Cushioning Performance of Hilbert Fractal Sandwich Packaging Structures under Quasi-Static Compressions

The sandwich structure of cushioning packaging has an important influence on the cushioning performance.Mathematical fractal theory is an important graphic expression.Based on Hilbert fractal theory,a new sandwich structure was designed.The generation mechanism and recurrence formula of theHilbert fractal were expressed by Lin’s language,and the second-orderHilbert sandwich structure was constructed fromthermoplastic polyurethane.The constitutive model of the hyperelastic body was established by using the finite element method.With the unit mass energy absorption as the optimization goal,the fractal sandwich structure was optimized,and the best result was obtained when the order was 2.5 and the unit layer thickness was 0.75 mm.TheHilbert sandwich structure was compared with the rice-shaped sandwich structure commonly used in industry,and the Hilbert fractal structure had better energy absorption.This has practical significance for the development and application of newcushioning packaging structures.

The effect of bucking on the mechanical properties of honeycomb sandwich structure

Static compression test on the Honeycomb sandwich structure with surface core defect carry out in this paper. The specimen divided into four groups, one had no defect, one had circle defect, the other two groups had rectangular defect in different direction. In the process of loading the strain gauge which located on the specimen surface in each group record the strain transformation of the specimen surface. Through the Static load test on the fatigue testing machine, fracture load of each specimen was record. According to the data, how the size and shape of the defect influence the compression static strength of Honeycomb sandwich was discussed, and inspecting defects direction how to affect the structural static slrength by means of theoretical analysis and data fitting, meanwhile the shape of the defects in structure how to effect buckling was discussed too.

Damage and failure rule of rock undergoing uniaxial compressive load and dynamic load

For understanding the damage and failure rule of rock under different uniaxial compressive loads and dynamic loads, tests on red sandstone were carried out on Instron 1342 electro-servo controlled testing system with different uniaxial compressive loads of 0, 2, 4 and 6 MPa. It is found that peak stress, peak strain, elastic modulus and total strain energy decrease with the increase of static compressive stress. Based on the test results, the mechanism on damage and failure of rock was analyzed, and according to the equivalent strain hypothesis, a new constitutive model of elastic-plastic damage was established, and then the calculated results with the established model were compared with test results to show a good agreement. Furthermore the rule of releasing ratio of damage strain energy was discussed.

基于BP神经网络的页岩静弹性模量预测研究

页岩的静弹性模量是页岩油气资源勘探开发整个过程的重要参数,现阶段页岩静弹性模量的预测往往是先使用岩芯纵波时差及密度计算出动态弹性模量,再寻找动、静态弹性模量之间的关系。岩石矿物组成的差异常常导致常规思路得到的动、静态弹性模量的相关性较差,预测结果难以满足工程需求。为完成对研究区块岩芯的静弹性模量预测研究,首先对岩芯进行密度及纵波时差的测量;而后运用全岩矿物分析、黏土矿物分析及三轴压缩试验的方法对岩芯静弹性模量进行对比分析;并由三轴压缩试获取岩芯静弹性模量。按输入变量的不同建立并训练了三个BP神经网络预测系统;并对三个预测系统的应用效果加以对比分析。分析结果表明:只以岩芯密度和纵波时差为输入变量的BP神经网络的预测效果较差;以岩芯密度、纵波时差、石英含量及伊利石含量为输入变量时的BP神经网络预测效果较好,以岩芯密度、纵波时差、石英含量、方解石含量、伊利石含量及伊/蒙混层含量为输入变量时的BP网络预测效果最好。

Investigation of creep behaviours of gypsum specimens with flaws under different uniaxial loads

The aim of this study is to identify the influence of the dip angle of a pre-existing macrocrack on the lifetime and ultimate deformation of rock-like material. Prediction of lifetime has been studied for three groups of specimens under axial static compressive load levels. The specimens were investigated from 65% to 85% of UCS(uniaxial compressive strength) at an interval of 10% of UCS for the groups of specimens with a single modelled open flaw with a dip angle to the loading direction of 30°(first group), at an interval of 5% of UCS increment for the groups of specimens with single(second group), and double sequential open flaws with a dip angle to the loading direction of 60°(third group). This study shows that crack propagation in specimens with a single flaw follows the same sequences. At first, wing cracks appear, and then shear crack develops from the existing wing cracks. Shear cracking is responsible for specimen failure in all three groups. A slip is expected in specimens from the third group which connects two individual modelled open flaws. The moment of the slip is noticed as a characteristic rise in the axial deformation at a constant load level. It is also observed that axial deformation versus time follows the same pattern, irrespective of local geometry. Specimens from the first group exhibit higher axial deformation under different load levels in comparison with the specimens from the second and third groups.