Shear Plane Direction Research Articles

Strain Rate of Metal Deformation in the Machining Process from a Fluid Flow Perspective

Metal cutting speeds are getting faster with the development of high-speed cutting technology, and with the increase in cutting speed, the strain rate will become larger, which makes the study of the metal cutting process more inconvenient. At the same time, with the increase in strain rate, the dislocation movement controlling the plastic deformation mechanism of metal will change from thermal activation to a damping mechanism, which makes the metal deformation behave more like a fluid. Therefore, it is necessary to explore new ways of studying machining from the perspective of fluid flow. Based on this, a fluid model of the metal cutting process is established, and a method for calculating the strain rate is proposed from the point of view of flow. The results of the simulation and measurements are compared and analyzed. The results show that the strain rate on the rake face will be affected by the friction between the chip and tool; the nearer the distance between the chip layer and tool rake face, the bigger the strain rate will be. The strain rate in the central shear plane is much larger than in other areas along the shear plane direction, and in which two ends are the biggest. It can achieve rougher, quantitative research. This shows it is feasible to study machining from the viewpoint of fluid flow, though it still needs a lot of theoretical support and experimental confirmation.

Prediction of die-roll in fine blanking by use of profile parameters

Abstract Fine blanking (FB) is a press shearing process that can obtain a smooth clean-cut sheared edge surface in one press stroke. However, the convex portion of the punched out part or product will generally include a large amount of die-roll or shear-droop defined by a component (Z) in the shear plane direction (z-direction) as well as in the planar direction (x-direction). The droop often will cause various product malfunctions, such as decrease in the contact length as in the engagement of a gear pair by the larger z-directional droop, and a reduction of the effective contact area with the x-directional droop. Since the FB process inevitably causes droop, leading to the reduced functionality of parts, the amount of droop is an important factor, when fabricating parts, using the FB method. Therefore, our final aim is to realize fine-blanked components without droop. As the first step, we attempted to predict the dependence of the amount of droop on the FB parameters which include the punch-die clearance, the material and its thickness, the included angle, and the radius of the convex portion in the case of common work piece profile components. From careful observation of the experimental results for various work materials and that were fine-blanked by an FB die set, we were able to obtain a simple and integrated formula to predict the amount of droop. We believe that the use of this formula will increase the efficiency of trial-and-error procedures performed before mass production, enabling the manufacture of components for customers with a shorter lead time.

Method of strain-rate difference calculation in high-speed metal cutting

Abstract High-speed machining has been widely studied around the world for its high efficiency and high quality. However, conducting a quantitative study on many physical parameters is difficult when cutting speed is high. A simple and effective measurement and calculation method is necessary in engineering application. From the flow point of view, a difference calculation method through mesh length measurement is proposed, which can be easily used to determine the strain rate distribution of high-speed cutting. The distribution of strain rates for aluminum alloy 7050 cutting has been obtained; the results show that the strain rates are as high as 10 5 s −1 during high-speed cutting, and the strain rates near the tool tip are higher than those in other areas in the second deformation zone. In the direction of shear plane, the strain rates are gradually reduced from the center of the first deformation zone to the exterior. The deformation rate in the rake face direction is higher than that in the shear plane direction.

Model for fracture initiation and propagation pressure calculation in poorly consolidated sandstone during waterflooding

During the process of waterflooding, the water injection pressure needs to be increased to improve the water absorption capability of formation. However, the injection pressure should be less than the fracturing pressure. Otherwise, it will cause lots of problems, such as casing failure, caprock damage and the reactivation of faults. The past works indicate that fracturing in poorly consolidated sandstone is different from fracture growth in brittle competent rocks due to strong poroelastic effect and low strength. This paper describes a new model with the consideration of fluid flow and thermal effect to calculate the fracture initiation and propagation pressure. The fracture initiation and propagation criterion for poorly consolidated sandstone is different from the conventional stress intensity factor approach and a new shear criterion with the consideration of the conjugate shear plane direction is proposed. Base on the mechanical and physical properties parameters from Bohai Bay in China, the stresses around the wells during water injection are calculated to determine the failure mode. And the fracture initiation and propagation pressure are obtained with the model. The results of the study show that the fracture in poorly consolidated sandstone during water injection is dominated by shear failure, and the fracture is perpendicular to the minimum horizontal stress. The fracture initiation pressure is less than that calculated by the traditional approaches and is related to the in-situ stress, rock strength, water temperature, water injection rate and Biot's constant. The fracture propagation pressure is related to the in-situ stress, fracture length, rock strength, water temperature, water injection rate and permeability of the fracture. Through this study, the maximum injection pressure can be determined during water injection in poorly consolidated sandstone. In addition, this study could also have application in other areas, such as wellbore stability, sand production, frac-packing.

Deformation Behaviour of Titanium in Torsion

The evolution of microstructure and texture in Hexagonal Close Pack commercially pure titanium has been studied in torsion in a strain rate regime of 0.001 to 1 s-1. Free end torsion tests carried out on titanium rods indicated higher stress levels at higher strain rate but negligible change in the strain-hardening behaviour. There was a decrease in the intra-granular misorientation while a negligible change in the amount of contraction and extension twins was observed with increase in strain rate. The deformed samples showed a C1 fibre (c-axis is first rotated 90° in shear direction and then +30° in shear plane direction) at all the strain rates. With the increase in strain rate, there was an increase in the intensity of the C1 fibre and it became more heterogeneous with a strong {11 6} component. In the absence of extensive twinning, pyramidal slip system is attributed for the observed deformation texture. The present investigation, therefore, substantiates the theoretical prediction of increase in strength of texture with strain rate in torsion.

Effect of pore size on the tensile behavior of open-cell Ti foams: Experimental results

Open-cell Ti foams having an average pore size of 50 and 150 µm, respectively have been subjected to room temperature tensile tests to explore their tensile properties. Since extensometry is difficult in foams due to problems such as localized surface deformation and attachment of clip gauges, the foams' mechanical properties have been measured in this work accurately by the help of a camera which records the resulting dimensional changes during the loading. The camera acts as a non-contact extensometer and thus it helps in avoiding any small amounts of pre-deformation that might be caused by the attachment of conventional extensometer to the sample's surface prior to testing. Ti foam samples of smaller pores were found to experience higher strength and elongation than those with larger ones. The cell walls in both foam samples failed suddenly in the 45° maximum shear plane direction.

Fatigue damage generation in ECAPed oxygen free copper

In order to understand the fatigue damage generation of ultra-fine grained copper, rotating bending fatigue tests were carried out. After the 4 and 8 pass of ECAP ( equal channel angular pressing) with B c route, grains with about 300 nm diameter were formed. The damage profile of fatigued surfaces between annealed pure copper and ECAPed one had substantial difference in morphology was observed. To clarify the formation process of surface damage, morphological change in surface caused by cyclic stresses was monitored successively by using optical microscope. It was found that the surface damages for the ECAPed copper propagated along the projected direction of shear plane in ECAP process.

Analysis of the Mechanism of Soil Cutting : 5th Report, Cutting Theories of Soils

Two-dimensional cutting theories of soils (dry quartz sand and plastic loam) are made. Such quantities of the cutting as the magnitude and directions of the cutting force, its application point, and the direction of shear plane are determined from geometrical cutting conditions, soil failure conditions and frictional conditions between soil and a cutting blade. Experimental results agree approximately with the theoretical results, and it is confirmed both experimentally and theoretically that the cutting force is reduced effectively by the application of electro-osmosis to the low-frictional cutting blade.