Sheet Strips Research Articles

Heat dissipation property of cover glasses with heat sink films for transparent organic light-emitting diodes

We investigate the thermal property of cover glasses with heat sink films and provide useful design guidelines of heat sinks for transparent organic light-emitting diodes (OLEDs). To this end, we inquire into the thermal effect of the thickness of cover glasses, Cu sheet or Cu strip lines attached to cover glasses, transparent metal meshes and polymer composite films fabricated on cover glasses, and their position (i.e., inner or outer surface of the cover glass). It is found that the heat sink property varies depending sensitively on the heat sink position and cover glass thickness. To enhance the heat transfer (sink) property, it is preferred to attach the heat sink to the inner surface of the cover glass without any air involved. If no heat sink is used, then thicker cover glasses are required to dissipate the Joule heat effectively. With high-transparency (>80%) metal meshes, we have achieved about 7% heat dissipation. The polymer composite films (poly(methyl methacrylate) (PMMA) binder mixed with cubic-boron nitride (c-BN) filler) show poor heat sink property due to difficulty in establishing an enough heat transfer pathway using a small amount of fillers.

Direct Evaluation of Coulomb Friction Coefficient from Sheet Strip Stretch Test on a Cylinder Surface

Knowing the flow curve of a sheet metal, strain distribution on a sheet strip may be used to roughly but quickly evaluate the Coulomb friction coefficient. Strain distribution on the strip being stretched on a cylindrical surface of interest may be measured by an optical strain measurement system. This could be used to estimate the stresses on the specimen. The capstan equation is then used to roughly evaluate the coefficient of friction acting between the sheet strip and the cylindrical surface. Validation of the approach is done using the simulation of the process. The corresponding experiments can be performed easily on a sheet metal testing device equipped with an optical strain measurement system, which is commonly used for the experimental evaluation of FLCs.

Study on Inspection Methods for High-Speed Progressive-Die Punched Strips

The inspection of sheet strips post high-speed punching mainly relies on the manual off-line inspection with basic inspection equipment or CCD equipment. Such inspections cannot reflect the real-time conformity of strip machining, and in severe cases, lead to rejects in batches, causing a tremendous waste in production. Now that the application of charge-coupled device (CCD) technology in product inspection is relatively mature, it would be a very good thought to adopt the CCD technology to realize real-time online inspection of conformity of the high-speed punched strips. KeyWords: CCD technology; strip; online automatic inspection; progressive die

Cyclic fatigue of a high-strength corrosion-resistant sheet TRIP steel

The mechanical properties of 0.3- and 0.8-mm-thick high-strength corrosion-resistant TRIP steel having various levels of strength properties are studied during static and cyclic loading in the high-cycle fatigue range. The fatigue fracture surface is analyzed by fractography, and the obtained results demonstrate ductile and quasi-brittle fracture mechanisms of this steel depending on the strength properties of the steel and the content of deformation martensite in it.

Experimental and numerical investigation of springback effect for advanced high strength dual phase steel

In sheet metal forming process of automotive components, the springback effect is crucial, in particular for Advanced High Strength Steels (AHSS), like the dual phase (DP) steel. Most construction parts in modern vehicles having very complex shapes require multi-step forming procedures. In this work, the influences of pre-deformation on the springback of steel AHSS sheets were investigated under consideration of the elastic modulus change. The sheet strips were firstly pre-stretched to a uniaxial engineering strain of 4% and 6%. The steel sheets prepared parallel, transverse, and 45° to the rolling direction were taken into account. A modified S-rail forming test was used to verify the degree of springback of the steel sheets after pre-straining. In parallel, Finite Element (FE) simulations of the S-rail forming test were performed, in which the planar anisotropic Hill’s 1948 material model, Barlat–Lian’s 1989 model, and Yoshida–Uemori kinematic hardening material model were applied. Experimental and numerical results were compared with regard to the final angles between the sample flanges. The effect of the elastic modulus change as a function of plastic strain was examined. It was found that higher pre-deformation state led to a noticeable increasing in springback effect. Considering the variable elastic modulus improved the accuracy of the springback prediction. The Yoshida–Uemori model showed better predictions of the final shape for the investigated steel parts in comparison with other models.

A Phenomenological Model for the Hysteresis Behavior of Metal Sheets Subjected to Unloading/Reloading Cycles

The springback phenomenon is defined as elastic recovery of the stresses produced during the forming of a material. An accurate prediction of the springback puts high demands on the material modeling during the forming simulation, as well as during the unloading simulation. In classic plasticity theory, the unloading of a material after plastic deformation is assumed to be linearly elastic with the stiffness equal to Young’s modulus. However, several experimental investigations have revealed that this is an incorrect assumption. The unloading and reloading stress–strain curves are in fact not even linear, but slightly curved, and the secant modulus of this nonlinear curve deviates from the initial Young’s modulus. More precisely, the secant modulus is degraded with increased plastic straining of the material. The main purpose of the present work has been to formulate a constitutive model that can accurately predict the unloading of a material. The new model is based on the classic elastic-plastic framework, and works together with any yield criterion and hardening evolution law. To determine the parameters of the new model, two different tests have been performed: unloading/reloading tests of uniaxially stretched specimens, and vibrometric tests of prestrained sheet strips. The performance of the model has been evaluated in simulations of the springback of simple U-bends and a drawbead example. Four different steel grades have been studied in the present investigation.

Towards better finite element modelling of elastic recovery in sheet metal forming of advanced high strength steel

The first part of this study discusses the influence of element type on parameters such asaccuracy of the FE simulation, simulation time and convergence. Guidelines on optimal implementation ofelement types are proposed. It is shown that an inappropriate choice of element type results in difficulties inconvergence of the simulation or gives rise to problems such as shear locking in elements. In the secondpart of this study a series of finite element simulations using the Hill’48 planar anisotropic yield criterion anda standard U-shape forming test based on the NUMISHEET’93 benchmark was performed. Theeffectiveness of different isotropic hardening laws and different contact models is investigated. The mostappropriate hardening and contact definitions are defined from the viewpoint of optimal springbackprediction. Finally, the influence of the orientation of sheet strips relative to the rolling direction onspringback angles is evaluated.

Bio-economic assessment of chemical and non-chemical weed management strategies in dry seeded fine rice ( Oryza sativa L.)

Dry seeding of rice offers potential to be opted as a resource conservation technology but its sustainability is endangered by heavy weed infestation. Experiments were conducted during summer season of 2009 to look for effective and economically viable weed control method(s) in dry seeded rice. Four mulching materials of natural origin as sorghum, sunflower and wheat residues each soil incorporated at 8 t ha -1 and black polyethylene sheet strips as artificial origins were used. A weedy check and manual weeding were included for comparison. Label doses of post emergence herbicides, bis-pyribac sodium and penoxsulam, at 30 and 15 g a.i. ha -1 were also used. Manual weeding accounted for maximum (99%) inhibition in weed density and dry weight. Bispyribac sodium suppressed weed count and dry weight by ≈ 80%. Among non-chemical weed management strategies, sorghum residues scored over 50% reduction in weed density and dry weight. Plastic sheet strips were least effective against weeds. Manual weeding scored highest paddy yield of 4.17 t ha -1 . Bispyribac sodium with 3.51 t ha -1 paddy yield appeared superior to penoxsulam. Sorghum, sunflower and wheat residues resulted in

Friction behavior of SUS 304 metastable austenitic stainless steel sheet against DC 53 die under the condition of friction coupling plastic deformation

Fe–Cr–Ni metastable austenitic stainless steel is widely used in industry because of its excellent performance of corrosion resistance in aggressive environment. The process of drawing austenitic stainless steel easily prompts to wear and the relevant friction behavior, under the condition of friction coupling plastic deformation, is seldom studied. This paper studies the friction behavior of SUS 304 metastable stainless steel sheet against DC 53 cold-working forming tool using a self-developed Tribo-tester that simultaneously deploys frictional sliding and tensile plastic deformation. Results indicated that the friction coefficients between SUS 304 sheet strip and DC 53 forming tool firstly descended rapidly in the initial stage A, which is followed by approaching an almost stable state in the successive stage B. In addition, friction coefficients under high sliding speed and large pressure head extension tend to decrease with the increasing of external weight loading. XRD investigation of phase transition reveals the relevant causing mechanisms. SEM observation allows identifying the wear of the SUS 304 steel slid against DC 53 forming tool being mainly adhesive wear and abrasive wear.

On the identification of kinematic hardening material parameters for accurate springback predictions

An experimental method that frequently has been used for the determination of material hardening parameters is the three-point bending test. The advantage of this test is that it is simple to perform, and standard test equipments can be used. The disadvantage is that the material parameters have to be determined by some kind of inverse approach. The test has then been simulated by means of the Finite Element Method, and the material parameters have been determined by finding a best fit to the experimental results by means of a Response Surface Methodology. An alternative method is the tensile/compression test of a sheet strip. In practice such a test is very difficult to perform, due to the tendency of the strip to buckle in compression. In spite of these difficulties some successful attempts to perform cyclic tension/compression tests have been reported in the literature. However, a few writers have reported that there are substantial differences between hardening parameters determined from bending tests and those determined from tensile/compression tests. The purpose of the present study is to try to understand the background of these differences, to find out the influence on predicted springback, and to determine which of the two methodologies for hardening parameter identification is the most suitable one.

Experimental Observation on the Effectiveness of Fiber Sheet Strip Stirrups in Concrete Beams

Experimental observations were made for the effectiveness of fiber sheet strips (FSSs) as internal stirrups in comparison with fiber-reinforced polymer (FRP) rod stirrups and steel stirrups. A total number of 10 concrete beams were tested under three-point loading. Each beam measured 1,400 mm long, 150 mm wide, and 250 mm deep. Their shear span-depth ratios were 2.5. The beams were composed of different shear reinforcements: one without stirrups, two with steel stirrups, one with carbon FRP rod stirrups, and the rest with different types of FSS stirrups. The main variables include stirrup types, strengthening of bent portions of FSS stirrups, impregnation, and shear reinforcement ratio for FSS stirrups. Test results indicated that concrete beams reinforced with FSS stirrups had enhanced shear strength over the beam without shear reinforcements. Moreover, the FSS stirrup-reinforced beams could maintain comparable shear behavior to that of the concrete beam reinforced with steel stirrups in overall load-def...

Use of fibre sheet strip stirrups for internal shear reinforcement of concrete beams

In this research, experimental observations were made for the possible application of fibre sheet strips (FSS) as internal stirrups in place of fibre-reinforced polymer (FRP) rod stirrups currently being used for reinforced concrete beams. A total number of eight concrete beams were tested under three-point loading. Each beam measured 1200 mm long, 150 mm wide and 250 mm deep. Their shear span/depth ratios were 2·1. The beams were composed of different shear reinforcements: one without stirrups, one with steel stirrups and the rest with different types of FSS stirrups. Commercially available carbon fibre sheets were used for FSS stirrups. The main variables included strengthening bent portions of FSS stirrups, surface treatment and impregnation for FSS stirrups. Test results indicated that concrete beams reinforced with FSS stirrups enhanced shear strength over the beam without shear reinforcements. Moreover some of them could maintain comparable shear behaviour to that of the concrete beam reinforced with steel stirrups in overall load–deflection relationships, shear strengths, crack patterns and crack widths at maximum load.

Anisotropic finite plasticity with combined hardening and application to sheet metal forming

In this work, we discuss a finite strain constitutivemodel combining both nonlinear isotropic and nonlinear kinematic hardening. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong-Frederick kinematic hardening. The evolution of elastic anisotropy is represented by defining the Helmholtz free energy as a function of a family of evolving structural tensors. In addition, plastic anisotropy is modelled via the dependence of the yield surface on the plastic deformation and on the structural tensors. The integration of the evolution equations has been performed by means of a new form of the exponential map algorithm which automatically satisfies plastic incompressibility and retains the symmetry of the internal variables. The model has been validated based on experimental data and simulations of draw bending of a sheet strip and deep drawing of a cup.

Experimental Study of Springback in Draw Bend Test of AZ31B Magnesium Alloy Sheet

Springback has been measured under various process conditions corresponding to those found in real press-stamping operations. The draw bend tests originally developed at Ohio State University (Carden et al., 2002 [1]) were conducted using a range of tool radii, direct controlled constraining forces, and friction conditions. Especially, the draw-bend test was able to apply precise constant restraining force and almost negligible friction by rotating the cylindrical tool with the same speed of drawn sheet strip. Springback angle changes were measured for the bending and sidewall curl regions to find the dependence on the process variables. As expected, tensile restraining force dominates the springback sensitivity, with higher forces reducing springback. The measured springback angles and curvatures were reported for use in modeling of springback of higly anisotropic and asymmetric magnesium alloy sheets.

Survey of the in situ configuration of cold-rolled, nickel-rich NiTi sheets to create variable component functions

An outstanding feature of shape memory alloys is their potential to produce different functional effects, like thermal shape memory or superelasticity in one component. The cold-rolled NiTi sheet strips presented in this study offer various options, since they do not feature perceptible thermal shape memory or superelasticity due to a high dislocation density. Instead, to achieve a specific local function, the sheet strips are subjected to in situ heat treatment carried out by a laser or a local resistive heating element. There is a need to adjust the duration and intensity of the heat input in order to obtain different functional properties.

Bending Under Tension Test with Direct Friction Measurement

A special bending-under-tension (BUT) transducer has been developed in which friction around the tool radius can be directly measured when drawing a plane sheet strip around a cylindrical tool pin under constant back tension. The front tension, back tension, and torque on the tool pin are all measured directly, thus enabling accurate measurement of friction and direct determination of lubricant film breakdown for varying normal pressure, sliding speed, tool radius, and tool preheat temperature. The transducer is applied in an experimental investigation focusing on limits of lubrication in drawing of stainless steel, showing the influence of varying process conditions and the performance of different lubricants.

Anticlastic curvature in draw-bend springback

Draw-bend springback shows a sudden decline as the applied sheet tension approaches the force to yield the strip. This phenomenon coincides with the appearance of persistent anticlastic curvature, which develops during the forming operation and is maintained during unloading under certain test conditions. In order to understand the mechanics of persistent anticlastic curvature and its dependence on forming conditions, aluminum sheet strips of widths ranging from 12 to 50 mm were draw-bend tested with various sheet tensions and tool radii. Finite element simulations were also carried out, and the simulated and measured springback angle and anticlastic curvature were compared. Analytical methods based on large deformation bending theory for elastic plates were employed to understand the occurrence and persistence of the anticlastic curvature. The results showed that the final shape of a specimen cross-section is determined by a dimensionless parameter, which is a function of sheet width, thickness and radius of the primary curvature in the curled region of an unloaded sample. When the normalized sheet tension approaches 1, this parameter rapidly decreases, and significant anticlastic deflection is retained after unloading. The retained anticlastic curvature greatly increases the moment of inertia for bending, and thus reduces springback angle.

Prediction of wrinkling initiation in sheet metal forming processes

The initiation and growth of wrinkles are influenced by many factors such as stress ratios, the mechanical properties of the sheet material, the geometry of the workpiece, contact condition, etc. It is difficult to analyze wrinkling initiation and growth while considering all the factors because the effects of the factors are very complex and studies of wrinkling behavior may show a wide scattering of data even for small deviations in factors. The finite element analyses of wrinkling initiation and growth in sheet metal forming process provide detailed information about the wrinkling behavior of sheet metal. The direct analysis of wrinkling initiation and growth, however, brings about a little difficulty in complex industrial problems because it requires large memory size and long computation time. From the industrial viewpoint of tooling design, therefore, readily available information on the possibility and location of wrinkling is sometimes more preferable to detailed and time‐consuming analysis results. In the present study, in order to give such readily available information on wrinkling initiation, the wrinkling factor, which shows the locations and relative possibility of wrinkling initiation, is proposed as a convenient tool of relative wrinkling estimation based on the energy criterion. The reliability of the wrinkling factor is verified through the buckling analyses of sheet strips. The location and relative possibility of wrinkling initiation are predicted by calculating the wrinkling factor in various sheet metal forming processes such as cylindrical cup deep drawing, spherical cup deep drawing, and elliptical cup deep drawing. Finally, the wrinkling factor proposed in the present study is also implemented in the prediction of wrinkling in the door inner stamping process. For verification of the calculated wrinkling factor, detailed zone analyses with fine meshes are carried out for the regions where wrinkling is predicted.

Characterization of interfacial friction in coated sheet steels: influence of stamping process parameters and wear mechanisms

By means of a tensile strip testing system, the nature of interfacial friction in stamping operations were investigated for three different coated sheet steels. Friction coefficient measurements were taken at seventeen distinct operating conditions by varying the sheet strip coating material (lead and zinc), applied lubricant (oil-base lubricants and greases) and pin radii (10 and 20 mm). In addition to determining the friction coefficient, the surface roughnesses of the sheet strips were measured before and after the completion of each test. From the experimental results, several relationships were ascertained for the role of the microscopic wear in determining the character of interfacial friction during stamping processes.

A frictional study of uncoated EBT steel sheets in a bending under tension friction test

A factorial design was used to investigate the frictional response of different uncoated EBT surface topographies. The test included three different topographies (Sibetex® materials), two lubricants, two contact pressures, and two sliding speeds. The steel sheet strips were subjected to a Bending Under Tension (BUT) friction test. Our findings indicate that the most significant factor, affecting friction, is lubricant viscosity, followed by sliding speed, contact pressure, and surface topography. For measurement of the sheet surface topography, a 3D stylus-instrument was used and the ball-filtering technique was applied. The surface topography was measured in the contact zone on the test samples. The results show that the surface topography is a significant factor, influencing friction in mixed lubrication. The larger the number of isolated lubricant pockets, the smaller is the friction coefficient. These isolated pockets identified here are located in the topmost area and are imprints from the rolls before the first textured rolls.