A Construction of Judging System of Welding under Pulsating Loads

海洋工程结构物、塔架、桥梁等在役结构物经常受到波、流、风或移动车辆等的脉动荷载作用，因此，对这些结构物进行焊接修复、加固或改造工程时，都要在脉动荷载作用下进行，为此，进行了脉动荷载作用下的焊缝开裂试验。作为试验结果，提出了在短时间内从液相线到固相线反复施加焊缝金属的累积应变Δ t作为判断脉动载荷下热裂纹萌生的尺度。用相对根部间隙张开位移Δ delta表示，Δ delta可在焊接前容易地测量。推导了用DELTAdelta计算脉动载荷下热裂纹萌生的实用判别方程。将该实用判定方程应用于均匀脉动载荷下的热裂纹试验结果，证明了其有效性，并通过对焊缝金属进行高温拉伸试验，发现脉动载荷下的热裂纹可分为固-液状态裂纹和固态裂纹。前者称为凝固裂纹，后者为HS（热裂纹）型裂纹。影响凝固裂纹萌生的主要因素是外载荷与重复次数的乘积。外荷载循环作用下的最大应变速率（根部间隙最大张开速率）是HS型裂纹萌生的主要因素，并将其应用于在役桥梁的实际工作中，验证了其有效性。

The structures in service conditions such as offshore structures, towers, bridges and so on are always suffered the pulsating loads by waves, current, wind or moving vehicles, etc. So, repair, reinforcement or reconstruction works by welding on these structures are done under the pulsating loads.The weld cracking test under the pulsating loads is carried out. As the results of the experiments, the accumulation strain, epsilon_t, by which the weld metal was repeatedly applied at a short time from the liquidus to the solidus was proposed as a measure for deciding hot crack initiation under the pulsating loads. epsilon_t was expressed with the relative root gap opening displacement, DELTAdelta, which can be easily measured before welding. The practical deciding equation for hot crack initiation under the pulsating loads using DELTAdelta was derived. Applying the practical deciding equation to the results of the hot cracking test for the case that the uniform pulsating loads are applied, its validity was shown.It is found that the hot cracks under the pulsating loads can be classified into crack of solid-liquid state and crack of solid state by conducting the high temperature tensile test on the weld metal. The former is called a solidification crack and the latter is HS (Hot Crack in Solid state) - type crack. Concerning the solidification crack initiation, the main factor was the product of DELTAdelta by the external loads and repeated number. The main factor for HS-type crack initiation was the maximum strain rate (the maximum root gap opening rate) by the external loads in a cycle.Welding is applied to the actual work for a bridge in service and its validity demonstrated.