冰—弹性平板相互作用的试验研究

Experimental Study of Interaction between Frozen Ice and Elastic Plates

  • 摘要: 为探究结构弹性对冰—结构相互作用过程的影响,在低温实验室开展冻结冰—弹性平板挤压模型试验。改变结构刚度和挤压速率,推动弹性平板与冻结冰试件在冰脆性破坏范围内进行挤压,记录不同工况下总载荷时程曲线和冰破坏模式。试验发现相互作用过程可分为“松接触”和“紧接触”两个典型阶段,部分压力—位移曲线在紧接触阶段呈现出锯齿状形式的“多级失效”。统计发现最大松接触位移集中在0-1.5mm范围内,紧接触阶段多级失效发生占比为43.3%且多发生在结构刚度较小的工况。冰破碎图像显示“多级失效”是接触面不断剥落小块造成压力下降形成的。冰—弹性平板耦合系统在紧接触阶段的系统刚度几乎保持不变,说明耦合系统在冰脆性破坏下呈现线性关系,满足双弹簧模型。本研究揭示了冰与弹性结构相互作用过程的典型特点,为冰区船舶冰载荷的准确预报提供了理论基础。

     

    Abstract: To investigate the influences of structural elasticity on ice-structure interaction process, model tests on interaction of frozen ice and elastic plates was conducted in a low temperature laboratory. Plate elasticity is modeled in the tests through varying the plate thickness. By indentating the elastic flat plate onto frozen ice specimen, the load time history and ice failure modes under different test conditions were recorded. The experimental results show that the interaction process is basically classified by two typical phases, that is, loose contact phase and tight contact phase. The loose contact phase results from uneven contact surface between the plate and ice specimen top. Simple data statistics show that the maximum loose contact displacements are concentrated within the range of 0-1.5mm. During the second tight contact phase some of the time histories of loads and displacements are normal single-stage curves, but some are saw-tooth shaped, exhibiting multi-stage failure modes with occurrence probability about 43.3%. From the tests it is established that stiffer plates (thicker plate) are likely to produce single-stage failure of ice, while more flexible plates (thinner plates) are more likely to result in multi-stage failures of ice. Through comparing video clips, we are able to correlate multi-stage failures with outward ice flaking. Observations show that flaking is concentrated in the 450 direction, thus resulting from shearing failure. This is a local failure mode. As the plate is pressed onto ice specimen further, a new flaking failure may occur. This may happen twice or even more times until finally the whole ice specimen fails. Experimental results show that the slope of load-displacement curve is nearly a constant for the multi-stage failure, indicating the stiffness of the ice-elastic plate coupling system remains unchanged during the tight contact phase. These experimental results may help the designer of an ice-going ship to have a better understanding of the complicated interaction mechanics between ice and ship structure, although the structure under consideration in this paper is simplified to a plate.

     

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