On the Effects of Duration of Impressive Loading and Time after Unloading upon the Rockwell Hardness Numbers for Plastics

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  • プラスチックスのロックウエル硬さにおける押込み加圧時間と除圧後の時間の影響について
  • プラスチックス ノ ロックウエル カタサ ニ オケル オシコミ カアツ ジカン ト ジョアツ ゴ ノ ジカン ノ エイキョウ ニ ツイテ

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The authors have inquired experimentally into the effects of the times of impressing the specimen and after unloading upon the Rockwell hardness numbers for plastics and steel.<br>The experiments have been carried out under the constant impressive load, 150kg, using the constant indentor, 1/4 inch steel ball. The materials of specimens tested are a soft steel and the five kinds of plastics, such as phenolic, urea, polyester, polystyrene and nylon.<br>As the results, two empirical formulas have been derived as follows: HR=H1-ΔH0·(logt)m (1) and HR=(H1-k·logt)+(n1+l·logt){log(logt')} (2) where HR is the total depth of indented hole under impressive loading in the scale of Rockwell hardness numbers, H1 hardness numbers at impressive loading instant, ΔH0 hardness numers' changes from H1 to 10sec impressive loading's, HR Rockwell hardness numbers, t duration of impressive loading, t' time after unloading, and H1, k, l, m and n1 are the constants proper to the materials.<br>Accordingly, the Rockwell hardness numbers HR1 for the standard duration of impressive loading t1 and time after unloading t'1 may be obtained by the following formula HR1=HR+k·logt/t1+n1·log(logt'1/logt')+l·{logt1·log(logt'1)-logt·log(logt')} (3) where HR is the Rockwell hardness numbers of the material for any duration of impressive loading t and time after unloading t'.

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