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Parametric Study of Dynamic Wrinkling in a Thin Sheet on Elastic Foundation  [PDF]
M. N. Hamdan, A. A. Al-Qaisia, S. Abdallah
International Journal of Modern Nonlinear Theory and Application (IJMNTA) , 2012, DOI: 10.4236/ijmnta.2012.13008
Abstract: This work presents an approximate analytical study of the problem of dynamic wrinkling of a thin metal sheet under a specified time varying tension. The problem is investigated in the framework of the dynamic stability of a nonlinear plate model on elastic foundation which namely takes into account the nonlinear mechanics of mid-plane stretching and the dependence of the membrane force on this mechanics. The plate is assumed to be a wide rectangular slab, hinged at two opposite ends and free at the long ends, which can be deformed in a cylindrical shape so that the governing in-plane bending equation of motion takes the same form as that of a beam (e.g. lateral strip) element. An approximate analytical analysis of the beam wrinkling behavior under sinusoidal parametric excitation is carried out by using the assumed single mode wrinkling motion to reduce the beam field nonlinear partial differential equation to that of a single degree of freedom non-linear oscillator. A first order stability analysis of an approximate analytical solution obtained using the Multi-Time-Scales (MMS) method is used to derive a criterion defining critical driving frequency in terms of system parameters for the initiation of wrinkling motion in the thin metal sheet. Results obtained using this criterion is presented for selected values of system parameters.
Effect of Various Parameters on the Wrinkling In Deep Drawing Cylindrical Cups
R. Venkat Reddy,Dr T.A. Janardhan Reddy,Dr.G.C.M. Reddy
International Journal of Engineering Trends and Technology , 2012,
Abstract: The appearance of dimensional deviations of shape and position, of the defectsin the metal sheets that have been subjected to a cold plastic deformation process (deepdrawing), represents a critical problem for the specific industry, especially for the massproduction, like the machine manufacturing industry. The aim of this publication is to present the principal aspects that effect of various factors like BHF, punch radius, die edge radius, and coefficient of friction on the wrinkling of cylindrical parts in deep drawing process. 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 work piece, and contact condition. 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. In the present study, the mechanism of wrinkling initiation and growth in the cylindrical cup deep drawing process is investigated in detail.
Optimization of Blank Holder Force to Control Wrinkling and Fracture of Cylindrical Cups in Deep Drawing
R. Venkat Reddy 1 Dr T.A. Janardhan Reddy2 Dr.G.C.M. Reddy3
International Journal of Engineering Trends and Technology , 2012,
Abstract: The Predominant failure modes in sheet metal parts (deep drawing process) are wrinkling, fracture. In many cases these defects may be eliminated by appropriate control of the blank holding force (BHF). This paper summarizes the results of a resent study on the formability of rectangular or cylindrical parts from Extra Deep Draw (EDD) steels. Wrinkling, fracture limits have been determined and BHF control methods have been developed to eliminate defects,improve part quality, and increase the draw depth.The prediction and prevention of wrinkling and fracture are extremely important in the design of tooling and process parameters in deep drawing process. Forming process of Extra Deep Draw (EDD) Steel alloy sheets can be investigated by using deep drawing process. When the BHF is 70-80 N/mm 2 the steel sheets with a thickness 5mm can be produced in the cups without any defects such as wrinkling, tearing.A 3-D explicit-finite element analysis is used to investigate the influence of various BHF schemes on sheet metal formability limits especially wrinkling, and fracture. The role of relevant parameters of each blank holding technique is also investigated. Experiments were conducted using a die block of 250 mm diameter and punch 240 mm on EDD steel alloys of blank size is 165mm and thickness 5 mm.
Overall Buckling and Wringkling of Debonded Sandwich Beams: Finite Element and Experimental Results
Bambang K. Hadi
ITB Journal of Engineering Science , 2006,
Abstract: Overall buckling and wrinkling of debonded sandwich beams under compressive loads were analyzed by both finite element and experimental methods. In the finite element method, a quarter and a half models of the specimens were analyzed. It shows that a quarter model is not adequate to analyze buckling of debonded sandwich beams, since it will disregard overall buckling mode that may occur in sandwich beams having compressive loads. At least a half model should be used to analyze buckling of sandwich beams. A finite element program UNA was used extensively to analyze the buckling loads. Experimental buckling of sandwich beams was carried out using a compression testing machine. Two LVDTs were used to measure deflections of the specimen during experimental loading. The loads were measured using load cells available in the machine. Specimens having core thickness of 45 and 75 mm were tested to represent overall and wrinkling modes respectively. The delamination lengths were 20, 60 and 80 mm, which represent 10, 30 and 40% of the beam length. The results show that the differences between experimental and finite element methods were less than 10%. Both overall buckling and wrinkling modes were shown in these specimens.
Research on Thermal Deep-drawing Technology of Magnesium Alloy (AZ31B) Sheets
Shihong ZHANG,Kun ZHANG,Zhongtang WANG,Chuanfu YU,Yi XU,Qiang WANG,
Shihong ZHANG
,Kun ZHANG,Zhongtang WANG,Chuanfu YU,Yi XU and Qiang WANG Institute of Metal Research,Chinese Academy of Sciences,Shenyang,China

材料科学技术学报 , 2004,
Abstract: Forming technology of Mg alloy (AZ31B) sheets can be investigated by thermal deep drawing experiments. In the experiments,the blank holder and die contacting with the blank were heated to the same temperature as the blank by using the heating facility. The circular blank heated in an oven is formed at a temperature range of 100~400℃ to obtain the optimum forming temperature range and the effects of major technical parameters on the workpiece quality. It is found that the blank is brittle at temperatures lower than 200℃. Temperatures higher than 400℃ are not suitable for forming of the sheets because of severe oxidation and wrinkling. AZ31B shows an excellent formability at temperatures from 300 to 350℃ and can be formed into a workpiece with good quality. When the blank holder force is 99 Kn, extruded sheets with a thickness of 1 mm can be formed into cups without wrinkling. Workpieces show strong anisotropic deformation behavior on the flanges.
The effect of transverse shear on the face sheets failure modes of sandwich beams loaded in three points bending
International Journal of Engineering Science and Technology , 2012,
Abstract: Sandwich beams loaded in three points bending may fail in several ways including tension or compression failure of facings. In this paper , The effect of the transverse shear on the face yielding and face wrinkling failure modes of sandwich beams loaded in three points bending have been studied, the beams were made of various composites materials carbon/epoxy, kevlar/epoxy, glass/epoxy at sequence [+θ/-θ]3s, [0°/90°]3s. . The stresses in the face were calculated using maximum stress criterion and the simple beam theory. The obtained different results show that the sandwich beams with carbon/epoxy, and glass/epoxy face sheets are the best materials, inreturn the kevlar /epoxy facing characterised by low resistance of transverse shear in compression and tensile.
Failure modes of composite sandwich beams
Gdoutos E.,Daniel I.M.
Theoretical and Applied Mechanics , 2008, DOI: 10.2298/tam0803105g
Abstract: A thorough investigation of failure behavior of composite sandwich beams under three-and four-point bending was undertaken. The beams were made of unidirectional carbon/epoxy facings and a PVC closed-cell foam core. The constituent materials were fully characterized and in the case of the foam core, failure envelopes were developed for general two-dimensional states of stress. Various failure modes including facing wrinkling, indentation failure and core failure were observed and compared with analytical predictions. The initiation, propagation and interaction of failure modes depend on the type of loading, constituent material properties and geometrical dimensions.
Free flow of sweat due to loss of surface tension at sweat droplets causes water-induced skin wrinkling
Soumya Marasakatla,Karunakar Marasakatla
PeerJ , 2015, DOI: 10.7287/peerj.preprints.57v4
Abstract: Water immersion skin wrinkling has long been used as a test for sympathetic nerve function. However, the cause of underlying mechanism remained elusive. In this article, we theoretically investigate a possible cause of the phenomenon by taking various properties of sweating into consideration. The pressure exerted by the surface tension of sweat droplets counterbalances the secretory pressure of sweat glands at the pore. When a hand is immersed in water, sweat droplets easily merge with the water, causing the pressure to drop at the pore. Our calculations, using earlier measurements of secretory pressure, show that the water pressure at the sweat pore will be less than the secretory pressure of sweat glands when the hand is immersed at a shallow depth. The resulting pressure imbalance enables the sweat to flow freely into the water. We believe that there will be an initial vasodilation to feed the excess generation of sweat. Sweat flow continues as long as there is blood flow to the hand. To prevent excessive loss of sweat from the body and to maintain homeostasis, sympathetic nerves trigger vasoconstriction to reduce the blood flow to the hand. The overlying skin wrinkles due to loss of volume under the skin. It is possible that denerved fingers remain in the vasodilation state during immersion due to a lack of sympathetic nerve function.

Huang Tao,Li Guochen,Hong Youshi,Xiong Dianyuan,

力学学报 , 1996,
Abstract: By comparing with the results given by analytic method,the advantages of employing numerical method to analyse material bifurcations are displayed in this paper.Under the loading conditions of uniaxial and slightly biaxial tension,the characteristics of material bifurcations(plane shear banding and surface wrinkling)are demonstrated. Uniaxial tension testings justify that the critical stresses given by calculations are reasonably fair.

WANG Changguo,DU Xingwen,WAN Zhimin,

力学与实践 , 2006,
Abstract: The space inflatable structure is a new construction technology and is the main demanding object in the future space activities. The inflatable structure is mainly made up of membrane; therefore, the maintenance of the structural surface accuracy is one of the most important problems. Wrinkling is the unique characteristic of the flexible membranes, and the wrinkles degrade the surface accuracy and the structural performance, so, the study on wrinkles in membrane structures is desirable and essential. In this paper, a prediction model of wrinkles is proposed, based on the buckling theory, and the wrinkles, including the wrinkle amplitude, wrinkle wavelength and the critical compressive stress, in a rectangular membrane subjected to in-plane horizontal shearing loads are predicted using the method proposed in the present paper. The predicted results show good agreement with our recent experiments and the reported data.
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