Roughness characterization and shearing dislocation failure for rock-backfill interface

Shearing dislocation is a common failure type for rock–backfill interfaces because of backfill sedimentation and rock strata movement in backfill mining goaf.This paper designed a test method for rock–backfill shearing dislocation.Using digital image techno-logy and three-dimensional(3D)laser morphology scanning techniques,a set of 3D models with rough joint surfaces was established.Further,the mechanical behavior of rock–backfill shearing dislocation was investigated using a direct shear test.The effects of interface roughness on the shear–displacement curve and failure characteristics of rock–backfill specimens were considered.The 3D fractal dimen-sion,profile line joint roughness coefficient(JRC),profile line two-dimensional fractal dimension,and the surface curvature of the frac-tures were obtained.The correlation characterization of surface roughness was then analyzed,and the shear strength could be measured and calculated using JRC.The results showed the following:there were three failure threshold value points in rock–backfill shearing dis-location:30%–50%displacement before the peak,70%–90%displacement before the peak,and 100%displacement before the peak to post-peak,which could be a sign for rock–backfill shearing dislocation failure.The surface JRC could be used to judge the rock–backfill shearing dislocation failure,including post-peak sliding,uniform variations,and gradient change,corresponding to rock–backfill disloca-tion failure on the field site.The research reveals the damage mechanism for rock–backfill complexes based on the free joint surface,fills the gap of existing shearing theoretical systems for isomerism complexes,and provides a theoretical basis for the prevention and control of possible disasters in backfill mining.

Interface,lattice strain and dislocation density of SiC_p/Al composite consolidated by equal channel angular pressing and torsion

Powder mixture of pure A1 and oxidized SiC was consolidated into 10% （mass fraction） SiCp/AI composites at 523 K by equal channel angular pressing and torsion （ECAP-T）. The interfacial bonding of the composites was characterized by transmission electron microscopy （TEM） and high resolution transmission electron microscopy （HRTEM）. The selected area electron diffraction （SAED） for the interface was investigated. The elements at the interface were scanned by energy dispersive spectroscopy （EDS） and the EDS mapping was also obtained. X-ray diffraction （XRD） analysis was carried out for the composites fabricated by 1 pass, 2 passes and 4 passes ECAP-T. According to the XRD analysis, the influences of ECAP-T pass on the Bragg angle and interplanar spacing for AI crystalline planes were studied. The results show that after ECAP-T, the interface between A1 and SiC within the composites is a belt of amorphous SiO2 containing a trace of A1, Si and C which diffused from the matrix and the reinforcement. With the growing ECAP-T pass, the Bragg angle decreases and interplanar spacing increases for A1 crystalline planes, due to the accumulated lattice strain. The increasing lattice strain of A1 grains also boosts the density of the dislocation within A1 grains.

INTERACTION OF A DISLOCATION DIPOLE WITH A MODE III INTERFACE CRACK

Interaction between a screw dislocation dipole and a mode III interface crack is investigated. By using the complex variable method, the closed form solutions for complex potentials are obtained when a screw dislocation dipole lies inside a medium. The stress fields and the stress intensity factors at the tip of the interface crack produced by the screw dislocation dipole are given. The influence of the orientation, the dipole arm and the location of the screw dislocation dipole as well as the material mismatch on the stress intensity factors is discussed. The image force and the image torque acting on the screw dislocation dipole center are also calculated. The mechanical equilibrium position of the screw dislocation dipole is examined for various material property combinations and crack geometries. The results indicate that the shielding or anti-shielding effect on the stress intensity factor increases abruptly when the dislocation dipole approaches the tip of the crack. Additionally, the disturbation of the interface crack on the motion of the dislocation dipole is also significant.

Plasticity and Interfacial Dislocation Mechanisms in Epitaxial and Polycrystalline Al Films Constrained by Substrates

Stresses in epitaxial and textured Al films were determined by substrate-curvature measurements. It was found that in both cases the flow stresses increase with decreasing film thickness. The flow stresses in the epitaxial Al films are in agreement with a dislocation-based model, while the same model strongly underestimates the flow stresses of textured Al films. In-situ transmission electron microscopy studies indicate that dislocations channeling through epitaxial Al films on single-crystalline (0001) α-AI2O3 substrates frequently deposit dislocation segments adjacent to the interface. Furthermore, the AI/α-AI2O3 interface acted as a dislocation source. In this case, the interface is between two crystalline lattices. In contrast, the interface of textured Al films on oxidized silicon substrates is between the crystalline Al and the amorphous SiOx interlayer. It is speculated that the different nature of the interfaces changes dislocation mechanisms and thus influences the flow stresses.

Modeling core-spreading of interface dislocation and its elastic response in anisotropic bimaterial

Interracial dislocation may have a spreading core corresponding to a weak shear resistance of interfaces. In this paper, a conic model is proposed to mimic the spreading core of interfacial dislocation in anisotropic bimaterials. By the Stroh formalism and Green＇s function, the analytical expressions of the elastic fields are deduced for such a dislocation. Taking Cu/Nb bimaterial as an example, it is demonstrated that the accuracy and efficiency of the method are well validated by the interface conditions, a spreading core can greatly reduce the stress intensity near the interfacial dislocation compared with the compact core, and the elastic fields near the spreading core region are significantly different from the condensed core, while they are less sensitive to a field point that is 1.5 times the core width away from the center of the spreading core.

REPRESENTATION OF PLASTICITY AT AN INTERFACE CRACK BY INCLINED STRIP YIELD SUPERDISLOCATION MODEL

The basic equations of the representation of plasticity at an interface crack by an inclined strip yield superdislocation model are derived. With a special combination of the material properties and small-scale yielding case, the problem is reduced to an algebraic equation in an unknown, the ratio of the plastic zone size. Some discussions on the limitations of this model are presented.

Interaction energy of interface dislocation loops in piezoelectric bi-crystals

Interface dislocations may dramatically change the electric properties, such as polarization, of the piezoelectric crystals. In this paper, we study the linear interactions of two interface dislocation loops with arbitrary shape in generally anisotropic piezoelectric bi-crystals. A simple formula for calculating the interaction energy of the interface dislocation loops is derived and given by a double line integral along two closed dislocation curves. Particularly, interactions between two straight segments of the interface dislocations are solved analytically, which can be applied to approximate any curved loop so that an analytical solution can be also achieved. Numerical results show the influence of the bi-crystal interface as well as the material orientation on the interaction of interface dislocation loops.

Dislocation stability in three-phase nanocomposites with imperfect interface

Interface imperfection can significantly affect the mechanical properties and failure mechanisms as well as the strength and toughness of nanocomposites. The elastic behavior of a screw dislocation in nanoscale coating with imperfect interface is studied in the three-phase composite cylinder model. The interface between inner nanoin- homogeneity and intermediate coating is assumed as perfectly bonded. The bonding between intermediate coating and outer matrix is considered to be imperfect with the assumption that interface imperfection is uniform, and a linear spring model is adopted to describe the weakness of imperfect interface. The explicit expression for image force acting on dislocation is obtained by means of a complex variable method. The analytic results indicate that inner interface effect and outer interface imperfection, simultaneously taken into account, would influence greatly image force, equilibrium position and stability of dislocation, and various critical parameters that would change dislocation stability. The weaker interface is a very strong trap for glide dislocation and, thus, a more effective barrier for slip transmission.

Effect of interaction of dislocations with core-shell nanowires on critical shear stress of nanocomposites

The contribution to the critical shear stress of nanocomposites caused by the interaction between screw dislocations and core-shell nanowires (coated nanowires) with interface stresses was derived by means of the MOTT and NABARRO's model. The influence of interface stresses on the critical shear stress was examined. The result indicates that, if the volume fraction of the core-shell nanowires keeps a constant, an optimal critical shear stress may be obtained when the radius of the nanowire with interface stresses reaches a critical value, which differs from the classical solution without considering the interface stresses under the same external conditions. In addition, the material may be strengthened by the soft nanowires when the interface stresses are considered. There also exist critical values of the elastic modulus and the thickness of surface coating to alter the strengthening effect produced by it.

Influence of Surface Oxide Films on Elastic Behaviors of Straight Screw Dislocations Parallel to the Surface of Pure Aluminum

The image stress of straight screw dislocations parallel to the medium surface covered by thin heterogeneous films was analyzed and deduced, in order to calculate the image shear stress. The relationship between image stress and distance from the screw dislocation to the interface of pure aluminum and its oxide covering was calculated based on the analysis. It was shown quantitatively that a sign conversion of the image stress appears in the case of thin oxide covering, while dislocation would pile up near the interface because of the possible slips of the screw dislocations induced by the image stress, which might break down the very thin oxide covering. Further investigation on edge dislocations or other dislocation configurations need to be done.

Growth of Nd : YAG Free from Core and Dislocation

Nd:YAG crystals free from core and dislocation have been grown by using the“controlled reversion of solid-liquid interface” method.The basic idea of the method is to combine the respective advantages of both the convex and the flat interface growth and to overpass "safely"the interface reversion so that the whole crystal could be grown in stable fluid How states.

Functional Divergences of Left Dislocation Construction in English and Chinese

This paper attempts to explore the functional divergence of LD （Left Dislocation） in English and Chinese. Through detailed analyzing, we find that LD in both languages shares only one function, the function of simplifying, but it is different in other functions and there are eight more functions in Chinese than in English. The interface study of LD in the two languages leads to the implications： The connections between syntactic form and discourse function are language-specific and arbitrary, and LD serves a wide variety of discourse functions and is motivated by a range of discourse circumstances

The role of melt cooling rate on the interface between 18R and Mg matrix in Mg_(97)Zn_(1)Y_(2) alloys

The role of melt cooling rate on the interface morphology and dislocation configuration between 18R long-period stacking ordered(LPSO)structure and Mg matrix in Mg_(97)Zn_(1)Y_(2)(at.%)alloys was investigated by atomic-scale HAADF-STEM imaging.The 18R/Mg interface is step-like both in the near-equilibrium alloy and non-equilibrium alloy.Lower cooling rate makes the step size more regular and larger.Only 54R structure can be observed at the interface in the near-equilibrium alloy,and the dislocations are highly ordered.54R and 54R′structure sandwiched by b1 and b2+b3 dislocation arrays,and new dislocation configuration can be detected at the interface in the non-equilibrium alloy,but the dislocations are less ordered.18R/Mg interface containing 54R or 54R′in equilibrium width,parallel to the(010)plane,should be most stable based on elastic calculation.The segregation of solute atoms and its strong interaction with dislocations dominate the LPSO/Mg interface via diffusion-displacive transformation.

电缆终端应力锥错位缺陷对界面温度及应力分布的影响

电缆终端内部缺陷会造成终端内部电场分布不均、局部温度升高与应力分布变化,可能引发局部放电造成绝缘击穿。为研究终端应力锥错位缺陷对电缆界面温度及应力分布的影响,分别建立了电缆终端安装不足与安装过盈情况下的电缆终端错位缺陷模型,并进行电-热-力多物理场耦合仿真分析。结果表明:电缆终端绝缘屏蔽层截断处是电缆终端的薄弱部位,终端界面温度和界面压力都会在绝缘屏蔽层截断处发生突变。当电缆终端存在安装不足缺陷时,终端屏蔽层截断处与应力锥根部之间会出现电场升高区域,在安装位置为-7.5 mm时界面温度最高,绝缘界面压力值升高,且安装位置为-2.5mm时绝缘承受的压力值最大;当电缆终端存在安装过盈缺陷时,绝缘屏蔽层截断处会发生电场畸变,电场突变量随着偏移量的增加而增大,在安装位置为+5.0mm时绝缘界面压力值最大,且界面压力突变量增加发生畸变。因此,在电缆终端实际设计安装与运行维护中,额外注意应力锥错位缺陷对终端内部应力分布的影响十分必要。

基于Cr-O-C钝化层改变多晶Cu表面能和表层位错的脱模力与脱模精度

Cr-O-C钝化层可以提高精密电铸脱模精度,但Cr-O-C钝化层对基底表面的钝化规律和对表层的影响尚未清楚。利用分子动力学方法,在多晶Cu表面沉积离散的Cr、O和C原子,获得不同比例和数量的Cr-O-C钝化层。计算结果表明,不同比例的Cr、O和C原子均可以大幅降低多晶Cu的表面能;随着原子数量的增加,多晶Cu的表面能呈下降趋势;Cr-O-C钝化层增加了多晶Cu表层的位错密度;新增加的位错以Shockley位错为主;在一定沉积原子数量内,位错密度有极值。在多晶Cu表面电沉积不同密度的Cr、O和C原子,通过接触角测试验证了Cr-O-C钝化层降低多晶Cu表面能的结论。电沉积脱模强度和脱模表面粗糙度结果显示,随着沉积原子数的增加,脱模强度和脱模表面粗糙度均降低。研究结果可为利用离散Cr-O-C界面辅助精密电铸脱模提供一种解释。

铜基金属纳米多层膜界面介导的损伤及断裂行为原位研究进展

作为一种典型异质结构材料,纳米金属多层膜的力学响应通常表现出界面介导的损伤及断裂行为。而基于电镜发展的原位力学测试方法,可实现多层膜变形过程中力学行为的精确刻画,从而有助于揭示其界面损伤及断裂的潜在物理机制。当前围绕纳米多层膜的原位研究已有诸多进展。以铜基金属纳米多层膜为例,从缺陷-界面交互行为出发,基于组元层厚对位错运动的影响,详细讨论了位错塞积、约束层滑移和位错穿越3种位错-界面交互机制导致界面损伤的原位研究进展;阐述了孪晶-界面交互行为对界面损伤的影响,进一步分析了因孪生导致的界面损伤行为。在此基础上,讨论了多层膜变形过程中界面介导的裂纹萌生和扩展行为;基于界面类型、载荷加载形式和裂纹偏转等因素,详细分析了多层膜界面介导的断裂机制。最后对材料损伤断裂行为的原位研究进行了展望。

Superb creep lives of Ni-based single crystal superalloy through size effects and strengthening heterostructure γ/γ' interfaces

This study presents a design strategy to enhance the high-temperature creep resistance of Ni-based superalloys.This strategy focuses on two principles:(1)minimizing the dimensions ofγ/γ′interfaces andγchannels by reducing the size of theγ′phase;(2)key alloy composition control to strengthen the heterostructureγ/γ′interfaces.This strategy proved very effective by the designed three superalloys'prolonged creep lives.An alloy exhibits ultra-long creep life by 388 h at 1100°C/137 MPa,which runs at the highest level among those alloys without Ru addition.With Ru addition,an alloy that lasted for 748 h with a creep strain of~6%at 1110°C/137 MPa is developed.This study provides a new route of high-temperature creep lives through heterostructure interfacial design with size effects and key alloying elements.

Analysis of interaction between dislocation and interface of aluminum matrix/second phase from electronic behavior

The inhibitory effect of the second phase on dislocation movement has long been deemed as a great con-tribution to the strengthening of alloys.We investigate the electronic behavior at theα-Al matrix/second phase interface to explore its inhibitory effect on dislocation movement.This work focuses on the dif-ficulty in dislocation movement on the interface ofα-Al/Al_(3)Sc,α-Al/θ’(Al_(2)Cu),andα-Al/T_(1)(Al_(2)CuLi)of aluminum-lithium-scandium alloy based on detailed transmission electron microscopy investigation and electron transport calculation.The more drastic the electron transport between two atoms at the inter-face,the more intense the interaction between them,corresponding to the larger difficulty in breaking and forming bonds between them during the movement process of the extra half plane of dislocation on the interface.The calculated difference in density of valence electrons and differential charge density atα-Al/second phase interface reveals that Al_(3)Sc is characterized by the largest resistance to dislocation movement compared toθ’(Al_(2)Cu)and T_(1)(Al_(2)CuLi).The large differential charge density between the in-terface of(100)Al_(3)Sc/(100)Al demonstrates the strong bonds betweenα-Al and Al_(3)Sc and the large difficulty for the extra half plane of dislocation to form or break bonds during the movement process atα-Al/Al_(3)Sc interface.The dislocation pile-up indicates a discernible hindering effect of theα-Al/Al_(3)Sc interface on dislocation movement.The hindering effect presented byα-Al/Al_(3)Sc interface is favorable for the tensile strength.

Fine structure characterization of an explosively-welded GH3535/316H bimetallic plate interface

An explosion-welded technology was induced to manufacture the GH3535/316H bimetallic plates to provide a more cost-effective structural material for ultrahigh temperature,molten salt thermal storage systems.The microstructure of the bonding interfaces were extensively investigated by scanning electron microscopy,energy dispersive spectrometry,and an electron probe microanalyzer.The bonding interface possessed a periodic,wavy morphology and was adorned by peninsula-or island-like transition zones.At higher magnification,a matrix recrystallization region,fine grain region,columnar grain region,equiaxed grain region,and shrinkage porosity were observed in the transition zones and surrounding area.Electron backscattered diffraction demonstrated that the strain in the recrystallization region of the GH3535 matrix and transition zone was less than the substrate.Strain concentration occurred at the interface and the solidification defects in the transition zone.The dislocation substructure in 316H near the interface was characterized by electron channeling contrast imaging.A dislocation network was formed in the grains of 316H.The microhardness decreased as the distance from the welding interface increased and the lowest hardness was inside the transition zone.

γ/γ' interface strengthening of Re in single crystal superalloys

Based on analysis of three alloys with various Re contents, the effects of Re on the interfacial structure characteristic and interfacial dislocations ofγ/γ' in single crystal superalloys were investigated. A high resolution transition electron microscopy (HRTEM) technique was used to detect the structure characteristic ofγ/γ' interface. The interfacial dislocations ofγ/γ' were analyzed with TEM. The results show that as Re content increases, the interfaces ofγ/γ' become orderly, the atomic arrangements at interfaces are more uniform, the number of mismatch dislocations increases and transition areas betweenγandγ' phases become narrow. That Re changes the interfacial structure promotes the formation of dense, regular and homogeneous interfacial dislocation networks in short time during creep at 1 100℃and 140 MPa, which results in strengthenedγ/γ' interface at elevated temperature.