A roughness parameter considering joint material properties and peak shear strength model for rock joints

This study aims at proposing a reasonable roughness parameter that can reflect the peak shear strength(PSS)of rock joints.Firstly,the contribution of the asperities with different apparent dip angles to shear strength is studied.Then the shear strength of the entire joint asperities is derived.The results showed that the PSS of the entire joint asperities is proportional to a key parameter hs,which is related to the geometric character of the joint surface and the joint material properties.The parameter hsis taken as the new roughness parameter,and it is reasonable to associate the PSS with the geometric characteristics of the joint surface.Based on the new roughness parameter and shear test results of 20 sets of joint specimens,a new PSS model for rock joints is proposed.The new model is validated with the artificial joints in this paper and real rock joints in published studies.Results showed that it is suitable for different types of rock joints except for gneiss joints.The new model has the form of the Mohr-Coulomb model,which can directly reflect the relationship between the 3 D roughness parameters and the peak dilation angle.

Characteristics of structural loess strength and preliminary framework for joint strength formula

The strength of structural loess consists of the shear strength and tensile strength. In this study, the stress path, the failure envelope of principal stress （ Kf line）, and the strength failure envelope of structurally intact loess and remolded loess were analyzed through three kinds of tests： the tensile strength test, the uniaxial compressive strength test, and the conventional triaxial shear strength test. Then, in order to describe the tensile strength and shear strength of structural loess comprehensively and reasonably, a joint strength formula for structural loess was established. This formula comprehensively considers tensile and shear properties. Studies have shown that the tensile strength exhibits a decreasing trend with increasing water content. When the water content is constant, the tensile strength of the structurally intact soil is greater than that ofremolded soil. In the studies, no loss of the originally cured cohesion in the structurally intact soil samples was observed, given that the soil samples did not experience loading disturbance during the uniaxial compressive strength test, meaning there is a high initial structural strength. The results of the conventional triaxial shear strength test show that the water content is correlated with the strength of the structural loess. When the water content is low, the structural properties are strong, and when the water content is high, the structural properties are weak, which means that the water content and the ambient pressure have significant effects on the stress-strain relationship of structural loess. The established joint strength formula of structural loess effectively avoids overestimating the role of soil tensile strength in the traditional theory of Mohr-Coulomb strength.

Digital mapping of soil physical and mechanical properties using machine learning at the watershed scale

Knowledge about the spatial distribution of the soil physical and mechanical properties is crucial for soil management,water yield,and sustainability at the watershed scale;however,the lack of soil data hinders the application of this tool,thus urging the need to estimate soil properties and consequently,to perform the spatial distribution.This research attempted to examine the proficiency of three machine learning methods(RF:Random Forest;Cubist:Regression Tree;and SVM:Support Vector Machine)to predict soil physical and mechanical properties,saturated hydraulic conductivity(Ks),Cohesion measured by fall-cone at the saturated(Psat)and dry(Pdry)states,hardness index(HI)and dry shear strength(SS)by integrating environmental variables and soil features in the Zayandeh-Rood dam watershed,central Iran.To determine the best combination of input variables,three scenarios were examined as follows:scenarioⅠ,terrain attributes derivative from a digital elevation model(DEM)+remotely sensed data;scenarioⅡ,covariates of scenarioⅠ+selected climatic data and some thematic maps;scenarioⅢ,covariates in scenarioⅡ+intrinsic soil properties(Clay,Silt,Sand,bulk density(BD),soil organic matter(SOM),calcium carbonate equivalent(CCE),mean weight diameter(MWD)and geometric weight diameter(GWD)).The results showed that for Ks,Psat Pdry and SS,the best performance was found by the RF model in the third scenario,with R2=0.53,0.32,0.31 and 0.41,respectively,while for soil hardness index(HI),Cubist model in the third scenario with R2=0.25 showed the highest performance.For predicting Ks and Psat,soil characteristics(i.e.clay and soil SOM and BD),and land use were the most important variables.For predicting Pdry,HI,and SS,some topographical characteristics(Valley depth,catchment area,mltiresolution of ridge top flatness index),and some soil characteristics(i.e.clay,SOM and MWD)were the most important input variables.The results of this research present moderate accuracy,however,the methodology employed provides quick and costeffective information serving as the scientific basis for decision-making goals.

Isotropic shear bond strength behavior of superficial bovine dentin: A pilot study

The aim of this pilot study was to evaluate the shear bond strength of superficial bovine incisor dentin in different crown regions. Bonding was performed to the incisal, middle and cervical thirds of superficial bovine coronal dentin (n = 20) with a two-step etch-and-rinse adhesive (Optibond Solo Plus) and resin composite (Z100). Shear bond strength was evaluated at 24 h and failure modes of representative specimens wereobserved with FE-SEM. Non-parametric Kruskal-Wallis test with a significance level of 0.05 was used for data analysis. Mean shear bond strength values for the incisal, middle, and cervical thirds were 36.9 (3.1), 42.6 (2.6), and 37.1 (2.1) respectively with no significant differences evidenced between the crown thirds (p = 0.19). Observation of the failure mode of representative specimens demonstrated that specimens with high bond strength values exhibited predominantly mixed-type failures whereas low strength specimens exhibited adhesive failures between the dentin and adhesive. The absence of significant differences in shear bond strength between crown thirds indicate that, regardless of tubule orientation, any crown region can be used when superficial bovine incisor dentin is used for shear bond strength testing.

Effects of the Tensile and Shear Properties of Bolts on the Shear Properties of Bolted Rock Joints

The mechanical properties of bolts are important factors affecting the shear behavior of bolted joints.In this study,tensile and pure shear tests were conducted on five kinds of bolts made from different materials to measure their tensile and shear parameters.Direct shear tests were conducted to analyze the effects of tensile and shear strength parameters on the shear behavior of bolted joints.The test results showed that the mechanical properties of bolts made from different materials were clearly different and that these differences mainly affected the plastic deformation stage of the bolted joints.The larger the bolt elongation was,the larger the joint shear displacement at bolt failure.The tensile and shear strengths of the bolts were positively correlated with the shear strength of the bolted joints.According to the standard regression analysis,the bolt shear strength had a greater influence than the bolt tensile strength on the bolt contributions when the bolts were perpendicular to the joint surface.Based on the empirical equation for the bolt contribution proposed by Spang,the maximum shear loads in the pure shear test were introduced,and a new equation was established to predict the contributions of bolts.The prediction results obtained using the modified equation were in good agreement with the experimental results.

Mechanical Properties of Methane Hydrate-Bearing Interlayered Sediments

The complex distribution of gas hydrate in sediments makes understanding the mechanical properties of hydrate-bearing sediments a challenging task.The mechanical behaviors of hydrate-bearing interlayered sediments are still poorly known.A series of triaxial shearing tests were conducted to investigate the strength parameters and deformation properties of methane hydrate-bearing interlayered sediments at the effective pressure of 1 MPa.The results indicate that the stress-strain curves of hydrate-bearing interlayered sediments are significantly different from that of hydrate-bearing sediments.The peak strength,Young's modulus,initial yielding modulus,and failure mode are deeply affected by the methane hydrate distribution.The failure behaviors and mechanism of strain softening and hardening patterns of the interlayered specimens are more complicated than those of the integrated specimens.This study compares the different mechanical behaviors between integrated and interlayered specimens containing gas hydrate,which can serve as a reference for the prediction and analysis of the deformation behaviors of natural gas hydrate reservoirs.

Mechanical properties of gas hydrate-bearing sediments during hydrate dissociation

The changes in the mechanical properties of gas hydrate-bearing sediments(GHBS) induced by gas hydrate(GH) dissociation are essential to the evaluation of GH exploration and stratum instabilities. Previous studies present substantial mechanical data and constitutive models for GHBS at a given GH saturation under the non-dissociated condition. In this paper, GHBS was formed by the gas saturated method, GH was dissociated by depressurization until the GH saturation reached different dissociation degrees. The stress–strain curves were measured using triaxial tests at a same pore gas pressure and different confining pressures. The results show that the shear strength decreases progressively by 30%–90% of the initial value with GH dissociation, and the modulus decreases by 50% –75%. Simplified relationships for the modulus, cohesion, and internal friction angle with GH dissociated saturation were presented.

Interfacial microstructure and mechanical properties of tungsten carbide brazed joints using Ag-Cu-Zn + Ni/Mn filler alloy

WC-Co hard metal was furnace brazed by Ag-Cu-Zn+Ni/Mn filler alloy using a tube furnace under high-purity argon at730°C.The influence of brazing time and gap size of joints was studied.The results revealed the maximum shear strength of(156±7)MPa for samples with150μm gap size at a holding time15min.The characterization and microstructure of the brazed joints were characterized by SEM,EDS and XRD.The results showed that increasing the time from5to15min could provide a better chance for the liquid interlayer to flow towards the base metal.However,the formation of some metallic phases such as Mn3W3C at brazing time longer than15min resulted in decreased shear strength of the joint.

Influences of gap size and cyclic-thermal-shock treatment on mechanical properties of TLP bonded IN-738LC superalloy

Influences of gap size and cyclic-thermal-shock treatment on the mechanical properties of transient liquid phase（TLP） bonded IN-738 LC superalloy were investigated. For this purpose, TLP bonding of IN-738 LC superalloy was carried out in a vacuum furnace using powdered AMS 4777 as the filler metal. The results showed that isothermal solidified zone（ISZ） consisted of Ni solid-solution and the distribution of alloying elements was homogeneous. High hardness of HV 409 and high shear strength of 506 MPa were observed in 40 μm gap sample. Alloying elements formed γ′ precipitates and the solid-solution in the ISZ. Hardness and shear strength of bonds were reduced with increasing the gap size（in range of 40-120 μm）. The fractured surfaces of complete isothermal solidified bonds showed dimpled rupture, but athermal solidified bonds showed cleavage fracture surface. 10, 20, 30 and 40 thermal-shock cycles were applied to 80 μm gap samples, respectively. The shear strength of the bond was measured to be 268 MPa after the 40 th thermal-shock cycle. The sample with gap size of 80 μm was failed due to crack nucleation on faying surface at 45 th thermal-shock cycle. The amount of the produced brittleness due to quenching the samples in water bath was attributed to the number of thermal-shock cycles.

Mechanical Properties of Deep-buried Marble Material Under Loading and Unloading Tests

The mechanical properties are essentially different when rock material is subjected to loading or unloading conditions. In this study, loading and unloading tests with various confining pressures are conducted to investigate the mechanical properties of marble material samples taken from the deep diversion tunnels of Jinping II Hydropower Station. The stress-strain relationship, failure characteristics and strength criterion are compared and analyzed based on the experiment results. The results show： in the loading and unloading test, peak strength, lateral strain, axial strain and plastic deformation increase significantly as the confining pressure increases. Lateral strain increased significantly and obvious lateral dilatancy can be observed to the change of confining pressure; The fracture mode is mainly the single shear fracture for the triaxial compression test and post-peak test, angle between the failure surface and the ends of the rock material becomes smaller as the confining pressure increases. Hock-Brown strength criterion reflects the strength characteristics of marble material under two different unloading conditions, and has some supplementary effects to the rock material of mechanical field.

Cohesive Strength and Seismogenic Stress Pattern along the Active Basement Faults of the Precordillera-Sierras Pampeanas Ranges,Western Argentina:An Experimental Analysis by Means of Numerical Model

A two-dimensional finite element method （FEM） model that incorporates faults, elastic rock physical properties, topographical load due to gravity and far-field plate velocity boundary conditions was used to recognize the seismogenic stress state along the fold-and-thrust belt of the Precordillera-Sierras Pampeanas ranges of western Argentina. A plane strain model with nine experiments was presented here to examine the fault strength with two major rock phyical properties： cohesion and angle of internal friction. Mohr-Coulomb failure criterion with bulk rock properties were applied to analyse faults. The stress field at any point of the model was assumed to be comprised of gravitational and tectonic components. The analysis was focused to recognize the seismogenic shear strain concentrated in the internal-cristaline domain of the orogene shown by the modeling. Modeling results are presented in terms of four parameters, i. e., （i） distributions, orientations, and magnitudes of principal stresses （σ1 and σ3）, （ii） displacement vector1 （iii） strain distribution, and （iv） maximum shear stress （τmax） contour line within the model. The simulation results show that the compressive stress is distributed in and around the fault systems. The overall orientation of of σ1 is in horizontal directions, although reorientations do occur within some stress weaker parts, especially subsequent to the faults. A large-scale shear stress is accumulating along the active faults of Tapias-Villicum Fault （TVF）, Salinas-Berros Fault （SBF）, Ampacama-Niquizanga Fault （ANF） and Las Charas Fault （CF）, which could act as local stress and strain modulators to localize the earthquakesoccurrence.

冻融循环对季冻土区粉质黏土-混凝土界面剪切性能的影响

为探究季冻土区粉质黏土-混凝土界面剪切性能,进行了不同冻融循环次数、土体含水率和法向应力的粉质黏土-混凝土二元体冻融循环试验和直剪试验,探讨了界面抗剪强度、抗剪强度参数和抗剪强度损伤度的变化规律。结果表明:直剪试验得到的应力-应变曲线均发生应变硬化现象,可分为弹性变形阶段(剪切位移为0~3 mm)和弹塑性变形阶段(剪切位移为4~15 mm);冻融循环对界面抗剪强度有劣化作用,即通过对土体造成损伤,导致界面内摩擦角和黏聚力下降,从而降低界面抗剪强度;随着冻融循环次数增加,界面抗剪强度损伤度增加,当冻融循环进行0、4次,抗剪强度损伤迅速,冻融循环进行12~20次,抗剪强度损伤较缓,最大界面抗剪强度损伤度为25%;土体含水率的增加对抗剪强度有削弱作用,随着土体含水率的增加,界面内摩擦角降低,但黏聚力先增加后减小,当土体含水率为20.7%时,黏聚力达到最大值;法向应力的增加对抗剪强度有增强作用。

新旧混凝土结合面剪切强度参数分析和计算研究

新旧混凝土结合面的抗剪强度是装配式混凝土结构和混凝土结构加固等领域重点关注的问题.基于搜集、整理的新旧混凝土结合面(以下简称结合面)的剪切试验数据库(含439个试件),对GB 50010―2010、ACI 318―19、Eurocode 2、PCI7th四个规范所给结合面抗剪建议计算式进行对比分析.结果表明:在各参数的影响下,ACI结果的保证率表现最好,而Eurocode 2计算强度的拟合效果最好;在结合面宽度达到300~400 mm时,GB 50010―2010的表现最好,但安全富余均较低,相对误差最大达到9倍.对数据库进行参数分析,发现结合面剪切强度τ_(exp)存在尺寸效应,与结合面的沿剪切方向尺寸关联较大;且τ_(exp)与夹紧力ρfy有较好的相关性.基于分析结果,根据叠加计算理论,对计算式提出建议和修正:分析引入尺寸效应系数β;同时修正了摩擦系数μ;应用了数据库拟合的销栓力分段函数,极大值为6.6 MPa.经对比验算证明,修正计算式在有无插筋及各种粗糙度情况下的误差最小,拟合效果最好,可为工程应用提供参考.

牛粪和核桃果枝混合发酵理化特性试验及设备工艺优化

通过鲜牛粪、牛粪与核桃果枝、牛粪核桃果枝加发酵菌剂三个不同配比的堆肥试验,开展牛粪和核桃果枝的化学特性参数试验;同时,参照土壤力学试验方法,对有机肥发酵各阶段的含水率、电导率、硬度、湿密度、抗剪强度等物理特性参数进行试验研究。试验结果表明,三种堆体有机质质量分数、总氮、总磷和总钾质量分数在堆肥初期都有所下降,随后缓慢上升,最后趋于平稳,分别稳定在32%、39%、40%,6.33%、9.48%、9.53%,0.95%、1.26%、1.29%和1.71%、2.59%、2.48%,添加果枝和菌剂的堆肥营养物质损失最少。三个堆体EC值的变化趋势基本一致,逐步升高,随着CO_(2)、NH_(3)的挥发,EC值开始缓慢下降,三个堆体EC值最终分别稳定在5.44ms/cm、5.94ms/cm、5.54ms/cm。3个堆体的湿密度在堆肥过程中都随着堆肥天数的增加总体呈下降趋势,堆肥结束时,三个堆体湿密度分别是0.71g/cm^(3)、0.65g/cm^(3)、0.45g/cm^(3)。

冷轧压下率对高强无取向电工钢变形组织和磁性能的影响

借助场发射扫描电镜(SEM+EBSD)、快速升温管式炉和交流磁性能测量仪研究高强无取向电工钢冷轧变形组织和磁性能随冷轧压下率的变化规律。结果表明:冷轧高强无取向电工钢中形成含有大量亚结构的粗糙条带和变形量较小的光滑条带。粗糙条带具有γ取向,主要为{111}〈110〉,光滑条带具有{112}〈110〉和{001}〈110〉取向。粗糙条带中存在大量宽度约为2~3μm的剪切带,与轧向呈20°~35°夹角,且随压下率增大,数量逐渐增多。剪切带与基体间具有一定取向差,随压下率增大,剪切带逐渐从{111}〈110〉取向转向{223}〈110〉取向,与基体间取向差逐渐增大。退火后Goss和{111}面织构增多,{001}面织构减少;轧向磁感应强度增大,横向磁感应强度减小,各向异性显著,铁损下降。

聚氨酯上浆剂处理PBO纤维复合材料的界面性能

为了提高聚对苯撑苯并二噁唑(poly-p-phenylenebenzobisoxazole,PBO)纤维/环氧树脂复合材料的界面性能,采用γ-氨丙基三乙氧基硅烷(KH550)改性水性聚氨酯得到上浆剂,然后对酸化后的PBO纤维进行表面涂覆处理。采用XPS和EDS分析PBO纤维表面的化学组成,利用SEM研究PBO纤维表面及其复合材料撕裂面的形貌,并对PBO纤维的单丝及复合材料的力学性能进行分析。结果表明:经过上浆剂包覆的PBO纤维表面活性基团明显增多,表面O/C(原子比)由0.16提升至0.25,上浆剂能有效修复纤维表面的缺陷;通过调控纤维表面上浆剂含量和结构,可使PBO纤维/环氧树脂单向复合材料的层间剪切强度提高到41.3 MPa,拉伸强度增加到1.70 GPa,相较于未处理的复合材料分别提高了44.9%和15.6%。

含镍铬合金丝纬编电加热层复合材料的层间剪切性能

为开发既具有电加热功能特性又满足承载结构基本力学性能要求的玻璃纤维/环氧层合复合材料,选取3种直径的镍铬合金丝,设计制备了平针、罗纹和双罗纹3种组织结构的纬编电加热织物,以镍铬合金丝纬编织物作为中间电加热层,优选热压罐复合成型工艺,制备了玻璃纤维/环氧层合复合材料。利用红外热像仪和万能试验机分别测试了复合材料的电加热性能和层间剪切性能。结果表明:在8 V直流电压下,6种复合材料均能升温到37℃以上,最高可达72℃,耗时30 s;最高平衡温度与镍铬合金丝直径成正相关,平针组织复合材料最高平衡温度最高,双罗纹组织复合材料表面温度均匀性最好;含镍铬合金丝纬编电加热层的玻璃纤维/环氧层合复合材料层间剪切强度相较于不含电加热层复合材料层间剪切强度保留率为74.1%~97.4%。初步研究工作表明,含镍铬合金丝纬编电加热层复合材料可同时实现玻璃纤维/环氧层合复合材料功能与结构的兼顾,有望满足直升机发动机进气道防/除冰系统的设计需求。

含硼三烯丙基化合物改性环氧树脂的研究

采用含硼三胺(TAB)和香草醛衍生的烯类化合物(AM)为原料,通过希夫碱合成反应设计制备了一种含硼三烯丙基化合物(TABM),通过改变TABM的添加量得到一系列改性树脂(E-51+TABM)。对固化后树脂的结构、热稳定性、热机械性能、拉伸剪切性能、阻燃性能以及微观断裂形貌进行了表征。研究结果表明:(1)红外光谱和核磁氢谱的测试结果均表明,成功地制备了目标产物TABM。(2)热稳定性和热机械性能研究表明,随着TABM用量的增加,固化后环氧树脂的储能模量和残碳率也随之增大,但其玻璃化转变温度和交联密度降低。这表明TABM的添加可以降低材料的刚性,提升环氧树脂的韧性。(3)添加TABM后,环氧树脂在室温和100℃条件下的拉伸剪切强度均得到提升,当添加10份TABM时,拉伸剪切强度在25℃的条件下提升了25.5%,在100℃的条件下提升了37.5%。(4)随着树脂中TABM含量的增加,固化后树脂的极限氧指数(LOI)值也随之提升,直到添加量达到20份时达到最大值,说明TABM的添加,使得固化后树脂的阻燃性得到了有效改善。(5)微观断裂形貌分析表明,共混树脂(E-51+TABM)的断裂韧性得到了提高。

工艺参数对5A90铝锂合金扩散连接质量的影响规律

采用金相显微镜、扫描电镜和真空热压烧结炉等设备探究了5A90铝锂合金的扩散连接工艺。结果表明,在扩散连接过程中,随着温度的升高和保温时间的延长,试样中白色强化相增多,空洞减少,焊合度明显提高。剪切强度随扩散连接温度的提高而降低,随保温时间的减少而降低,进而使连接强度降低;这主要是由于扩散温度及保温时间对原子扩散过程产生影响。试样界面15μm的粗糙度避免了氧化铝薄膜的过厚,并保证了扩散连接时接头处的局部接触,使氧化膜破裂,得到最佳接头质量。典型参数下的断裂发生在母材中,以穿晶断裂为主要断裂形式,证明了5A90铝锂合金扩散连接接头的可靠性。通过对比分析,得到扩散连接最佳工艺参数为:连接温度540℃、保温2.5 h、表面粗糙度15μm。

5种流体树脂与牙釉质粘接性能的对比研究

目的通过比较Beautifil Flow Plus F00、FiltekTM Z350 XT、SDR、Tetric®N-Flows、Constic 5种流体树脂与牙釉质的粘接性能,为流体树脂的临床选择提供参考。方法选择因正畸拔除的成人离体前磨牙50颗,将离体牙随机分为5组(n=10),分别为F00组、Z350组、SDR组、Tetric组、Constic组,每组之间互为平行对照组。每颗离体牙颊侧中1/3磨除厚度为0.5 mm牙釉质,以直径为3 mm的圆形形态作为粘接面,每种树脂制作直径和长度均为3 mm圆柱形树脂试件10个,与预备好的牙釉质面进行粘接,自凝树脂进行包埋。将试件进行3000次冷热循环交替实验和37℃恒温水浴24 h实验后,进行剪切强度测试,记录数据;切断的粘接界面在扫描电镜下观察。结果F00组的剪切强度为(18.39±2.93)MPa、Z350组的剪切强度(11.03±1.55)MPa、SDR组的剪切强度为(12.77±1.55)MPa、Tetric组的剪切强度为(15.25±1.88)MPa、Constic组的剪切强度为(12.79±2.78)MPa,对所得数据进行ANOVA检验和SNK检验后得出,F00组的剪切强度显著高于其他4组(Z350组、SDR组、Tetric组、Constic组)(P<0.05);Tetric组的剪切强度显著高于其余3组(Z350组、SDR组、Constic组)(P<0.05);Z350组、SDR组、Constic组3组之间的剪切强度没有显著性差异(P>0.05)。结论5种流体树脂中Beautifil Flow Plus F00流体树脂粘接性能最高,Tetric®N-Flow流体树脂次之,FiltekTM Z350 XT、SDR、Constic这3种流体树脂粘接性能较低。