A Construction of Judging System of Welding under Pulsating Loads

在使用条件下的结构，如海上结构、塔、桥梁等，经常受到波浪、水流、风或移动车辆等的脉动荷载。因此，这些结构的修复、加固或焊接改造都是在脉动荷载下进行的。进行了脉动载荷作用下焊缝开裂试验。实验结果表明，在脉动载荷作用下，焊缝金属在短时间内从液相态向固相态反复施加的累积应变epsilon_t可作为判断热裂纹萌生的指标。epsilon_t用相对根隙张开位移DELTAdelta表示，该位移在焊接前易于测量。利用DELTAdelta导出了脉动载荷下热裂纹起裂的实用判定方程。将实际决定方程应用于均匀脉动载荷作用下的热裂试验结果，验证了该方程的有效性。通过对焊缝金属进行高温拉伸试验，发现脉动载荷作用下的热裂纹可分为固液态裂纹和固态裂纹。前者称为凝固裂纹，后者称为固态热裂纹（HS）型裂纹。对于凝固裂纹萌生，主要影响因素是外加载荷与重复次数的δ δ δ积。hs型裂纹萌生的主要因素是在一个周期内外载荷作用下的最大应变速率（最大根隙张开率）。将焊接技术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.