DC-V型通用电桥电路技术在机械量测试中的应用

介绍了一种新型的DC-V型通用电桥电路的构成及基本原理。对比分析电阻应变式电桥的各自工作状态性能。所提出的DC-V型通用电桥电路可显著提高测量精度,保证测量精度的稳定性,同时实现了测量电桥的互换。

新型机械量测试仪开发与应用

介绍了以计算机为基础、以软件技术为核心的新型机械量测试仪的软硬件结构设计方法 ,以及它在测量与分析应变、振动等各种机械量时的应用 。

Quality assurance for computed-tomography simulator: In home Z-phantom for mechanical tests of the couch and the gantry

Objective:The main purpose of this work was to present a Z-phantom manufactured in home (at National Cancer Institute Cairo University) and it's use in a simple way to check the accuracy of the computed-tomography (CT) table movement and CT gantry tilt, also the other general quality control (QC) tests of the CT simulator used at radiotherapy department. Methods:The laser phantom was used to check the external mobile laser position accuracy, for internal image indicator laser beam (light field) the coincidence between light field and radiation exposure at CT simulator was checked using X-Omat ready back film. The Z-phantom was used to check the slice thickness and the table movement and so the gantry tilts. The image quality testes were checked using the CT image quality phantom. TLDs were inserted to the Cicil phantom at the center of each scan volume to estimate the patient dose. Results:The results showed that the difference in the fixed distance between the external mobile laser and the internal image indicator laser beam was less than ± 1 mm; the orientation of the two mobile lateral lasers was coincident. The mechanical movement and the image quality of the CT simulator were within the tolerances and the results were 0.5 mm, 0.2% and 0.6% for the mechanical movement, noise and image uniformity respectively. Conclusion:A CT simulator with a good performance is important for the radiotherapy treatment planning specially with the extremely revolution in radiotherapy techniques, also a rotten quality assurance (QA) program is very important to be shore about the reproducibility of the CT performance. The use of Z-phantom to check the gantry tilt and the table movement is faster than the use of ready back films in these tests.

Study on the performance of the micropile-mechanically stabilized earth wall

The Micropile-Mechanically Stabilized Earth(MSE) wall, specially designed for mountain roads, is proposed to improve the MSE wall local stability, global stability and impact resistance of roadside barriers. Model tests and the corresponding numerical modeling were conducted to validate the serviceability of the Micropile-MSE wall and the reliability of the numerical method. Then, a parametric study of the stress and deformation of Micropile-MSE wall based on the backfill strength and interfacial friction angle between backfill and backslope is conducted to evaluate its performance.The test results indicate that the surcharge-induced horizontal earth pressure, base pressure and lateral displacement of the wall panel of Micropile-MSE wall decrease. The corresponding numerical results are nearly equal to the measured values. The basic failure mode of MSE wall in steep terrain is the sliding of backfill along the backslope, while A-frame style micropiles are capable of preventing the sliding trend.The maximum resultant displacement can be decreased by 6.25% to 46.9% based on different interfacial friction angles, and the displacement canbe reduced by 6% ~ 56.1% based on different backfill strengths. Furthermore, the reduction increases when the interfacial friction angle and internal friction angle of backfill decrease. In addition, the lateral displacement of wall panel, the deformation of backfill decrease and the tension strain of geogrid obviously, which guarantees the MSE wall functions and provides good conditions for mountain roads.

Effect of Micro Silica on Compressive Strength of Plastic Concrete

This research describes a series of laboratory tests performed to characterize the mechanical properties of plastic concrete. The mechanical properties of plastic concrete are studied using a series of compression tests. Stress relaxation and controlled rate of loading tests are also performed to investigate the rate sensitivity and time-dependency of plastic concrete. An important requirement for the plastic concrete in such applications is adequate strength for the design loads. The replacement of cement content of plastic concrete by micro silica does not result in any significant decrease in workability of plastic concretes and hence, unlike the case for normal concretes, plasticizers or super plasticizers are not required to rectify the adverse effect of micro silica on workability. The aim of the experimental research was to investigate the effects of various levels of cement replacement by micro silica, including 0%, 3%, 6%, 9%, 12% and 15% on strength of plastic concrete. Obtained results show that the effect of micro silica on strength enhancement of plastic concretes is substantial and a replacement level of 15% resulted in 70%-180% increase in strength compared to the control mix. For normal concretes, the increase in strength due to incorporation of micro silica was generally reported as 30%-50%.

An index for deformation controllability of small-volume materials

Mechanical tests on small-volume materials show that in addition to the usual attributes of strength and ductility, the controlla- bility of deformation would be crucial for the purpose of precise plastic shaping. In our present work, a ＂mechanical controlla- bility index＂ （MCI） has been proposed to assess the controllability of mechanical deformation quantitatively. The index allows quantitative evaluation of the relative fraction of the controllable plastic strain out of the total strain. MCI=0 means completely uncontrollable plastic deformation, MCI=∞ means perfectly controllable plastic shaping. The application of the index is demonstrated here by comparing two example cases： 0.273 to 0.429 for single crystal A1 nanopillars that exhibit obvious strain bursts, versus 3.17 to 4.2 for polycrystalline A1 nanopillars of similar size for which the stress-strain curve is smoother.