无裂纹扭转试样充氢后在恒定的扭矩作用下能产生氢致滞后开裂。顺时针扭转时裂纹面和扭转轴成45°;反时针扭转则沿-45°面产生裂纹。计算表明,如果氢原子在α-Fe中的应变场是非球对称的,则氢原子的应变场和扭转应力场之间存在有互作用能,而且在45°面(顺时针扭转时)上具有极小值。这就将导致氢原子向45°面扩散和富集,当其浓度达到临界值时就会引起氢致滞后开裂。对于充氢的缺口或预裂纹扭转试样(即Ⅲ型裂纹)上述结论也成立。
Hydrogen induced delayed cracking of charged smooth torsional specimens was observed on the planes inclined at an angle of 45° (clockwise twisting) or-45°(counter-clockwise twisting)to the torsional axis, after a large enough torque had been sustained for a long time. Calculation shows that if the strain field of an interstitial hydrogen atom in α-Fe has tetragonal symmetry, the interactive energy between the strain field and the torsional stress field has a minimal value on the planes inclined at an angle of 45°. Hydrogen atoms will diffuse to and be enriched on the planes and then hydrogen induced delayed cracking can occur on the planes, when the hydrogen concentration on the planes reaches a critical value. For a charged notched or cracked torsional specimen, i. e. Type Ⅲ crack, above conclusions are also correct.
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