PLASTIC DEFORMATION AND DISLOCATION STRUCTURE IN γ'-PHASE OF A DIRECTIONALLY SOLIDIFIED Ni-BASE SUPERALLOY

The dislocation structure of directionally solidified(DS)Rene 80 superalloy during tensile and creep deformation has been studied by TEM.In tensile deformation,γ'shearing occurs by slip of APB-coupled(1/2)<110>dislocation pairs on{111}planes at temperatures below 760℃.and by slip of SISF-seperated(1/3)<112>superpartials which have dissociated on {111}planes into a(1/2)<110>screw superpartial and a(1/6)<112>edge superpartial with an APB in between at temperatures equal to or above 760℃.In creep deformation,γ'shearing occurs again by slip of SISF-seperated(1/3)<112>superpartials which have not dissociated on{111}planes and by diffusive slip of APB-coupled(1/2) <110>dislocation pairs at 760℃,618 MPa.However,no γ'shearing occurs at 980℃,190 MPa.During secondary creep at 760℃,618 MPa or at 980℃,190 MPa,2-dimensional net- works have formed at γ/γ'interfaces,and the strain is mainly the result of diffusion control- led climb of dislocation networks at γ/γ'interfaces.The dependence of secondary creep rate ε upon size a and volume fraction v_■ of cubic γ' has been found to be ■∝α/v_f^(2/3).

Real-time accurate Free-Form Deformation in terms of triangular Bézier surfaces

We implemented accurate FFD in terms of triangular Bezier surfaces as matrix multiplications in CUDA and rendered them via OpenGL. Experimental results show that the proposed algorithm is more efficient than the previous GPU acceleration algorithm and tessel- lation shader algorithms.

Effect of strain rate on the compressive deformation behaviors of lotus-type porous copper

Lotus-type porous copper was fabricated by unidirectional solidification, and compressive experiments were subsequently conducted in the strain rate range of 10-3-2400 s-1 with the compressive direction parallel to the pores. A GLEEBLE-1500 thermal-mechanical simulation system and a split Hopkinson pressure bar （SHPB） were used to investigate the effect of strain rate on the compressive deforma-tion behaviors of lotus-type porous copper. The influence mechanism of strain rate was also analyzed by the strain-controlling method and by high-speed photography. The results indicated that the stress-strain curves of lotus-typed porous copper consist of a linear elastic stage, a plateau stage, and a densification stage at various strain rates. At low strain rate （〈1.0 s^-1）, the strain rate had little influence on the stress-strain curves; but when the strain rate exceeded 1.0 s^-1, it was observed to strongly affect the plateau stage, showing obvious strain-rate-hardening characteristics. Strain rate also influenced the densification initial strain. The densification initial strain at high strain rate was less than that at low strain rate. No visible inhomogeneous deformation caused by shockwaves was observed in lotus-type porous copper during high-strain-rate deformation. However, at high strain rate, the bending deformation characteristics of the pore walls obviously differed from those at low strain rate, which was the main mechanism by which the plateau stress exhibited strain-rate sensitivity when the strain rate exceeded a certain value and exhibited less densification initial strain at high strain rate.

The Skin Deformation of a 3D Virtual Human

This paper presents a skin deformation algorithm for creating 3D characters or virtual human models. The algorithm can be applied to rigid deformation, joint dependent localized deformation, skeleton driven deformation, cross contour deformation, and free-form deformation （FFD）. These deformations are computed and demonstrated with examples and the algorithm is applied to overcome the difficulties in mechanically simulating the motion of the human body by club-shape models. The techniques described in this article enables the reconstruction of dynamic human models that can be used in defining and representing the geometrical and kinematical characteristics of human motion.

Effect of processing parameters on the electromagnetic radiation emission during plastic deformation and crack propagation in copper-zinc alloys

This paper presents some investigations on the effect of processing parameters on the emission of electromagnetic radiation (EMR) during plastic deformation and crack propagation in copper-zinc alloys. Timing of the EMR emissions, maximum stress during crack instability, stress-intensity factor, elastic strain energy release rate, maximum EMR amplitude, RMS value of EMR amplitude, EMR frequency and electromagnetic energy release rate were analysed for the effect of rolling directions at different percentage of zinc content in Cu-Zn alloy specimens. The same parameters were also analysed for 68-32 Cu-Zn alloy specimens at different annealing temperatures and at different angles θ, to the rolling direction. EMR emissions are observed to be highly anisotropic in nature. At θ=45° to 60°, marked changes in mechanical and electromagnetic parameters were observed. Specimens annealed at 500 °C, just above the recrystallization temperature, and at 700 °C, when grain-size growth is rapid, EMR responses have been found to have well-defined patterns.

Image Deformation by User-Defined Force Fields

We present a new method for image deformation. The warping technique provides smooth distortion with intuitive and easy manipulation. Driven by a restrained force field, the input image is deformed gradually and continuously. The method allows us to customize the force fields and the region of interest manually through some simple steps. Experimental results demonstrate the effectiveness and convenience of the approach.

盾构直削始发方案研究

随着盾构施工工艺的发展,越来越多的工程开始采用盾构直削始发.盾构法施工中,始发是易发生事故的重要环节.相对于传统的人工凿除洞门,直削始发时刀盘直接切割洞门,避免了掌子面土体形成临空面,从而降低了施工风险.以郑州某地铁区间隧道工程盾构直削始发为例,采用Midas GTS NX有限元软件,考虑洞门破除及盾构动态掘进的影响,对盾构直削始发时围护结构变形、土体变形和周围管线变形等进行了计算分析,验证了盾构端头直削始发方案的合理性.为验证数值模拟的可靠性,将数值计算结果和现场监测结果进行了对比分析,对比结果显示二者的变化规律一致,表明数值模拟结果合理.

N36锆合金背压多向压缩变形行为模拟

采用有限元模拟方法对不同背压力和背压距离的N36锆合金背压多向压缩变形行为开展了研究,分析了背压作用对金属流变过程与损伤行为的影响规律。结果表明,单次压缩会产生4个变形区域。一道次背压多向压缩变形后,金属变形历史的差异引起了试样等效应变的不均匀累积。施加背压力能增加试样累积应变和大变形区体积占比、改善小变形区变形不足问题,并提高试件变形均匀性。同时,增大背压力、减小背压距离有利于增加累积应变量、提高应变均匀性、减小损伤层厚度、降低损伤区域体积占比。当背压力为100 kN、背压距离为5 mm时,试样累积应变升至4.05、大变形区体积占比升至0.87,试样损伤层厚度和损伤区域体积占比分别为2.74 mm和2%,与无背压条件相比,试样变形均匀性得到明显改善,损伤层厚度显著降低,材料利用率得到充分提升。

双作用液环压缩机壳体型线响应面分析及多目标优化

为探究双作用液环压缩机壳体型线对其内流场及性能的影响机理,采用DFFD参数化方法对多级双作用液环压缩机椭圆形壳体型线进行响应面优化分析,并结合NSGA-II多目标优化方法对吸排气区壳体型线进行协同优化。采用VOF多相流模型对该液环压缩机全流域进行非定常计算,双作用液环泵内相态场、压力场基本呈径向对称分布,吸排气区域及叶轮壳体内流场与单作用液环泵分布规律基本一致,随着级数增大液环内的气相区域逐渐减小。响应面结果表明吸气量的大小主要取决于吸气口始端和末端的壳体型线,当R_(A)值趋于0水平,R_(B)处于低水平时,吸气量趋于最大值。轴功率主要受吸、排气口始端位置壳体型线影响,R_(A),R_(C)值越小,轴功率越小。效率的大小主要取决于吸气口始端和末端的壳体型线,且R_(A)值越大,R_(B)值越小,效率越高。在额定出口压比条件下,以吸气量和效率作为优化目标对液环压缩机进行NSGA-II多目标优化,获得其Pareto前沿的最优效率设计J和和最优流量设计K,J方案流量和效率分别高于原方案1.40%和2.53%,K方案流量和效率分别高于原方案16.4%和0.61%。

An Efficient Optimization Design Framework for Low-Resistance Shape of Bionic Amphibious Robot

To realize the low-resistance shape optimization design of amphibious robots,an efficient optimization design framework is proposed to improve the geometric deformation flexibility and optimization efficiency.In the proposed framework,the free-form deformation parametric model of the flat slender body is established and an analytical calculation method for the height constraints is derived.CFD method is introduced to carry out the high-precision resistance calculation and a constrained Kriging-based optimization method is built to improve the optimization efficiency by circularly infilling the new sample points which satisfying the constraints.Finally,the shape of an amphibious robot example is optimized to get the low-resistance shape and the results demonstrate that the presented optimization design framework has the advantages of simplicity,flexibility and high efficiency.

基于直接拉伸试验的沥青胶浆低温性能研究

文中设计直接拉伸试验对拉伸曲线进行形态分析,并提出延伸量、拉伸柔量、残余延伸量比,以及黏韧性等评价指标.通过灌浆成型制备沥青混合料基于展小梁弯曲试验评价其低温变形性能.在此基础上,通过胶浆低温性能指标与混合料最大弯拉应变相关性分析验证基于直接拉伸试验的胶浆低温性能指标的合理性.结果表明:粉胶比对沥青胶浆的低温变形性能有显著影响,粉胶比越大胶浆的脆性特征越明显,其低温性能越差;为保证胶浆的低温变形性能,建议粉胶比不大于1.5;基于直接拉伸试验得到的胶浆低温性能评价指标随粉胶比变化的趋势不受沥青类型的影响,用于评价胶浆低温性能合理可行;相关性分析表明0℃条件下的延伸量、黏韧性,以及韧性比是胶浆低温性能评价的最佳指标.

基于增强特征提取网络与语义特征融合的多方向文本检测

针对自然场景文本长度不定、角度倾斜等难题,提出了一种基于增强特征提取网络与语义特征融合的文本检测方法。通过结合可变形卷积与空洞卷积,设计了一种增强扩张残差模块EDRM(Enhanced Dilated Residual Module),将其应用于ResNet18的conv4_x与conv5_x层,并以此作为骨干网络,在改善网络特征提取能力的同时提高特征图像分辨率,减少空间信息丢失。其次,针对现有算法提取文本语义特征仍不充分的问题,将双向长短期记忆网络BiLSTM(Bi-directional Long Short-Term Memory)引入特征融合部分,增强融合特征图对自然场景文本的表征能力以及特征序列的关联性,同时提高模型的文本定位能力。在多方向文本数据集ICDAR2015、长文本数据集MSRA-TD500上对模型展开评估,实验结果表明,该算法与当下高效的DBNet算法相比,F值分别提升1.8%、3.3%,表现出良好的竞争力。

主应力方向对红黏土变形与破坏的影响研究

我国西南地区广泛分布有红黏土,受重塑黏土空心圆柱试样制备技术制约,关于主应力方向变化对红黏土力学特性影响的现象与机理尚不清晰。为此,本文采用自主研发的制样装置,通过分层欠压法制备了饱和重塑红黏土空心圆柱试样,并开展了纯主应力轴旋转试验和定轴剪切试验。结果表明:试样的变形、强度、形态等宏观力学行为均与绕第二主应力旋转角密切相关,且表现出了较为明显的分段特征;应力的加载方向对试样的拉压状态起着决定性作用,导致试样随应力主轴旋转而存在“压缩臌胀”、“纯扭破坏”和“拉伸颈缩”现象,决定了试样的整体变形规律;产生上述现象的原因可能是重塑试样制备过程中,沿轴向所受压实作用强于径向与环向,使得试样沿轴向的模量、强度等参数异于水平方向,即具有横观各向同性特征,试验过程中沿不同方向施加的应力“激活”了这种差异性,进而使得试样在宏观上表现出不同的力学性质。关于应力方向对土体变形与破坏影响的研究应综合考虑应力加载方向和试样各向异性。

暗挖车站施工中拱部预应力锚杆不同支护方向的地层变形研究

传统的暗挖车站施工,洞内多设置临时支撑协助抵抗围岩变形,存在施工工期长、拆除困难、费用高等问题。本文以新建暗挖地铁车站为工程背景,通过数值计算的方法对分部台阶法-预应力锚杆支护的大断面隧道施工的地层变形进行了研究。研究结构表明:车站拱顶沉降是暗挖施工中车站沉降的主要方面,拱部支护完成后车站沉降基本趋于稳定。分部台阶法-拱部预应力锚杆竖向布置的施工方法对地层变形控制更有利,拱部预应力锚杆竖向布置,车站开挖完成后拱顶沉降在7.7 mm;拱部预应力锚杆垂直布置,车站开挖完成后拱顶沉降在10.4 mm,拱部预应力锚杆竖向布置对周边建构筑物的变形控制更有利。研究成果可为类似工程提供借鉴。

Reduction of Residual Stress in Low Alloy Steel with Magnetic Treatment in Different Directions

The behavior that different magnetic treatment directions induce various amounts of welding residual stress reductions in low alloy steel was studied. Reductions of 26%-28% in the longitudinal stress σ x were obtained when low frequency alternating magnetic treatment was applied perpendicularly to the welding bead, whereas reductions of 20%-21% in σ x were measured by using the same treatment parameters except that the field direction was applied parallel to the bead. It is proposed that different extent of stress reductions caused by the above two treatment directions is attributed primarily to the alteration of the energy absorbed by domains from the external magnetic field, which part of energy can arouse plastic deformation in microstructures by the motion of domain walls.

Numerical study of AE and DRA methods in sandstone and granite in orthogonal loading directions

The directional dependency of the acoustic emission （AE） and deformation rate analysis （DRA） methods was analyzed, based on the contact bond model in the two-dimensional particle flow code （PFC2D） in two types of rocks, the coarse-grained sandstone and Aue granite. Each type of rocks had two shapes, the Brazilian disk and a square shape. The mechanical behaviors of the numerical model had already been verified to be in agreement with those of the physical specimens in previous research. Three loading protocols with different loading cycles in two orthogonal directions were specially designed in the numerical tests. The results show that no memory effect is observed in the second loading in the orthogonal direction. However, both the cumulative crack number of the second loading and the differential strain value at the inflection point are influenced by the first loading in the orthogonal direction.

Conformal manufacturing of soft deformable sensors on the curved surface

Health monitoring of structures and people requires the integration of sensors and devices on various 3D curvilinear,hierarchically structured,and even dynamically changing surfaces.Therefore,it is highly desirable to explore conformal manufacturing techniques to fabricate and integrate soft deformable devices on complex 3D curvilinear surfaces.Although planar fabrication methods are not directly suitable to manufacture conformal devices on 3D curvilinear surfaces,they can be combined with stretchable structures and the use of transfer printing or assembly methods to enable the device integration on 3D surfaces.Combined with functional nanomaterials,various direct printing and writing methods have also been developed to fabricate conformal electronics on curved surfaces with intimate contact even over a large area.After a brief summary of the recent advancement of the recent conformal manufacturing techniques,we also discuss the challenges and potential opportunities for future development in this burgeoning field of conformal electronics on complex 3D surfaces.

Microstructure and mechanical properties of AZ61 Mg alloy prepared by multi directional forging

AZ61Mg alloy was multi directionally forged(MDFed) during decreasing temperature condition from 643 K to 483 K at a true strain rate of 3×10-3 s-1 up to cumulative strain of∑△ε=4.0 at maximum.A pass strain of△ε=0.8 was employed.While average grain size decreased gradually with increasing cumulative strain,the evolution of fine-grained structure strongly depended on the MDF temperature.Under the condition where the temperature was higher than the most adequate one,grain coarsening partially took place during MDF.In contrast,at lower temperature,inhomogeneous microstructure composed of the initial coarse and newly appeared fine grains was evolved.After straining over∑△ε=3.2(i.e.,over 4 passes of MDF) ,equiaxed ultrafine grains(UFGs) having average size of about and lower than 1μm were uniformly evolved.While the MDFed alloy to∑△ε=4.0 possessed relatively high hardness of HV 99,and it accepted further about 20%cold rolling almost without cracking.Because of the superior formability of the UFGed AZ61Mg alloy,the hardness was further easily raised to HV 120 by following cold rolling.

Direct Digital Manufacturing Industry Ascendant

The paper introduces the origin of the word of Direct Digital Manufacturing and other forms of address, and the working principles of Direct Digital Manufacturing technology and major types of the technology, hard- ware and software development, use of materials, applications, market growth and its development prospects. Focused presentations of Direct Digital Manufacturing （additive manufacturing） compared to traditional mechani- cal manufacturing industry in the use of prices, processing speed, reliability and cost advantages and characteris- tics. Particularly the significant challenges and competitiveness of Direct Digital Manufacturing technology in the processing of any complexity created directly the number of objects, internal structure and channel function, as well as the shape of the chassis components and structure of the matching and optimization.

直接顶-基本顶耦合作用下采场顶板断裂力学模型研究与应用

周期来压是矿山压力显现的典型特征,准确进行采场周期来压步距预测是有效降低采场事故发生的重要途径。针对基本顶自身缺陷与直接顶耦合作用对周期来压步距的影响,视采场顶板为自带裂缝的有限板模型,根据覆岩协调变形机理,基于断裂力学理论建立采场顶板断裂力学模型,推导直接顶-基本顶耦合作用下周期来压步距函数式,以陕北某矿区2个工作面为例,分析基本顶岩石断裂韧度、裂缝深度、直接顶厚度和弹性模量等参数对周期来压步距的作用规律。研究表明:基本顶断裂韧度与周期来压步距呈近似线性关系;裂缝深度比(裂缝深度/顶板厚度)对周期来压步距影响较大,裂缝深度比达到0.8后,基本顶失稳破坏;直接顶厚度小于3 m时对周期来压步距影响较小,超过3 m后对周期来压步距影响显著。研究结果对采场顶板周期来压步距预测及支架选型具有重要的理论意义和工程价值。