• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.9
• /
• pp.740-753
• /
• 2008

The conventional Split Hopkinson Pressure Bar (C-SHPB) technique with aluminum pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials such as hot temperature degraded POM (Poly Oxy Methylene) and PP (Poly Propylene) to obtain more distinguishable experimental signals is used to obtain a dynamic behavior of material deformation under a high strain rate loading condition. An experimental modification with Pulse shaper is introduced to reduce the nonequilibrium on the dynamic material response during a short test period to increase the rise time of the incident pulse for two polymeric materials. For the dynamic stress strain curve obtained from SHPB experiment under high strain rate, the Johnson-Cook model is applied as a constitutive equation, and we verify the applicability of this constitutive equation to the probabilistic reliability estimation method. The methodology to estimate the reliability using the probabilistic method such as the FORM and the SORM has been proposed, after compose the limit state function using Johnson-Cook model. It is found that the failure probability estimated by using the SORM is more reliable than those of the FORM, and the failure probability increases with the increase of applied stress. Moreover, it is noted that the parameters of Johnson-Cook model such as A and n, and applied stress affect the failure probability more than the other random variables according to the sensitivity analysis.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.7 no.9
• /
• pp.112-118
• /
• 1999

Shrinkage behavior was investigated to obtain more accurate dimensions of injected molding parts for free and restricted shrinkage conditions. various parameters for metal inserted injection process, such as thickness of resin, holding pressure and time, mo이 temperature and restriction condition of mold, were considered for the analysis of shrinkage phenomena. For numerical analysis, MOLDFLOW software was used to find the deterministic parameters of filling time, temperature, pressure and holding time. Also , experimental shrinkage effects were measured through actual injection molding process and the resin thickness was under controlled as 3 mm , 5 mm, and 7mm for the shapes of plastic gear made of Polymide(PA) and Polyxymethlene(POM). The main parameters of these injection processes were found to be holding pressure, holding time and mold temperature in the case of metal inserted molding.

• Journal of Power System Engineering
• /
• v.2 no.1
• /
• pp.80-85
• /
• 1998

Engineering plastics have been magnified its usability due to its outstanding mechanic al, electrical and chemical properties, for example, in the area of computer, electricity, electronics, automobile, camera industry. In recent, automobile speedometer system is changing from manual operation to motor operation. All plastic gears inserted by metal shaft are used In motor operated speedometer system. Therefore, in this research, experimental investigation of the shrinkage phenomenon was executed according to various inserted depth and injection conditions. In experiments, the inserted depth was controlled as 30% and 90% of the total thickness of the plastic gear. The main parameters of injection process were selected as injection pressure, holding pressure, melt temperature, injection rate. As main results, free shrinkage rate of the test part is increased about 4 times to restricted shrinkage rate and shrinkage phenomenon against all injection conditions have a trivial effect on the test parts as conventional parts.