Results 1 - 10 of 476
Results 1 - 10 of 476. Search took: 0.021 seconds
|Sort by: date | relevance|
[en] This work aims to characterize the 36 NiCrMo 6 steel in monotic traction. The tested samples were subjected to mechanical surface treatment (MST) by diamond ball burnishing. This process allow it possible to modify the physical and geometrical properties of the material. The stress-strain diagram obtained were processed and digitalised. The hardening domain was modelled and rational curves were established, taking into account the stresses triaxiality. Thus, the work hardening exponent of material considered was evaluated. The effect of ball burnishing on this exponent has studied in proceeding a comparative manner between burnished and machined surface. The results obtained show that by applying the optimal parameters for burnishing, the work hardening exponent of pre-machined surface layer can be increased by 10%, where nB = 0.407 (nT = 0.312 machined surface). (paper)
[en] The Structural Concrete Spanish Code (EHE-08) set up the basis to select the most appropriate materials and concrete composition for structural purposes. Given that, the material designers have a really good tool to achieve the designing of strong and safe structures over time . Therefore, the projected service life would be guaranteed by using such Code. In particular, a series of specifications are provided for the cement, aggregates, water, additives and so on, to produce strong and durable concrete. The EHE-08 also contains a series of requirements specifically concerning the building materials, exposition environment, calculation methodology, and materials characterization. It is the inadequacy of Annex 9 th of the Structural Concrete Spanish Code (EHE-08) in technical terms that has been increasingly debated and criticized (Figure 1). The aim of this paper is to assess the application of Annex 9 th in some coastal buildings
[en] The studies of mechanical property, microstructure evolution and fracture analysis in pure titanium processed by torsion deformation at 298, 673 and 1073 K are conducted systematically. The variations of mechanical property of deformed pure titanium are shown through Vickers hardness evaluation. During torsion at 298 K, the grains are refined and elongated, but the α phase with different shapes precipitates for twisted samples at 673 and 1073 K. The fracture appearance indicates that the elongated dimples occur on fracture surface at 298 K. Besides, a large number of shear facets are arranged. However, typical intergranular fracture appearance with lots of blocks in polyhedral shape covers the fracture surface at 673 and 1073 K, respectively.
[en] In this study, effects of cooling rate on the solidification microstructure and mechanical properties of Al-Cu alloys were investigated by casting in different molds (sand/steel/copper molds). The phase composition, thermodynamic phase transition process and mechanical properties of Al-Cu alloys were studied. The cooling rate has a significant effect on the morphology of primary α-Al phase and θ-Al2Cu phase. When the cooling rate increases, the microstructure is significantly refined and the mechanical properties of Al-Cu alloys are improved. As the Cu content increases before the eutectic point, the content of primary α-Al phase in the alloy decreases to a small amount, and the hardness increases correspondingly as the ratio of intermetallic θ-Al2Cu phase increases in the whole solidified microstructure. In addition, the thermal reaction of Al-Cu alloys was determined according to the peak temperature in the DSC curves, and the results were consistent with the solidification morphology. When the cooling rate is faster, the peak area of DSC curve of Al-Cu alloys is smaller than that of the corresponding sand-cooled sample. It is expected to provide a beneficial guidance for the preparation and application of heat-resistant Al-Cu alloy in the field of foundry alloys. (paper)
[en] Carbide-reinforced Ti2AlNb matrix composites were spark plasma sintered at 1100 °C by incorporating CNTs into single-B2-phase Ti-22Al-25Nb powders. The as-SPSed alloys were solution treated and then aged in different phase regions. By kinetics analysis and energy-dispersive spectroscopy, it is found carbon will stabilize α2 phase during solution treatment, and the formation of carbide results in the Nb-depleted regions, which further induces the formation of curly B2 + O Widmanstätten structure during quenching. Different from the general Widmanstätten structure in the aged Ti2AlNb alloy, the remained α2 will consume the B2 within the Widmanstätten structure, when the carbon-added alloy is aged in B2 + O phase region. Compared to the alloy without CNTs, the Vickers hardness of the aged carbon-added Ti2AlNb alloy is increased significantly, which is related to the uniform and abundant columnar carbides within the O-phase matrix.
[en] The mechanical behavior of nanostructured bulk aluminum samples processed by means of ball milling and hot consolidation was investigated at various temperatures. Stress-Strain Microprobe® system and its Automated Ball Indentation® (ABI®) test were used for non-destructive determination of the mechanical properties of nanostructured Al samples under various variables. High purity aluminum was processed by means of ball milling for 6 hours and ball to powders weight ratios (BPR) of 30:1 and 90:1. The sintered bulk Al samples were subjected to ABI tests at room temperature, 200 °C and 400 °C to investigate the effect of BPR and test temperature on the mechanical behavior of these samples. Aluminum samples (C90-RT) which were ball milled using high BPR of 90:1 and tested at room temperature displayed the greatest values of final indentation load (303; ± 10 N); YS (228 ± 9 MPa); UTS (394 ± 11 MPa) and ABI hardness value of 113 ± 4, as compared to all samples under examination. On the other hand, the samples tested at 400 °C (C90-400 sample) revealed the least values of final indentation load (156 ± 4 N); YS (113 ± 1 MPa); UTS (220 ± 4 MPa) and ABI hardness value of 61. (paper)
[en] The graphene/Al composites were prepared by a selective laser melting technique. The effects of different graphene contents on the hardness and the tribological behaviour of the composites were investigated, and the wear mechanism of that was discussed. The experiment results showed that as the content of graphene increases, the hardness of the composites increased first and then decreased, and the hardness of AlSi10Mg-0.5 wt% graphene composite was about 10% higher than the hardness of AlSi10Mg alloy. The wear loss of the composites decreased first and then increased under the same conditions of experiment. The reason for the above phenomenon was that when the graphene content was too high, the graphene in the matrix could not be uniformly distributed causing holes, which led to a reduction in the relative density of the composites. (paper)
[en] In this study, the influence of operating parameters on the mechanical properties of Dual Phase (DP) steels was investigated, using response surface methodology (RSM) to develop a prediction model. In developing the model, temperature and holding time were considered as the model variables. To establish this fact, an experiment based on statistical four-level two factorial design method was carried out. Based on the statistical analysis, surface hardness (SH) shows a correlation coefficient of R2 = 0.9607 while Ultimate Tensile strength (UTS) gave R2 = 0.9297, this suggests that the proposed quadratic model is suitable for use. The optimum operating parameters were predicted using the user-defined design (UDD) under RSM and the result was confirmed through experiments, which predict at a temperature (T) of 800 °C and holding time (HT) of 60 min, hardness value was given as 157.798 HV and UTS as 553.648 Mpa. This result indicates that RSM is a suitable method to optimize the process variables for mechanical properties of DP steels. (paper)
[en] The effects of 0.5 wt% In as well as 0.5 wt% In and 1 wt% Zn double (In & Zn) additions to eutectic Sn58Bi alloy on the microstructure and mechanical properties were investigated. Newly designed In & Zn-added Sn58Bi alloy showed much finer microstructure than eutectic Sn58Bi and In-added Sn58Bi alloys. The elongation improvements of 36% and 41% before and after 1008 h aging were obtained in In & Zn-added Sn58Bi alloy compared to eutectic Sn58Bi alloy. Nanoindentation tests revealed that In had solid solution softening (SSS) effect on Sn phase. A hardness decrease and a large creep displacement obtained in both In- and In & Zn-added Sn58Bi served as evident of the SSS. The effects of Zn and In were combined responsible for the elongation improvement of In & Zn-added Sn58Bi.
[en] Powder thixoforging was used to produce amorphous Ni55Nb35Si10-reinforced Al matrix composites from recycled Al powders obtained from ball-milled Al520 end-milled billets. The amorphous reinforcing material was uniformly dispersed in the Al matrix and bonded adequately with it without undesired interfacial reactions. The compressive yield strength of composites with 45% reinforcement content increased 248% to 794 MPa over as-cast samples. The maximum elongation and hardness of samples were 15%, and 60.4 HRA, respectively. The relative density of the unreinforced thixoforged sample was 99.8%, indicating near-perfect compaction of Al powders. The maximum elongation, hardness, and compressive yield strength of thixoforged monolithic matrix alloys were, respectively, 40%, 56.9 HRA, and 747 MPa (a 228% increase in CYS over the cast alloy). In contrast, cold-forged samples showed only 82% increase in compressive yield strength over the as-cast alloy. Powder thixoforging introduced in this study—even without reinforcement—delivers better mechanical properties compared to cold forging most likely due to the refinement and modification of the microstructure during powder ball milling.