Sheet Metal

This paper describes a versatile, and simple synthetic route for the preparation of a range of reduced graphene oxide (RGO)-metal/metal oxide composites and their application in water purification. The inherent reduction ability of RGO has been utilized to produce the composite structure from the respective precursor ions. Various spectroscopic and microscopic techniques were employed to characterize the as-synthesized composites. The data reveal that the RGO-composites are formed through a redox-like reaction between RGO and the metal precursor. RGO is progressively oxidized primarily to graphene oxide (GO) and the formed metal nanoparticles are anchored onto the carbon sheets. Metal ion scavenging applications of RGO-MnO2 and RGO-Ag were demonstrated by taking Hg(II) as the model pollutant. RGO and the composites give a high distribution coefficient (Kd), greater than 10 l g-1 for Hg(II) uptake. The Kd values for the composites are found to be about an order of magnitude higher compared to parent RGO and GO for this application. A methodology was developed to immobilize RGO-composites on river sand (RS) using chitosan as the binder. The as-supported composites are found to be efficient adsorbent candidates for field application.

Sheet and film processes include polymer film extrusion, coating processes of many types, paper manufacturing, sheet metal rolling, and plate glass manufacture. Identification, estimation, monitoring, and control of sheet and film processes are of substantial industrial interest ...

The idea of incremental forming technique has been investigated for production of sheet metal components. With this technique, the forming limit curve (FLC) appears in a different pattern, revealing an enhanced formability, compared to conventional forming techniques. In the present study, the formability of an aluminum sheet under various forming conditions was assessed and difficult-to-form shapes were produced with the technique. By utilizing knowledge and experience obtained during the present study, it became possible to produce some free surfaces.

This paper presents a closed-form theoretical analysis modelling the fundamentals of single point incremental forming and explaining the experimental and numerical results available in the literature for the past couple of years. The model is based on membrane analysis with bi-directional in-plane contact friction and is focused on the extreme modes of deformation that are likely to be found in single point incremental forming processes. The overall investigation is supported by experimental work performed by the authors and data retrieved from the literature.

On the basis of the microstructural evolution after two-stage non proportional loading at finite strains, a so-called microstructural model was developed by that accurately describes the macroscopic anisotropic behaviour such as the Bauschinger effect, the work-hardening stagnation and the work-softening of polycrystalline metals. Many intragranular deformation mechanisms, corresponding to the formation and the evolution of persistent dislocation structures, have been taken into account in choosing the scalar and tensorial internal variables of the elastoplastic model and postulating their evolution equations. In the work discussed here, after a detailed description of Teodosiu-Hu model, several rheological tests and their numerical simulations on different polycrystalline materials are performed in order to evaluate the accuracy and the efficiency of the proposed model. To this aim, a sensitivity study of the material parameters is first carried out in order to show their different effects on the macroscopic behaviour. Therefore, a strategy for their identification is discussed. Regarding to the respective mechanical response of several materials, two simplifications of the proposed model are presented in order to take into account their specific behaviour. Finally, identification of the proposed models is performed and compared to more classical anisotropic work-hardening phenomenological models.

An experimental platform capable of measuring forces in process during an incremental forming procedure is described and some of the earliest measurements of forces in incremental forming with the changes induced on the measured load are reported. Using a table type force dynamometer with incremental forming fixture mounted on top, three components of force were measured throughout the forming process. They were found to vary as the parts were made. The reported experimental test program was mainly focused on the influence of four different process parameters on the forming forces: the vertical step size between consecutive contours, the diameter of the tool, the steepness of the parts' wall and the thickness of the sheet metal being formed. The effect of lubrication and the geometry of the test part in the incremental forming process were investigated by a set of initial experiments. Part failure prediction based on the shape of the force curve is explained. For the tested materials, analytical results demonstrating the relationship between the respective process parameters and the induced forces are presented in this paper.

The paper starts with a brief historical overview to the attempts of numerical simulation of sheet metal forming. Comparison between bulk and sheet metal forming processes from the simulation point of view is given. Basic requirements of the applier to the simulation tools are summarized. Various possible methodologies are brie¯y discussed. Special emphasis is given to the static explicit and dynamic implicit ®nite element procedures. Also different element types are overviewed. Available important commercial ®nite element packages are given. The current state of the application of the simulation tools is discussed. Some typical industrial applications are reviewed to demonstrate the current abilities of analysis. Finally, an attempt to prognosticate some future developments is made. #

This paper presents a new method for fault diagnosis using a newly developed method, support vector machine (SVM). First, the basic theory of the SVM is briefly reviewed. Next, a fast implementation algorithm is given. Then the method is applied for the fault diagnosis in sheet metal stamping processes. According to the tests on two different examples, one is a simple blanking and the other is a progressive operation, the new method is very effective. In both cases, its success rate is over 96.5%. In comparison, the success rate of the popular artificial neural network (ANN) is just 93.3%. In addition, the new method requires only few training samples, which is an attractive feature for shop floor applications. r From a theoretical point of view, fault diagnosis problems have a close relationship with the pattern recognition, in which one wishes to classify the data to pre-defined classes. Hence, pattern classification methods, including machine learning (ML) and statistics, can be applied.

The main goal of this study is to evaluate the influence of work-hardening modeling in springback prediction in the first phase of the Numisheet’05 “Benchmark 3”: the U-shape “Channel Draw”. Several work-hardening constitutive models are used in order to allow the different materials’ mechanical behavior to be better described: the Swift law (a power law) or a Voce type saturation law to describe the classical isotropic work-hardening; a Lemaître and Chaboche type law to model the non-linear kinematic hardening, which can be combined with the previous two; and Teodosiu’s microstructural work-hardening model. This analysis was carried out using two steels currently used in the automotive industry: mild (DC06) and dual phase (DP600). Haddadi et al. [Haddadi, H., Bouvier, S., Banu, M., Maier, C., Teodosiu, C., 2006. Towards an accurate description of the anisotropic behaviour of sheet metals under large plastic deformations: Modelling, numerical analysis and identification. Int. J. Plasticity 22 (12), 2226-2271] performed the mechanical characterization of these steels, as well as the identification of the constitutive parameters of each work-hardening model, based on an appropriate set of experimental data such as uniaxial tensile tests, monotonic and Bauschinger simple shear tests and orthogonal strain-path change tests, all at various orientations with respect to the rolling direction of the sheet. All the simulations were carried out with the in-house FE code DD3IMP. The selected sheet metal formed component induces high levels of equivalent plastic strain. However, for the several work-hardening models tested, the differences in springback prediction are not significantly higher than those previously reported for components with lower equivalent plastic strain levels. It is shown that these differences can be related to the predicted through-thickness stress gradients. The comparative significance of both equivalent plastic strain levels and strain-path changes in the through-thickness stress gradients is discussed.

Limiting principal strains were measured by two different techniques of biaxial stretching of sheets, one of which permits free deformation in a flat plane, while the other causes constrained deformation in contact with a rigid or rubber punch. The latter method, which relates well with industrial experience, produces larger limiting strains under identical degrees of biaxiality. A possible explanation is based on the process of instability and strain localization.

Optimization of process parameters in sheet metal forming is an important task to reduce manufacturing cost. To determine the optimum values of the process parameters, it is essential to find their influence on the deformation behaviour of the sheet metal. The significance of three important process parameters namely, die radius, blank holder force and friction coefficient on the deep-drawing characteristics of a stainless steel axi-symmetric cup was determined. Finite element method combined with Taguchi technique form a refined predictive tool to determine the influence of forming process parameters. The Taguchi method was employed to identify the relative influence of each process parameter considered in this study. A reduced set of finite element simulations were carried out as per the Taguchi orthogonal array. Based on the predicted thickness distribution of the deep drawn circular cup and analysis of variance test, it is evident that die radius has the greatest influence on the deep drawing of stainless steel blank sheet followed by the blank holder force and the friction coefficient. Further, it is shown that a blank holder force application and local lubrication scheme improved the quality of the formed part.

The effect of changing strain paths on the forming limit stresses of sheet metals is investigated using the Marciniak-Kuczyń ski model and a phenomenological plasticity model with non-normality effects . A phenomenological plasticity model with non-normality effects representing observations in crystal plasticity. J. Mech. Phys. Solids 49, 1239-1263]. Forming limits are simulated for linear stress paths and two types of combined loading: a combined loading consisting of two linear stress paths in which unloading is included between the first and second loadings (combined loading A), and combined loading in which the strain path is abruptly changed without unloading (combined loading B). The forming limit stresses calculated for combined loading A agree well with those calculated for the linear stress paths, while the forming limit curves in strain space depend strongly on the strain paths. The forming limit stresses calculated for the combined loading B do not, however, coincide with those calculated for the linear stress paths. The strain-path dependence of the forming limit stress is discussed in detail by observing the strain localization process.

The perceived wisdom about thin sheet fracture is that (i) the crack propagates under mixed mode I & III giving rise to a slant through-thickness fracture proÿle and (ii) the fracture toughness remains constant at low thickness and eventually decreases with increasing thickness. In the present study, fracture tests performed on thin DENT plates of various thicknesses made of stainless steel, mild steel, 6082-O and NS4 aluminium alloys, brass, bronze, lead, and zinc systematically exhibit (i) mode I "bath-tub", i.e. "cup & cup", fracture proÿles with limited shear lips and signiÿcant localized necking (more than 50% thickness reduction), (ii) a fracture toughness that linearly increases with increasing thickness (in the range of 0.5 -5 mm). The di erent contributions to the work expended during fracture of these materials are separated based on dimensional considerations. The paper emphasises the two parts of the work spent in the fracture process zone: the necking work and the "fracture" work. Experiments show that, as expected, the work of necking per unit area linearly increases with thickness. For a typical thickness of 1 mm, both fracture and necking contributions have the same order of magnitude in most of the metals investigated.

The intent of this paper is to show that a two dimensional (2D) Arbitrary Lagrangian Eulerian (ALE) finite difference computer code can accurately predict the dynamics of the electromagnetic sheet metal forming process. The challenging aspect of simulating the deformation of thin metal parts which have been loaded by magnetic forces is solving a highly coupled system of partial differential equations. The material motion and the magnetic physics require two drastically different time steps to maintain numerical stability. The CALE computer code has the ability to solve such challenging problems. This paper highlights the CALE modeling of a number of electromagnetic sheet metal forming operations.

The Marciniak-Kuczynski (MK) forming limit model is extended in order to predict localized necking in sheet metal forming operations in which Through-Thickness Shear (TTS), also known as out-of-plane shear, occurs. An example of such a forming operation is Single Point Incremental Forming. The Forming Limit Diagram (FLD) of a purely plastic, isotropic hardening material with von Mises yield locus is discussed, for monotonic deformation paths that include TTS. If TTS is present in the plane containing the critical groove direction in the MK model, it is seen that formability is increased for all in-plane strain modes, except equibiaxial stretching. The increase in formability due to TTS is explained through a detailed study of some selected deformation modes. The underlying mechanism is a change of the stress mode in the groove that results in a delay of the onset of localized necking.

The electromagnetic forming (EMF) process relies on a driving force that is induced by eddy current and magnetic field, both of which are generated in the workpiece by a transient current in a nearby coil. The high deformation rates achievable using this forming method enhances the formability of materials such as aluminum. Also, the dynamics of contact with the forming die can eliminate springback, an undesired effect that can be problematic in other forming techniques such as stamping. The advancement of the EMF technology is currently awaiting rigorous numerical modeling capabilities that can adequately simulate the forming process and be used to design the forming system. Such capabilities must be based on physical models that address the strong coupling between the electromagnetic, deformation and thermal response of the deforming workpiece and other system structure. In this paper, a brief exposition of the EMF method and its applications and a review of the existing models are given. In addition, a mathematical framework, which can be further developed numerically for the purpose of process simulation, is outlined. Finally, the paper discusses the challenges to advancing the EMF technology.

Reliable material models are necessary for accurate analysis of micro-forming and micro-manufacturing processes. The grainto-feature size ratio (d/D c ) in micro-forming processes is predicted to have a critical impact on the material behavior in addition to the well-known effect of the grain size (d) itself as manifested by the Hall-Petch relation. In this study, we investigated the ''size effects'' on the material flow curve of thin sheet metals under hydraulic bulge testing conditions. The ratio of the sheet thickness to the material grain size (N ¼ t 0 /d) was used as a parameter to characterize the interactive effects between the specimen and the grain sizes at the micro-scales, while the ratio of the bulge die diameter to the sheet thickness (M ¼ D c /t 0 ) was used to represent the effect of the feature size in the bulge test. Thin sheets of stainless steel 304 (SS304) with an initial thickness (t 0 ) of 51 mm and three different grain sizes (d) of 9.3, 10.6, and 17 mm were tested using five bulge diameters (D c ) of 2.5, 5, 10, 20, and 100 mm. A systematic approach for determining the flow curve of thin sheet metals in bulge testing was discussed and presented. The results of the bulge tests at different scales showed a decrease in the material flow curve with decreasing N value from 5.5 to 3.0, and with decreasing M value from 1961 to 191. However, as M value was decreased further from 191 to 49, an inversed relation between the flow curve and M value was observed; that is, the flow curve was found to increase with decreasing M value from 191 to 49, a new observed phenomenon that has never been reported in any open literature. New material models, both qualitatively and quantitatively, were developed to explain the size effects on the material flow curve by using the N and M as the characteristic parameters of relative size between the grain, the specimen (i.e., sheet thickness), and the part feature (i.e., bulge diameter). The explanation and prediction of the flow curve behavior based on these models were shown to be in good agreement with the bulge test results in this study and in the literature. r

This paper deals with the identification of material parameters in a constitutive model for sheet metals using the bending moment versus curvature diagrams obtained by cyclic bending tests. The model can describe the cyclic strain hardening by the isotropic hardening and the Bauschinger effect by the kinematic hardening. An optimization technique based on the iterative multipoint approximation concept was used for the identification of the material parameters. This paper describes the experimentation, the fundamentals and the technique of the identification problem, and the verification of this approach.

Clinching is a mechanical joining technique which involves severe local plastic deformation of two or more sheet metal parts resulting in a permanent mechanical interlock or joint. The required forming load and energy can be determined with the aid of the finite element method. However, a good knowledge of the elasto-plastic properties is of utmost importance to perform a sufficiently accurate simulation. This paper presents two alternative material tests to identify the hardening behaviour of sheet metal beyond the point of maximum uniform elongation. In addition, the material tests were applied to DC05 and the identified material behaviour is evaluated through the prediction of the forming load during clinching.

Sheet metal forming processes generally involve large deformations together with complex loading sequences. In order to improve numerical simulation predictions of sheet part forming, physically-based constitutive models are often required. The main objective of this paper is to analyze the strain localization phenomenon during the plastic deformation of sheet metals in the context of such advanced constitutive models. Most often, an accurate prediction of localization requires damage to be considered in the finite element simulation. For this purpose, an advanced, anisotropic elastic-plastic model, formulated within the large strain framework and taking strain-path changes into account, has been coupled with an isotropic damage model. This coupling is carried out within the framework of continuum damage mechanics. In order to detect the strain localization during sheet metal forming, Rice's localization criterion has been considered, thus predicting the limit strains at the occurrence of shear bands as well as their orientation. The coupled elastic-plastic-damage model has been implemented in Abaqus/implicit. The application of the model to the prediction of Forming Limit Diagrams (FLDs) provided results that are consistent with the literature and emphasized the impact of the hardening model on the strain-path dependency of the FLD. The fully three-dimensional formulation adopted in the numerical development allowed for some new results -e.g. the out-of-plane orientation of the normal to the localization band, as well as more realistic values for its in-plane orientation.

Purpose of this paper is to offer the reader an overview of recently performed and ongoing research related to process planning for sheet metal bending, thus providing a starting point for further exploration of this field. The scope of this review paper is limited to sheet metal bending as performed on numerically controlled press brakes, with special focus on air bending. Automatic process planning requires a good understanding of the material behaviour under process conditions. Therefore, some space has been reserved for an overview of bend modelling efforts and, directly linked to this, in-process measurement and adaptive control methods. Part representation and feature classification methods for bent sheet metal parts are also discussed. Sections are dedicated to the core problems of fully automated process planning in sheet metal bending: bend sequencing, collision detection, tolerance verification and tool selection. The state of the art review is completed with an overview of ergonomic analysis methods for process plan evaluation. #

Different form traditional forming process, sheet soft punch process uses only a rigid die and the other tool set is a flexible medium, such as natural or synthetic rubbers. In this study, a kind of micro/meso sheet soft punch stamping process to fabricated micro channels is investigated via numerical simulations and experiments. Plane strain finite element analysis (FEA) models of different channel geometry (h=w) are established to analyze the significant parameters associated with this process. Grain size of sheet metal and some key process parameters, such as the hardness of soft punch and lubricant condition, are detailed studied in this paper. Finally, the numerical results are partly validated by experiments.

The wipe-bending is one of processes the most frequently used in the sheet metal product industry. Furthermore, the springback of sheet metal, which is defined as elastic recovery of the part during unloading, should be taken into consideration so as to produce bent sheet metal parts within acceptable tolerance limits. Springback is affected by the factors such as sheet thickness, tooling geometry, lubrication conditions, and material properties and processing parameters. In this paper, the prediction model of springback in wipe-bending process was developed using artificial neural network (ANN) approach. Here, several numerical simulations using finite element method (FEM) were performed to obtain the teaching data of neural network. The learned neural network is numerically tested and can be easily implemented springback prediction for new cases.

Direct integration of dye-sensitized solar cells (DSSC) onto industrial sheet metals has been studied. The stability of the metals, including zinc-coated and plain carbon steel, stainless steel and copper in a standard iodine electrolyte was investigated with soaking and encapsulation tests. Stainless and carbon steel showed sufficient stability and were used as the cell counter-electrodes, yielding cells with energy conversion efficiencies of 3.6% and 3.1%, respectively. A DSSC built on flexible steel substrates is a promising approach especially from the viewpoint of large-scale, costeffective industrial manufacturing of the cells.

To reduce the computational time of ÿnite element analyses for sheet forming, a 3D hybrid membrane/shell method has been developed and applied to study the springback of anisotropic sheet metals. In the hybrid method, the bending strains and stresses were calculated as post-processing, considering the incremental change of the sheet geometry obtained from the membrane ÿnite element analysis beforehand. To calculate the springback, a shell ÿnite element model was used to unload the sheet. For veriÿcation purposes, the hybrid method was applied for a 2036-T4 aluminum alloy square blank formed into a cylindrical cup, in which stretching is dominant. Also, as a bending-dominant problem, unconstraint cylindrical bending of a 6111-T4 aluminum alloy sheet was considered. The predicted springback showed good agreement with experiments for both cases. ?

In this paper, we present the results of our studies on conceptual design and feasibility experiments towards development of a novel hybrid manufacturing process to fabricate fuel cell bipolar plates that consists of multi-array micro-channels on a large surface area. The premises of this hybrid micro-manufacturing process stem from the use of an internal pressure-assisted embossing process (cold or warm) combined with mechanical bonding of double bipolar plates in a single-die and single-step operation. Such combined use of hydraulic and mechanical forming forces and in-process bonding will (a) enable integrated forming of micro-channels on both surfaces (as anode and cathode flow fields) and at the middle (as cooling channels), (b) reduce the process steps, (c) reduce variation in dimensional tolerances and surface finish, (d) increase the product quality, (e) increase the performance of fuel cell by optimizing flow-field designs and ensuring consistent contact resistance, and (f) reduce the overall stack cost. This paper explains two experimental investigations that were performed to characterize and evaluate the feasibility of the conceptualized manufacturing process. The first investigation involved hydroforming of micro-channels using thin sheet metals of SS304 with a thickness of 51 m. The width of the channels ranged from 0.46 to 1.33 mm and the height range was between 0.15 and 0.98 mm. Our feasibility experiments resulted in that different aspect ratios of micro-channels could be fabricated using internal pressure in a controllable manner although there is a limit to very sharp channel shapes (i.e., high aspect ratios with narrow channels). The second investigation was on the feasibility of mechanical bonding of thin sheet metal blanks. The effects of different process and material variables on the bond quality were studied. Successful bonding of various metal blanks (Ni201, Al3003, and SS304) was obtained. The experimental results from both investigations demonstrated the feasibility of the proposed manufacturing technique for making of the fuel cell bipolar plates.

Pancreatic cancer is a highly lethal malignancy whose aetiology is largely unknown. The only firmly established and modifiable risk factor is smoking, but it explains only a fraction of cases, 1 and the association seems somewhat weaker in Mediterranean countries. 2,3 A recent meta-analysis on occupation has concluded that occupational exposures may increase the risk of exocrine pancreatic cancer. 4 However, studies have often been negative, and no single occupation has consistently been shown to increase the risk of this malignancy. 1,4-9 Because of the clinical aggressiveness of the disease, many occupational studies have been based on deceased cases; this fact limits the quality of the information available for cases and constrains the selection of controls. On the other hand, studies on pancreatic cancer relying on personal interviews 10-12 have achieved response rates of 40-60%. In spite of these and other limitations, an increased risk has been observed among for the PANKRAS II Study Group h Background Occupational exposures may increase the risk of exocrine pancreatic cancer. This study aimed to identify occupations that in Spain may be associated with such risk.

As failure criterion for sheet metal forming, conventional forming limit diagrams (FLD) are often used. The FLD is a strain based criterion, which evaluates the principal deformations at failure. Different investigations show that the FLD is dependent on the forming history and strain path. However, this is not the case for forming limit stress diagrams (FLSD). For this failure criterion, the principal stresses at failure are determined by FEM simulation of the Nakazima-test. Both, the FLD and the FLSD experimental investigations provide the basis for the sheet metal failure criterion. In contrast, continuum damage mechanics describe the damage evolution in the microstructure with physical equations, so that crack initiation due to mechanical loading can be predicted. By using the Gurson–Tvergaard–Needleman (GTN) damage mechanical model, a failure criterion based on void evolution was examined in this work. The parameter identification for the damage model will be discussed. The investigations demonstrate that FLD is inapplicable for complex forming processes with strain path changes. The FLSD is better suitable than the FLD for multi step forming processes. Micro-mechanical damage modelling with the GTN model also shows acceptable formability predictions, in spite of its generally insufficient consideration of the effective deviatoric stress fractions. The quality of failure prediction using continuum damage mechanics models is able to be increased by applying a more suitable damage models and a modern overall-scale modelling approach.

Springback remains a major concern in sheet metal forming process. Springback, shape discrepancy between fully loaded and unloaded configuration due to elastic recovery of material, is mainly affected by geometrical parameters, material properties of sheet and lubrication condition between the blank and the tool. A total-elastic-incremental-plastic (TEIP) algorithm, for large deformation and large rotational problems, was incorporated in indigenous Finite Element software. This software was used to predict the springback in a typical sheet metal bending process and to investigate the influence of these parameters on springback. The results of simulation are validated with own experiments and published experimental results.

This article demonstrates the optimum working areas and cutting conditions for the laser cutting of a series of advanced high strength steels (AHSS). The parameters that most influence the cutting of sheet metal have been studied and the results have been divided into two large groups with thickness of more and less than 1 mm. The influence of the material and, more important, the effect of coating have been taken into account. The results, have demonstrate very different behaviours between the thinnest and thickest sheets, whilst the variation of the cutting parameters due to the influence of the material is less relevant. The optimum cutting areas and the quality of the cut evaluated with different criteria are presented. Finally, the best position for the laser beam has been observed to be underneath the sheet.

We studied a homogeneous atmospheric pressure dielectric barrier discharge in helium with small admixtures (-10 ) of y3 hexamethyldisiloxane (HMDSO) vapor for the deposition of thin silicon organic films on a technical aluminum sheet metal. The powered (100 kHz) plane electrode (80=15 mm ) is covered by a glass insulator layer. Power absorption, sustaining voltage (2 2 kV ), gap voltage (700 V), current density (;20 mA cm ), and total light emission are monitored to characterize the discharge y2 pp in the gap (1-1.5 mm). The gas composition of the exhaust gas is studied by mass spectrometry. During discharge operation a decrease of the precursor concentration is observed, due to dissociation and thin film deposition. Typical deposition rates range from approximately 0.2 to 2.0 nm s , as measured by substrate weighing. The films display water contact angles of 63"38. A y1 protection of the Al sheet metal against 0.1n-NaOH for 3 min is observed. FT-IR (dominant Si-O-Si band) and XPS (low C content) measurements both reveal the dominance of non-organic components in the film. The spatially averaged electron concentration (2=10 to 5=10 cm ) is experimentally determined by heterodyne interferometry. Discharge properties and 11 11 y3 thin film deposition are discussed in relation to the ionization rate of the precursor molecules and the current density. ᮊ

The purpose of this study is to present a methodology for prediction of the forming limit stress diagram (FLSD) and reexamine the effect of strain path on prediction of FLSD. The methodology is based on the Marciniak and Kuczynski model. For calculation of sheet metal limiting strains and stresses, a numerical approach using the Modified Newton-Raphson with globally convergence method has been used. The conditions for non-proportional loading have been achieved by imposing two types of pre-straining on the sheet metal. The effects of grain size, surface roughness and sheet thickness on the FLSD have also been presented. The evaluation of the theoretical results has been performed by using the published experimental data for ST12 low carbon steel alloy.

The blanking of thin sheet (0.1±1 mm) of mild steel has been analysed using an elastic±plastic ®nite element method based on the incremental theory of plasticity. The blank diameters are considered in the range 1±4 mm. The study has helped to evaluate the in¯uence of tool clearance, friction, sheet thickness, punch/die size and blanking layout on the sheet deformation. The punch load variation with tool travel and stress distribution in the sheet have been obtained. The results indicate that a reduction in the tool clearance increases the blanking load. The blanking load increases with an increase in the coef®cient of friction. These observations are very similar to the case of blanking of component of large size. Further, these effects are very similar in the case of both single and double blanking. An interblanking site distance of about twice the sheet thickness is good to reduce the thinning of sheet at the intermediate regions between the two blanking sites. For a particular sheet thickness, the blanking load requirement reduces as the blank diameter increases. # 2000 Elsevier Science S.A. All rights reserved.

The concentrations of contaminants in the supply air of mechanically ventilated buildings may be altered by pollutant emissions from and interactions with duct materials. We measured the emission rate of volatile organic compounds (VOCs) and aldehydes from materials typically found in ventilation ducts. The emission rate of VOCs per exposed surface area of materials was found to be low for some duct liners, but high for duct sealing caulk and a neoprene gasket. For a typical duct, the contribution to VOC concentrations is predicted to be only a few percent of common indoor levels. We exposed selected materials to approximately 100-ppb ozone and measured VOC emissions. Exposure to ozone increased the emission rates of aldehydes from a duct liner, duct sealing caulk, and neoprene gasket. The emission of aldehydes from these materials could increase indoor air concentrations by amounts that are as much as 20% of odor thresholds. We also measured the rate of ozone uptake on duct liners ...