Sheet Stock Research Articles

Open-source cold and hot scientific sheet press for investigating polymer-based material properties

To produce samples for both material testing and molded sheets/parts, this article details an open-source scientific cold and hot press design. It consists of two independent and modular upper and lower plate (929 cm2) assemblies each containing four 125 W insulated steel strip heaters. The steel housing for these heaters is entirely modular and designed for ease of manufacture, assembly, and customization. This system allows a researcher with access to a hydraulic press to repurpose existing equipment into a multipurpose hot and cold press, or if an independent machine is warranted, an additional welded support frame and commercially available bottle jack offer standalone operation. By utilizing this small-scale hot press either in conjunction with a hydraulic press or on its own, samples can be produced to determine the critical material properties of any polymer, composite, or polymer blend. A series of modular molds allow for the rapid production of flat sheet stock and solid testing samples adhering to the ASTM D695 standard for rigid plastics tested in compression and ASTM D638 standard for testing plastics in tension. The sheet mold offers the user the ability to produce stock sheets that can be cut and assembled into 2.5-D applications with post processing.

Prediction of shear deformation and thickness gradients in deep-draw forming of ultra-high molecular weight polyethylene

Ultra-high molecular weight polyethylene (UHMWPE) composite armor offers a high level of lightweight protection. In the manufacturing of complex curvature UHMWPE based protective materials, UHMWPE composites are transformed from flat sheet stock to a near net shape complex curvature preform through deep-draw forming. The development of a deep-draw forming process model is critical for predicting UHMWPE sheet deformation during processing and knowing the fiber orientations at each location in the entire final part. This work introduces a robust methodology to model the deep-draw forming process. The model is validated by comparing critical output with experimental results for multiple UHMWPE materials and over a range of part thicknesses. A hemispherical geometry is used to demonstrate the methodology. A homogenization strategy for grouping sheets is presented and validated, which is critical for keeping computational times manageable. The influence of the material in-plane shear response, a critical model input, is investigated. The model developed in this work represents a valuable tool for selecting deep-draw forming parameters and accelerates the evaluation of new and emerging UHMWPE materials for application in manufacturing complex curvature protective armor.

Addressing corrugated board warp with a 23 factorial design

The corrugator is a machine that produces combined corrugated sheet stock from roll stock. A 23 factorial experiment was used to determine which factors and levels provide the optimal result - flat, rather than warped, sheet stock in a full-line box plant located in the Southeast. The factors include Edge Tension (T), Preheater Wrap Pressure (P), and Run Speed (S). The response variable is board warp, measured in 1/64ths of an inch. The two levels are indicated by (+) or (-) signs to indicate high and low levels, respectively. In a 23 factorial design, there are 8 treatment combinations and n = 20 samples of each combination of factors and levels were collected and analyzed using one replication for immediate use in a real-time production environment. The conclusion yielded the following best settings to produce flat 200#C sheet stock: loose tension, 25% pressure on the preheater wrap, and a run speed of 380 ft/min.

Rolling of ingots of third-generation high-strength steels into sheets

One of the essential branches of today’s engineering production involves the production of sheet stock by rolling. In the automotive industry is used the majority of steel sheet stock. In recent decades, this sector has been striving to reduce vehicle emissions. One of the available solutions involves the use of advanced high-strength steels whose chemical composition and strengthening mechanisms make it possible to build the car body with thinner sheet blanks than before. For rolling trials in which ingots were converted into 1.8 mm sheet by combined hot and cold rolling were used two advanced high-strength steels containing 0.2 wt. % carbon and additions of manganese, silicon and different levels of aluminium. This procedure was found to produce strengths in excess of 1000 MPa combined elongation of more than 15 %.

Modeling drawings of a cylinder detail without clipping a working flange from an isotropic and anisotropic metal

The issue of drawing a cylindrical part without pressing the flange of a flat workpiece in the form of numerical simulation using the software package “Simullia Abaqus” is considered. In this case, isotropic and anisotropic sheet metal is modeled in order to identify the features of their deformation and the validity of assumptions in the analytical models of the isotropy of the material. It is shown that the distribution of stresses and strains for anisotropic and isotropic billets is identical. To conduct a qualitative analysis of the drawing processes, it is sufficient to limit itself to an isotropic metal model. This will greatly simplify the resulting analytical expressions and the time for interpreting the results. To clarify the solutions, it is necessary in mathematical models to take into account the anisotropy of the sheet stock, which will make it possible to identify areas of increased strength and ductility of the workpiece, as well as quantitatively predict thinning in a dangerous section. It is shown that the initial anisotropy increases the stiffness coefficient of the stress state scheme. This leads to a worsening of the deformation conditions and the exhaustion of the ductility resource earlier than for an isotropic billet. At the same time, the appearance of corrugations is accompanied by displacements and rotations of material points of the initially flat billet, however, for anisotropic billet, these displacements develop faster along the course of forming, but destruction of the billet may occur later due to the greater strength of the billet in thickness in comparison with the strength in the sheet plane. Three-dimensional modeling allowed us to study the distribution of normal stresses acting across the thickness of the workpiece. At the radii of curvature of the punch and the bottom of the workpiece, compressive stresses act, in the flange and walls - tensile stresses. It was established that an increase in the strength over the thickness of the workpiece in the form of an increase in the elastic modulus of the first kind made it possible to reduce the deformation of the anisotropic workpiece in a dangerous section. To increase the degree of deformation during drawing in one transition, it is necessary to choose a metal with enhanced strength indicators for thickness or to carry out preliminary preparation of sheet metal before shaping. This will make it possible to reduce the thickness of the workpiece without losing the strength of the final product and, thereby, reduce the metal consumption of the assembly unit.

Quasi-static and dynamic mechanical behavior of transparent graft-interpenetrating polymer networks (graft-IPNs)

Mechanical characterization of transparent graft Interpenetrating Polymer Networks or graft-IPNs based on polyurethane and acrylic copolymer are reported under both quasi-static and dynamic loading conditions. This study builds on an earlier work detailing the synthesis of the graft-IPNs [1]. Optically transparent graft-IPNs were synthesized using elastomeric polyurethane (PU) phase and stiff acrylate-base copolymer (CoP) phase. The ratios of CoP:PU were varied from 90:10 up to 60:40 by weight. Two grades of graft-IPNs were synthesized by using 650 g mol−1 and 1400 g mol−1 poly (tetramethylene ether) glycol (PTMG) during synthesis to study the molecular weight effect. Quasi-static tensile and fracture tests as well as dynamic fracture tests were performed. The dynamic fracture tests were carried out at high strain rate using a modified-Hopkinson pressure bar in conjunction with an optical technique called Digital Gradient Sensing (DGS) and ultrahigh-speed photography. Quasi-static tests indicate significant enhancements in crack initiation toughness and change in failure mode (brittle to ductile) when the constituents were varied. Enhancements in crack inititation toughness were also observed under dynamic loading. These results were further compared with those for commercial poly (methyl methacrylate) (PMMA) and polycarbonate (PC) sheet stock. Further improvement in fracture properties were observed under quasi-static loading conditions with increase in molecular weight of PTMG. The relatively high values of fracture toughness obtained for graft-IPNs is attributed to the crosslinks generated between the CoP and PU networks.

Characterization of He-Induced Bubble Formation in Tungsten due to Exposure from an Electron Cyclotron Resonance Plasma Source

A compact electron cyclotron resonance plasma source has been utilized at Sandia National Laboratory to expose heated W samples (1270 K) to 50–75 eV He ions at fluxes on the order of 1019 m−2 s−1 and fluences on the order of 1024 m−2. Scanning electron microscopy (SEM) analysis of the surface has indicated bubbles up to 150 nm in diameter that exhibit signs of bursting near the surface. Comparisons have been made between W samples prepared from warm-rolled W sheet stock and ITER-Grade W rod stock. Focused ion beam (FIB) cross sectioning has been used with SEM and transmission electron microscopy (TEM) to identify large sub surface bubbles (100 nm diameter) at depths up to one micron as well as a dense layer of smaller bubbles (<10 nm diameter) within the first 100 nm of the surface, similar to bubble layers observed on higher flux experiments. SEM-Electron Backscatter Diffraction (EBSD) analysis has identified a unique surface morphology feature associated with the exposed ITER-Grade W as well as features similar to previous EBSD studies of rolled W stock. Thermal desorption spectroscopy (TDS) analysis has identified that pre-existing He bubbles found in the Sandia He-ion exposed samples do alter the D trapping and desorbing behavior in W. The findings from these preliminary characterization studies are presented and discussed in context with results from similar plasma exposure stages at other facilities around the world.

Probabilistic fracture of Ti–6Al–4V made through additive layer manufacturing

The large deformation response of Ti–6Al–4V parts made through additive layer manufacturing is investigated. A wire-feed process is chosen instead of a powder process in an attempt to reduce the oxide contaminations of the final part. The experimental program includes uniaxial tension experiments along different part directions and fracture experiments on flat specimens with cut-outs covering stress states ranging from pure shear to equi-biaxial tension. More than 100 experiments are performed in total to characterize the randomness in the material's fracture response. It is found that the stress-strain response of the ALM material is comparable to that of Ti–6Al–4V sheet stock, while its average ductility is substantially lower. For example, for pure shear loading, the average strain to fracture for the ALM material is 0.47, while the mill product of the same alloy failed at a strain of 0.65. A probabilistic extension of the stress state dependent Hosford–Coulomb fracture initiation model is proposed to account for the significant standard deviation in the identified strains to fracture. Microscopic and surface strain field analysis demonstrate that the initiation and propagation of ductile fracture in the ALM material is strongly affected by the presence of prior-beta grains.

Recent developments in aluminium sheet manufacture for car body panels

The formability of the aluminium used in automobile bodies is due not only to the chemical composition, but also to the sheet stock fabrication process. The Valais works of Alusuisse have developed a manufacturing process for Anticorodal–120® sheets (an age–hardening alloy type AlSi1.2Mg0.4 patented by Alusuisse). This paper describes the influence of the various process steps on the main formability parameters, such as uniform elongation, strain hardening and the ratio UTS/yield. The very slow natural ageing of Anticorodal–120®, which is a great advantage for the customer, is also presented. Thanks to optimization of composition and processing, Anticorodal–120® has been chosen by several major automobile manufacturers for new models and especially for difficult parts.

A Composite Surface Formation during Friction Surfacing for Aluminum Pipe Internally Coated With Zinc

Coating involves the application of a thin film of functional material to a substrate, such as paper, fabric, film, foil or sheet stock. Coatings may be applied as liquids, gases or solids. Coatings can be measured and tested for proper opacity and film thickness by using a draw down card. At the lower speed and lower forward time, the hardness is approximately equal but a slightly difference in hardness. The hardness increases with an increase in reverse time at high speed of the pipe and higher forward time but there is a difference in hardness at lower forward time and higher forward time. The thin film is formed during machining between aluminum and zinc. The hardness of the internal surface of the pipe varies with the speed of the pipe at the constant forward time and reverse time. This happens due to lower speed and at higher forward and lower reverses time results higher friction leads to more deposition. The coating thickness is increases with an increase in forward time at low speed and low reverse time. The coating thickness is higher at higher forward time and lower reverse time due to more amount of zinc deposition due to more axial compressive forces. The coating thickness is increases with an increase in forward time at the condition of higher pipe speed and at lower reverse time due to higher plastic deformation which results coarse grain structure. The coating thickness of the internal surface of the pipe varies with the speed of the pipe at the constant forward time and reverse time. This happens due to lower speed and at higher forward and lower reverses time results higher friction leads to more deposition. The study reveals it is a technique to improve the properties at the interface between aluminum and zinc.

Architecture Options for Carbon Nanotube Papers

This report discusses nonwoven papermaking as a method for producing varieties of binderless, free-standing carbon nanotube (CNT) sheets. Examples portray how papers may be prepared from mixtures of different nanotube types to tailor them for use in specific energy storage applications. The technique’s ability to craft sheets for composition, air flow, density, etc. will only expand as more nanomaterials become commercially available. The advantages and limitations of the method are offered, and a pilot production process that can continuously produce 12” wide sheet stock is described.

Nondestructive evaluation of transparent sheets using a full-field digital gradient sensor

Abstract A full-field, non-contact, optical inspection tool for transparent materials is demonstrated. The technique is sensitive to refractive index and thickness variations caused by inhomogeneities and defects in an otherwise uniform sheet stock. The technique utilizes a 2D digital image correlation method to visualize and quantify angular deflections of light rays in two orthogonal directions to assess the uniformity. The principle of the method and its feasibility is demonstrated by visualizing the heat affected zone in a uniform borosilicate sheet sample.

Hot deformation behavior of friction-stir processed strip-cast 5083 aluminum alloys with different Mn contents

Abstract Fine grained 5083 aluminum alloy is the most common Al–Mg alloy for superplastic forming (SPF) of lightweight sheet metal parts in the automotive and aerospace industries. The fine grained sheet is industrially produced by massive cold rolling of conventionally rolled sheet stock at high cost. Friction stir processing (FSP) as a thermomechanical process is very effective in refining the microstructure of as-cast alloys such as that produced by continuous strip casting (CC). In this work, the effect of friction stir processing on the superplastic properties of three CC 5083 aluminum alloys, with different Mn content, has been investigated. The three alloys were friction stir processed. Very fine microstructures with grain sizes less than 3 μm were obtained. Tensile tests revealed elongations of over 600% at a high strain rate of 10−1 s−1 in all 3 alloys. The maximum tensile elongation of 800% was achieved in the alloy with the lowest Mn content at 490 °C and strain rate of 3 × 10−2 s−1. The stability of the microstructure was an important concern above 500 °C.

The fundamental relationships between grain orientation, deformation-induced surface roughness and strain localization in an aluminum alloy

Abstract Polycrystalline AA6022 tensile specimens were cut from sheet stock, mechanically polished, and uniaxially strained in situ under a scanning laser confocal microscope (SLCM) using a sub-sized universal testing apparatus. Prior to deformation, electron backscatter diffraction (EBSD) was performed on the gauge sections of one specimen in the rolling direction of the sheet and one in the transverse direction. Maps of the largest displacements in the surface morphology were constructed from the SLCM data and overlaid onto maps derived from the crystallographic orientation data to examine the strength of the influence that grain orientation effects have on critical strain localization. The roles of Taylor factors, grain boundary misorientation, largest Schmid factors, grain sizes, coincident site lattice orientations, and local grain breakup were considered. The largest surface displacements were observed to be concentrated at triple junctions where there is a large difference between the Taylor factors of the individual grains. The high degree of correlation between the density and location of these large surface displacements and the local plasticity conditions indicate that a critical localization event is most likely to initiate in grain boundary regions where unfavorable slip interactions produce the largest plastic strains.

Sequential quadratic programming method with a global search strategy on the cutting-stock problem with rotatable polygons

The cutting-stock problem, which considers how to arrange the component profiles on the material without overlaps, can increase the utility rate of the sheet stock. It is thus a standard constrained optimization problem. In some applications the components should be placed with specific orientations, but in others the components may be placed with any orientation. In general, the methods used to solve the cutting-stock problem usually have global search strategies to improve the solution, such as the Genetic Algorithm and the Simulated Annealing Algorithm. Unfortunately, many parameters, such as the temperature and the cooling rate of the Simulated Annealing method and the mutation rate of the Genetic Algorithm, have to be set and different settings of these parameters will strongly affect the result. This study formulates the cutting-stock problem as an optimization problem and solves it by the SQP method. The proposed method will make it easy to consider different orientations of components. This study also presents a global search strategy for which the parameter setting is easy.

Blotching in roll coating

After thermoforming, plastic parts are stacked for shipping, and these parts tend to stick together. Called nesting, sheet stock is often first coated with a silicone compound before thermoforming to prevent this. The coating usually consists of a small amount of lubricant dispersed in a majority of carrier fluid, and this fluid must then dry before reaching the sheet winder or else the coating blotches. This coupling of coating and drying to determine when to expect blotching is examined. Roll coating involves a dimensionless group called the elasticity number that governs the thickness of the coating to be dried. The drying section involves the evaporation of the coating carrier fluid, and then diffusion into the dry surrounding atmosphere. When analyzing the drying, a new dimensionless group that governs blotching is discovered, called blotchability. The result of this analysis allows practitioners to determine which operating conditions cause blotching, and how to eliminate it. Roll coating uses a deflecting rubber roll to apply vanishingly thin coatings (≤1 μm), an interesting elastohydrodynamic problem.

Rotational Placement using Simulated Annealing and Collision Free Region

Abstract The packing problem, which considers how to arrange items on a container without overlaps, can increase the utility rate of the sheet stock. This paper investigates the irregular shape rotational packing problem. In this work the Simulated Annealing (SA) is combined with deterministic heuristics (larger first (LF), bottom left (BL) and translations only (Tr)). The problem is represented as an ordered list of items to be packed, and the items are placed touching already placed items or container. The items are placed on the vertices of the collision free region (CFR). The CRF is determined by a robust implementation of non manifold Boolean operations. Several results comparing the SA with deterministic heuristics are presented.

Fundamental relationships between deformation-induced surface roughness, critical strain localisation and failure in AA5754-O

This research employs two approaches to characterise the apparent structure observed in localised strain maps constructed from surface topography data acquired from AA5754-O sheet stock that was deformed in three in-plane stretching modes. The first uses a conventional two-point autocorrelation function (ACF), while the second uses the combination of the eigenvalue spectrum associated with each map and information theory. The results from the ACF analysis are inconclusive, implying that this technique lacks the sensitivity necessary to quantify the relationships between multi-point clustering and strain localisation. The information theory-based approach reveals that the relative spectral entropy increases monotonically, attains a maximum and then decreases sharply to the failure strain. This behaviour occurs in all three strain modes and results from two competing processes: one where the formation of structure is favourable and one where it is not. The crossover point is a clear indicator of the onset of critical strain localisation and, therefore, can be regarded as a precursor to failure because once the dominant process shifts, additional strain results in the precipitate formation of a critical strain localisation event.

A study at understanding the mechanisms governing the high cycle fatigue and final fracture behavior of the titanium alloy: Ti–4Al–2.5V

In this research paper, the cyclic stress amplitude-controlled high cycle fatigue properties and fracture behavior of a titanium alloy are presented and discussed. The material chosen for this study is a Ti–Al–V–Fe–O 2 alloy that is marketed under the trade name ATI 425™. This alloy was initially developed and put forth for use as a ballistic material but through the last few years it gained in stature for use in other areas due to a healthy combination of physical and mechanical properties. Test specimens were prepared, in conformance with the ASTM E-8 standard, from the as-received sheet stock, which was cold rolled and mill annealed, with the rolling direction both parallel (longitudinal) and perpendicular (transverse) to the length of the sheet. The test specimens were cyclically deformed at three different load ratios ( R = 0.1, R = 0.3 and R = 0.033) and the cycles-to-failure ( N f) was recorded. The fatigue fracture surfaces were examined in a scanning electron microscope to examine the macroscopic fracture mode, the intrinsic features on the fatigue fracture surface and the role of magnitude of applied stress–microstructural feature interactions in governing failure.

Rolling of Plates and Sheets from As-Cast Ti-6Al-4V-0.1B

Trace boron addition (~0.1 wt.%) to conventional titanium alloys reduces the as-cast prior-beta grain size by an order of magnitude to about 200 μm, a grain size typically observed after ingot breakdown. In this study, the feasibility of producing plate and sheet by hot rolling of as-cast Ti-6Al-4V-0.1B (wt.%) was evaluated. Starting from an initial thickness of 25 mm, as-cast Ti-6Al-4V-0.1B was successfully rolled to 2 mm sheet in a multistep rolling process. As-cast Ti-6Al-4V (without boron addition) rolled under similar conditions exhibited severe cracking. Tensile properties of the sheets and plates made from the boron-containing alloy met or exceeded AMS 4911 specifications for Ti-6Al-4V plates and sheets produced by conventional processing route. The process of making plate and sheet stock from cast titanium alloy ingots, without recourse to expensive ingot breakdown, can significantly reduce the number of expensive and time-consuming processing steps for making titanium alloy components, thereby enhancing the affordability and expanding the range of titanium applications.