N) carbonitrides highly facilitates this process. However, slow strain-induced coarsening of M23C6 carbides and M(C,N) carbonitrides provides the suppression of the knitting reaction between mobile lattice dislocations and intrinsic dislocations of lath boundaries and replacement of TMLS by subgrain structure. Ostwald ripening of boundary M23C6 carbides and Laves phase leads to rapid creep rate increase with strain in tertiary creep and premature rupture owing to the formation of subgrain structure replaced TMLS and further subgrain growth.
Abstract: The processing of metals through the application of high-pressure torsion (HPT) provides the potential for achieving exceptional grain refinement in bulk metal solids. These ultrafine grains in the bulk metals usually show superior mechanical and physical properties. Especially, the development of micro-mechanical behavior is observed after significant changes in microstructure through processing and it is of great importance for obtaining practical future applications of these ultrafine-grained metals. Accordingly, this presentation demonstrates the evolution of small-scale deformation behavior through nanoindentation experiments after HPT on various metallic alloys including a ZK60 magnesium alloy, a Zn-22% Al eutectoid alloy and a high entropy alloy. Special emphasis is placed on demonstrating the essential microstructural changes of these materials with increased straining by HPT and the evolution of the micro-mechanical responses in these materials by measuring the strain rate sensitivity.
Abstract: Magnesium alloys with refined grain structure are often superplastic at elevated temperatures with maximum elongations up to more than 1000%. The superplastic behavior of this material agrees with deformation by grain boundary sliding. Dislocation climb becomes the rate controlling mechanism at higher stresses but the rate controlling mechanism at lower stresses is not fully documented. This report examines the development of superplasticity in a magnesium ZK60 alloy and shows that an increase in stress exponent and decrease in elongation takes place at low stresses. Deformation mechanism maps are constructed considering Regions I, II and III and Coble creep.
Abstract: As the result of the international standardization work in Japanese IST project, ISO 27306 were published in 2009 for correction of CTOD fracture toughness for constraint loss in steel components. ISO 27306 employs an equivalent CTOD ratio based on the Weibull stress criterion, which leads to more accurate fracture assessment than the conventional fracture mechanics assessment. On the occasion of the 1st periodical review, the revision of ISO 27306 has been proposed from Japan. This paper describes the key contents of the new ISO 27306. A case study is included on the fracture assessment of a wide plate component according to FAD (failure assessment diagram) approach specified in BS 7910:2013.
Abstract: This study deals with the evaluation of self-healing ability of conducting polymer corresponding to a corrosion process. Poly ortho-anisidine (PoA) was doped with Phosphomolybdic acid (PMA) and Tungstosilicic acid (TSA) and incorporated in polyvinyl butyral (PVB) coatings. The self-healing abilities of coatings were evaluated using open circuit potential (OCP) in 0.1 M NaCl solution for 45 hours of immersion. The coatings containing doped PoA showed increased positive potential of OCP after 45 hours of immersion as compare toblank PVB which showed a constant profile of OCP over the time indicating uniform corrosion under the coating.Thermogravimetric analysis (TGA) showed that PoA doped with TSA is more stable and more effective in the coating. High resolution Transmission Electron microscopy (HR-TEM) and Energy dispersive x-ray spectroscopy (EDX) confirms the doping of PoA.