• 한국정밀공학회지
• /
• 제17권2호
• /
• pp.169-175
• /
• 2000

The object of this study was to investigate the feasibility of solid-phase forming of the composites and to characterize the material behavior in the biaxial stretch forming. The materials tested contained 20%, 30%, and 40% glass fibers by weight in a polypropylene matrix. Biaxial stretch forming tests were performed at three forming speeds of 10mm/sec, 1mm/sec, and 0.1mm/sec and at four forming temperatures of $75^{\circ}C, 100^{\circ}C, 125^{\circ}C, and 150^{\circ}C$ to investigate effects of forming speed and forming temperature. The microscopic observation of a formed part was conducted at various strain levels to characterize the material behavior. The strain distribution on a formed part was measured and displayed on the farmed geometry with a contour display The material behavior of the composite in the biaxial stretch forming was strongly influenced by the forming conditions.

• 한국해양공학회지
• /
• 제32권4호
• /
• pp.253-260
• /
• 2018

Recently, the application of non-steel materials in ships and offshore plants is increasing because of the development of various nonlinear materials and the improvement of performance. Especially, hyper-elastic materials, which have a nonlinear stress-strain relationship, are used mainly in marine plant structures or ships where impact relaxation, vibration suppression, and elasticity are required, while elasticity must be maintained, even under high strain conditions. In order to simulate and evaluate the behavior of the hyperelastic material, it is very important to select an appropriate material model according to the strain of the material. This study focused on the selection of material models for hyperelastic materials, such as rubber used in the marine and offshore fields. Tension and compression tests and finite element simulations were conducted to compare the accuracy of the nonlinear material models due to variations in the stretch ratio of hyper-elastic material. Material coefficients of nonlinear material models are determined based on the curve fitting of experimental data. The results of this study can be used to improve the reliability of nonlinear material models according to stretch ratio variation.

• 대한안전경영과학회지
• /
• 제17권1호
• /
• pp.139-148
• /
• 2015

For design research of teenagers' posture correcting shirt, postures of teenagers were analyzed and became the base of inventing suitable patterns. The subjects of this study were 198 of both female and male middle school students from the city of Seoul. Students' postures in classroom and length change of body surface were observed and analyzed; based on this, total of 5 postures was selected, and length changes of body surface were applied. The patterns in this study were designed with stretch material to help antagonism by muscle movements. Each fabric that was used in this study had 110% of stretch, 120~140% of stretch, and 150~170% of stretch. Both of one-way-fabric and duplex-fabric were used in this study, depending on application site.

• 소성∙가공
• /
• 제7권1호
• /
• pp.36-48
• /
• 1998

In order to analyze the stretch flange forming characteristics of tailored blanks. laser welded blanks of different thickness and strength combinations were prepared and hole expansion tests were done. The stretch flange formability of laser welded blanks was reduced as increasing the deformation restraining force($strength{\times}thickness$) ratio between two welded sheets. Simulation of stretch forming mode deformation and comparson with experimental results showed that the stretch flange formabili-ty was influenced not only by the difference of the deformation restraining forces between two base sheets but also by the difference of the deformation restraining forces between base sheet and weld. Therefore the stretch flange formability was reduced more rapidly than tensile elongation as increas-ing the deformation restraining force ration. It was also found that simulation of stretch flange forming was more accurate when material properties of weld was given.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2008년도 추계학술대회 논문집
• /
• pp.118-121
• /
• 2008

Flexible die is more efficacious than fixed die which is generally used in stretch forming process in view of production cost. Accordingly, in order to verily the validity of the flexible forming process, curved thin skin structure forming analyses using the fixed and flexible die were performed. As results, merit and demerit with regard to the fixed and flexible die were confirmed. The result of the stretch forming process analysis using the flexible die was better than that using the fixed die in view of the elastic recovery. However wrinkles were occurred on the sheet material due to die cavities between the punches in the flexible forming process, thus the solutions against these problems were presented.

• 한국축산시설환경학회지
• /
• 제5권2호
• /
• pp.79-86
• /
• 1999

Recently more dairy farmers are interested in the utilization of stretch film for wrapping silage material. Most of stretch film are imported from abroad and one domestic product was developed, but its quality has not yet been tested. Therefore this study was executed to offer basic data on this material to the farmers. Measured items were tensile load, extension ratio, and tear propagation strength of stretch films. Comparisons were made among the white color of domestic product(Kw), and white(Fw), black (Fb) and green color(Fg) of foreign products. The result were summarized as follows: 1. Tensile loads of lengthwise direction in stretch films were 557.4, 377.4, 282.6 and 398.4kgf/$\textrm{cm}^2$ in Kw, Fw, Fb and Fg, respectively, and tensile loads of width direction were 415.9, 418.1, 360.2 and 433.0kgf/$\textrm{cm}^2$ in Kw, Fw, Fb and Fg, respectively. 2. Extension ratios of lengthwise direction were 650, 462.5, 512.5% and 537.5% in Kw, Fw, Fb and Fg, respectively, Extension ratios of width direction were 930, 962.5, 950 and 1,000% in Kw, Fw, Fb and Fg, respectively. 3 Tear propagation strength of lengthwise direction 187.9, 148.9, 157.3 and 142.8kgf/cm, and tear propagation strength of width direction were 141.4, 129.8, 140.4 and 106.6kgf/cm in Kw, Fw, Fb and Fg, respectively. 4. In the light transmittance, there was no difference between white and green color stretch film, but it was very low in black one. Therefore, it is thought that research on quality of roll bale silage treated with each stretch film would be needed.

• 한국기계가공학회지
• /
• 제17권1호
• /
• pp.153-160
• /
• 2018

A pressure vessel consists of an inner tank and the outer tank; the material of the inner tank is austenite stainless steel, and the outer tank is general carbon steel. As the storage amount increase, the size of the inner tank for LNG also increases, which eventually increases the weight of the LNG storage tank. The Cold Stretch method can transport and store the LNG in a larger amount than the conventional pressure container, and the weight of the pressure vessel can also be reduced at 50 70% due to the reduction of the thickness, which is excellent from an economic and energy consumption perspective. Although the Cold Stretch method has these advantages, the domestic situation has not developed any related legislation. In this study, the actual production of pressure vessels using the Cold Stretch method will be processed and the volume expansion after the Cold Stretch will be checked and compared with the mechanical properties.

• 복식문화연구
• /
• 제16권1호
• /
• pp.48-57
• /
• 2008

The purpose of this study was to examine the inconvenience when putting on stretchable pants and to analyze the whole actual conditions of making of the lining fabrics. For this study, we conducted a survey of women in their twenties and collected the basic data and master pattern through material of a woman's wear brand and the interview and questionnaires. The results of this study were as follows. First, the survey result for the woman consumers it showed that the most uncomfortable problem about the lining of pants was not sufficient stretch as much as the out-shell. Secondly, it was shown that many brands(46.7%) were using the lining fabrics of stretch clothes mixed with 'non-stretch fabrics' and 'stretch fabrics'. The result of lining pattern making for the stretch pants showed that the ease of the lining fabrics was 0 to 4cm in the hip girth more than out-shell. The ease in crotch width was 0 to 1.3cm for lining fabrics. But in the stretch lining fabrics the ease for front crotch width was 0 to 1cm more than out-shell. The lengths of crotch rising were -0.7 to 1.3cm for the non-stretch lining fabrics and -1 to 1cm for the stretch lining fabrics.

• 복식문화연구
• /
• 제16권4호
• /
• pp.609-618
• /
• 2008

The purpose of this study is to examine the inconvenience when putting on stretch pants and to compare and analyze the pattern making method of pants made of the stretch and non-stretch fabric to develop functional and good looking stretch pants. For this study, we conducted a survey of women in their twenties and collected the basic data and master pattern through material of a woman's wear brand and the interview and questionnaires. The results of this study are as follows. First, the survey result for the woman consumers showed that pants were estimated as the most uncomfortable item among the stretch clothes and when they put the stretch pants on, the most uncomfortable parts of out-shell were the hip girth and rise. Secondly, the result of pattern making method of the pants was as follows. The ease of the stretch pants pattern was 0cm in the waist girth and -1 to -1.5cm in the hip girth more than non-stretch pants. The ease in crotch, inseam and outseam length was 0cm for both.

• 한국정밀공학회지
• /
• 제11권1호
• /
• pp.129-137
• /
• 1994

A rigid-viscoplastic finite element method has been used for modeling superplastic stretch/blow process design to improve thickness distribution. Punch velocity-time relationship of the stretch forming and pressure-time cycle of the blow forming for a given strain rate are calculated. A superplastic material is assumed to be isotropic and a plane-strain line element based on membrane approximation is employed for the formulation. The effects of the width, corner radius and height of the punch during stretch forming are examined for the final thickness distribution, and the process design to improve thickness distribution can be established.