脐橙采摘执行器的设计与研究

针对目前脐橙采摘机械化程度低的问题，设计了一种环抱吞咽的采摘执行器。采摘执行器的执行结构主要由多组滑块摇杆机构构成。首先，根据设计的脐橙采摘执行器的工作原理，绘制采摘执行器的结构简图，并进行了运动学和静力学分析；然后，依据采摘时间最短，建立了目标函数的数学模型，利用Matlab软件得到了相关结构的优化尺寸；最后，根据计算得到的尺寸，完成了执行器三维模型的建立，利用Adams软件进行了运动学仿真，验证了脐橙采摘执行器设计的合理性和可行性，为进一步实际采摘实验提供了理论支撑

针对久坐人群保健办公椅的设计及位置分析

以人机工程学原理与方法为依据，分析了人体腰关节的结构及运动特性；结合一种四杆运动限定机构，提出了一种能实现人体腰关节运动且具有运动分岔性的三转动混联机构的保健办公椅；并对其进行操作模式分析。结果表明，机构处于分岔奇异点时动平台瞬时自由度为3，此时采用冗余驱动的方法可将三转动模式转为两转动模式。最后，推导了混联机构在不同操作模式时的位置正解分析方程，结果证明，该机构具有完全解耦性

Simultaneous improvement of tensile strength and ductility in micro-duplex structure consisting of austenite and ferrite

A micro-duplex structure consisting of austenite and ferrite was produced by equal channel angular pressing and subsequent intercritical annealing. As compared to coarse-grained (CG) counterpart, the strength and ductility of micro-duplex samples are enhanced simultaneously due to smaller grain sizes in both phases and more uniformly distributed austenite in ferrite matrix. The average yield stress and uniform elongation are increased to 540&nbsp;MPa and 0.3 as compared to 403MPa and 0.26 of its CG counterpart respectively. The Hall&ndash;Petch coefficients of austenite and ferrite grain boundaries were quantitatively measured as 224.9 and 428.9&nbsp;MPa&nbsp;&mu;m1/2&nbsp;respectively. In addition, a Hall&ndash;Petch type coefficient was used to describe the ability of phase boundary to obstruct dislocation motion, which was measured as 309.7&nbsp;MPa&nbsp;&mu;m1/2. Furthermore, the surface-to-volume ratio of phase boundary in micro-duplex structure was estimated to be 1.17&times;106&nbsp;m&minus;1, which is increased by an order of magnitude as compared to 1.2&times;105&nbsp;m&minus;1&nbsp;of its CG counterpart. Based on the strain gradient theory, a model was proposed to describe the effect of surface-to-volume ratio of phase boundary on strain hardening rate, which shows a good agreement with the experimental results.</span

Ultrahigh surface hardness and excellent hardness gradient induced by ultrafine dual-carbides in a novel stainless bearing steel

A novel alloy composition design (Fe-14Cr-13Co-5Mo-2Ni-1W-1V-0.16C-0.12Nb-0.074Si-0.027Mn, wt. %) was proposed for modification on that of the conventional CSS-42L stainless steel. The present homogeneous structure without carburizing displays an excellent synergy of yield strength and fracture toughness, which should improve the performance of the corresponding case-carburized steels under the contact/bending fatigue conditions. An ultrahigh surface hardness (71 HRC) and an excellent hardness gradient along the depth are achieved in the present case-carburized gradient structure. Higher surface hardness at a temperature range of 200-400 degrees C is also observed in the present case-carburized gradient structure, as compared to the other casecarburized advanced bearing/gear steels, such as the M50 steel, the M50NiL steel and the conventional CSS42L steel. Besides the previously reported M6C carbides in the case-carburized conventional CSS-42L steel, M7C3 carbides are newly discovered in the present case-carburized gradient structure due to the novel chemical design. The ultrahigh surface hardness at both room and high temperatures and the excellent hardness gradient distribution in the present case-carburized gradient structure should be attributed to the increased amount of dual-carbides, as well as the ultrafine dual-carbides embedded in the ultrafine martensite matrix. The superior mechanical properties of the present case-carburized gradient structure should be desirable for real bearing/gear applications

Analysis of spherical indentation of materials with plastically graded surface layer

In the present work, a comprehensive parametric study for establishing contact mechanics of instrumented normal spherical indentation on homogeneous materials and materials with plastically graded surface layer (PGSL) was undertaken by dimensional analysis and finite element modeling. The spherical indentation response for homogeneous materials can be described only by two dimensionless parameters: strain hardening exponent and a unified parameter that can describe effects of both the normalized yield strength and the normalized indentation depth. The influences of these two parameters were investigated for a wide range of engineering materials, and the results may be used as an estimate of loading response and pile-up/sink-in behavior when the material properties are known. In the materials with PGSL, a linear gradient in yield strength, and no variation in elastic modulus and strain hardening exponent were explored. The indentation response of the materials with PGSL can be described only by three dimensionless parameters: the normalized indentation depth, the dimensionless strength gradient parameter, and the normalized PGSL thickness. The effects of these three parameters were studied systematically. The normalized pile-up/sink-in parameter is found to be an increasing function of the strength gradient parameter. The normalized pile-up/sink-in parameter increases (decreases) with increasing PGSL thickness for a fixed positive (negative) gradient case at large indentation depth. The results also indicate that the materials with positive PGSL can bear more loads and have significantly more resistance to contact crack formation