不同应力水平对塑料土工格栅拉伸强度影响

       塑料土工格栅的蠕变是影响加筋土结构AQ的重要因素,经过蠕变后的塑料土工格栅在各项拉伸性能上会有变化,为了确定塑料土工格栅在蠕变后各项拉伸指标的变化,进行了1000 h的室内螨变试验,并设置了4种不同荷载级别。通过记录卸载后塑料土工格栅的收缩应变,得出收缩应变随时间变化的3个阶段和各应力水平下的残余应变。拉伸试验结果表明:2%和5%伸长率的拉伸强度随蠕变时所受应力水平的增加而增加,断裂伸长率和**限拉伸强度随着蠕变时所受应力水平的增加而降低,并且在60%应力水平下**限拉伸强度降低了17.3%。

The creep of plastic geogrid is an important factor affecting the safety of reinforced earth structure. After creep, the tensile properties of plastic geogrid will change. In order to determine the changes of tensile indexes of plastic geogrid after creep, a 1000 h indoor mite test was carried out, and four different load levels were set. By recording the shrinkage strain of plastic geogrid after unloading, the three stages of shrinkage strain changing with time and the residual strain at each stress level are obtained. The tensile test results show that the tensile strength of 2% and 5% elongation increases with the increase of stress level during creep, the elongation at break and ultimate tensile strength decrease with the increase of stress level during creep, and the ultimate tensile strength decreases by 17.3% at 60% stress level.

       在移除荷载的瞬间塑料土工格栅出现了弹性收缩变形,并且大部分的收缩变形在这段时间内完成,在弹性收缩结束后图中曲线出现了一段圆弧,表明收缩回弹速率逐渐减少,塑料土工格栅在蠕变过程中出现了塑性变形,这段时间持续到400h,在400h之后收缩变形基本停止。

At the moment when the load is removed, the plastic geogrid appears elastic shrinkage deformation, and most of the shrinkage deformation is completed in this period of time. After the elastic shrinkage, a section of arc appears in the curve, indicating that the shrinkage rebound rate is gradually reduced, and plastic deformation occurs in the creep process of the plastic geogrid, which lasts for 400H, and the shrinkage deformation basically stops after 400H.

       4种应力水平下的塑料土工格栅均没有收缩回弹到原来的尺寸,且在20%、30%.40%、60%应力水平下,塑料土工格栅zui后的残余变形分别为1. 19%、1.99%、2.42%、3.13% ,表明随着应力水平的增加塑料土工格栅恢复原有尺寸的能力下降。塑料土工格栅有粘弹性材料性质,在蠕变过程中随着粘性应变增加，会导致格栅变形恢复力逐渐降低。由此可以看出塑料土工格栅的残余变形与时间和施加的应力水平有关。

At 20%, 30%, 40% and 60% stress levels, the final residual deformation of plastic geogrid is 1.19%, 1.99%, 2.42% and 3.13% respectively, which shows that the ability of plastic geogrid to restore the original size decreases with the increase of stress level. Plastic geogrid has viscoelastic properties. With the increase of viscous strain in creep process, the deformation restoring force of geogrid will decrease gradually. It can be seen that the residual deformation of plastic geogrid is related to time and applied stress level.

        在塑料土工格栅中纵向的肋条宽度大于斜向的肋条宽度,所以纵向肋条的拉伸强度大于斜向拉伸强度。随着应力水平的增加,塑料土工格栅的**限拉伸强度呈现下降趋势,并且在应力水平为0~20%时，下降zui为明显,随后**限拉伸强度下降变缓,在应力水平为60%时,斜向和纵向的塑料土工格栅**限拉伸强度分别下降11.5%和17.3%,表明格栅在蠕变过程中,发生了不能恢复原状的塑性变形,格栅中的肋条被拉长变细,引起拉伸强度的降低。

In the plastic geogrid, the longitudinal rib width is larger than the oblique rib width, so the tensile strength of the longitudinal rib is larger than the oblique tensile strength. With the increase of stress level, the ultimate tensile strength of plastic geogrid shows a downward trend, and when the stress level is 0-20%, the decline is most obvious, and then the decline of ultimate tensile strength slows down. When the stress level is 60%, the ultimate tensile strength of oblique and longitudinal plastic geogrid decreases by 11.5% and 17.3% respectively, which shows that during the creep process of the geogrid, The plastic deformation which can not be restored to the original state occurs, and the ribs in the grid are elongated and thinned, resulting in the decrease of tensile strength.

       随着应力水平的增加,断裂伸长率不断减小，结合收缩应变-时间曲线可以看出:各应力水平下的断裂伸长率加上相应的残余应变伸长率所得到的值基本相等,这说明格栅断裂时总的伸长量是不变的。随着残余应变的增加,格栅的韧性逐渐降低。

With the increase of the stress level, the elongation at break decreases continuously. Combining with the shrinkage strain time curve, it can be seen that the elongation at break plus the corresponding elongation at residual strain at each stress level is basically the same, which shows that the total elongation at break of the grid is unchanged. With the increase of residual strain, the toughness of the grid decreases gradually.

       随着应力水平的增加,2%和5%伸长率的拉伸强度在不断地增加,并且呈现出线性的变化规律。另外还可以看出纵向肋条拉伸强度的增长速率比斜向要快,这和三向格栅中纵向和斜向肋条的受力方式有关,纵向肋条与拉力的方向一致,斜向肋条与受力方向有60°的夹角,从力学角度分析其原因为:纵向肋条在蠕变过程中受到更大的力分量,因此其在蠕变过程中的应变更大。综上可知:经过蠕变的格栅与未经过蠕变的格栅相比,延伸性能下降,材料变得更脆。

With the increase of stress level, the tensile strength of 2% and 5% elongation increases continuously, and shows a linear change rule. In addition, it can be seen that the growth rate of tensile strength of longitudinal ribs is faster than that of oblique ribs, which is related to the stress mode of longitudinal and oblique ribs in three-way grid. The longitudinal ribs are consistent with the direction of tension, and the oblique ribs have an angle of 60 ° with the direction of stress. From the mechanical point of view, the reason is that the longitudinal ribs are subject to greater force component in the creep process, Therefore, the creep process should be changed greatly. In conclusion, compared with the grid without creep, the elongation of the grid after creep decreases and the material becomes more brittle.

       塑料土工格栅在经过拉伸蠕变后,自然回弹可以分为3个阶段,分别为弹性回缩阶段、粘弹性回缩阶段、回弹停止阶段。回弹结束后,土工格栅的残余应变与蠕变过程中所受到的应力水平和时间呈现出正比关系,并在60%的应力水平下,残余应变达到了3. 13%。经过长期拉伸蠕变后的塑料土工格栅,**限拉伸强度随着应力水平的增加而呈现出下降的趋势,并且在较低应力水平下下降zui为明显,之后随着应力水平的增加,下降趋势变缓。

After tensile creep, the natural rebound of plastic geogrid can be divided into three stages: elastic shrinkage stage, viscoelastic shrinkage stage and rebound stop stage. After the rebound, the residual strain of geogrid is in direct proportion to the stress level and time in the creep process. At 60% stress level, the residual strain reaches 3.13%. After long-term tensile creep, the ultimate tensile strength of the plastic geogrid shows a downward trend with the increase of the stress level, and the decline is most obvious at the lower stress level, and then the downward trend slows down with the increase of the stress level.

       相信大家看完以上内容以后，应该也对不同应力水平对塑料土工格栅拉伸强度影响有了一定的了解了，希望会对大家有所帮助吧。

I believe that after reading the above content, you should also have a certain understanding of the influence of different stress levels on the tensile strength of plastic geogrid. I hope it will help you.

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