Papers by Keyword: Ductility

Abstract: Doping high-zinc aluminium alloys with Ti builds in-situ composites reinforced with ternary aluminides Ti (Al,Zn)₃ with a significantly grain-refined matrix. In a series of studies, Ti was introduced with Al-6 wt% Ti (AlTi6) and Zn-4 wt% Ti (ZnTi4) master alloys in amount to contribute about 3 wt% Ti in the examined alloys. The alloy microstructure has been studied using light microscopy, SEM / EDS and XRD measurements. The observed significant refinement of the alloys matrix should lead to improvement in ductility, while the in-situ reinforcement should improve tensile strength and wear properties.

Abstract: Hydrogen embrittlement (HE) is increasingly becoming a critical issue for using high-strength steels in the automotive and infrastructure industries. To overcome the risk posed by HE of structural components under a hydrogen uptake environment in long-term service, it is necessary to clarify the mechanism of HE. In the present study, the presence of hydrogen-enhanced strain-induced vacancies (HESIVs)—one type of defect associated with proposed HE mechanisms—was validated by low-strain-rate tensile tests with in-situ electrochemical hydrogen charging for tempered martensitic steel showing quasi-cleavage fracture with a tensile strength. The effect HESIVs on the mechanical properties of tempered martensitic steel was also studied. The combined use of low-temperature thermal desorption spectroscopy and tensile tests led to the following observations: (i) hydrogen enhanced the accumulation of vacancy-type defects under plastic strain, (ii) accumulated vacancy-type defects adversely affected the ductility of the tempered martensitic steel after hydrogen release, and (iii) aging at 150 °C after applying a given plastic strain with hydrogen charging decreased the amount of newly formed vacancy-type defects and resulted in recovery of ductility.

Abstract: As a new trend in modern structural design, the high-performance steels are increasingly used in steel structures, due to their superior mechanical properties, which could have decisive impact on the resistance and deformation capacity of structural components. High-performance steels include stainless and high-strength steels. The higher proof stress of the high-strength steels allows using thinner sections and material economy for those structural elements that do not experience stability problems. Austenitic stainless steel shows a series of advantages, including low maintenance costs and an excellent toughness at low temperatures. But the main characteristic which matters especially in seismic design, is the higher ductility, larger strain hardening and elongation at fracture in comparison with carbon steels. In this paper, the analysis of the behaviour of 1.4404 austenitic stainless steel and of S690 high-strength steel, in comparison with a reference S235 mild carbon steel is presented. This paper presents the assessment of the monotonic and cyclic performance of these steel grades, as well as the failure pattern, in order to assess the potential use in structural applications.

Abstract: This work is aimed at uncovering the hidden value of waste cow bones towards their use as a sustainable biofiller for hot-mix asphalt (HMA) paving applications. To do so, the effect of various contents of calcined cow bone powder (e.g., 5, 10, and 15 wt. % CBP) on the AP-5 bitumen performance was investigated. Numerous lab techniques were adopted to assess the physicochemical attributes of finished filler-asphalt mastics, namely: elemental analysis, Fourier transform-infrared spectroscopy (FT-IR), thin-layer chromatography-flame ionization detection (TLC-FID), needle penetration, ring and ball softening point, Brookfield viscometer, and ductility. Iatroscan analysis revealed that the CBP treatment did not alter the saturates but induced an increase in the fractions of aromatics/asphaltenes and a decrease in the resins. The FT-IR scan highlighted that the CBP–binder interactions were mainly governed by physical mechanisms rather than chemical ones. The empirical methods showed that the CBP incorporation enhanced the stiffness/hardness, the consistency, as well as the high-temperature performance of bituminous mixtures. Overall, the use of waste cow bones as a green biofiller is viable and profitable, and it has the potential to reduce the environmental pollution caused by the livestock industry while also improving the performance of hot-asphalt mixes and extending the pavement life at a low cost.

Abstract: In this current article, an effort was made to briefly study the impact of magnesium content on the mechanical and metallurgical performance of as-cast Zn-Al-Si-Mg alloy. Zinc, aluminium, and silicon of appropriate weight quantities were melted in an electric furnace, and magnesium of varying quantities (1-5wt%) was added to the melt to obtain rectangular cast specimens. Microstructural, hardness and mechanical property analysis was conducted for the developed alloy in the as-cast condition. It was noted that an addition of Mg to the Zn matrix refines the grains but more than 3wt-% of Mg to the matrix forms clusters which deteriorate the property of the alloy in the as-cast condition. The value of hardness and tensile strength were noted to enhance, and ductility was observed to decrease from the baseline alloy to the alloy with 3wt% of Mg. Further addition of Mg decreased the properties of the alloy.

Abstract: In this study, a multi-directional forging process was conducted on AA 7075. Analysis of the evolution of the mechanical properties (tensile and hardness) and the microstructure was done. The effects of the process parameters (temperatures, die speed, and strain per pass) on the process outputs were investigated. The hardness of the MDF processed samples was determined using Brinell hardness tester, the tensile tests were conducted on a universal tensile machine (GT-7001-LS50), while the grains were observed using the Zeiss Axio Zoom V16 microscope and Tescan VEGA3 scanning electron microscope. It was observed that the MDF process leads to grain refinement with increase temperature and strain per pass. However, large strains per pass caused damages to the samples. The hardness and the tensile strength were seen to generally improve with an increase in strain per pass.

Abstract: Adobe masonry (AM) dwellings are a considerable portion of existing buildings stock worldwide, particularly in developing countries. Several earthquakes occurred during last decades dramatically showed a high seismic vulnerability of such constructions, which are not generally engineered. Therefore, several research groups have been involved in the investigation about effective and viable retrofitting solutions for AM buildings. Currently, most of studies available in literature addressed the issue by means of experimental programs consisting of dynamic or static tests on reduced- or full-scale specimens, representing partial or complete AM dwellings. Nevertheless, in those works, limited or no attention was generally paid to the crucial issue of the spatial variability of material properties within AM, which can produce critical forms of mechanical response and premature failure. In this study, three series of seven AM wallets were tested under monotonic diagonal compression load: one series consisted of unreinforced specimens (used as benchmark) and the remaining series were strengthened with two textile reinforced matrix (TRM) systems, made of either hemp or glass meshes. Masonry joints and matrix were produced using the same mud mortar, which is a typical mortar of existing Italian AM buildings. Experimental outcomes of tests in terms of observed damage and response curves are presented, along with a comprehensive characterization of mortar and bricks. Then, with the aim to draw out general and robust trends about TRM effectiveness as strengthening solution in the improvement of shear strength and ductility capacity, the response variability was quantitatively investigated via statistical analysis of recorded stress–strain samples.

Abstract: Different commercial Finite Element Codes proved to be able to describe the mechanical behavior of masonry materials externally reinforced by means of Carbon Fiber Reinforced Polymers (CFRP); the behavior of fracturing materials, characterized by low tensile strength, with adhered strips can be reproduced relying on parameters based on fracture mechanics and the theories of adhesion.In this report the comparison is made of previous experimental test results with numerical analysis, carried out on masonry panels reinforced with CFRP strips and subjected to out of plane actions. The comparison is especially addressed to the evaluation of the post peak branch; in addition to the slopes of the diagram in the pre-critic phase, available kinematic ductility and energy shares both prior and after the peak load were considered in order to interpret the capability of the micro-mechanical model implemented in the FEM Code to account for the local phenomena influencing the interaction between masonry and FRP strengthening systems.

Abstract: Over the past two decades, different innovative systems have been developed for the rehabilitation and retrofitting of existing structures. In particular, SRG (Steel Reinforced Grout) strengthening systems have proven to be very effective in increasing the load carrying capacity and global ductility of reinforced concrete and masonry structures, and their use as an alternative seismic retrofitting solution is increasing rapidly. Although several studies have focused on the characterisation of the mechanical performance of SRG composites subjected to direct tension or bonded to concrete/masonry substrates, the local bond behaviour of steel cords to mortar, which is critical for the overall structural performance of these composites systems, needs to be examined in more depth. To this end, a series of pull-out tests was carried out to study the bond stress transfer of high strength galvanized steel cords embedded in two types of inorganic matrices, including a cementitious and a lime based mortar. In addition, the steel cord to mortar bond was examined through the implementation of a surface-based cohesive contact model in a non-linear finite element framework and the distribution of stresses within the mortar surrounding the steel cord was analysed.

Abstract: The given study is dedicated to optimization of dispersion-strengthened material based on copper powder of the Cu-Al-C-O system used for valve guides of internal combustion engines. The developed material containing 3 % wt aluminum, 0.6 % wt carbon and not more than 0.02 % wt oxygen has the recrystallization temperature of 1000^оС and exhibits higher tribotechnical properties comparing to the prototype. In particular, the wear out intensity of the developed material is 2.5 times lower. The material production technology is based on the method of reactionary mechanical alloying in the attritor and powder and granular metallurgy technologies.