Advanced Materials Research Vols. 834-836

Abstract: A method to analyze the shape of three-dimensional curve surface for flexible rolling forming metal plate is proposed based on the traditional rolling and multi-point adjustment technology. It has smaller rebound and better forming in comparison with the traditional method which is using the surface deformation. The simulation experiments are implemented using the developed experimental device to demonstrate the feasibility and practicality of the flexible rolling forming. The proposal could be used in the various industries.

Abstract: For almost all materials the hypervelocity regime has been reached when the impact speed above 2 km/s. A double-barreled two-stage light gas gun (TSLGG) system used for the hypervelocity impact tests is described. The proposed TSLGG can accelerate 50 g projectile masses up to velocities of 2.2 km/s. The craters produced with this equipment reach a diameter of up to 20 cm, a size unique in laboratory cratering research. The experiment results show our TSLGG system work effectively, velocity of the projectile mass is measured highly accurate by means of the proposed optical method.

Abstract: The heavy forging ingots of steel 20Mn5N have been extensively used to fabricate the hydropower shaft steel, which plays as an extremely important part in industry. However, the quality of the heavy ingots has been commonly affected by various inner defects. One of the most typical defects is internal cracks, which has been found to be always accompanied by inclusions. In order to effectively analyze the formation of internal cracks, a 30-ton 20Mn5N ingot has been cut along the axle plane. Exceeding macroscopic cracks can be found in macro-segregation area gathered many large and grid inclusions (Al₂O₃). Based on the experimental results and FEM simulation method we have investigated that large and grid inclusions accompanied by other macro-visible defects such as banded structure could lead to the forging cracks easily. FEM simulation result shows that the stress concentration resulting from the large and grid inclusions (Al₂O₃) is relatively large. These large and grid inclusions accompanied by banded structure are the fundamental cause of cracks.

Abstract: Industrial pure aluminum has been widely used in industry. However, it caused great difficulties in welding process due to its characteristics such as easy oxidation, high thermal conductivity and specific volume, low melting point. In order to overcome this problem, improving the welding quality of industrial pure and reducing the welding defects is of great significance. In this paper, the weldability of 1050A industrial pure aluminum plate (5 mm thick) with HS331, SAl-2, 1050A leftover materials and homemade welding wire with Ni-Cr alloy as four different filler materials was studied by using manual TIG welding. Metallographic test and mechanical performance test were used to assess microstructure and mechanical properties of the resulting welding joint. The results show that the microstructure and mechanical properties of the resulting welding joint with homemade welding wire with Ni-Cr alloy is relatively better than the others, which offers important implication for the improvement of the welding properties of industrial pure aluminum.

Abstract: The exploration of marine resources is becoming more and more important, underwater weld technology is an important technology for the exploration. However, the underwater weld technology is very immature; the underwater weld quality is not as good as the offshore welding. To control and improve the underwater weld quality automatically, arc and visual sensors were used to obtain the information reflecting the weld quality, and ARX (AutoRegressive eXogenous) model was use to model the process, experiment result showed that the prediction results of the model were accurate enough for automatically controlling the process.

Abstract: PLGA (polylactic-co-glycolic acid) is an ideal material for biodegradable medical suture. PLGA fibers and fiber membrane was prepared by using electrostatic spinning, the surface morphology of PLGA fibers and fiber membranes was observed by SEM, and mechanical properties of PLGA fibers and fiber membranes were tested by self-developed micro-force loading system. Experimental results were found that the arrangement of PLGA fibers due to surface tension and friction between fibers was the main factor on mechanical properties of PLGA fibers. The tensile strength of two fibers in winding arrangement was 1.81 times of fibers arranged in parallel at a given number. The tensile strength of three fibers in winding arrangement was 1.25 times of fibers arranged in parallel at a given number. For 80.6 % porosity and 1.028-5.764 mm width PLGA fiber membranes, tensile strength was 1.06-1.47 MPa, tensile modulus was 9.14-13.6 MPa, and elongation at break was 10.8 % to 11.6 %. The tension of fiber membranes increased with its width.

Abstract: Interaction between a crack and a rectangular particulate in a single edge notched beam is simulated using a boundary element program of automatic crack extension. The stress intensity factors of the growing crack are obtained from the J-integral. Three crack extension paths: deflecting around the particulate, growing along the interface and penetrating into the particulate are achieved in terms of the mismatch state of mechanical characteristics of matrix and particulate. The toughening is also given by the ratio of stress intensity factors. The results reveal that as stress shielding occurs, large toughening is obtained when the crack is approaching to a stiff and strong particulate weakly bonded to a relatively soft matrix; inversely the soft particulate is functional to attract the crack tip toward it, and obvious toughening arises when the tip is within this soft particulate. The present work intends to help for the design of particulate reinforced composites.

Abstract: An experimental study was conducted to determine cutting parameters of high-speed milling of Ti-17 according to their effects on residual stresses. First, three groups of single factor experiments were carried out to reveal the effects of cutting parameters on residual stresses. Then sensitivity models were established to evaluate the influence degrees of cutting parameters on residual stresses. After that, three criteria were proposed to determine cutting parameters from experimental parameter ranges. In the experiments, the cutting parameter ranges are recommended as [371.8, 406.8] m/min, [0.363, 0.412] mm and [0, 0.018] mm/z for cutting speed, cutting depth and feed per tooth, respectively.

Abstract: Carbon Fiber Reinforced Plastics ( CFRP) is a typical difficult to machine material which is prone to disfigurements such as burrs, avulsion and delamination, and rapid tool wear, high processing cost. Aimed at the defect of Carbide Twist Drillbit (CTD) when drilling on CFRP, a new type of drillbit, which is called Drilling-Reaming Composite Drillbit (DRCD), was designed and used to drill holes on a plate of CFRP. Through experimental study and analysis, and compared with CTD, we found that drilling with DRCD have higher dimension accuracy and better surface quality when drilling on CFRP, and it has minor wear on its cutting edges and its tool life at least ten times that of CTD. So we draw conclusion that DRCD with high wear resistance and good stability is more suitable for drilling CFRP.

Abstract: The primary goal of this research is the effects of laser process parameters on surface roughness of metal parts built by selective laser melting. The main processing parameters used to control the surface roughness of melted layers are laser power, scanning velocity and overlap ratio. In our work, an orthogonal experimental design was employed to find the changing rules of the surface roughness through changing SLM processing parameters. The results show that the overlap ratio is the most important factor to affect the surface roughness. When the overlap ratio is below 50%, the surface roughness value of melted layers will decrease with laser power density increasing. When the overlap ratio is higher than or equal to 50%, the surface roughness value increases with the laser power density increasing. The optimal parameters of laser power 143W, scanning velocity 5m/min and overlap ratio 30% can be used to achieve melted layers with the best surface quality in our experiments, and the roughness value increases with slicing thickness increasing and the surface bias angle decreases.