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EN
Due to the increased use of lightweight sheet materials, there has been a significant increase in the use of self-pierce riveting. This paper deals with the strength and fracture mechanism of single-lap self-pierce riveted joints. The online window technique was introduced in the single-lap self-pierce riveting processes for evaluating the quality of joints. Signals obtained from sensors were amplified and transferred to the data acquisition system which measures, processes and saves the signals. Monotonic tensile tests were carried out to measure the ultimate tensile strengths for the single-lap self-pierce riveted joints. For investigating the fracture mechanism of the single-lap self-pierce riveted joints, the electrolytic polishing and anode film coating were used for dealing with the cross-section. The differential interference contrast method was used for observing the micro-structure of the cross-section of the joints. The distribution of the hardness in the cross-section of the single-lap self-pierce riveted joints was also studied. The normal hypothesis tests were performed to examine the rationality of the test data.
EN
Mechanical fastening techniques are used extensively in different industry fields for joining various materials in the assembly of components and structures. The use of mechanical clinching is of interest to different industries such as aerospace, automotive, packaging and domestic appliance. This, together with increasing use of light-weight materials, has produced a significant increase in the use of mechanical clinching in light-weight structures in recent years. This paper deals with the mechanical properties and fracture analysis of extensible die clinched joints in the dissimilar metal sheets combinations of titanium sheet material and aluminum sheet material. Tensile-shear tests were carried out to characterize the mechanical properties of different clinched joints made of the dissimilar metal sheets combinations. The normal hypothesis tests were performed to examine the rationality of the test data. The load-bearing capacity and failure modes of different titanium sheets clinched joints were studied. Results showed that most titanium sheets clinched joints failed in the neck fracture mode. Results also showed that the load-bearing capacity of clinch joints with titanium as upper sheets is higher than that of the clinched joints with titanium as lower sheets.
EN
Clinching is an effective joining technique for lightweight sheet materials that are difficult or impossible to weld. A theoretical model for clinched joints in metal sheets was established and a design method for improving joint strength by selecting different clinching tools was proposed. The analytic model is defined as a function of the neck-thickness and the undercut, which are the key parameters of joint geometry. Based on the analytic model, the design method of clinched joint strength that can satisfy required strength was proposed. Clinching experiments were conducted with 2.00 mm thick aluminium alloy 5052 sheets. Various conditions were used during the clinching process to validate the joint strength model. Tensile-shear strength of clinched joints was measured by a servo-hydraulic testing machine. The calculated joint strength was in good agreement with the experimental results.
EN
The structural stabilities, elastic properties and charge transfers of EuX (X = O, S, Se, Te) compounds as a function of pressure are investigated extensively using first-principles calculations. The ground-state parameters, such as lattice constants, bulk modulus are predicted and compared with the available data, our results are satisfactory. The calculated phase transition pressures from the NaCl-type (B1) structure to the CsCl-type (B2) structure for EuX (X = O, S, Se, Te) also accord with the experiments. Particularly, the elastic constants of EuX (X = O, S, Se, Te) under zero pressure and high pressure are simulated appropriately for the first time via density functional theory. The softening behaviors of the elastic shear modulus C_{44} under pressure for the B1 phase of EuX (X = O, S, Se, Te) are captured, which should be responsible for the pressure-induced structural phase transition in the EuX system. It is also suggested that the softening behavior might be induced partly by the p → d and f → d electron transfers of Eu atom under pressure. In addition, the aggregate elastic modulus (B, G, E), Poisson's ratio (σ), Debye temperature Θp_{D} are also successfully obtained for both B1 and B2 phases of EuX.
EN
The article presents the dynamic mechanical properties of two types of high manganese austenitic TWIP steels. The investigations were carried out for the wide range of strain rates from 10¯² s¯¹ up to 4×10³ s¯¹ using servo-hydraulic testing machine and split Hopkinson bar for the quasi-static and dynamic loading regime, respectively. The mechanical properties at different strain rates like yield strength and true stress were calculated out on the base of the results of impact tests. In the next step, the microstructure of the analyzed steels after different deformation rates were observed by scanning transmission electron microscopy technique in order to disclose a dislocation structures and mainly the TWIP effect. In the studies observed that with the strain rate increasing yield strength as well as true stress for 0.3 true strain increasing in both steels. The microstructure observations reveal the influence of strain rate on the structure evolution for analyzed steels.
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