关于动态合力曲线的初步分析研究

我们采用应变传感器式力测定仪加以改进，并与动态电阻应变仪及紫外光线示波器联接，记录措力及胎力曲保，建立动态力曲线测试系统，并利用该系统对３９名正常受试者第一恒磨牙最大力及力变化情况进行测定及分析研究。验征了正常左右侧力的对称性，对一些影响因素进行了讨论，为临床的进一步研究提供了依据和参考，对病理状态下的力变化的进一步深入研究打下了基础。

撑杆跳高支撑力测试装置的设计及动态特征分析

撑杆跳高运动插斗处动态力的测试受到多种因素的影响 ,分析测力平台在测试中的受力状态 ,指出装置的设计中应重点考虑装置的实用性 ,分析其刚性、质量及阻尼的影响 。

Microscopic damage and dynamic mechanical properties of rock under freeze-thaw environment

For understanding the rock microscopic damage and dynamic mechanical properties subjected to recurrent freeze-thaw cycles, experiments for five groups of homogeneous sandstone under different freeze-thaw cycles were conducted. After freezethaw, nuclear magnetic resonance(NMR) tests and impact loading tests were carried out, from which microscopic damage characteristics of sandstone and dynamic mechanical parameters were obtained. The results indicate that the porosity increases with the increase of cycle number, the rate of porosity growth descends at the beginning of freeze-thaw, yet accelerates after a certain number of cycles. The proportion of pores with different sizes changes dynamically and the multi-scale distribution of pores tends to develop on pore structure with the continuing impact of freeze-thaw and thawing. Dynamic compressive stress-strain curve of sandstone undergoing freeze-thaw can be divided into four phases, and the phase of compaction is inconspicuous compared with the static curve. Elastic modulus and dynamic peak intensity of sandstone gradually decrease with freeze-thaw cycles, while peak strain increases. The higher the porosity is, the more serious the degradation of dynamic intensity is. The porosity is of a polynomial relationship with the dynamic peak intensity.

Moisture effect on compressive behavior of concrete under dynamic loading

The effect of moisture content upon compressive mechanical behavior of concrete under impact loading was studied. The axial rapid compressive loading tests of over 50 specimens with five different saturations were executed. The technique "split Hopkinson pressure bar"(SHPB) was used. The impact velocity was 10 m/s with corresponding strain rate of 50 s-1. The compressive behavior of materials was measured in terms of stress-strain curves, dynamic compressive strength, dynamic increase factor(DIF) and critical strain at a maximum stress. The data obtained from test indicate that both ascending and descending portions of stress-stain curves are affected by moisture content. However, the effect is noted to be more significant in ascending portion of the stress-strain curves. Dynamic compressive strength is higher at lower moisture content and weaker at higher moisture content.Furthermore, under nearly saturated condition, an increase in compressive strength can be found. The effect of moisture content on the average DIF of concrete is not significant. The critical compressive strain of concrete does not change with moisture content.

Dynamic recrystallization behavior and kinetics of high strength steel

The dynamic recrystallization behavior of high strength steel during hot deformation was investigated.The hot compression test was conducted in the temperature range of 950-1150 °C under strain rates of 0.1,1 and 5 s-1.It is observed that dynamic recrystallization(DRX) is the main flow softening mechanism and the flow stress increases with decreasing temperature and increasing strain rate.The relationship between material constants(Q,n,α and ln A) and strain is identified by the sixth order polynomial fit.The constitutive model is developed to predict the flow stress of the material incorporating the strain softening effect and verified.Moreover,the critical characteristics of DRX are extracted from the stress-strain curves under different deformation conditions by linear regression.The dynamic recrystallization volume fraction decreases with increasing strain rate at a constant temperature or decreasing deformation temperature under a constant strain rate.The kinetics of DRX increases with increasing deformation temperature or strain rate.

Fracture energy evaluation on 7075-T651 aluminum alloy welds determined by instrumented impact pendulum

By using an instrumented impact pendulum, the force versus time curves of 7075-T651 aluminum welds were obtained from standard Charpy-V samples. Considering the force-time curves and constant impact velocity, the fracture energies for different zones were quantified. A fracture energy improvement for the HAZ(33.6 J) was observed in comparison with the weld metal(7.88 J), and base metal(5.37 J and 7.37 J for longitudinal and transverse directions, respectively). This toughness increment was attributed to the microstructural transformation caused by the thermodynamic instability of η′ precipitates during the welding. Fracture energy for weld metal was higher than that for base metal, probably due to pores created during solidification. Regarding the dynamic yielding force obtained from the force-time curves, an approximation to the dynamic yield strength for weld, HAZ and base metal was determined. Fracture surfaces revealed an intergranular failure for base metal in longitudinal direction, whereas a predominately brittle failure(cleavage) with some insights of ductile characteristics was observed for the transverse direction. In contrast, a ductile failure was observed for weld metal and HAZ.

汽车空气悬架设计中空气弹簧的匹配选择

本文介绍了空气悬架较传统钢板弹簧(或螺旋弹簧)的优势,分析了空气弹簧的结构特点、性能,并对一种空气弹簧参数化和模块化的匹配选择方法进行了介绍,同时也计算了空气弹簧在设计高度处的动态刚度和频率。