Occurrence Of Wrinkles Research Articles

Inhibitory effects of a flexible steel pad on wrinkling in multi-point die forming

A flexible steel pad was applied in multi-point die forming to inhibit wrinkling from occurring in sheet metal, which is based on the idea of sheet metal flexible forming method. In numerical simulations, three multi-point die forming processes, namely without a polyurethane cushion, with a cushion, and with a flexible steel pad, were carried out for a complex three-dimensional part. Comparison of simulation results indicates that adding the flexible steel pad could effectively improve the stress and strain distribution, forming precision, and surface quality as well as effectively suppressed the occurrence of wrinkles and dimples. Experimental results of the three forming processes are consistent with the simulations, which proves the inhibitory effect of the flexible steel pad on wrinkling and the accuracy of the numerical simulations.

Active forming manipulation of composite reinforcements for the suppression of forming defects

For composite applications in automotive serial production, reinforcement textiles are brought into the desired shape by forming processes. The preform quality depends on the interacting factors of tool geometry, textile material, and forming process. The primary cause of defects in multilayer draping is relative movements of the plies, and the occurrence of wrinkles. Thus, the reduction of the interactions between plies is crucial to enhance preform quality. This was achieved with active metal sheets between the fabric layers. Those intermediate layers are additionally stimulated with piezo actors to reduce friction. Additional local and ply-specific clamping of layers was achieved with tension rods and segmented actuators. Defects and wrinkles in the preform could be eliminated or reduced significantly and fiber orientation could be controlled. Thus, a forming process providing high-quality preforms from multiple fabric layers was developed. Furthermore, automation complexity could be reduced significantly by utilizing rigid interlayers.

Bending behavior of multilayered textile composite prepregs: Experiment and finite element modeling

An accurate model and assessment of out-of-plane bending properties can improve the forming predictions of multilayered textile prepregs using a suitable modeling technique. This paper aims to investigate the bending properties of multilayered textile thermosetting composite prepregs under conditions relevant to the forming process. A finite element model based on a viscoelastic approach has been developed to predict the bending behavior of different stacking sequences at different processing parameters, including temperature and rate. This model allows the modeler to determine the correct bending parameter values to set during the forming simulation process. The effect of stacking sequences on out-of-plane bending deformation was studied experimentally and numerically through the developed modeling methodology. Furthermore, the paper analyzes the feasibility of using a viscoelastic material model to model the bending behavior of rate-dependent material and its application in forming simulation. A comparison between elastic and viscoelastic material models showed the importance of considering the rate dependency to describe the bending behavior of prepreg materials. The experimental and numerical results show that the bending properties strongly depend on the fabric lay-up inside multiple stacked plies. Bending and friction properties were also found to significantly influence the occurrence of wrinkles during the forming simulation.

Wrinkle prediction of seat cover considering cyclic loading-unloading with viscoelastic characteristics

The purpose of this study is to predict the wrinkling of leather seat covers created by repeated loading–unloading conditions and long-term driving conditions. To predict wrinkling, this paper describes a numerical analysis process and material test methods. Viscoelasticity is considered to express the time-dependent deformation of the seat cover and a leather material is selected. To evaluate the viscoelastic behavior of leather seat covers in accordance with time and the number of times being seated, cyclic tests are conducted using leather specimens of a strip type. In the cyclic tests, one cycle consisted of loading–creep–unloading conditions; the viscoelastic (creep) time is 1h, and the total repeated number is 60. To perform the seating simulation, PAM-COMFORT, a commercial software package for seat modeling, is used, and permanent deformation of the seat cover is predicted. It can be difficult to predict viscoelasticity using explicit code. As such, a material modeling and evaluation process is suggested. Test results obtained using a model construct are compared with experimental test results with good agreement. The numerical process is then applied to a seat module with an HPM1 dummy model, and quantitative wrinkle deformation is predicted. The proposed process was used to determine the material properties that had deteriorated due to the viscoelastic characteristics of the seat covers. The viscoelastic effects on wrinkle occurrence were confirmed analytically by applying these properties to the seat modules.

Does “lie to me” lie to you? An evaluation of facial clues to high-stakes deception

During a forensic interview, high-stakes deception is very prevalent notwithstanding the heavy consequences that may result. Studies have shown that most untrained people cannot perform well in discerning liars and truth-tellers.Some psychological studies have stated that certain facial actions are more difficult to inhibit if the associated facial expressions are genuine. Similarly, these facial expressions are equally difficult to fake. This has cast light on the possibility that deception could be detected by analyzing these facial actions. However, to the best knowledge of the authors, there is no computer vision research that has attempted to discriminate high-stakes deception from truth using facial expressions. Therefore, this paper aims to test the validity of facial clues to deception detection in high-stakes situations using computer vision approaches.We also note that only a limited number of the existing databases have been collected specifically for deception detection studies and none of them were obtained from real-world situations. In this paper we present a video database of actual high-stakes situations, which we have created using YouTube.We have adopted 2D appearance-based methods as the methodology to characterize the 3D facial features. Instead of building a 3D head model as is the current trend, we have extracted invariant 2D features that are related to the 3D characteristic from nine separate facial regions by using dynamic facial analysis: eye blink, eyebrow motion, wrinkle occurrence and mouth motion. Then these cues are integrated to form a facial behavior pattern vector. A Random Forest was trained using the collected database and applied to classify the facial patterns into deceptive and truthful categories.Despite the many uncontrolled factors (illumination, head pose and facial occlusion) contained in the videos in our database, we have achieved an accuracy of 76.92% when discriminating liars from truth-tellers using methods based on both micro-expressions and “normal” facial expressions. The results have shown that using facial clues for automated lie detection is very promising from the point of view of practice.

Numerical and experimental analysis of wrinkling during the cup drawing of an AA5042 aluminium alloy

The recent trend to reduce the thickness of metallic sheets used in forming processes strongly increases the likelihood of the occurrence of wrinkling. Thus, in order to obtain defect-free components, the prediction of this kind of defect becomes extremely important in the tool design and selection of process parameters. In this study, the sheet metal forming process proposed as a benchmark in the Numisheet 2014 conference is selected to analyse the influence of the tool geometry on wrinkling behaviour, as well as the reliability of the developed numerical model. The side-wall wrinkling during the deep drawing process of a cylindrical cup in AA5042 aluminium alloy is investigated through finite element simulation and experimental measurements. The material plastic anisotropy is modelled with an advanced yield criterion beyond the isotropic (von Mises) material behaviour. The results show that the shape of the wrinkles predicted by the numerical model is strongly affected by the finite element mesh used in the blank discretization. The accurate modelling of the plastic anisotropy of the aluminium alloy yields numerical results that are in good agreement with the experiments, particularly the shape and location of the wrinkles. The predicted punch force evolution is strongly influenced by the friction coefficient used in the model. Moreover, the two punch geometries provide drawn cups with different wrinkle waves, mainly differing in amplitude.

New Criterion for Prediction of the Wrinkle Formation in Deep Drawing Process

Wrinkling is one of the primary failure modes in deep drawing of sheet metal parts. Previous studies showed that the second principle stress can be a measure for the initiation and growth of wrinkles. The wrinkling analysis is usually made with using conical cup geometries. Recent experiments and numerical simulation results at the Institute for Metal Forming Technology (IFU) showed that the wrinkling analysis using simple conical cup geometries is not suitable for description of complex wrinkling conditions for real deep drawing processes. In the presented experimental results, fender shaped geometry was chosen as an example. During deep drawing of this geometry, different wrinkling formulation mechanisms were observed. Regarding these wrinkling mechanisms, a new wrinkling limit curve can be determined. By use of this new wrinkling limit curve, it is possible to detect the occurrence of wrinkles in each area of the formed sheet metal part until the wrinkle is finally formed.

엠보싱 알루미늄 판재의 기계적특성과 스프링백 평가 (제1보)

엠보싱된 알루미늄 판재는 표면적이 증가하여 방열효과가 뛰어나고 가공경화에 의해 굽힘강성이 증가하여 자동차 열차단기에 널리 사용된다. 하지만 판재의 특성상 주름발생률이 높아 프레스 성형에 많은 제약이 따른다. 본 연구에서는 3차원 구조 알루미늄 판재의 프레스 성형성 평가를 위한 기초연구로 3차원 구조 엠보싱 콘 형상 판재의 기계적특성을 평가 하고 굽힘실험을 통해 프레스 가공 후 발생하는 스프링백을 정량적으로 평가하였다. 엠보싱 판재는 패턴의 방향에 따라 인장특성이 상이하다. 특히 평행 엠보싱 시편의 경우 항복응력이 감소하며 대각 엠보싱 시편의 경우 항복응력이 증가하게 되고 영률의 감소가 크게 나타난다. 그 결과 굽힘 성형가공 후에 스프링 백에 영향을 미친다.

Superplastic forming process applied to aero-industrial strakelet: wrinkling, thickness, and microstructure analysis

Superplastic forming (SPF) of an aluminum sheet trough with a large depth to width ratio is challenging because of the difficulties in obtaining a satisfactory, uniform thickness distribution. To address this problem, two different SPF techniques, namely, two-stage gas forming (TSGF) and hot-bend assisted gas forming (HBAGF), were used to fabricate airplane strakelets. Undesirable wrinkling occurred in both cases, but the sites and causes of wrinkle formation were different. Thickness measurements around the edge of the circumference were relatively uniform, with a minimum thickness of ∼1.32 mm (∼34.0 % thinning percentage) for the HBAGF sample. This thickness significantly exceeded that of a sample processed by a previously developed TSGF method (∼0.8 mm, ∼60 % thinning percentage). Three-dimensional finite element analysis was implemented to accurately predict the shape and occurrence of wrinkling. Furthermore, experimental forming trials with the HBAGF die led to significant improvement of the thickness profile of superplastically formed parts.

Effect on Deformation in Hydroforming under Different Forming-Control Paths

Weight reduction and the structural strengthening of frameworks have always been of great interest for automobile and bicycle manufacturers. In order to achieve this goal, manufacturers have always been looking for new materials and their corresponding processing technology. This paper focuses on investigating the most suitable forming-control path pattern for manufacturing magnesium-based alloy quadrilateral tubular components using the tube-hydroforming (THF) process for framework components. Conventionally, there are three usual patterns of forming-control path. Through numerical simulation, it was found that forming-control path C provided the best profile results. The simulation results were also verified by physical THF experiments which were carried out at around 270oC to fabricate the quadrilateral tubular component. A good agreement between simulation and experimental result was achieved, indicating that employing forming-control path C in the actual THF process provides the best forming results, minimizing the occurrence of wrinkling. The formability of such high value-added hydroformed tubular components can be predicted. Trial-and-error during the design stage can be avoided, which contributes to lower production costs.

The influences of skin visco‐elasticity, hydration level and aging on the formation of wrinkles: a comprehensive and objective approach

Various skin parameters including skin visco-elasticity and hydration level affect the formation of wrinkles. The aim of this study was to investigate the comprehensive and objective relationship between age, skin visco-elasticity, hydration level, and the occurrence of wrinkles using bioengineering equipments for the first time. A total number of 97 healthy women were included in this study. Age, Fitzpatrick skin type, skin mechanical parameters obtained with Cutometer(R0~R9), hydration level measured with Corneometer, as well as wrinkle parameters (SEsm, SEr, SEsc, and SEw) assessed with Visioscan, were analyzed with the Pearson's correlation test. The skin fluidity (R6) increased while the elastic recovery ratio (R7) decreased with the age. The wrinkle parameter (SEw) also increased with the age. The higher skin hysteresis values (R4 and R9) coincided with the higher SEw values. Skin hydration significantly lowered the hysteresis (R9), the wrinkles (SEw), and the depth of wrinkle furrows (R3mr). The elderly have less elastic skin and more wrinkles. Skin hysteresis most closely related with the degree of wrinkles. Drier skin showed more wrinkles and deeper furrows, with wider intervals. On the basis of these objective findings, we propose several skin parameters associated with wrinkles, and hypothesize the mechanism of wrinkle generation.

Spontaneous growth of self-relief wrinkles in freely floating lipid-based nanomembranes, formed on a reactive bath of polyoxometalate aqueous solution

Wetting and capillarity have appeared over the last decadesas potential tools for the guided actuation, self-assembly and nanostructuration, and most recently as powerful “tool-free” techniques of micro-, and nano-fabrication, in the field of nanotechnology. The present work deals with such a use of wetting, achieving for the first time the spontaneous growth of composite (lipid-capped polyoxometalate) nanomembranes, using the reactive spreading film formed by the droplets of a lipid solution, on an aqueous foundation hosting the polyoxometalate ions. Moreover, we show that the internal stress produced by the reactive wetting, and the resulting self-movements of the drop could be accumulated within the drying spreading film, driving the spontaneous occurrence of wrinkles, in the freely floating nanomembranes that are thus formed. Finally, we showed that gravity-driven scaling relations for buckling instabilities apply to these spontaneously occurring wrinkles, allowing the in situ characterization of the physical properties of the nanomembranes. This approach that allowed producing floating nanomembranes of “lipid-capped Keggin ions” that were collectable as freestanding nanosheets may constitute a potential route for the fabrication of a wide range of functional (copolymers/metal nanoparticles) nanocomposite membranes.

Development of a Simple Closed-Loop Type Algorithm for Determination of Variable Blank Holder Force Trajectory and Its Applications to Square Cup Deep Drawing

In deep drawing, a low blank holder force (BHF) can cause wrinkling, while a high BHF can lead to tearing. In this study, a variable blank holder force (VBHF) approach to deep drawing is employed, and a simple closed-loop type algorithm is developed for the VBHF trajectory. The proposed algorithm is divided into two phases. The objective of the first phase is to check wrinkling and tearing. In this phase, a low BHF is used as the initial BHF, which is then increased to prevent wrinkling while controlling tearing. This phase of the algorithm is terminated when tearing occurs. In numerical simulation, the distance between the die and the blank holder is used to measure wrinkling, and the minimum thickness of the blank is used to determine the tearing. In the second phase of the algorithm, the deviations in thickness of the part are iteratively examined, without neglecting the occurrence of wrinkling. One of the advantages of using VBHF instead of constant BHF is that it reduces the forming energy. The validity of the proposed algorithm is examined comparing numerical simulation and experimental results. Finally, the proposed algorithm is also applied to obtain the segmented VBHF trajectory.

Sensitivity Analysis Method for Membrane Wrinkling Based on the Tension-Field Theory

This paper presents a new method for the sensitivity analysis of membrane wrinkling based on the tension-field theory. This method can be applied to design membrane structures to reduce the occurrence of wrinkles. In this method, the wrinkle intensity in a partly wrinkled membrane is evaluated from an apparent strain energy resulting from the deformation through wrinkling. This wrinkle intensity is used as an objective function for wrinkle-reduction membrane design. Further, the sensitivity of the wrinkle intensity with respect to an arbitrary design parameter is derived by employing a semi-analytical differentiation technique and is used to resolve the minimization problem of the objective function. Some design examples show that this minimization problem can be effectively resolved by the proposed sensitivity analysis method and the occurrence of membrane wrinkles can be considerably reduced by minimizing the wrinkle intensity.

Deep-drawing and ironing of 1050 aluminum sheets loaded with vibration using NC servo press machine

Recently, high-torque AC servomotors have been developed, and NC servo press machines equipped with these servomotors have become commercially available in Japan. The NC servo press machine has a programmable function for fully controlling the position and velocity of the slide on the machine, as well as for setting its motion such that the slide descends while it is vertically vibrating. In this study, we carried out forming experiments on a 1050 aluminum sheet by vibratory deep-drawing and vibratory ironing using the low-frequency vibration motion of the slide, and experimentally examined the improvement effects of vibration load on the forming limit during each machining process. As results, when the NC servo press machine was used in conventional die machining, (1) the limiting drawing ratio increased by 0.15 during vibratory deep-drawing and (2) the limiting ironing rate increased by approximately 10% during vibratory ironing, without using a special vibration machine. For deep-drawing, the occurrence of wrinkles was prevented when vibration was applied.

A neural networks approach to investigating the geometrical influence on wrinkling in sheet metal forming

In sheet metal industries, the ability to predict and avoid surface failures, such as wrinkling, is of great importance. Wrinkling behaviour can be affected by various factors. However, little research has focused on generalisation of the role of geometry on the occurrence of wrinkling. In this paper, the geometrical features of various formed parts are generalised and correlated with surface behaviour (wrinkled or wrinkle-free). A model based on an artificial neural network is introduced to reveal the critical geometrical criteria for wrinkling. This model is a feed forward back propagation neural network with a set of geometrical variables as its inputs and the possibility of the occurrence of wrinkling as its output. After using experimental data to train and test it, the model was applied to new data for prediction of the occurrence of wrinkling. The results are promising. The network can correctly forecast a large portion of the occurrence of wrinkling based on the given information on the geometrical features of points. Besides, by examining the contribution factors of the neural network in its prediction performance, we may also obtain certain information regarding the relative importance of each geometrical variable investigated. It is believed that the neural model can be a useful tool for the product design engineer as well as the workshop practitioner.

Evaluation Method of Bend Formability of Copper Alloy Strips for Spring Applications

With the miniaturization of switches, relays, connectors and so on, more severe bend formability is required for copper alloy strips, which are main comprising materials of these electronic components. Therefore, it is inevitably necessary to find a quantitative evaluation method for the bend formability of copper alloy strips besides development of these materials.In this research, the authors have deveroped a newmethod to estimate the bend formability of copper alloys using their three basic mechanical propertiesobtained from tensile test, and made an attempt to improve the bend formability of copper alloys for spring applications with the help of thismethod.The results are summarized as follows:1) To evaluate the bend formability of copper alloy strips, strain distribution coefficient (f), which is a new representation of basic mechanical property, is proposed in addition to uniform strain (eu) and maximum strain due to necking (em). Derivation method of f from tensile test results is shown.Furthermore we present quantitative relation between the bend formability and the three basic mechanical properties.2) To improve the bend formability, it is necessary to control the three basic mechanical properties, especially, increasing eu and f, which suppress wrinkle occurrence and development during bend process, is effective.3) For improving the bend formability of NB-109 alloy for spring use, it is effective to maintain large eu and f through decreasing cold rolling ratio after recrystalization treatment. In the case of high cold rolling ratio, it is effective to increase eu and f through rising final annealing temperature.

Closed-loop control of the blank-holder force in deep-drawing: finite-element modeling of its effects and advantages

As a steelmaker specialized in the manufacturing of flat coated sheets, the authors' company started some research into the stamping domain with a special focus on the influence of friction, on material modeling and on the improvement of drawing performances. The main purpose in doing such research is to enhance the company's knowledge in the final use of its products and to know how to orientate that use. Therefore, from a technological point of view, the company developed a completely new (and patented) regulation system to control the blank-holder pressure. In this system, working in closed-loop, the feedback-loop controlling the variation of the blank-holder pressure can be based on several process parameters such as the punch force or the detection of the occurrence of wrinkling. From a numerical point of view, the effects and the impacts of this new system have been simulated, in the cases of both potential laboratory and industrial applications. Those simulations were performed with a commercial finite-element code using an explicit integration scheme, and are mainly related to the following applications: (i) the minimum blank-holder pressure needed to avoid the occurrence of wrinkling; and (ii) the improvement of drawing performance through the increase of the LDR value, this being done by maximizing the blank-holder pressure.

Sensing strategy to detect wrinkles in components

Wrinkling is a common phenomena in a range of manufacturing processes. The ability to sense the occurrence of wrinkles is useful in deep-drawn sheet metal forming to make on-line closed-loop feedback control of the binder forces feasible. This would lead to higher productivity and better-quality of deep-drawn components. The sensing of wrinkles as they occur in manufacturing applications is considered here. The sensors used are of a noncontact type, either a fiber optic displacement sensor or a laser range finder. The size constraint is particularly relevant for the on-line sensing application. The use of two displacement sensors to detect the wrinkle and estimate its peak amplitude is explained. The sensing strategy is experimentally verified. >

Effects of different epoxies on avoiding wrinkles in thin sections of botanical specimens

AbstractFold or wrinkles appear frequently in thin sections cut from botanical material embedded in epoxy resin such as Epon 812 (Polysciences) or EM‐bed‐812 (Electron Microscopy Sciences). Small wrinkles may occur more or less perpendicular to the cutting direction and mostly across the cell wall, causing problems in the examination of the ultrastructure. We studied the occurrence of wrinkles and folds by methodological sectioning, with regard to block hardness, use of Formvar‐support film, and chloroform vapor. Methodological sectioning or changing the block hardness did not reduce the occurrence of wrinkles in sections. Chloroform vapor improved the result as did also the use of uncoated grid. Wrinkles and folds could be avoided completely by embedding the specimens in LX‐112 (Ladd) or ERL‐4206 (Polysciences) low‐viscosity epoxy resins, in which case Formvar‐coated grids could be used, and chloroform vapor was not necessary.