残余压应力对低合金高强钢热预应力增韧效应的影响

Influence of residual compressive stress on warm prestress toughening of HSLA steel

通过对三点弯曲预制裂纹试样在室温下 (2 0℃ )预加载 -卸载 -冷却至 - 1 96℃或 - 1 30℃下断裂 (LUCF) ,以及加载 -冷却至 - 1 96℃或 - 1 30℃下卸载 -断裂 (LCUF)的预应力循环试验 ,测定了其宏微观力学参数并计算了裂纹尖端应力、应变和三向应力度的分布 ,模拟了在相同裂纹钝化半径下没有残余压应力的直接冷却断裂行为 (CF)与有残余压应力的 WPS循环 (LUCF)的断裂行为并进行比较 ,研究了残余压应力对低合金高强钢预裂纹试样 WPS增韧效应的影响 .结果表明 :残余压应力对低温断裂韧性的提高在不同的终断温度下的作用不同 ,- 1 96℃下断裂时有增韧作用 ,其作用是抵消了一部分低温断裂再加载时的正应力 .同时 ,残余压应力通过减缓三向应力度随外载增加而增加的速度对 - 1 96℃断裂时的增韧起作用 .- 1 30℃下残余压应力作用不明显 ,并且对低温断裂时裂纹的钝化有拘束作用 .

By means of warm prestress fracture test of pre-cracked specimens under three-point bending at room temperature (20 ℃) in the manner of loading-unloading-cooling down to -196 ℃ or -130 ℃-fractture (LUCF) and loading-cooling down to -196 ℃ or -130 ℃-unloading-fracture (LCUF), the macroscopic mechanical parameters of fracture are measured and the distribution of stress, strain, and stress triaxiality around the crack tip are calculated by using FEM. In addition, the fraeture processes both the cooling-fracture and warm prestress (WPS) eycle (LUCF) with the same blunt tip radius of the crack are simulated by using the FEM also, the former being without residual compressive stress and the latter-with one, so that the influence of residual compressive stress on WPS toughening of pre-cracked HSLA steel specimens is investigeted. The result shows that the effects of residual compressive stress on the improvement of low-temprature fracture toughness are different due to different terminate temperature; fracture at -196 ℃ would result in toughening effect because a portion of normal stress is offsetted. Besides, the moderation of the increase of trianial stress with the loading at -196 ℃ fracture may benefit the toughening effect. The effect of residual compressive stress is found unremarkable when fracture occurs at -130 ℃ and ,in addition, it would restrict the blunting of the crack.