Determination of the metal/die interfacial heat transfer coefficient and its application in evaluating the pressure distribution inside the casting during the high pressure die casting process

Abstract

High pressure die casting (HPDC) experiments were conducted on a 650 t cold chamber die casting machine to study the interfacial heat transfer behaviour between casting and die. A 'step shape' casting and two commercial alloys namely ADC12 and AM50 were used during the experiments. Temperature and pressure measurements were made inside the die and at the die surface. The metal/die interfacial heat transfer coefficient (IHTC) was successfully determined based on the measured temperature inside the die by solving the inverse heat transfer problem. The IHTC was then used as the boundary condition to determine the 3-D temperature field inside the casting. Based on the predicted temperature distribution, the pressure distribution inside the casting was evaluated by assuming that the transferred pressure from the plunger tip of the injection side to the casting is primarily influenced by the solid fraction of the casting. Reasonable agreement was found between the determined pressure values and the measured pressures at the die surface of the casting.     

Effect of grain size on grain boundary strengthening of copper bicrystals under cyclic loading

Abstract

To clarify the strengthening effect of grain boundaries (GB), cyclic deformation behaviour of really grown [4¯79] ∥ [1¯25] copper bicrystals with different widths (4, 6, and 8 mm, denoted RB-4, RB-6, and RB-8) of com-ponent crystals and a combined copper bicrystal (denoted CB-6), obtained by sticking component single crystals G1 [4¯79] and G2 [1¯25] together, was investigated. The results showed that the cyclic saturation stresses increased in the order of bicrystals of CB-6 < RB-8 < RB-6 < RB-4. It is indicated that the GB effect caused different degrees of strengthening, which increased with the decreasing width of the RB bicrystals. By surface observation, it was found that only the primary slip system was activated in the combined bicrystal during cyclic deformation. However, an additional slip system appeared near the GB within the crystal G2 [1¯25] in the RB bicrystals (except in the primary slip system), and formed a GB affected zone (GBAZ). The width of the GBAZ was about 400 and 600 μm at plastic strain amplitudes of 0·1% and 0·2% respectively. Meanwhile, using an electron channelling contrast (ECC) technique in the SEM, the dislocation patterns near the GB and within the component crystals were observed. It was found that a two phase structure of persistent slip bands (PSBs) and matrix (or veins) can form in these bicrystals, similar to that in copper single crystals. But these PSBs cannot transfer through the GB during cyclic deformation. Based on the results above, the effect of grain size on GB strengthening of copper bicrystals was discussed.     

Modelling the evolution of particle size distribution during nucleation,growth and coarsening

Abstract

A model, based on the numerical framework of Kampmann and Wagner, has been developed to predict the evolution of particle size distribution (PSD) during the decomposition of supersaturated solid solutions by nucleation, growth, and coarsening. During the early stages of transformation, where nucleation and growth are dominant, the PSD shape is predicted to be constantly evolving. Only during the latter stages of transformation, when coarsening becomes dominant, does the PSD tend towards a steady state shape, which closely matches that expected from classical coarsening theory. It is also predicted that as the PSD evolves, a transient double peak forms and then decays. The physical basis of this double peak has been investigated and the effect of supersaturation on its formation has been predicted.     

BODY PRESSURE DISTRIBUTION OF AUTOMOBILE DRIVING HUMAN MACHINE CONTACT INTERFACE

Aiming at the fatigue and comfort issues of human-machine contact interface in automo- bile driving and based on physiological and anatomical principle,the physiological and biochemical process of muscles and nerves in the formation and development of fatigue is analyzed systematically. The fatigue-causing physiological characteristic indexes are mapped to biomechanical indexes like muscle stress-strain,the compression deformation of blood vessels and nerves etc.from the perspec- tive of formation mechanism.The geometrical model of skeleton and parenchyma is established by applying CT-scanned body data and MRI images.The general rule of comfort body pressm'e distribu- tion is acquired through the analysis of anatomical structure of buttocks and femoral region.The comprehensive test platform for sitting comfort of 3D adjustable contact interface is constructed.The test of body pressure distribution of human-machine contact interface and its comparison with subjec- tire evaluation indicates that the biomechanical indexes of automobile driving human-machine con- tact interface and body pressure distribution rule studied can effectively evaluate the fatigue and comfort issues of human-machine contact interface and provide theoretical basis for the optimal de- sign of human-machine contact interface.     

Ladder Climbing Method for the Limb Mechanism Robot ASTERISK

A ladder climbing method for the limb mechanism robot ASTERISK is proposed. This robot has six legs. The upper three legs hold on to the upper rung from both sides alternately, just like pinching it. The lower three legs hold on to the lower rung in the same way. Hence, the robot can take hold of the ladder stably. First, the robot releases the left upper and lower legs from the current rungs, and hangs them on the next rungs while supporting itself with the other four legs. Then, the mid two legs and the right two legs are moved to the next rungs in sequence. Finally, the robot lifts up its body using the six legs. Depending on the relative pose of the robot to the ladder, the robot automatically selects the legs that can support vertical and/or horizontal forces applied by the rungs. The robot then distributes its weight to the legs supporting the vertical force based on their force margins. The legs that cannot support forces are controlled to always touch the rungs slightly in order to pinch the rungs with the other legs. The advantages of the proposed gait and control method are verified by analysis of the leg workspace for generating the ladder climb gait, analysis of the range of force direction that the legs can support, analysis of the joint torques required for ladder climbing and an experiment on force distribution. Finally, the range of ladder pitch variation that ASTERISK can climb is clarified.     

Torque distribution using a weighted pseudoinverse in a redundantly actuated mechanism

When mobility, the number of independent variables to describe system motion exactly, is greater than the degree-of-freedom of task space, the system is called a kinematically redundant system. On the other hand, redundant actuation indicates a situation when there are more actuators than a system's mobility. Redundant actuation yields many advantages. First, actuation redundancy can increase the force, velocity and acceleration of an end-effector. Second, if some actuators are out of order, the system can still work well. This fault-tolerant capability is useful for remote control robots in space or nuclear plants. Impulsive force can decrease when modulating arbitrary stiffness without feedback control. The performance of a system can be improved by optimizing redundancy. However, there are some issues of economic efficiency and minimization of a system, because redundant actuation may involve more actuators than non-redundant actuation. In addition, there are infinite torque sets of motors for the same task. We used a weighted pseudoinverse matrix for torque distribution. To reduce the maximum torque, we suggested the use of the minimum norm torque as the weighting values. This method allows for smaller motor capacity, and can contribute to economic efficiency and minimization of a system.     

Size distribution of oxides and toughness of steel weld metals

Abstract

Experiments have been conducted to modify the size distribution of oxide particles in steel weld metals which have predominantly martensitic microstructures. It is found that the toughness improves significantly when the particles are refined, even when the total concentration of oxygen is unchanged in the process.     

Dependence of kaolinite content on particle size distribution in Ugandan kaolin clay

Abstract

Semiprocessed kaolin clay was sieved through sieves of various particle size ranges. Particle size distribution was determined using a Malvern laser particle sizer and kaolinite content in each particle size range was determined by X-ray diffractometry. It was found that kaolinite content increased with decreasing particle size range.     

Slag–graphite wettability and reaction kinetics Part 1 Kinetics and mechanism of molten FeO reduction reaction

Abstract

The present paper reports results relating to the kinetics and mechanism of FeO reduction by graphite, the data being obtained from experimental investigations into the wettability of graphite by molten slag containing FeO. The rate of FeO reduction was determined by measuring the volume of CO gas formed as a result of the reduction of FeO in experiments conducted in the same sessile drop apparatus. The reduction reaction initiated by direct slag–graphite contact produces CO gas which spreads into the molten slag droplet causing foaming of the slag; further reduction of FeO proceeds mostly via indirect reduction. The rate of reduction was found to depend directly on the initial FeO content. An increase in temperature improves the rate of reaction, which has an activation energy of 112·18 kJ mol^-1. These results indicate that transport of FeO (Fe²⁺, O^2- ) in the liquid slag phase is probably the slowest step.