Showing 7 results for Wrinkling
Volume 7, Issue 1 (11-2008)
Abstract
In this paper comparison of finite element results and experimental observations of the hydroforming deep drawing is considered in which fluid pressure is used instead of die. Effects of hydroforming parameters during the process are studied, and a comparison with conventional method in deep drawing of aluminum alloys sheets with different blank diameters is presented. Large strain effects, anisotropic material properties, and the Coulomb friction theory in contact surfaces have been considered. ABAQUS code was used for simulation of process. In the first step, the numerical results have been verified by available experimental results, which showed a good agreement. These results contain force-punch travel and thickness strain. In the next step, the effects of initial pressure, friction, and punch radius on wrinkling, tearing, earring, and thickness strain have been studied. The results showed the range of pressure container for the hydroforming deep drawing. A comparison between some of the common deep drawing methods has been presented based on two main failure criteria and thickness strain criteria. Finally it is concluded that the hydroforming process is a more efficient method for achieving the higher drawing rate with respect to the conventional methods.
, Faramarz. Javanroodi, M. Pakbaz,
Volume 8, Issue 1 (10-2008)
Abstract
In this paper comparison of finite element results and experimental observations of the hydroforming deep drawing is considered in which fluid pressure is used instead of die. Effects of hydroforming parameters during the process are studied, and a comparison with conventional method in deep drawing of aluminum alloys sheets with different blank diameters is presented. Large strain effects, anisotropic material properties, and the Coulomb friction theory in contact surfaces have been considered. ABAQUS code was used for simulation of process. In the first step, the numerical results have been verified by available experimental results, which showed a good agreement. These results contain force-punch travel and thickness strain. In the next step, the effects of initial pressure, friction, and punch radius on wrinkling, tearing, earring, and thickness strain have been studied. The results showed the range of pressure container for the hydroforming deep drawing. A comparison between some of the common deep drawing methods has been presented based on two main failure criteria and thickness strain criteria. Finally it is concluded that the hydroforming process is a more efficient method for achieving the higher drawing rate with respect to the conventional methods.
Volume 11, Issue 4 (12-2011)
Abstract
Abstract:
Plastic axial strain, local buckling, wrinkling and plastic buckling of pipeline are caused by cyclic
compression and tension loadings. This kind of local buckling is amplified by initial defect, heat
affected zone and circular welding. Progressive plastic failure or ratcheting is caused by frequent
periods of cyclic loading. On the other hand, life time of the offshore pipelines is decreased by the
corrosion effect caused by fluids inside the pipeline and the sea Environment. This kind of corrosion
can be found with variable size and depth in the inner or/and the outer surface of the pipeline.
Corrosion can effect on the strength of pipeline.
In the current study, an advanced finite element program has been used to simulate the ratcheting
response of carbon steel tubes. The numerical model has been applied to reproduce a series of
laboratory tests on small-scale tubes. These tests were carried out by the authors on intact and defected
tubes, in which wrinkling and ratcheting behaviour of tubes under axial monotonic and cyclic loads
were studied. A nonlinear isotropic/kinematic hardening model has been employed to represent the
cyclic behaviour of the material. The verified model has then been used for a parametric study on
ratcheting behaviour of the defected tubes under cyclic axial loading. Several stabilized cycles of
specimens that are tested experimentally under symmetric strain cycles are used to obtain stress-strain
data and hardening parameters of the material.
The numerical model has then been used to investigate the effect of mean stress, stress amplitude and
geometrical defects on the ratcheting response of steel tubes. It has been noticed that:
a) The ratcheting strain rate was governed by (a) the initial non-linear strain in the tube, (b) by the
stress amplitude and (3) by the mean stress, respectively.
b) The ratcheting strains in the defected tubes had significantly higher rates in comparison to those in
the intact tubes and very rapidly turned exponential.
c) In defected tubes the local wrinkling first initiated from the damaged part. This local buckling then
gradually proceeded to the entire circumference. The ratcheting strains in the defected area very
rapidly turned exponential, while the ratcheting strains in the perfect zone still remained linear
trajectory.
d) It showed that surface corrosion imperfections had a very pronounced effect on the ratcheting
response of the defected tubes, as compared to their monotonic response.
e) The wrinkles in the defected tubes were non-axisymmetric and initiated from the damaged part of
the tube
Maziar Khademi, Mohammad Bakhshi Jooybari, Abdolhamid Gorji Valokola, Milad Sadegh Yazdi,
Volume 17, Issue 5 (7-2017)
Abstract
Prediction and prevention of wrinkling are very important in tool design and determining the effective parameters in sheet metal forming processes. In forming metallic cups, wrinkling generally occurs in the two regions of flange and wall. The control of wrinkling in flange area is not so difficult by controlling the blankholder pressure, but it is difficult in the wall region because the sheet is not supported in this area. In this paper, using a geometric method based on numerical simulation, the wrinkling in the wall of the symmetric conical parts in the developed hydrodynamic deep drawing with radial pressure and inward flowing liquid is investigated. In the process, two independent pressure supplies have been used for forming the sheets. Due to the nature of the process, the effects of radial and cavity pressures on wrinkling have been investigated. In addition, the effects of material, initial blank thickness and punch velocity on wrinkling in wall area were investigated. To verify the results of the simulation, several experimental tests have been done on the St13 and copper sheets. Good agreement between the simulation and experimental results shows the reliability of this method in the wrinkling study. It was also demonstrated that increasing the maximum radial pressure or decreasing cavity pressure leads to increasing wrinkling. Additionally, wrinkling was decreased with increasing blank thickness. Moreover, it was shown that wrinkling simulation is much depended on input parameters such as punch velocity and appropriate element size
Mohammad Pakdaman, Abdolrahman Jaamialahmadi,
Volume 17, Issue 10 (1-2018)
Abstract
In this article, the influence of process parameters on warm deep drawing of PVC/fiberglass composite laminates (FRP) is investigated through the experimental tests. Fiberglass reinforced polymer (PVC) composite laminate sheets are new emerging materials that have many potential applications. FRP/composites provide high strength to weight ratios exceeding those of aluminum or steel. For the experimental tests, composite samples with [0/90]2, [0/90]4, [-30/30]2, [-30/30]4 lay ups were produced in using film stacking procedure. Statistical analyses based on Taguchi's method are used to reduce the number of experiments and to investigate the effect of process variables on the output results. The results show that the two variables of temperature and blank holder force have the most influence on output parameters. Furthermore they demonstrate that a high interaction between the forming temperature and blank-holder force is required to remove the wrinkling.
H. Faraji, Kh. Khalili , A. Ashrafi,
Volume 19, Issue 8 (8-2019)
Abstract
In this study, the use of internal mechanical insert to prevent wrinkling defects in the process of T-shape tube hydroforming and expanding the window of the hydroforming process is presented. The study was performed both experimentally and by finite element simulation. In wrinkling limit testing, the use of internal mechanical insert for different modes prevented 100% of wrinkling and the T-joint was formed flawless, so that the wrinkles with high lengths such as 69.5 and 67.1 mm were prevented. Also, in the case of an internal pressure of 13 MPa and displacement of 33 mm, despite the high amount of axial displacement and the low internal pressure, the internal mechanical insert caused a reduction of 85.06% of the wrinkling length and the wrinkling length reduced from 74.3 to 11.1 mm. To study the conditions of the hydroforming process for both cases of with and without internal mechanical insert, the simulation of finite element was used. Experimental tests were also carried out to verify the validity of simulation results. By comparing the results of the experimental study and the simulations, an appropriate match was found between them. The results showed that the use of internal mechanical insert prevents wrinkling in the piece. Therefore, it can be used to produce a piece without defects and develop the window of the hydroforming process.
Fatemeh Taghizadeh Rami, Majid Elyasi,
Volume 22, Issue 6 (5-2022)
Abstract
In this study, bending of titanium tubes using steel balls in 0.5 and 0.85 mm sizes and resistance heating with experimental and simulation methods have been investigated. In order to apply temperature in rotatory draw bending of tubes, electric current cables were connected to both sides of the tube, and experiments were performed at room temperatures, 100℃, 200℃, 300℃ and 400 ℃ with a bending ratio of 1.8 and a bending angle of 90 ° was done. After the experiments, cross-sectional distortion, wrinkles, cracking and thickness distribution of bent tubes were investigated. The results of this study showed that in the case of bending at room temperature with and without metal balls, the tubes could not be bent. In the bending process with a constant speed of 0.8 Rad/s, by placing metal balls inside the tube and increasing the temperature 100℃, 200℃ and 300℃, the thickening in the intrados of the bent tube decreased by 9.8% and the thinning at the extrados of the bent tube increased by 8.4%. Also, by changing the bending speed from 0.8 to 0.4 Rad/s the cracking defect was eliminated at 400℃. Due to increased pressure due to steel balls in bending area, cross section distortion in tubes decreased by 10.4%. The best bending conditions and the least amount of defects were obtained at 300℃ with steel balls.
