Relative Slip Research Articles

A DEM-based approach for modeling the thermal-mechanical behavior of frozen soil

The mechanical characteristics of frozen soil under various temperatures have theoretical and engineering significance for improving the efficiency of permafrost excavation and ensuring the stability of permafrost area engineering. A novel approach based on Discrete Element Method (DEM) is proposed to simulate the temperature effect of frozen soil. An existing 3D contact model for cemented granular material is extended to include the effects of temperature on bond strength and modulus of ice cementation, which are verified by existing analytical solutions and experimental data, and a simplified method is employed to simulate the influence of ice crystal expansion on the void ratio of frozen soil, whereafter, the modified contact model is calibrated by the results of the temperature-controlled triaxial test. This approach was proven to be effective by comparing the simulation results with the experimental results. The micro mechanical behavior of frozen soil samples was studied. The results showed that different types of bond contact had different effects in the shearing stage. The structural ‘weakening’ and ‘strengthening’ of the frozen soil occur simultaneously during the loading process, and the structural damage is mainly caused by the plastic damage induced by the relative slip between soil and ice particles.

Prestress loss and flexural behavior of precracked RC beams strengthened with FRP/SMA composites

This paper explored a kind of fiber reinforced polymer (FRP)/shape memory alloy (SMA) composite prestressed strengthening system, and studied the prestress loss and flexural behavior of precracked reinforced concrete (RC) beams strengthened with FRP/SMA composites by experiments. In the experiment, the length ratio of SMA wires to FRP sheets, the type of FRP sheets, and the area ratio of SMA wires to FRP sheets were selected as the main parameters. The prestress loss test results indicated that the elongation of FRP sheets in the strengthening zone, relative slip between SMA wires and FRP sheets, and crack closure are the main causes of prestress loss in beams strengthened with FRP/SMA composites. Among these, the prestress loss caused by the elongation of FRP sheets in the strengthening zone accounted for a significant proportion of the total loss, while the remaining two losses accounted for a minor proportion. The increase of the length ratio of SMA wires to FRP sheets could effectively reduce the prestress loss due the decrease of SMA shrinkage strain. The type of FRP sheets in the strengthening zone affected the prestress loss mainly by affecting the elongation of FRP sheets. The area ratio of SMA wires to FRP sheets influenced the total recovery force level. The prestress loss mainly occurred within 12 h (initial curing of epoxy resin) after thermal activation of SMA wires, and then the prestress loss was small in the following 60 h (complete curing of epoxy resin). The flexural test results of beams strengthened with FRP/SMA composites showed that the flexural capacity was significantly improved, and the yield and ultimate load significantly increased. At the same time, the service performance was also improved due to the introduction of SMA wire recovery stress. In addition, the introduction of prestress to FRP sheets in the strengthening zone delayed the debonding failure induced by the crack. Lastly, the sectional analysis method was also applied to predict the load-deflection responses of the strengthened beams, which was validated through comparisons with the test results.

THEORETICAL CALCULATION AND EXPERIMENTAL TESTING OF IMPROVED BELT TRANSMISSION FOR COTTON CLEANING MACHINES

The article considers the object of belt transmission driving all the drums of the USK cotton[1]cleaning unit, most commonly used in the cleaning shop of cotton-cleaning plants, and theoretically calculates the improved design of belt transmission consisting of two pulleys and a belt. Traction power of belt and belt transmission according to experimental methods is characterized by dependence of belt relative slip and efficiency on transmission resistance coefficient. A mathematical model of new belt transmission design has been developed, which allows theoretical estimating of belt tensile strength and rational operating mode in elastic slipping zone; the design has been installed at the machinery of the cotton-cleaning plant, a part of unitary enterprise “Real Agro Cotton”. The results of the experiment were analyzed.

Bond-slip behavior between reactive powder concrete and H-shaped steel

The mechanical performance of the steel reinforced reactive powder concrete (SRRPC) structural components significantly depends on the steel-concrete interfacial bond behavior. This paper presents an experimental and analytical investigation on the bond-slip behavior between the reactive power concrete and the H-shaped steel. A total of 11 specimens, considering the cover thickness, embedded length, stirrup ratio and bonding part (whole section, flange and web), were tested through the push-out configurations. Results showed that the cover thickness has the most significant impact on the interfacial properties. Moreover, the SRRPC exhibited the highest residual bond strength compared with the other steel reinforced concretes. The five-stage model and the modified tri-linear model were proposed to describe the average bond stress-slip relationship. It was found that the five-stage model had an excellent accuracy while the modified tri-linear model can reasonably predict the average bond stress-slip relationship. Finally, a comprehensive analytical model was developed to investigate the local longitudinal strain of the shape, bond stress and relative slip.

Experimental and numerical study on shear performance of grouped bolt–UHPC pocket connections under static loading

Prefabricated steel–ultra-high-performance concrete (UHPC) composite beams using grouped single embedded nut bolts (SENBs) in full-depth precast slabs are a competitive alternative for accelerated bridge construction (ABC), with advantages such as shortening on-site construction time, improving structural quality, and conveniently dismantling deteriorated components. In this study, a systematic experimental and numerical study was conducted to investigate the shear performance of grouped bolt–UHPC pocket connections. The experimental results indicated that a dense arrangement of SENBs led to a slight reduction in shear capacity (less than 5%) and ductility. Increasing the number of bolts in the pockets can effectively improve the shear performance of the connections. Significant reductions in the per-bolt ultimate shear capacity and initial shear stiffness were observed for specimens with multi-row bolts compared to their single-row counterparts. In addition, specimens with grouped bolt–UHPC pocket connections achieved a considerable shear capacity, low shear stiffness, and better slip capacity than those with monolithic casting slabs. Based on the validated finite element models, extensive parametric studies were carried out. Accordingly, a conservative recommendation of 4d (d is the bolt diameter) was suggested as the minimum bolt spacing in both the longitudinal and transverse directions. Furthermore, more accurate formulae were developed to predict the ultimate shear resistance and load–slip relationship of the grouped bolt–UHPC pocket connections in prefabricated steel–UHPC composite beams.

Shear-bond behavior of nanocellulose-modified SHCC composite slabs: Translating material-level capacity into improved structural performance

Owing to their exceptional tensile properties, strain-hardening cementitious composites (SHCC) are indispensable for building and maintaining sustainable and resilient civil infrastructure. As such, to propel the structural implementation of SHCC, it is critical that their intriguing tensile characteristics be effectively translated into improved structural performance. Herein, we capitalize on the intrinsic pseudo-ductility of a novel SHCC—incorporating nanocellulose fibers and post-consumption glass powder (hereafter referred to as “nSHCC-GP”)—to mitigate shear-bond failure caused by the relative slip between steel and concrete in composite deck slabs. Twelve full-scale composite deck slabs, six with conventional high-performance concrete (HPC) incorporating steel mesh and six steel-mesh-free nSHCC-GP slabs, were subjected to monotonic bending. With the concrete for both slab sets designed for similar compressive strengths, the influence of concrete type (HPC or nSHCC-GP), decking profile (trapezoidal or reentrant), and shear span (520–770 mm) on the flexural capacity and shear-bond resistance was examined. The use of nSHCC-GP as a concrete topping improved the flexural capacity of composite slabs by >50 % and the shear-bond resistance by up to 40 %. Thus, the strain-hardening characteristics of nSHCC-GP were effectively translated into the structural scale, providing steel-mesh-free, high-performance composite deck slabs.

Unraveling the self-annealing behavior of cryo-rolled Cu-Fe-P alloy sheets: Evidence and implications

Deformation of Cu-Fe-P alloys at cryogenic temperature (CT) leads to the evolution of a complex microstructure, which includes deformed and recrystallized grains, strain localizations (SLs), and heterogeneous deformation. In this study, specimens of Cu-Fe-P alloy were subjected to cryogenic rolling (CR) at reduction ratios (RR) of 20, 40, 60, and 80%. The microstructural evolution of the CR specimens was characterized using electron back-scattered diffraction (EBSD) and high-resolution transmission electron microscopy (HR-TEM). Severely deformed CR specimens showed SLs, which formed predominantly in the Copper and S oriented grains. After deformation, the CR specimens exhibited self-annealing behavior, which is also referred to as static recrystallization (SRX). Self-annealing at room temperature (RT) caused grain nucleation at the deformed grain boundaries (GBs) and at the SLs. The nucleation of new grains was attributed to both discontinuous SRX (DSRX) and continuous SRX (CSRX) phenomena. The characteristics of DSRX and CSRX grains were analyzed based on transmission Kikuchi diffraction (TKD) and HR-TEM investigations. DSRX grains were surrounded by high-angle GBs, whereas CSRX grains showed sub-boundaries with no dislocations inside. The as-received Cu-Fe-P specimen showed a weak plane-strain texture that intensity increased with an increase in the RR. The CR-80 specimen showed the highest-intensity for plane-strain texture components. SRX at the SLs showed preferential formations of Copper, Brass and S-nucleated grains in the CR-80 specimen. In this study, crystal plasticity finite element method (CPFEM) was used to calculate the stored energy, relative slip activity and texture fractions for the CR specimens. Copper and S oriented grains showed the occurrence of predominant single-slip systems near the severely deformed regions which was the primary cause of SLs formation.

Tangential contacts of three-dimensional power-law graded elastic solids: A general theory and application to partial slip

New technologies in additive manufacturing have enabled the cost-effective production of gradient materials with desired multifunctional properties. In mechanical engineering, such functionally graded materials (FGMs) are often used within mechanical joints, as they ensure higher strength as well as wear resistance and prevent fretting fatigue. However, due to the variations in their composition and structure, theoretical predictions of their contact-mechanical behavior are significantly complicated. In this work, a general theory for solving tangential contacts between 3D power-law graded elastic solids of arbitrary geometry is presented. For multiple contacts, such as those occurring between two nominally flat but rough half-spaces, the well-known Ciavarella–Jäger theorem is established accompanied by a discussion of tangential coupling. Nevertheless, the focus of the work is on axisymmetric single contacts under arbitrary unidirectional tangential loading, for which closed-form analytical solutions are derived based on the Mossakovskii–Jäger procedure. In comparison to the results of common approximate methods, the solutions include the non-axisymmetric components of tangential displacements, which are indispensable for the accurate determination of the relative slip components and thus the surface density of frictional energy dissipation in the partial slip regime. Although a simplified approach is used for the calculation of the dissipated energy density, the results in the limiting case of homogeneous material are in excellent agreement with those from a full numerical computation. As an application example, the complete solutions for the tangential contact of parabolically shaped power-law graded elastic solids in the partial slip regime are derived and the influence of the material gradient as well as Poisson’s ratio on the surface density of dissipated energy is investigated.

Modelling of rolling contact fatigue under various interface conditions

This study presents the results of modelling the rolling contact of the elastic sphere and the elastic half-space in the presence of a thin intermediate viscoelastic layer which properties are described by an elastic nonlinear Winkler body in the normal direction and a viscoelastic Maxwell body in the tangential direction. The analytical–numerical approach for the estimation of contact fatigue damage, accumulated in the elastic half-space under rolling friction conditions, is developed. The proposed model can be used, in particular, to study the effect of mechanical properties of the friction modifiers (elastic moduli and relaxation times) and its thickness as well as the relative slippage on the formation of the surface and under surface contact fatigue cracks in rails. The results of the analysis can also be applied for the estimation of efficiency of solid lubricants in rolling contacts under given operating conditions.

Research and application of time-varying law of anchoring force of split-set bolt based on field measurement

Split-set bolt is widely used in supporting stope and roadway surrounding rock in metal mines. The maximum pull-out force generated by the relative slippage between the anchor bolt and the drill hole can serve as an indicator for assessing its anchoring force, and the anchoring force of the grouted anchor bolt exhibits certain regularity over time. This pull-out test was carried out at different time points after the construction of the split-set bolt by using the drawing equipment, and the variation law of its anchoring force with time was studied. The anchoring force on per unit area of surrounding rock is selected as a evaluation parameter, and the reinforcement support scheme of surrounding rock is optimized from the aspects of stress release of surrounding rock in the initial stage of excavation and stability of anchoring force on per unit area of surrounding rock. The convergence monitoring measurement method of roadway surrounding rock is adopted, and the same bolt drawing area is selected to verify the feasibility of the reinforcement support scheme. The effectiveness of the reinforcement scheme is verified by monitoring and comparing the roof subsidence and the lateral convergence of two walls between two different support schemes.

Systematically Study the Tensile and Compressive Behaviors of Diamond-like Carbon.

It is important to understand the mechanical properties of diamond-like carbon (DLC) for use not only in frictionand wear-resistant coatings, but also in vibration reduction and damping increase at the layer interfaces. However, the mechanical properties of DLC are influenced by the working temperature and its density, and the applications of DLC as coatings are limited. In this work, we systematically studied the deformation behaviors of DLC under different temperatures and densities using compression and tensile testing of DLC by molecular dynamics (MD) methods. In our simulation results, the values of tensile stress and compressive stress decreased and tensile strain and compressive strain increased as the temperature increased from 300 K to 900 K during both tensile and compressive processes, indicating that the tensile stress and tensile strain depend on the temperature. During the tensile simulation, Young's modulus of DLC models with different densities had a different sensitivity to the increase in temperature, and the DLC model with a high density was more sensitive than that with a low density, which was not seen in the compression process. We conclude that the Csp3-Csp2 transition leads to tensile deformation, while the Csp2-Csp3 transition and relative slip dominate compressive deformation.

Experimental studying structural behavior of shear connector in cold-formed steel - concrete composite beam

An experimental push-out test was carried out on 12 specimens in 6 groups to investigate the mechanical behavior of shear connectors in cold-formed steel-concrete composite beams. Specimen groups have differences in rivet spacing, shear connector spacing, tab aspect, and rebar through shear connectors. The mechanical behavior was evaluated through quantities such as shear resistance, relative slip between the steel beam and concrete slab, and failure modes. The results show that screw significantly affects the mechanical behavior of shear connectors in cold-formed steel-concrete composite beams.

Study on Load–Slip Curve of a PBL Shear Key at a Steel–Concrete Composite Joint

The steel–concrete composite truss adopts a new type of steel-concrete composite joint with high rigidity and load-carrying capacity. In order to more conveniently and clearly grasp the working mechanism of Perfobond Leiste (PBL) shear keys in the core area of new composite structures such as steel–concrete composite trusses, the lack of strong theoretical support for the theoretical formula of load–slip relationships in the entire loading process of single PBL shear keys is solved. By proposing a straight–curved–straight three-stage simplified load–slip curve with respect to the PBL shear key, the stress process of the PBL shear key is divided into three stages—the elastic stage, plastic stage, and strengthening stage—based on the compressive yield and failure critical point of tenon concrete in the shear key. With reference to the calculation method of the bearing capacity of the order pile under horizontal loads and by calculating the shear stiffness of the shear key, a theoretical formula suitable for separating the load–slip relationship of a single PBL shear key in the entire loading process of the ear plate composite joint is proposed. The results show that, in the elastic section, the slope of the curve is related to the concrete reaction coefficient and the material parameters of the penetrating steel bar; moreover, in the strengthened section, the coefficient is related to the shear modulus of the penetrating steel bar, and a more uniform length distribution of the penetrating steel bar between the two joint plates will improve the initial stiffness of the PBL shear key to a certain extent. The results of the proposed method are in good agreement with the finite element results and experimental values. This research study’s results can provide a convenient design method for the design of the internal PBL shear keys of new composite structure joints, promoting the promotion and application of new composite structures and advancing the development of the engineering field.

Experimental investigation on mechanical behavior of T-type perfobond rid shear connectors under combined shear and tension

The stress of shear connectors becomes more complicated as the span length of steel-concrete composite bridges increases. To bear the great shear and uplift forces, a T-type perfobond rib (T-type PBL) shear connector with sufficient stiffness and ductility is proposed. While the shear behavior of T-type PBL connectors has been evaluated in previous studies, its mechanical performance under combined shear and tension is not well understood due to the particular shape and numerous impact factors. Therefore, one pull-out test considering pure tension and seven modified push-out tests considering combined shear and tension were carried out to investigate the failure mode, bearing capacity, and load-slip behavior of T-type PBL connectors under combined actions. The pull-out test was performed to determine the tensile resistance, followed by a series of modified push-out tests with constant horizontal tension to investigate the structural behaviors. Additionally, the effects of the rib height, flange width, and hole numbers were evaluated. Based on the test results, conical failure surfaces formed from the flange of the T-type PBL to the concrete surface for all specimens, and the concrete failure angle was approximately 32°. The bearing capacity of the specimen improved by 26% when the perfobond rib height increased from 100 mm to 120 mm, but the flange width barely had any effect. The capacity of 1-hole specimen dropped by 20% while 2-hole specimen increased by 8% compared to the standard specimen, which may relate to the distance between adjacent holes. Increasing the rib height by 25% and 50% reduced the initial relative slip (S90) by 30% and 32%, respectively, indicating the improvement in initial stiffness. Generally, the pull-out resistance of the T-type PBL shear connector was enhanced by increasing the flange width, rib height, and number of holes. An evaluation equation considering the hole number and hole spacing was suggested for the bearing capacity of T-type PBL shear connectors under the combined actions. The validity was verified by test results, with a calculated-to-test-result ratio of 1.12 and standard deviation of 0.15. This study could enhance the understanding of the behavior of T-type PBL connectors under the combined actions, and promote the potential application in long-span composite bridge decks.

Analysis of the dislocation activity of Mg-Zn-Y alloy using synchrotron radiation under tensile loading.

An understanding of deformation behavior and texture development is crucial for the formability improvement of Mg alloys. X-ray line profile analysis using the convolutional multiple whole profile (CMWP) fitting method allows the experimental determination of dislocation densities separately for different Burgers vectors up to a high deformation degree. A wider use of this technique still requires exploration and testing of various materials. In this regard, the reliability of the CMWP fitting method for Mg-Zn-Y alloys, in terms of the dislocation activity during tensile deformation, was verified in the present study by the combined analysis of electron backscatter diffraction (EBSD) investigation and visco-plastic self-consistent (VPSC) simulation. The predominant activity of non-basal 〈a〉 dislocation slip was revealed by CMWP analysis, and Schmid factor analysis from the EBSD results supported the higher potential of non-basal dislocation slip in comparison with basal 〈a〉 dislocation slip. Moreover, the relative slip activities obtained by the VPSC simulation also show a similar trend to those obtained from the CMWP evaluation.

Microseismicity clustering and mechanic properties reveal fault segmentation in southern Italy

We analyze the clustered microseismicity recorded over more than one decade in the Irpinia region, an active seismic area in Southern Italy. We studied the spatiotemporal properties of rate, source parameters and slipping mechanisms of the clustered seismicity in relationship with local medium properties and the deformation signal. Spatial pattern of both medium properties and source parameters indicates a segmentation along strike of the fault network with evidence of a high- and a low-coupling segments separated by a region with diffused microseismicity and high b-value. The high-coupling segment shows high fraction of clustered seismicity, low b-value, high relative coseismic slip, low Vp/Vs (1.7–1.75) and near-repeating earthquakes. We find that the seismicity in this high-coupling segment is triggered by non-tectonic loading, such as the recharge of a karst aquifer, suggesting a system close to critical conditions. The high-coupling segment can be identified as a potential strong motion area for future earthquakes, while the intermediate segment can mark the edges of an extensional transfer zone, which can act as a discontinuity for slip propagation. The low-coupling segment is the same where the Ms. 6.9, 1980 Irpinia earthquake nucleated. This segment shows today both relatively high b-values and high coseismic slip, but above all it shows temporal dependencies in its properties, which leads us to pay attention to it for the future spatiotemporal evolution of microseismicity in this area.

Hysteretic behaviors of Pingshenke Dou-Gong brackets of ancient timber buildings under different loading directions

To study the effect of loading directions on the seismic behavior of Dou-Gong bracket, numerical analysis was conducted on two Pingshenke Dou-Gong brackets under the overhanging direction (DG-1) and width direction (DG-2). The simulated hysteretic characteristic, stiffness degradation, and energy dissipation of Dou-Gong brackets were compared and validated by the test results. The horizontal displacement and relative slip of Dou-Gong components were discussed. Besides, parameter analyses considering the loading direction, wood grain direction, and material properties were performed. Results indicate that DG-2 has higher stiffness, bearing and energy dissipation capacity than DG-1, but poor deformation capacity. The positive component displacement of DG-1 is greater than DG-2, while the negative is the opposite. The relative slip between Da-Dou and Pingban-Fang is larger than other components. The overhanging and width direction are the most adverse direction for DG-1 under positive and negative load, respectively. DG-1 has the largest bearing capacity when Da-Dou is friction in the longitudinal surface under the tangential grain direction, but the grain direction has little influence on DG-2. The larger the friction coefficient and compressive strength, the greater the bearing capacity, but the initial stiffness is not improved. The elastic modulus has little effect on the initial stiffness and bearing capacity of Dou-Gong bracket.

Experimental study on the flexural performance of steel-concrete composite section of self-anchored suspension bridge

In order to study the flexural performance of the steel-concrete composite section of self-anchored suspension bridge, a test model of the steel-concrete composite section was fabricated according to the scale of 1 : 3 based on the Wushui Bridge, and a four-point negative bending test was carried out. The results show that the residual displacement ratio is 0.7%, and the experimental model is in the elastic stage under the design load condition, which incidate that the component is safe under normal service condition. Under the overloading condition, the residual displacement ratio is 19%, the experimental model is in the elastic-plastic stage, but the stress of materials still meets the requirements. Under the two conditions, the deformation angle of the composite section is small and the stiffness transition is stable. The relative slip between the steel plate and concrete in the composite section is small (no more than 0.25 mm). The stress in the top steel plate and bottom steel plates of the composite section are gradually decreases during the transfer from the steel stiffening beam to the concrete side. The design of the steel-concrete composite section is reasonably loaded, and the mechanical properties are smoothly transferred.

Experimental and Analytical Investigation on Flexural Behavior of High-Strength Steel-Concrete Composite Beams

This research investigated the flexural behavior of high-strength steel (HSS)—concrete composite beams. The effect of concrete strength on the load-deflection behavior, flexural capacity, and ductility of HSS—concrete composite beams was investigated. Four full-scale HSS—concrete composite beam specimens were tested under static load. The test results demonstrate that the failure mode of HSS—concrete composite beams is flexural failure of the steel member and compression fracture of concrete at mid-span. The HSS—concrete composite beam exhibits good mechanical performance and deformation behavior. The ultimate bending strength and ductility of HSS—concrete composite beams were improved with the increased concrete strength. The theoretical results demonstrate that the simplified plastic method overestimates the ultimate bending strength of HSS—concrete composite beams. The main reason is that only a small part of the steel beam bottom shows plastic strengthening, which is not enough to make up for the strength loss caused by the steel near the neutral axis failure to yield and the relative interface slip. The nonlinear method based on material constitutive model could predict the load-bearing capacity accurately. After analyzing the ultimate bending capacity of 192 sample beams, the simplified plastic method was modified, and the theoretical method for ultimate bearing capacity of HSS—concrete composite beams was proposed.

Experimental study on the direct shear behavior of multiple shear keys at concrete glue joints subjected to uneven normal stress

Ten ‘Z’-shaped shear specimens were fabricated to study the effect of uneven normal stress on the shear performance of glue joints. The test parameters included the roughness of the joint surface, the level of lateral normal stress, and the uniformity of lateral normal stress. The crack development, failure mode, ultimate bearing capacity, and relative slip data of the specimens were recorded in detail, and the load-strain curve and load-relative slip curve were plotted according to the test results. The results show that all specimens were brittle failures. After roughening the surfaces of the joints, the deformation resistance, overall strength, and overall stiffness of the specimens all got a little better. Increasing the level of lateral normal stress and the uniformity of lateral normal stress, the cracking load and ultimate bearing capacity of the specimen were increased. In addition, a coefficient η that quantifies the degree of uniformity of the lateral normal stress was defined, and a formula for predicting the direct shear bearing capacity of glue joints was proposed. The results show that the average ratio between the calculated values from the proposed formula and the test values was 0.96.