静动荷载作用下小麦剪切特性试验研究

为研究静动载荷作用下的粮食剪切特性，利用开发的新型粮食动直剪仪，设计了孔隙率为39%、36%、33%以及竖向压力为50、100、150、200 kPa下的小麦单调直剪、往复剪切及往复后单调直剪试验，研究了小麦静动力剪切特性，并对比分析了小麦单调直剪与往复后单调直剪的强度、变形结果。研究结果表明：单调直剪试验中，同一孔隙率下，竖向压力越大，其软化现象越明显，剪胀现象越不明显，剪胀角越小，竖向压力为50、100、150、200 kPa下对应的剪胀角分别为4.5°、3.6°、2.4°、0.7°；同一竖向压力下，随着小麦孔隙率减小，其软化现象越明显，内摩擦角也越大，孔隙率为39%、36%、33%的小麦对应的内摩擦角分别为22.2°、24.4°、28.1°。剪胀角也随着小麦孔隙率减小而增大，对应的剪胀角分别为1.3°、3.6°、9.9°；往复剪切试验中，孔隙率越小，小麦往复剪切软化现象越明显，剪缩现象越不明显，最大剪缩量越小，孔隙率为39%、36%、33%的小麦对应的最大剪缩量分别为2.77、1.74、1.15 mm。往复后单调直剪与单调直剪试验结果对比表明，往复后单调直剪的小麦抗剪强度明显增大，其剪胀现象更明显，最大剪胀量也增大。试验结果可为粮仓结构安全性设计，尤其是粮仓结构动力分析提供依据。

Experimental study on shear performance of wheat under static and dynamic loading

Abstract: When grain is stored in the granary, it will be subjected to static and dynamic loads under the circumstances such as loading and unloading, earthquake and so on. And then these effects will act on the wall of the granary, affecting the stress of the wall. A new dynamic direct shear apparatus which consisted of shear box connecting components, horizontal thrust system and data acquisition system was used to provide a test platform for testing the mechanical properties of grain under static and dynamic loads. In order to investigate the dynamic mechanics of grain，the wheat direct shear experiments under static and dynamic loads were carried out. Meanwhile, the horizontal shear stress, shear displacement, vertical displacement and other relations in the dynamic test results were also analyzed. Using the new dynamic direct shear apparatus for grain, a series of tests were designed to study the dynamic characteristics of reciprocating shear considering three different porosities of 39%, 36%, 33% and four vertical pressures of 50, 100, 150, 200 kPa. These test results of strength and deformation were compared among the monotonic and post-reciprocating monotonic loading direct tests. The results showed that the stress-strain curves showed a softer curve and less dilatancy phenomenon with increasing vertical pressure during the monotonic direct shear test for the same porosity, thus a smaller dilatancy angle was also obtained. Under the vertical pressure of 50, 100, 150, 200 kPa, the corresponding dilatancy angles were 4.5°, 3.6°, 2.4°, 0.7°, While with the decreasing wheat porosity, the softening phenomenon became more obvious and the internal friction angle became larger. The internal friction angles of wheat with porosity of 39%, 36%, and 33% were 22.2°, 24.4°, 28.1°. What's more, the dilatancy phenomenon became more obvious with the decreasing porosity, inducing the increasing dilatancy angle. The corresponding dilatancy angles are 1.3°, 3.6°, 9.9°during the monotonic direct shear test. In the reciprocating direct shear test, with the decrease of porosity, the softening phenomenon of wheat was more obvious, and the dilatancy phenomenon was less evident. The maximum dilatancy are decrease with decreasing porosity, which corresponding with the maximum dilatancy deformation were 2.77, 1.74, 1.15 mm. These results of monotonic direct shear tests and post-reciprocating monotonic direct shear tests were compared. The results showed that the shear strength of wheat after reciprocating shear were significantly higher than those directly from the monotonic direct shear tests. The shear dilatation was also more obvious after reciprocating shear, corresponding with larger dilatancy deformation. The results showed that the strength and dilatancy characteristics of wheat were changed after the dynamic effect, which would affect the lateral pressure on the silo wall, which indicated that the lateral pressure coefficient of the silo wall need to be further improved when considering the dynamic effect. The results take into account the loading and unloading process, the static and dynamic characteristics of vibration, and the static characteristics after the dynamic effect. These results are necessarily provided for the engineers in the design and dynamic analysis of granary structure.