努氏硬度測試

努氏壓痕和維氏壓痕不同，它是不對稱的。當(dāng)使用努氏標(biāo)尺，尤其是200gf以下時(shí)，會(huì)使硬度值的變化體現(xiàn)得更為明顯。

雖然如ASTM標(biāo)準(zhǔn)中的500gf提供了努氏硬度結(jié)果轉(zhuǎn)換為其它硬度標(biāo)尺的硬度轉(zhuǎn)換，但通常努氏硬度測試不用于定義宏觀硬度。通常努氏試驗(yàn)力不超過1000gf, 特殊情況或材料需要更高試驗(yàn)力如2和5kgf時(shí)除外，期望使用這些試驗(yàn)力時(shí)將得到更大的硬度變化。

努氏金剛石壓頭的長對角線長度遠(yuǎn)大于短對角線長度，相對于維氏壓頭，努氏壓頭能更好地獲得很短距離內(nèi)的硬度變化。

是否能成功地消除試樣準(zhǔn)備過程中造成的損傷將會(huì)影響到測試的結(jié)果；當(dāng)試驗(yàn)力降低時(shí)，此問題將變得更為突出。

KNOOP HARDNESS TESTER

The Knoop resulting indentation is not symmetrical as Vickers indentions and will be subject to more variations of the resulting hardness values when testing to Knoop scales, especially below 200gf.

HOW DOES THE KNOOP HARDNESS TESTER WORK?

Knoop hardness is not typically being used to define bulk hardness, although at 500 gf standards like ASTM provide conversions of Knoop results to other hardness test scales. Knoop tests are not typically performed at test forces above 1000 gf although particular circumstances and or materials may need higher forces like 2 and 5 kgf. Expect larger variations in results at these loads. The Knoop diamond indenter is designed with a significant difference between the long and short Knoop diagonals, which is often better suited for determining variations of hardness over very small distances compared to the Vickers indenter.

The success of the specimen preparation procedure in removing preparation-induced damage can, and will, influence test results; this problem becomes more critical as the test force decreases.