A review of models for single particle compression and their application to silica microspheres

We report on the deformation behavior of single silica microspheres. For the first time a detailed discussion on the quantitative evaluation of force–deformation data in the elastic and plastic regime is given. The microspheres are compressed between two flat plates of a custom built manipulation device supported by a scanning electron microscope. The device allows a high sample throughput enabling full statistical evaluation of force–deformation data of single microspheres. Existing theories describing the deformation behavior of single spheres are discussed and applied to the elastic and plastic deformation regime of silica microspheres. The results obtained from the theories are compared between each other and values reported in literature. The silica microspheres exhibit a significantly different deformation behavior than expected from bulk fused silica, i.e. a distinct plastic deformation behavior. Furthermore, a significant decrease in Young’s modulus and hardness was observed caused by high porosity and reduced crosslinking of silicon atoms, respectively, that is inherent to silica produced by Stöber synthesis. However, the calculated contact pressures exceed the compressive strength of bulk fused silica by at least a factor of two as an effect of a reduced amount of material flaws in microstructures.     

断层构造带下支护技术的研究与应用

该文指出了断层构造带下支护方式存在的问题,阐述了在断层构造带附近围岩独特的变形特征。提出了新的支护方案,确保了巷道的长期稳定。     

相邻深基坑同时开挖的变形性状分析

本文首先对国内有关研究深基坑开挖对周围环境的影响作了简单的总结,并结合工程实例,利用数值分析方法,分析了相邻深基坑同时开挖对彼此的变形性状影响,其结论可供其他类似工程应用参考。     

Vacuum-drain consolidation induced pressure distribution and ground deformation

The method of using a surface or subsurface soil layer as an air-sealing layer to carry out vacuum consolidation is referred to as the vacuum-drain method. A method of determining the vacuum-drain consolidation induced vacuum pressure distribution in the ground has been proposed based on unit cell finite element analysis results. With the calculated vacuum pressure distribution, a method for calculating the settlement–time curve and the lateral displacement profile at the edge of the vacuum consolidation area has been established. Finally, the proposed methods were applied to a project using the vacuum-drain method at Tokyo Bay in Japan. Comparing the calculated results with the measured field values indicates that the methods can be a useful tool for designing vacuum consolidation project.     

Investigations for indications of deliberate blasting on the front bulkhead of the ro-ro ferry MV ESTONIA

The roll-on-roll-off passenger ferry MV ESTONIA sank during the night of 28 September 1994 in the Baltic Sea. In October 2000, divers recovered two palm-sized test pieces from the front bulkhead of the wreck. The investigators analysed these specimens to determine whether there were any indications of deliberate blasting. Since the wreck had been submerged for almost six years, it was clear that chemical traces would not be present on the surfaces of the test pieces. Therefore, the investigators performed comparative tests on shipbuilding steel to find a microstructural criterion that exclusively characterises a blast. The shipyard Jos. L. Meyer, Germany, had built the ESTONIA and supplied shipbuilding steel plates similar to that used for building the vessel in 1979/1980. The comparative tests comprised mechanical tests, shot peening tests and blasting tests using different explosives. Testing demonstrated that blasting always formed twinned ferrite grains in the microstructure over the whole cross-section of each of the 8 mm thick comparative plates. Although one of the original test pieces of the ESTONIA showed deformation twins, this was only confined up to 0.4 mm underneath the surfaces and not spread over the whole cross-section. Comparative shot peening tests produced the very same pattern of subsurface deformation twins. Therefore, the twins detected in the microsection of the test pieces of the ESTONIA wreck traced back to the shot peening process performed by the shipyard in 1979/1980 and not to a deliberate blast.     

The effect of a non-circular drawing sequence on delamination characteristics of pearlitic steel wire

In this study, a non-circular drawing (NCD) sequence was applied to investigate the effect of deformation behavior, microstructure and texture evolution on delamination characteristics of pearlitic steel wire under torsional deformation mode. The multi-pass NCD sequence was numerically and experimentally applied up to the 12th pass in comparison with conventional wire drawing (WD). For investigation of the deformation characteristics of the drawn wires, three-dimensional finite element and flownet analyses were carried out. These simulation results indicated that the NCD could impose relatively homogeneous plastic deformation on the wire compared to the WD. From the scanning electron microscopy and X-ray diffraction results, globular cementite and cylindrical texture component, which might increase likeliness of delamination fracture, were rarely observed in the NCD drawn wire. In the torsion test, the delamination fracture was observed in the WD drawn wire for the 10th pass while it did not occur for the 12th pass NCD. In addition, the ultimate tensile strength (UTS) of 2300 MPa grade wire was manufactured by the NCD and the UTS value was 257 MPa higher than the one of the WD. Therefore, it was demonstrated that the multi-pass NCD could impose relatively homogeneous plastic deformation on the wire, resulting in high-torsional ductility with better strength compared to the WD.     

A research on the creep properties of titanium matrix composites rolled with different deformation degrees

(TiB + La₂O₃)/Ti composites were in situ synthesized and deformed with different deformation degrees. The influence of TiB whisker orientation and grain refinement on the creep properties of titanium matrix composites (TMCs) are discussed. The creep test reveals that the steady state creep rate of TMCs first decreases and then increases with the increase of deformation degree, which can be attributed to competing effects: TiB whisker rotating to the rolling direction, α plate grain boundary hindering and pinning dislocations can all decrease the creep rate, however, dislocation movement on the α plate grain boundary and dislocation emitting from the α plate grain boundary can both increase the creep rate.     

Modelling the effect of strain rate on the thermomechanical behaviour of AISI 304 stainless steel

The present work deals with the interdependences between the strain rate and the strain hardening on stainless austenitic steels. Uniaxial tension tests were conducted on a 304 stainless steel at different strain rates in order to analyse the influence of this parameter on the strain hardening and on the material formability. For the strain rates levels analysed (10^‐4 to 10^‐1 s^‐1) it was also observed that increasing the strain rate from 10^‐4 up to 10^‐1 s^‐1 leads to a 25 % difference in uniform tension elongation revealing the curve‐crossing phenomenon. Namely, strain rates equal or higher than 10^‐2 lead to a stagnation of strain hardening after a tensile strain of about 0.2. In order to investigate the results obtained, microstructural and thermal analyses were conducted and numerical simulations were performed. It was observed that the decreasing of formability of the material is essentially due to thermal aspects. In the discussion, the experimental and numerical results are analysed in terms of thermal softening, phase transformation and strain rate sensibility.     

Development of numerical scheme for phase field crystal deformation simulation

The phase field crystal (PFC) method is anticipated as a new multiscale method, because this method can reproduce physical phenomena depending on atomic structures in metallic materials on the diffusion time scale. Although the PFC method has been applied to some phenomena, there are few studies related to evaluations of mechanical behaviors of materials by appropriate PFC simulation. In a previous work using the PFC method, tensile deformation simulations have been performed under conditions where the volume increases during plastic deformation. In this study, we developed a new numerical technique for PFC deformation simulation that can maintain a constant volume during plastic deformation. To confirm that the PFC model with the proposed technique can reproduce appropriate elastic and plastic deformations, we performed a series of deformation simulations in one and two-dimensions. In one- and two-dimensional single-crystal simulations, linear elastic responses were confirmed in a wide strain rate range. In bicrystal simulations, we could observe typical plastic deformations due to the generation, annihilation and movement of dislocations, and the interaction between the grain boundary and dislocations. Moreover, the deformation behaviors of a nanopolycrystalline structure at high temperature were simulated and the intergranular deformations caused by grain rotation and grain boundary migration were reproduced.     

EFFECT OF HEATING MODES ON INTERNAL STRAIN-STRESS FORMATION DURING DRYING OF MOLDED CERAMICS

Parametric analyses in drying processes of molded ceramics are performed to investigate the influence of heating modes on the formation of drying-induced strain-stress as well as the drying characteristic. The transient three-dimensional problem of strain-stress and heat and moisture transfer in a slab is solved simultaneously by the finite element method. Three modes of hot air, intermittent and internal heating are compared by modeling in the normalized parameters. The tensile and compressive stresses fluctuate, and fall remarkably during the low Biot number period when the slab is heated intermittently. In the internal heating mode, the drying rate is the fastest but stress formation is maintained at the lowest level among the three modes. This effectiveness of the internal heating is investigated experimentally by employing the microwave heating as well.