• Transactions of Materials Processing
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• v.7 no.6
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• pp.539-544
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• 1998

Hemi-spheroidal punch stretching test was developed to evaluate the press formability of sheet materials. In the plane strain stretching tests our specially designed hemi-spheroidal head punch were used. In the experiment the circular sheet blanks with parallel edge sides are uniformly stretched up to fracture by raising these punches to assure plane strain stretching deformation along the longitudinal direction of the specimens. The press formability was evaluated by limit punch height(LPH) and minor strain mea-surement around the fracture area. Compared with the hemi-spherical punch and the hemi-cylindrical one our hemi-spheroidal punch was more useful in the experimental reproduction and reliance for press formability test.

• Transactions of Materials Processing
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• v.7 no.4
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• pp.354-363
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• 1998

In order to analyze the stretch forming characteristics of tailored blanks, laser welded blanks of different thickness and strength combinations were prepared and stretching tests were done. The stretching formability of laser welded blanks was reduced as increasing the deformation restraining force ($strength{\times}thickness$) ratio between two welded sheets. Weld line movement was attributed to strain concentration at weaker sheets and resulted in fracture at weaker sid, so that fracture could be predicted by the forming limit of the weak sheet. In the case of a welded blank with the similar deformation restraining force rations between two welded sheets, crack occurred at weld and its forming limit was about 15% less than the base sheet. The effects of lubrication and weld line position on stretch-ing formability were also investigated by experiments. Lower friction did not always give better formability for tailored blanks. Stretching formability was observed to be improved as increasing the area of weak sheet.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1132-1137
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• 1993

A simple simulative test was developed to evaluate stamping formability in plane strain stretching mode. The stamping formability was evaluated by limit punch height(LPH) in plane strain punch stretching test(PSST) compared to limit dome height(LDH) in hemispherical punch stretching test. PSST shows stable plane strain condition and good reproducibility with minimum scatter. Moreover LPH-value in PSST well ranks the stamping formability of various material and correlates with press performance.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.2
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• pp.121-129
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• 1993

Plane strain punch stretching test (PSST) was developed to evaluate stamping formability of sheet materials. In this test, the rectangular specimen of sheet material is uniformly stretched up to fracture by raising a specially designed punch to certainly assure plane strain stretching deformation along the longitudinal direction of the specimen. The stamping formability was evaluated by limit punch height(LPH) in plane strain punch stretching test compared to limit dome height(LDH) in hemispherical punch stretching test. LPH-value in PSST well ranks the stamping formability of various material and correlates with press performance. Moreover by using ultrasonic thickness gauge the plane strain intercept-limit plane strain(FLCo)-in forming limit curve can be accurately determined from thickness measurement around the fracture area. The FLCo derived from thickness measurement well correlates with the results from circle grid analysis for the deformed circle grid marked on the surface of the specimen.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.06a
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• pp.164-170
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• 1998

Hemi-spheroidal punch stretching test was developed to evaluate the press formability of sheet materials. In the plane strain stretching tests, our specially designed hemi-spheroidal head punch, hemi-cylindrical head punch(RIST type) and hemi-spherical head punch were used, respectively. In this experiment, the circular sheet blanks with parallel edge sides are uniformly stretched up to fracture by raising these punches to assure plane strain stretching deformation along the longitudinal direction of the specimens. The press formability was evaluated by limit punch height(LPH) and minor strain measurement around the fracture area. Compared with the hemi-spherical punch and the hemi-cylindrical one, our hemi-spheroidal punch was more useful in the experimental reproduction and reliance for press formability test.

• Transactions of Materials Processing
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• v.18 no.1
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• pp.73-79
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• 2009

In order to investigate the formability of friction stir welded(FSW) tailor welded blanks(TWB) with respect to the base material's directional combination, aluminum alloy AA6111-T4 sheets were welded with three different conjoining types: RD-RD, TD-RD and TD-TD. Here, RD and TD represent rolling and transverse directions, respectively. For experimental formability study, three tests with gradual complexity were performed: the simple tension test with various weld line directions for uni-axial elongation, the hemisphere dome stretching test for biaxial stretching and the cylindrical cup deep drawing test. As a result, all three forming tests showed that RD-RD type samples exhibited the best formability, while TD-TD type sheets showed the least formability performance.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.341-344
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• 2008

In order to study the effect of shot blasting condition on the formability of thin high strength steels, specimens were made by changing line speed of a commercial shot blasting plant with maintaining constant impeller condition. Surface roughness of prepared specimens was multiplied by lowering line speed or increasing density of shot impact. Formability was reduced as increasing shot impact. The elongation and stretching formability of shot blasted sheet were decreased by about 10% compared to original sheet. More significant decrease in bending formability was observed after shot blasting. This might be due to the concentrated impact near the surface where major strain occurs during bending process.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.1
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• pp.73-83
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• 1994

Press formabilities of aluminum sheets for automobile body were investigated. Plane strain stretching test (called RIST-PSST), cupping test and U bending test were performed to assess the press formability of aluminum sheets respectively. The results showed that aluminum sheets are generally inferior to cold-rolled steel sheet of deep drawing quality (CSP3N) in press formability. The limiting punch height (LPH) and limiting plane strain (FLCo) of aluminum sheets are 50%-70% level compared to that of CSP3N. Moreover, the limiting drawing ratios(LDR) of aluminum sheets are ranged between 1.95 and 2.1. The poor press formability of aluminum sheets is responsible for low values of total elongation and plastic anisotropy parameter in tensile characteristic. The shape fixability of aluminum sheets evaluated in U bending test is very poor due to its low elastic modulus compared to CSP3N.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.62-65
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• 2001

The effects of the initial torture of workpiece as well as the process conditions such as punch speed and lubrication on the formablity of sheet stretching are investigated by experiments. Two types of the initial textures of aluminum sheet plane strain compression torture and recrystallization texture are chosen since those are the most common in practice. Punch loads vs depth and thickness strain distributions along radial directions having the slope of $0^{\circ},\;45^{\circ},\;90^{\circ}$ with rolling directions are reported for hemishperical punch stretchings under a variety of process conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.380-388
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• 2016

Commercially pure titanium (CP Ti) has been actively used in plate heat exchangers due to its light weight, high specific strength, and excellent corrosion resistance. However, compared with automotive steels and aluminum alloys, there has not been much research on the plastic deformation characteristics and press formability of CP Ti sheet. In this study, the mechanical properties of CP Ti sheet are clarified in relation to press formability, including anisotropic properties and the stress-strain relation. The flow curve of the true stress-true strain relation is fitted well by the Kim-Tuan hardening equation rather than the Voce and Swift models. The forming limit curve (FLC) of CP Ti sheet was experimentally evaluated as a criterion for press formability by punch stretching tests. Analytical predictions were also made via Hora's modified maximum force criterion. The predicted FLC with the Kim-Tuan hardening model and an appropriate yield function shows good correlation with the experimental results of the punch stretching test.