Microstructure and mechanical properties of curved AZ31 magnesium alloy profiles produced by differential velocity sideways extrusion

Lightweight curved profiles are widely utilised in the transportation industry considering the increasing need for improving aerodynamic efficiency,aesthetics and cutting emissions.In this paper,curved AZ31 Mg alloy profiles were manufactured in one operation by a novel process,differential velocity sideways extrusion(DVSE),in which two opposed rams were used.Effects of extrusion temperature and velocity(strain rate) on curvature,microstructure,and mechanical properties of the formed profiles were examined.Profile curvature was found to be more readily controlled by the velocity ratio of the bottom ram v2to the top ram v1,whereas extrusion temperature(T=250,300,350℃)and extrusion velocity(v_(1)=0.1,1 mm/s) slightly affect curvature for a given velocity ratio.A homogeneous microstructure with equiaxed grains(~4.5 μm) resulted from dynamic recrystallisation(DRX),was observed after DVSE(v_(2)/v_(1)=1/2) at 300 ℃ and v_(1)=0.1 mm/s,where the initial billet had an average grain size of ~25 um.Increasing extrusion temperature leads to grain growth(~5 μm) at 350 ℃ and v_(1)=0.1 mm/s.DRX is incomplete at the relatively low temperature of 250℃(v_(1)=0.1 mm/s),and higher strain rate with v1=1mm/s(T=300℃),resulting in inhomogeneous bi-modal necklace pattern grains ranging in size around 1-25 μm for the former and 2-20μm for the latter.Grain refinement is attributed to DRX during the severe plastic deformation(SPD) arising in DVSE,and initiates at the prior boundaries of coarse grains in a necklace-like manner.Compared with the billet,micro-hardness and ultimate tensile strength of the profiles have been enhanced,which is compatible with grain refinement.Also,an obvious increase in tensile ductility was found.However,yield strength slightly decreases except for the complete DRXed case(300℃,v_(1)=0.1 mm/s),where a slightly higher value was found,indicating strengthening by grain refinement is greater than softening caused by texture modification.The initial billet had a strong basal texture wherein the {0002} basal plane is oriented parallel to the extrusion direction(’hard’ orientation),while DVSE results in the profiles having weak basal textures and the {0002} basal plane oriented ~5-10° to the extrusion direction(i.e.towards the orientation for easier slip).This significantly modified texture contributes to the softening of the profiles in the extrusion direction,in which tensile tests were performed,and the related elongation improvement.

TRIGONOMETRIC CURVE MODIFICATION OF SCROLL PROFILE AND ITS EFFECT ON PERFORMANCES OF A SCROLL COMPRESSOR

A modification of central profile with trigonometric curve is proposed based on the theory of engagement of scroll compressor. General modification equations for central profile of a pair of scrolls are given and various modification patterns are discussed. The equidistant method is employed to calculate the volume of a sealed chamber and a set of general equations is represented. Modification parameters affecting geometric and dynamic property of a scroll compressor are analyzed systematically, and the relations between them are accurately determined. The condition for transforming a trigonometric curve modification into an arc-curve modification is explained. The conclusions can also be applied to other scroll fluid machines.

THEORETICAL TOOTH PROFILE AND ITS SUBSTITUTE CURVE OF THE PINION CUTTER FOR PINHOLES

The formula for the engaging curve of the pinion cutter with pitholes and the formula forthe theoretical tooth profile of the tinion cutter for the generating gearing of pinhoes are developedbased on the engaging theory. The substitute curve of the theoretical tooth profile of the pinion cut-ter is determined by the least square method.

Experimental Study on Reflection Coefficient of Curved Perforated Plate

A set of experiments is carried out in a towing tank to study the effects of the curvature of perforated plates on the wave reflection coefficient （Cr）. The curvature of a perforated plate can be changed by rotating a reference perforated plate about its origin point according to the parabolic equation y=-x2 A plunger-type wave maker is used to generate regular waves. The reflection coefficients are calculated using Goda and Suzuki’s （1976） method. The results are compared with those of vertical or sloped passive wave absorbers. The comparison shows that a perforated plate with a curved profile is highly efficient in terms of reducing the wave reflection coefficient. A correlation is established to estimate the reflection coefficient of curved perforated plates as a function of both flow and geometry characteristics.

Research on Complexity of Surface Undulating Shapes of Rock Joints

The surface undulating shapes of rock joints have been described qualitatively or experimental quantitatively for a long time. The non determined describing method can not fit quantitative evaluation of mechanical parameters of rock joints in engineering. In this paper, relative amplitude ( R A) is chosen as a quantitative describing index of surface measurement of 1 023 surface undulating curves which conducted by profile curve device(PCD). We discuss the nonuniformity,anisotropy and unhomogeneity of surface undulating shapes of joints. A new method that analyzes the complexity of surface undulating shapes of rock joints directional statistically in various rock joints is also put forward.

A Study on Application of Fractal Theory in Examination of Striation Marks

Use scissors and cutting pliers to produce some striation marks. The data collection apparatus is used to collect the surface data of such marks produced by scissors and cutting pliers, and then get the profile curve that is vertical to the surface of striation marks. In tha application of fractal theory, the fractal dimension of such a profile curve is then calculated, and further studies are made on its fractal characteristics. As an exploration on tool types and individual identification, this is aimed to provide a new theory and approach to examination and identification of striation tool marks.

Design methodology of an osculating cone waverider with adjustable sweep and dihedral angles

When considering the practical engineering application of a waverider,the on-design and off-design aerodynamic characteristics of the design conditions,especially the lift-to-drag ratio and the stability,deserve attention.According to recently studies,the planform and rear sight shape of a waverider are closely related to the above aerodynamic performance.Thus,the planform leading-edge profile curve used to design the planform shape of a vehicle is applied to designing an osculating cone waverider.Two key parameters concerned in planform and rear sight shape,namely the plan view sweep angle of the leading edge and the dihedral angle of the underside are introduced to the waverider design process.Each parameter is inserted in the control curve equation.Especially,a parameterization scheme is put forward for the free adjustment of the sweep angle along the leading edge.Finally,three examples are generated for verification and investigation.After the verification process based on the inviscid flow field of one case,the influences of the sweep and dihedral angles on the lift-to-drag ratio and the lateral static stability are evaluated,and meaningful results are obtained.Based on these results,we can conclude that,considering the maximum lift-to-drag ratio,the sweep angle plays a role on the lift-to-drag ratio only at subsonic and trans/supersonic speed as a negligible effect is observed at hypersonic speeds,whereas the dihedral angle is seem to produce a relevant difference at hypersonic speeds.Considering the lateral static stability,the dihedral angles have more influence on the waverider than the sweep angles.