不同恒温时间加热下花岗岩冲击压缩力学特性及破碎特征

为研究不同恒温时间的实时高温作用对花岗岩冲击压缩力学特性与破碎特征的影响,开展了高温时SHPB冲击压缩试验及筛分试验。首先,将花岗岩加热到700℃并进行0、30、60、90及120 min这5种不同时间的恒温热处理;其次,不对试样做冷却处理,利用同步对杆装置进行高温时SHPB试验,收集破碎试件并开展筛分试验;最后,结合抗压强度、分形维数等数据,分析花岗岩的力学特性及破碎特征。研究结果表明:恒温时间对花岗岩动态抗压强度影响较大,试件抗压强度随恒温时间增加而呈明显下降趋势;花岗岩破碎程度随恒温时间增加而不断加剧,表现在破碎试件中细块数量逐渐减少,细粒数量不断增多。不同恒温时间加热下花岗岩冲击压缩破坏的分形维数集中在2.2~2.7之间,且与恒温时间呈现正相关关系。实时高温作用下花岗岩动态抗压能力与宏观破碎分形特征均具有明显的应变率强化效应。

大豆茎秆压缩力学特性的研究

为了研究大豆茎秆力学性能与大豆倒伏现象的相关性及对大豆的优种筛选进行评价,通过对大豆茎秆的轴向压缩试验,测定了3个品种、不同含水率和不同距地高度的最大承载力、最大应力、弹性模量和惯性矩。结果表明:干大豆茎秆的最大承载力、最大应力和弹性模量明显高于湿大豆茎秆;沿茎秆高度方向,最大承载力和惯性矩基本呈线性下降趋势,最大值在距地高度5cm以下;而最大应力基本上不变,弹性模量变化小,最大值在距地8～30cm处,最小值均在大豆茎秆顶端。不同品种间茎秆平均最大承载力、最大应力的差异明显:品种3的茎秆两者最小,品种2的茎秆两者最大。不同品种间的平均弹性模量和惯性矩也有差异:品种3的两者最小,品种1的两者最大。

棉秆压缩力学特性的研究

通过对棉秆的轴向压缩试验研究,得出其试验结果表明:棉秆在相同加载速率、不同节间、不同含水率条件下,其轴向弹性模量与抗压强度不同。棉秆的节间位置、含水率是影响弹性模量和抗压强度的重要因素。干棉秆的弹性模量与轴向抗压强度明显高于湿棉秆,而弹性模量与轴向抗压强度受节间影响,其平均值在节间2时最大。

黍子籽粒压缩力学特性试验研究

为了降低黍子籽粒在生产和加工过程中的挤压损伤,对不同含水率黍子籽粒的压缩力学特性进行了试验研究。测定了黍子籽粒的力——变形曲线,分析其挤压破碎过程,得到了籽粒初始损伤产生时的破坏力、变形量和破坏能,并计算了其表观弹性模量和最大挤压应力。同时,获得各压缩力学特性参数随含水率的变化规律及相应的拟合关系方程。研究结果表明,随着含水率增加,黍子籽粒挤压破坏力减小,变形量和破坏能先降低后升高,表观弹性模量和挤压应力均呈线性递减,可为黍子生产、加工等相关机械装备的设计和技术参数的确定提供参考依据。

碳及内嵌金属原子富勒稀分子的压缩力学特性

采用分子动力学(MD)与量子力学(QM)相结合的方法,模拟了Cn(n=20、60、80、180)富勒稀分子,以及M@C60(M=Na、Fe、Al)内嵌金属原子富勒稀分子的对径压缩过程,获得了各种富勒稀分子的系统能量-变形曲线、载荷-变形曲线、最大承受载荷、失效应变以及压缩刚度等压缩力学性能数据.根据模拟的结果,分析了具有不同幻数n、不同内嵌金属原子的富勒稀分子压缩力学特性的差异.研究表明,碳富勒稀分子具有出色的压缩力学性能;幻数n较大的富勒稀分子的最大承受载荷和压缩刚度较大,但失效应变较小;与未填充碳富勒稀分子相比,内嵌金属原子富勒稀分子具有更好的承载能力.

C32C60C180、C60@C180富勒烯分子的压缩力学特性

采用Tersoff-Brenner势与L—J势的分子动力学方法，研究了双石墨层作用下C32、C60、C180以及C60@C180富勒烯分子的压缩力学特性。根据计算结果，讨论了几种富勒烯压缩过程中的变形、能量、压缩栽荷等的变化及其差异。研究表明，由于分子几何构形上的差异，压缩时，C180出现了明显的“塌陷”现象，“塌陷”过程中，能量及外载荷一度下降；几种富勒烯压缩时的能量吸收能力排序为：C32〉C60〉C60@C180〉C180，承载能力的排序为：C60@C180〉C180〉C60〉C32。

碳富勒稀分子C_n(n=20、60、80、180)的压缩力学特性

采用分子动力学与量子力学相结合(MD/QM)的方法,模拟了C_n(n=20、60、80、180)富勒稀分子的对径压缩过程,获得了各种富勒稀分子的系统能量-变形曲线、载荷-变形曲线、最大承受载荷、失效应变和压缩刚度等性能数据。研究结果表明,碳富勒稀分子具有出色的压缩力学性能,幻数n较大的富勒稀分子的最大承受载荷和压缩刚度也较大,但失效应变较小。

曲线折痕折纸力学超材料可定制压缩力学特性

针对现有折纸力学超材料大多基于直线折痕图折叠而成,一定程度上限制了其可定制力学特性。本文将曲线折痕引入到二维折痕图,提出了一种曲线折痕圆柱折纸力学超材料。利用金属增材制造方法制备了折纸力学超材料样品,并借助三维CT扫描证实了较高制造精度。采用基于超算平台并行计算的显式动力学数值仿真和物理试验法阐明了曲线折痕圆柱折纸力学超材料的变形模式和压扭特性。进一步,研究了改变曲线山折和曲线谷折可实现曲线折痕圆柱折纸力学超材料的可定制压缩力学特性。所提曲线折痕圆柱折纸力学超材料为可定制力学特性需求的新型力学超材料提供了一种新的思路。

青红杨梅果实生物力学特性研究

为探究青红杨梅的生物力学特性,进一步降低清选分级过程中的损耗,文章以湖南娄底青红杨梅为研究对象,测量并分析了杨梅果实的基本物理特性参数,利用质构仪对杨梅果实进行了压缩力学特性试验。结果显示:青红杨梅果实的外径分布集中在20~26 mm范围内,质量分布集中在4~10 g范围内;含水率与外径、质量都不相关,均值约为82.57%;静摩擦系数约为0.19。青红杨梅果实的破裂力为44.38 N,破裂变形量为8.11 mm,破裂形式决定了杨梅分级运储时应当避免碰撞和持续性单载荷挤压。

甘薯块根物理机械特性试验研究

甘薯机械化生产机具大多数参考马铃薯生产机具研制,缺乏理论设计和分析依据。为了给甘薯收获、运输、分选机械的设计和优化提供相关理论参数及分析依据,探究成熟期甘薯块根不同方向、不同部位的压缩物理机械特性,为高性能机具研制奠定基础。以辽宁地区广泛种植的烟薯25品种为研究对象,测定成熟期块根含水率及密度,确定试验块根的基本物理参数;利用INSTORN5944型电子万能试验机进行块根轴向、径向以及不同部位压缩力学特性试验,得出破裂力随加载速度变化趋势,分析不同压缩方向和不同部位薯块的弹性模量、泊松比以及剪切模量,确定甘薯材料特性。结果表明:成熟期烟薯25含水率为79.64%,密度为1 028 kg·m^(-3);不同压缩方向上薯块的弹性模量、泊松比及剪切模量差异不显著,甘薯为各向同性材料;不同部位薯块弹性模量、泊松比及剪切模量差异不显著,甘薯为均质材料;甘薯弹性模量为3.22~4.19 MPa,泊松比为0.28~0.40,剪切模量为1.26~1.50 MPa。研究结果对甘薯生产机械化机具设计及后续仿真分析模型的建立具有重要意义。

基于SHPB试验的桦木压缩动力学特性

【目的】利用木材动态压缩加载试验研究热磨机研磨解离破碎阶段木材原料受动态压缩载荷的动力学特性,并研究应变率、加载方向对木材原料动力学特性的影响,旨在深化木材原料研磨解离机制的研究,为热磨法纤维分离设备及磨片的齿形结构优化设计提供理论指导。【方法】利用Hopkinson杆试验装置对含水率为12.65%、密度为0.50 g·cm-3的桦木试件进行应变率约为400,800,1 200 s-1,加载方向为径向、弦向和轴向的动态压缩试验,获得桦木在不同应变率及方向上动态压缩加载的解离特征、动态应力-应变曲线及相应的力学特性。【结果】对比分析各组试验后试件的破坏形态发现:1)当应变率约为400 s-1时,径向、弦向和轴向加载的试件主要发生塑性变形;2)当应变率约为800 s-1时,径向加载试件被解离成几大块,并且有一些"火柴棍"状的小试件从大试件上剥离;弦向加载试件沿加载方向上产生更大的塑性变形,并且在试件上、下两端处沿加载方向产生贯穿性裂纹,试件被解离成三大块;轴向加载试件受载面边缘处的纤维大量产生压溃现象,在加载面上产生贯穿性裂纹且有片状小试件从大试件上剥离;3)当应变率约为1 200 s-1时,径向加载试件被解离成大量"火柴棍"状的小试件,并且小试件的尺寸明显小于应变率为800 s-1时;弦向加载试件沿加载方向上产生的塑性变形与应变率为800 s-1时相当,但是试件上端处被解离成许多片状的小试件,并且沿加载方向试件上产生了数条贯穿整个试件的大裂纹;轴向加载试件被解离成大量短粗状的小试件,并且小试件上带有明显的褶皱。对比分析各组试验试件的应力-应变曲线发现:1)动态压缩加载条件下桦木的应力-应变曲线可以由屈服点应变分为弹性阶段和屈服后弱线性强化阶段2部分;2)桦木沿径向加载应变率约为400,800,1 200 s-1时,其屈服强度和韧性模量分别为4.56,10.49,14.22 MPa和2.88,8.32,20.70 k J·cm-3,应变率从400 s-1增加到1 200 s-1时,屈服强度和韧性模量分别增加了2.11和6.19倍;3)桦木沿弦向加载应变率约为400,800,1 200 s-1时,其屈服强度和韧性模量分别为5.87,7.90,9.65 MPa和2.53,7.41,12.92 k J·cm-3,应变率从400 s-1增加到1 200 s-1时,其屈服强度和韧性模量分别增加了0.64和4.10倍;4)桦木沿轴向加载应变率约为400,800,1 200 s-1时,其屈服强度分别为22.90,71.41,96.37 MPa和18.79,67.74,114.32 k J·cm-3,应变率从400 s-1增加到1 200 s-1时,其屈服强度和韧性模量分别增加了3.21和5.08倍。【结论】随着应变率的增加,桦木的解离程度加大,径向加载最易解离,轴向加载最难解离;桦木的动态压缩屈服强度、动态压缩韧性模量具有很强的应变率敏感性,是一种应变率敏感材料。

花椒力学特性的测定与分析

研究分析成熟期花椒的力学特性,旨在为花椒机械采收方式的选择及机构的设计提供理论依据。以山西省临汾市成熟期的大红袍花椒为试验对象,分别测定了花椒果实的压缩力学特性、穗柄的剪切力学特性、花椒果实与果柄连接处及穗柄的拉伸力学特性。结果表明,成熟期花椒的压缩、剪切、拉伸等力学特性指标值的变化范围:花椒果实受压的屈服载荷为31.40~66.34 N,平均屈服载荷为49.01 N;穗柄剪切力为2.18~5.58 N,平均剪切力为4.15 N,平均抗剪强度为1.60 MPa;穗柄抗拉力为5.03~15.04 N,平均抗拉力为8.60 N,平均抗拉强度为4.61 MPa;果实与果柄连接处抗拉力为2.30~4.83 N,平均抗拉力为3.86 N,显著小于穗柄抗拉力,平均抗拉强度为4.08 MPa。因此,机械采收花椒时机构作用在花椒果实上的压缩载荷应低于所测屈服载荷最小值31.40 N,否则会对花椒果实造成损伤;若采用剪切式采收方式,施加在穗柄处的剪切力应不低于2.18 N,采用负压等拉伸式采收方式应尽量选择在果实与果柄连接处进行分离采收。

Effect of fractures on mechanical behavior of sand powder 3D printing rock analogue under triaxial compression

In practical engineering applications,rock mass are often found to be subjected to a triaxial stress state.Concurrently,defects like joints and fractures have a notable impact on the mechanical behavior of rock mass.Such defects are identified as crucial contributors to the failure and instability of the surrounding rock,subsequently impacting the engineering stability.The study aimed to investigate the impact of fracture geometry and confining pressure on the deformation,failure characteristics,and strength of specimens using sand powder 3D printing technology and conventional triaxial compression tests.The results indicate that the number of fractures present considerably influences the peak strength,axial peak strain and elastic modulus of the specimens.Confining pressure is an important factor affecting the failure pattern of the specimen,under which the specimen is more prone to shear failure,but the initiation,expansion and penetration processes of secondary cracks in different fracture specimens are different.This study confirmed the feasibility of using sand powder 3D printing specimens as soft rock analogs for triaxial compression research.The insights from this research are deemed essential for a deeper understanding of the mechanical behavior of fractured surrounding rocks when under triaxial stress state.

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.

A numerical study of macro-mesoscopic mechanical properties of gangue backfill under biaxial compression

Based on the Particle Flow Code(PFC^(2D)) program,we set up gangue backfill models with different gangue contents and bond strength,and studied the stress-strain behaviours,the pattern of shear band and force chains,motion and fragmentation of particles under biaxial compression.The results show that when the bond strength or contents of gangue are high,the peak strength is high and the phenomena of post-peak softening and fluctuation are obvious.When gangue contents are low,the shape of the shear band is symmetrical and most strong force chains transfer in soil particles.With an increase in gangue content,the shape of the shear band becomes irregular and the majority of strong force chains turn to transfer in gangue particles gradually,most of which distribute along the axial direction.When the gangue content is higher than 50%,the interconnectivity of strong force chains decreases gradually:at the same time,the strong force chains become tilted and the stability of the system tends to decrease.With an increase in external loading,the coordination numbers of the system increase at first and then decrease and the main pattern of force chains changes into columnar from annular.However,after the forming of the advantageous shear band,the force chains external to the shear band maintain their columnar shape while the inner ones bend obviously.As a result,annular force chains form.

Mechanical and damage evolution properties of sandstone under triaxial compression

To study the mechanical and damage evolution properties of sandstone under triaxial compression, we analyzed the stress strain curve characteristics, deformation and strength properties, and failure process and characteristics of sandstone samples under different stress states. The experimental results reveal that peak strength, residual strength, elasticity modulus and deformation modulus increase linearly with confining pressure, and failure models transform from fragile failure under low confining pressure to ductility failure under high confining pressure. Macroscopic failure forms of samples under uniaxial compression were split failure parallel to the axis of samples, while macroscopic failure forms under uniaxial compression were shear failure, the shear failure angle of which decreased linearly with confin- ing pressure. There were significant volume dilatation properties in the loading process of sandstone under different confining pressures, and we analyzed the damage evolution properties of samples based on acoustic emission damage and volumetric dilatation damage, and established damage constitutive model, realizing the real-time Quantitative evaluation of samnles damage state in loading process.

In situ strength of coal bed based on the size effect study on the uniaxial compressive strength

In the early 1990 s, the Foundation for Science and Technology of Rio Grande do Sul State(CIENTEC)developed a pioneering study in Brazil, related to the simultaneous mining of multiple coal seams.One of the activities included detailed studies on the geomechanical characterization of materials present in the Irapua coal seam, under exploitation in the A-Sangao Mine, located near the city of Criciuma-SC,within the South-Catarinense coalfield. The goal of the laboratory tests was to define the behavior of the uniaxial compressive strength of the Irapua coal seam and establish a first approximation for the in situ strength value of this coal seam, since existing knowledge is solely based on practical mining experience over the years. Large samples of the coal seam were collected, using special techniques to maintain the integrity of the material, and a set of 56 uniaxial compression tests in cubic specimens, with side length ranging from 4.5 to 31 cm, were conducted in laboratory. This paper describes the experimental techniques used in the assays, and also presents the uniaxial compression strength results obtained.Moreover, important aspects of this type of study are considered, highlighting the size effect for the carbonaceous bed and the estimation of in situ strength values for the Irapua coal seam.

轴向变密度铝泡沫件的动态和静态压缩实验与有限元模拟分析

针对工程中常见的厚度方向变密度的闭孔铝泡沫材料,该文通过动态和静态压缩实验与模拟分析,探讨了大尺度变密度铝泡沫部件变形与吸能特性分析的有限元模型构建方法。对变密度铝泡沫大试样的准静态压缩和冲击压缩实验研究表明:厚度方向变密度铝泡沫材料的压缩过程呈现从低密度层开始的逐层屈服变形伴随整体变形的特性,与密度均匀的铝泡沫材料的变形特性显著不同。该文建立了变密度铝泡沫大试样的分层变密度变尺度有限元模型和近似的密度和尺度均匀的有限元模型,计算结果对比分析表明:分层变密度变尺度有限元模型能够模拟实际材料的逐层屈服变形特性,计算的试样准静态和冲击压缩变形与吸能特性等与实验结果相符;而基于均匀模型的计算结果则不能模拟逐层变形特性,与实验结果及理论特性明显不相符。分层变密度变尺度有限元模型的单元尺度会影响逐层屈服变形特性模拟结果,基于单元尺度接近实际铝泡沫材料胞元尺度的分层有限元模型的计算结果与实验结果一致性较好。这些研究结果对各种结构的铝泡沫材料应用研究具有重要意义。

Mechanical Behavior of Concrete Block Masonry

The main objective of this study is to verify, through compression tests on different prisms, the vertical and horizontal deformability and the failure modes of the components of concrete blocks under compression. In this study two mortar mixes were tested, along with two types of prism, with and without the presence of a vertical joint. The conclusions were： the appearance of non-linearities of the masonry corresponds to an increase in the lateral strain due to extensive cracking of the material and a progressive increase in the Poisson ratio, the cracks in the three-block prisms built with the mortar type I were vertical, occurring symmetrically on both sides; the prisms built with mortar type II had, as a consequence of localized crushing, an association with vertical cracks due to the concentrations of stresses at some points, the presence of a vertical joint led to the appearance of separation cracks between the middle block and the vertical mortar joint, when the stress reached approximately 30% of the compressive strength of the set; the prisms with two whole blocks and one vertical joint （B） built with the mortars of mixes I and II had a compressive strength of the order of 42% and 66% of the prisms with three whole blocks （A）, respectively.