Material Properties and Tensile Behaviors of Polypropylene Geogrid and Geonet for Reinforcement of Soil Structures

The properties and tensile behaviors of polypropylene (PP) geogrids and geonets for reinforcement of soil structures are investigated.Mass per unit area of the geogrids and geonets was weighed using an electronic balance and aperture sizes of the geonets were exactly measured using a computer.Laboratory tests were performed using a small tensile machine capable of monitoring tensile force and displacement.Tensile failure behaviors were described,and tensile index properties such as tensile strength,maximum tensile strain,tensile forces corresponding to different strains in the geogrids and gronets were obtained.The characterization of these indexes is discussed.

Tensile Structures of Cables Net, Guidelines to Design and Applications

The structural engineering design of not conventional typologies imposes a complex path that begins evaluating procedures of a preliminary design and ends with complex procedures to validate the analysis response. Any guide lines to follow are often available. About complex shapes, in particular, any details are presented in the codes to evaluate wind action and so wind tunnel experiments are necessary to valuate this. The evaluation of wind tunnel data is a complex process that often needs new and specific subroutines programmed by researchers. The difficult increases when the objective is to study a not specific building but general aspects as for examples the dependence of a generic phenomenon by a geometric sample;in this case it is necessary to design and to program numerical subroutines before and then the wind tunnel experiments. Often, these subroutines are left detached and are non-generalizable process. Purpose of this paper is to describe a complete procedure to pre- and post-process wind tunnel data with the objective to design a not convectional structure as a tensile structure. In this particular case the research aim is a parametrization of the aerodynamic behavior of Hyperbolic Paraboloid roofs, shape used for cables net. The reason of the experiments is the absence in the international codes of the pressure coefficients for these geometries. The paper describes the numerical procedure evaluated to choose a sufficient representative geometric sample, the numerical procedure evaluated to design and to construct the wind tunnel models and FE models, the numerical procedure to evaluate and to use for FEM analyses of the wind tunnel data, the numerical procedure to calculate nonlinear structural analysis, and, finally some applications. All these numerical procedures use basic theory derived for example by the cable theory, the fluid mechanic, the nonlinear geometric analysis and other. However specific codes were necessary and were programmed to apply the theories on the specific case of study;the complete methodology followed is presented. The goal is to create a free open domain where the numerical procedures evaluated are merged, added, modified by researchers with the aim to obtain a common space of use for wind engineering of not conventional structure.

Multiscale tensegrity model for the tensile properties of DNA nanotubes

DNA nanotubes(DNTs)with user-defined shapes and functionalities have potential applications in many fields.So far,compared with numerous experimental studies,there have been only a handful of models on the mechanical properties of such DNTs.This paper aims at presenting a multiscale model to quantify the correlations among the pre-tension states,tensile properties,encapsulation structures of DNTs,and the surrounding factors.First,by combining a statistical worm-like-chain(WLC)model of single DNA deformation and Parsegian's mesoscopic model of DNA liquid crystal free energy,a multiscale tensegrity model is established,and the pre-tension state of DNTs is characterized theoretically for the first time.Then,by using the minimum potential energy principle,the force-extension curve and tensile rigidity of pre-tension DNTs are predicted.Finally,the effects of the encapsulation structure and surrounding factors on the tensile properties of DNTs are studied.The predictions for the tensile behaviors of DNTs can not only reproduce the existing experimental results,but also reveal that the competition of DNA intrachain and interchain interactions in the encapsulation structures determines the pre-tension states of DNTs and their tensile properties.The changes in the pre-tension states and environmental factors make the monotonic or non-monotonic changes in the tensile properties of DNTs under longitudinal loads.

Global structure stability of impact-induced tensile waves in phase-transforming materials

The global structure stability of the impact-induced tensile waves mentioned by Huang （Huang, S. J. Impact-induced tensile waves in a kind of phase-transforming materials. IMA Journal of Applied Mathematics, 76, 847-858 （2011）） is considered. By introducing Riemann invariants, the governing equations of motion are reduced into a 2 ~ 2 diagonally strictly hyperbolic system. Then, with the aid of the theory on the typical free boundary problem and maximally dissipative kinetics, the global structure stability of the impact-induced tensile waves propagating in a phase-transforming material is proved.

Effects of Zr additions on structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti(wt.%) alloy

The effects of different Zr additions(0.05wt.%-0.5wt.%)on the structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti(wt.%)alloy solidified under a high cooling rate(18℃·s^(-1)),in as-cast and T6 heat-treated conditions were studied.The as-cast structure of the alloy consists of equiaxed grains ofα-Al with an average size of 64μm which is unaffected by the Zr additions,indicating the ineffectiveness of Zr in the grain refinement of the alloy.Scanning electron microscopy,along with X-ray diffraction analysis revealed the presence of elongatedθ-Al2Cu at the grain boundaries;in addition,coarse Al3Zr particles exist in the intergranular regions of the 0.5wt.%Zr-containing alloy.After the T6 heat treatment,the elongatedθparticles were fragmented;however,the coarse Al3Zr particles remained unchanged in the microstructure.Also,the formation of fineβ’-Al3Zr andθ’’-Al3Cu/θ’-Al2Cu phases during T6 heat treatment was revealed by transmission electron microscopy.The results of the tensile tests showed that the Zr additions increase the strength of the alloy in both as-cast and T6 heat-treated conditions,but reduce its elongation,especially with 0.5wt.%Zr addition.The 0.3wt.%Zr-added alloy in the T6 heat-treated condition has the highest quality index value(249 MPa).Fractography of the fracture surfaces of the alloys revealed ductile fracture mode including dimples and cracked intermetallic phases in both conditions.

A simple method for determining independent fracture toughness and tensile strength of rock

This paper develops a model that only requires two sets of small-size rock specimens with the ratio of the structural geometry parameter maximum to minimum ae,max:ae,min≥3:1 to determine the rock fracture and strength parameters without size effect and predict the actual structural performance of rock.Regardless of three-point-bending,four-point-bending,or a combination of the above two specimen types,fracture toughness KICand tensile strength ftof rock were determined using only two sets of specimens with ae,max:ae,min≥3:1.The values KICand ftwere consistent with those determined using multiple sets of specimens.The full structural failure curve constructed by two sets of small-size specimens with ae,max:ae,min≥3:1 can accurately predict large-size specimens fracture failure,and±10%upper and lower limits of the curve can encompass the test results of large-size specimens.The peak load prediction curve was constructed by two sets of specimens with ae,max:ae,min≥3:1,and±15%upper and lower limits of the peak load prediction curve can cover the small-size specimen tests data.The model and method proposed in this paper require only two sets of small-size specimens,and their selection is unaffected by the specimen type,geometry,and initial crack length.

Microstructures and properties of welded joint of TiNi shape memory alloy and stainless steel

The fracture characteristics of the joint were analyzed by means of scanning electron microscope. Microstructures of the joint were examined by means of optical microscope, SEM and an image analyzer. The results show that the tensile strength of the inhomogeneous joint of TiNi shape memory alloy and stainless steel is lower than that of the homogeneous joint and a plastic field appears in the heat affected zone on the side of TiNi shape memory alloy. Because TiNi shape memory alloy and stainless steel melted, a brittle as-cast structure was formed in the weld. The tensile strength and the shape memory effect of the inhomogeneous joint are strongly influenced by the changes of composition and structure of the joint. Measures should be taken to reduce the base metal melting and prevent the weld metal from the invasion by O for improving the properties of the TiNi shape memory alloy and stainless steel inhomogeneous joint.

Structures and Properties of Hygroscopic Thermal Fiber—EKS

EKS fiber,as a new type of hygroscopic thermal fiber,whose properties meet the requirement of warm clothing with environmental,healthy,and fashionable traits,attains more and more attention. The chemical composition and morphological structure of EKS fiber were confirmed by infrared spectrum,pyrolysis gas chromatography-mass spectrometry( Py-GC-MS),and microscope respectively. In addition, burning performance,dissolving property,and tensile properties were tested respectively.It fills in the gaps in characterization of EKS structure and properties.

TENSILE BEHAVIOUR OF ROTOR SPUN YARNS

This paper deals with the tensile behaviour of rotor spun yarns. Having regard to the spe-cial construction of rotor spun yarn, some modifications for Hearle’s theory have been made inorder to apply Hearle’ s theory to rotor spun yarn. The paper then goes into calculating thetensile curve and investigating the effect of main parameters and spinning conditions on thetensile behaviour of rotor spun yarn. It was found that the following facts are noteworthy forimproving the mechanical properties of rotor spun yarn: (1) Selecting suitable navel so as tocontrol the P. T. E. length within a reasonable range. (2) Improving the design of single fibresupply device to decrease the amount of spoiled fibre and hence increase the effective fibrelength. (3) Increasing spinning yarn tension without yarn break to enhance the fibre migrationratio. (4) For the rotor spun yarn of industrial use, it is the way to increase the yarn strengththat the rotor groove should be designed with the groove angle beneficial to decrease the yarnspecific volume.

Prediction Method for Tensile Property of Woven Fabrics in Lower Loads

A prediction method for tensile properties of woven fabrics in lower loads was developed, where the yarns axes in the weave structure were assumed to be sine curves and the measured yarn mechanical properties and weave structure parameters were used as the input information for estimating the fabric properties. The predicted properties were compared with those measured and also with those calculated values based on Kawabata’s straight line model. The results suggested that this method is a more reliable means to predict the tensile characteristics of woven fabrics.

AN INVESTIGATION ON TENSILE FRACTURE FEATURE FOR THREE KINDS OF POLYESTER FIBERS

This paper deals with the fracture feature of three kinds of polyester fibers with differentstructures under different tensile conditions.We studied fracture initiation,crack propagationand ultimate fracture characteristics under tension of polyester fibers.The fracture features ofpolyester fibers are related with fiber structure and tensile condition.Crack is initiated in fibersurface.It propagates from outside to inside and eventually causes rupture of the fiber.In addi-tion,it is stated also that the analysis on tensile fracture feature of fibers might be confirmed bydynamic testing technique of scanning electron microscopy.

Deformation Mechanism of Bimodal Structured 2205 Duplex Stainless Steel in Two Yield Stages

A kind of micro/nanostructured 2205 duplex stainless steel(DSS)with uniform distribution of nanocrystals was prepared via aluminothermic reaction method.The analysis of stress-strain curve showed that the fracture strength and elongation of the specimen were 946 MPa and 24.7%,respectively.At present,the research on microstructure of bimodal 2205 DSS at room temperature(RT)mainly depended on scanning electron microscope(SEM)observation after loading experiments.The test result indicates that there are two different yield stages in stress-strain curve of specimen during tensile process.The microstructure of duplex bimodal structured stainless steel consists of two pairs of soft hard regions and phases.By studying deformation mechanism of bimodal structured stainless steel,the interaction between soft phase and hard phase are discussed.The principle of composition design and microstructure control of typical duplex stainless steel is obtained,which provides an important research basis for designing of advanced duplex stainless steel.

含镍铬合金丝纬编电热层复合材料的拉伸性能

为开发一种航空飞行器防冰用电热复合材料,选取3种细度的镍铬合金丝,基于平针、罗纹和双罗纹3种纬编结构,优选了6种镍铬合金丝纬编电加热织物,以镍铬合金丝纬编织物为电热层,制备玻璃/环氧电热复合材料,并采用实验方法研究了镍铬合金丝细度和纬编结构对电加热织物及其复合材料的电热性能和对复合材料拉伸性能的影响。结果表明:同种纬编结构,镍铬合金丝细度较大,织物电热转换效率较低,电加热织物及其复合材料表面最高平衡温度较高,电热复合材料拉伸强度较小;同种镍铬合金丝细度,在11 V直流电压30 s下,平针组织电加热织物为电热层的复合材料表面温度由室温升高到74.1℃,升温速率达1.63℃/s,较罗纹和双罗纹组织升温速率分别高154.69%和33.61%;平针组织电加热织物为电热层的复合材料的拉伸强度为450.2 MPa,较罗纹和双罗纹组织拉伸强度分别高3.68%和4.53%。初步工作表明,含镍铬合金丝纬编电热层复合材料有望满足航空飞行器防冰用电热复合材料的需求。

钢结构模块新型自锁-可解锁式连接节点的抗拉研究

为提高建筑用钢结构模块的施工效率、实现模块单元的快捷装配与拆卸,提出一种新型自锁-可解锁式连接节点方法,用Abaqus数值模拟软件建立了节点的精细化与半精细化有限元模型,探究了摩擦因数对节点抗拉承载性能的影响。选取上限位板厚度、下限位板厚度和上部滑块宽度为关键参数进行有限元模拟,研究各参数对节点抗拉承载力及破坏模式的影响。最后与实际节点抗拉承载力进行对比。结果表明:当摩擦因数为0.3时,新型节点承受最大拉力为1345.49 kN,较角件旋转式连接节点提升约为152%。节点抗拉承载力受上部滑块宽度影响较大,受上限位板厚度与下限位板厚度影响相对小。当上、下限位板厚度均为25mm时,在10~12mm内增加上部滑块宽度可提升节点承载拉力。

PBL抗剪传力钢筋连接接头受拉力学性能试验

装配式混凝土构件间钢筋的连接是其适用性和经济性的关键环节,针对国内工程常用的灌浆套筒和约束浆锚钢筋连接技术存在施工难度大、效率低、质量不易检验等问题,本文提出了PBL-穿孔钢筋连接接头、PBL-穿孔钢管连接接头和PBL-U形钢筋连接接头3种钢筋连接接头,实现预制混凝土单元间钢筋应力的传递,具有施工简便、质量易保证、成本低等优势。对这3种钢筋接头进行了6组参数共18个钢筋接头试件的拉伸性能试验,研究了新型接头试件的破坏模式、承载力和变形能力等,得到各参数对新型接头拉伸强度的影响规律,并对不同接头的受拉力学性能进行对比分析。研究结果表明:3种钢筋连接接头能够实现钢筋应力的有效传递,验证了新型钢筋连接接头的可行性。

喷射混杂纤维混凝土抗冻性及损伤模型

目的为提高高寒地区喷射混凝土耐久性,改善冻融环境下普通喷射混凝土易开裂、抗冻性能差等问题。方法在喷射混凝土中掺入混合纤维,通过冻融循环试验、超声波检测、压拉性能试验以及气孔结构测试等方法,研究不同冻融循环次数下喷射混杂纤维混凝土的相对纵波波速、相对压拉强度以及试件内部气孔结构变化规律。通过压拉性能损伤量对试件冻融损伤进行多项评价,分析钢纤维和聚丙烯纤维贡献率与喷射混凝土抗压强度之间的关系,并根据钢纤维和聚丙烯纤维贡献率公式建立喷射混凝土冻融损伤模型。结果与单掺钢纤维和聚丙烯纤维试件相比,混合掺入1%钢纤维、0.1%聚丙烯纤维喷射混凝土试件的抗压强度损失分别降低了7.5%、33.3%,劈裂抗拉强度损失分别降低了15.6%、35.0%。在弦长尺寸0.1mm<d<1mm处,混合掺入0.1%聚丙烯和1%钢纤维喷射混凝土气泡弦长频率比单掺1%钢纤维喷射混凝土和单掺0.1%聚丙烯喷射混凝土分别降低了24.9%和27.3%。钢纤维和聚丙烯纤维对抗压强度的贡献率呈现先增长后下降趋势。基于冻融损伤与钢纤维和聚丙烯纤维贡献率建立冻融损伤模型。结论喷射混杂纤维混凝土力学性能损伤量低,不易开裂,抗冻性能好,可为高寒地区喷射混凝土结构提供理论参考。

层合多孔结构拉剪力学行为分析

基于层合多孔拉剪结构,考虑孔隙率、胞元铺设角度、胞元孔型及复合层数对结构承载力和稳定性的影响,通过实验和有限元仿真计算研究了平面多孔结构的力学性能和破坏形式。结果表明,孔隙率越小,单双层结构抗拉剪性能越大,双层模型增强幅度也越大;多孔结构胞元铺设角度为15°时具有更好的塑性变形和抗拉剪性能;正六边形孔型的塑性变形较好,正方形孔型的抗拉剪力较强;多层结构可以增强抗拉剪强度,层合多孔结构裂纹由单层模型发生脆性断裂的裂纹耦合而成。

La/Nd比对AZ91-RE合金显微组织和拉伸性能的影响

研究La/Nd比对AZ91-RE合金显微组织和拉伸性能的影响。采用经典表征方法分析第二相的体积分数、平均最近邻距离(NND)和数量密度。利用第一性原理计算确定第二相的形成焓、力学性能和热力学性质。结果表明,La与Nd的质量分数比(w_(La)/w_(Nd))为3/2的合金具有最小的平均晶粒尺寸、最小的平均最近邻距离和最高的第二相数量密度。计算结果表明,Al_(11)La_(3)和Al2Nd的形成在能量上有利。此外,Al_(11)La_(3)和Al_(2)La在抗变形能力、抗剪切变形能力、固体刚度和热稳定性方面都明显优于其他第二相。因此,提高Al_(11)La_(3)和Al_(2)La相的含量有利于改善AZ91-RE合金的力学性能。

结构参数对选区激光熔化成形AlSi10Mg金刚石点阵结构拉伸性能的影响

选区激光熔化制备金属点阵结构由于具有结构设计自由度大、成形零件具有轻量化、缓冲吸震、隔热散热等优势在航空航天等领域具有广泛的工程应用前景。随着应用的不断拓展,对点阵结构的拉伸性能也提出了要求。通过有限元模拟,研究了金刚石单元结构参数对Al Si10Mg点阵结构拉伸性能的影响,并进行了试验验证。结果表明:所设计的点阵结构成形效果较好,具有稳定的力学性能;支杆杆径和孔隙率对点阵结构抗拉强度存在显著影响;随着支杆长径比的减小,点阵结构应力集中区域由节点处向支杆中间位置移动,长径比在1.4左右时点阵结构具有较为均匀的应力分布;在点阵结构外层包裹薄壳结构,可使点阵结构整体应力分布更为均匀。试验与仿真结果相吻合,可通过有限元方法对点阵结构的拉伸性能和变形失效方式进行有效预测。

通过基体晶粒和颗粒分布异质结构的调控协同提升AlN_(p)/Al复合材料的强度-塑性

为了获得优异的强塑性能,采用液固反应结合后续的热机械处理方法制备了3种具有不同微观组织构型的异构AlNp/Al复合材料,详细研究了AlN颗粒分布和基体晶粒组织构型对拉伸强度和塑性的影响。结果表明,复合材料的强度和塑性同时提高。其中,具有较弥散颗粒分布的Uniformed-AlNp/Al复合材料表现出优异的极限抗拉强度(~387 MPa)和断裂伸长率(~9.1%)。与其他文献报道的颗粒增强铝基复合材料相比,该复合材料具有较好的比强度和延展性组合。此外,计算了异质变形诱导(HDI)应力。结果表明,在Uniformed-AlNp/Al复合材料中,HDI应力显著增加。揭示了HDI应力在提高AlNp/Al复合材料的强度和塑性中起着至关重要的作用。