vX`bNΜκiKθΧd έd³±Ι»κιSe«»ΫΜ_IEΐ±I€.II. Se«»ΫΜ`Τ
Theoretical and Experimental Viscoelastic Properties of Plastics in One-stage Constant Load Ball Indenting Hardness Tests.II. Forms of Viscoelastic Phenomena
Ξ΄BνEΏ²ηqE¬FK¬
Ishibashi, Tatsuya / Sukigara, Sachiko / Oguma, Yukinari
The Non-dimensional indentation function Βa/i under constant load is formulated as follows using the non-dimensional elapsed time ta/i a constant load ball indenting creep factor C and a creep index m ; Βa/i=1+C (log ta/i)m. In order to calculate the time dependences of total strain ratio Γa/Γi, flow stress ratio Ya/Yi, elastic/total strain ratio Γra/Γa and plastic/total strain ratio Γpa/Γa of plastics for various values of C and m, the expression for Βa/i is applied to the theoretical expressions for the viscoelastic-characteristic function P(ta/i) and indentation/recovery ratio Qi. The results show that the time dependence of total strain ratio Γa/Γi is small and the values of Γa/Γi are about unity. On the other hand the time dependence of flow stress ratio Ya/Yi are large compared to that for Γa/Γi and values of Ya/Yi decrease with elapsed load holding time. Consequently, it thus appears that the viscoelastic phenomenon which is observed for this constant load situation is a form of stress relaxation.
Key words: Plastics / Ball Indenting Hardness Test / Viscoelastic Phenomena / Various Indenting Curves / Stress Relaxation Form