Advanced Materials Research Vols. 557-559

Abstract: Based on the estimation of the critical hydrogen pressure and concentrations required for hydrogen-induced delayed cracking in high-strength steel, the conclusion that welded joints are hydrogen pressure microcracks body can be drawn under certain conditions. Through the analysis of the relationship between the microstructure evolution of welded joints, diffusion enrichment of hydrogen and cracking behavior, the formation mechanism of hydrogen-induced delayed cracking in weld center of high-strength steel joints is analyzed and the mechanism that stress induced the residual diffusion hydrogen gathered to promote the hydrogen pressure microcracks propagation is proposed. The research shows that the initation and propogation of hydrogen-induced delayed cracking in weld center can be divided into two stages, i.e. irreversible hydrogen damage stage and reversible hydrogen damage stage. In irreversible stage hydrogen pressure is the main causes of the initation of microcracks, while in reversible stage welding residual stress and residual diffusible hydrogen are necessary conditions for microcracks growth. The microcracks growth can be controlled by regulating welding residual stress.

Abstract: In this paper, cold bending properties of Q620-CF steel butt joints were analyzed based on the finite element method. Finite element analysis (FEA) results indicate that the flush under-matched butt joints have lower bending properties than the flush equal-matched butt joints, but under-matched butt joints with definite reinforcement shape can get greater bending force and better cold bending angles than the flush equal-matched butt joints. It shows that shape design of the reinforcement can improve the bending load-carrying capacity of under-matched joints. The reliability of the FEA has been verified by the experiment.

Abstract: Glass fiber reinforced polypropylene composites were joined by ultrasonic welding, employing various weld conditions. Single-lap shear testing was used to evaluate the effect of weld time and weld pressure on the weld performance. The weld strength increased with increasing weld time and weld pressure until a plateau or maximum strength was reached. The required weld time to obtain a complete weld became shorter when the weld pressure was increased. As lower weld pressure was applied, a complete weld could not be obtained unless relatively longer weld times were employed. A welding map, showing conditions of weld time and weld pressure to get a good weld, was obtained.

Abstract: In ultrasonic welding of fiber reinforced thermoplastic, heat is generated by means of interfacial friction at the interface to be bonded and internal friction of the polymer chains. A finite element model, using ANSYS software, was developed to calculate the transient temperature profile in glass fiber reinforced polypropylene joint in the transverse direction during ultrasonic welding. The results showed that the temperature in the joint increased with increasing weld time. With higher weld pressure, the temperature of molten point of polyprolylene can be reached within a shorter weld time. The weld map obtained from the finite model was in agreement with the results obtained experimentally.

Abstract: A novel femtosecond laser directly writing method was utilized to fabricate microchannels on silicon carbide (SiC) substrate. The micro patterns were transferred to a Polydimethylsiloxane (PDMS) stamp, characterized by both optical microscope and scanning electron microscope (SEM). The relationship between size (depth and width) of channels and power of laser pulse were discussed in detail.

Abstract: Lagging melt phenomenon is the special phenomenon of flux cored arc welding, studying lagging melt phenomenon is very valuable for the design and improvement of flux cored wire. Used digital camera technology, recorded the lagging melt phenomenon of acid、basic and metallic slag systems flux cored arc welding in CO₂ protective atmosphere. Analyzed its mechanism and influencing factors of lagging melt phenomenon. The results shows that lagging melt phenomenon under low welding criterion is not obvious in comparison to high welding criterion but still shows lagging melt tendency. Under high welding criterion lagging melt degree increases and metal droplet separated from lagging melt flux core forms separated transfer. Under same welding criterion, lagging melt degree of basic slag system is maximum, acid slag takes the second place and metallic slag system is minimum.

Abstract: According to the characters, technological condition and requirements of automotive front axle forging, both the process of exact roll-forging billet and die design are studied, as the result, roll- forging die of front axle billet, pre-completed roll-forging die and final roll-forging die are design respectively, finally the groove with hat cross-section is analyzed and top pressure rolling method is proposed during blank-making roll-forging process. The precision rolling forging performing deformation process of automobile front axle is simulated with finite element software Deform-3D by using 3D thermo-mechanical coupled rigid plastic FEM. The metal flow process, equivalent stress and strain field, temperature field and load status of rolling die are analyzed, and they are consistent with experiments. This provides a dependable theoretical basis for understanding the deforming mechanism and selecting reasonable parameters for the precision rolling forging performing of front axle.

Abstract: This paper proposes an idea for manufacturing internal patterns using a femtosecond laser. The femtosecond laser can easily be focused within transparent materials because of the advantages of multi-photon absorption and high energy density. The parameters of a femtosecond laser can be adjusted to modify the local area inside the glass and to design internal structures. The internal structures can produce optical effects. Through this process, optical plates can be manufactured in glass without wasting excess space.

Abstract: According to the characteristics of threaded plastics in the focusing handwheel of the light machine, a kind of new type injection mould is designed to take off thread. The mould core consists of six flaps and a guide posts, and the whorl is taken off automatically through the relative motion by guide posts and flap. The injection mould effectively avoids the interference effect in the course of taking off thread. The productivity is increased effectively, and the stable plastics quality is kept in practical application.

Abstract: The microstructure and macrotexture of ZK60 alloy sheet were investigated through OM and XRD, which were produced by twin roll casting and sequential warm rolling. Microstructure of twin roll cast ZK60 alloy changed from dendrite structure to fibrous structure with elongated grains and high density shear bands along the rolling direction after warm rolling process at different rolling parameters. The density of shear bands increased with the decreasing of the rolling temperature, or the increasing of per pass rolling reduction. Dynamic recrystallization could be found during the warm rolling process at and above 350oC, and many fine grains could be found in the shear band area. The warm rolled ZK60 alloy sheet exhibited strong (0001) basal pole texture. The formation of the shear bands tends to cause the basal pole tilt slightly to the transverse direction after warm rolling. The intensity of (0001) pole figure increased with the decreasing of rolling temperature, or the increasing of per pass rolling reduction.