Soft Interlayer Research Articles

Tensile modeling of titanium-aluminum composite with a wave profile of a welded joint and local melts

Finite element simulation of tensile deformation of titanium-aluminum composite D20 – AD1 – VT6 was carried out. The joint boundary had a wave profile and local melts. 3D modeling of deformation of the composite D20 – AD1 – VT6 with a wave profile of the welded joint was carried out using the SIMULIA / Abaqus software. The relative thickness of the AD1 interlayer and the area of the melt were varied during the simulation. To determine for metal hardening during plastic deformation and the failure deformations for aluminum and aluminum alloy both Johnson-Cook deformation and fracture models was used. The influence of the size of the local melting zone and thickness of the soft interlayer on the distribution of stresses and strains in the composite is shown. The wave profile of the boundaries junction leads initially to localization of plastic deformation in the aluminum interlayer in the zone of free surfaces of the sample near the interface with the titanium alloy. A change in the length of vortices with areas of local melting near the tops of the wave profile from 0.3 to 0.8 mm had little effect on the profile of the curves “equivalent stress-absolute elongation of the sample”.

Obliquely incident P-SV wave scattering by multiple structures in layered half space using combined zigzag-paraxial boundary condition

Seismic wave scattering by multiple structures in layered half space is a classically multiple scattering problem in infinite domain. The computationally efficient substructure method is commonly adopted to solve this problem, because the structures can be modelled by the finite element scheme with the combination of the high-accuracy boundary condition to provide the dynamic stiffness of the truncated infinite rock or soil media. However, it is difficult to establish a high-accuracy boundary condition for multiple scattering problem in layered half space. In this paper, a combined zigzag-paraxial boundary condition is presented, and it is coupled with the seismic wave input method, as well as with the finite element scheme, to form the substructure method for solving the multiple scattering problem in layered half space. To verify the proposed substructure method, it is firstly applied to obliquely incident P-SV wave scatterings by a canyon, a cavity and an alluvial basin in homogeneous half space. The results are validated by comparing with several existing analytical and numerical methods. To demonstrate the capability of the proposed substructure method, it is finally applied to obliquely incident P-SV wave scattering by multiple tunnels in layered half space, and the effects of twin tunnels, soft soil interlayer and a V-shaped canyon on the structural response are discussed.

Analytical higher-order-theories for noise reduction analysis of viscoelastic composite multilayered shells

The noise transmission of aeronautical panels is an important phase of the design process of an airplane. In this work an analytical Navier-type solution, based on higher-order layer-wise shell models, is proposed for the analysis of the sound insulation of laminated panels. The considered multilayered structures are laminated with cross-ply composite layers embedded with interlaminar viscoelastic sheets. The use of the soft interlayers permits to have a passive insulation effect in the study of the sound transmission. In order to take into account the frequency depedent properties of a realistic viscoelastic layer, the damping behavior is modeled through a fractional derivative Zener model. The Rayleigh integral method is used to extrapolate the acoustic indicators for the sound transmission analysis. Some results are presented to validate the efficiency of the present approach, comparing the present solutions with others taken from the literature.

Flash sintering of 3YSZ and in-situ joining with 304 stainless steel using copper as an interlayer

We demonstrated the feasibility of flash sintering of 3 mol% yttria-stabilized zirconia (3YSZ) and its in-situ joining with metal by applying an electric field. Herein, rapid densification of 3YSZ and its robust joining with 304 stainless-steel by using copper as a soft interlayer were achieved under a preset alternating current/direct current (AC/DC) field within only 1 min at 950 °C. Nevertheless, defects were present in the microstructures of the joints under the application of a single AC or DC field. The sintering-joining mechanisms were addressed in view of electric field-induced Joule heating and internal electrochemical reaction.

Research progress in the mining technology of the slowly inclined, thin to medium thick phosphate rock transition from open-pit to underground mine

Abstract This paper takes the deep ore body of Yunnan Phosphate Group Co. Ltd, the largest open-pit chemical mining enterprise in China, as the research background, and systematically introduces the technical problems recognised by many Chinese researchers in the past eight years on the open-pit to underground mining of gently inclined thin to medium-thick ore bodies with a soft interlayer. It shows that the mining of open-pit transferred to underground is a complex engineering system, and the underground stope surrounding rock and overlying strata present a nonlinear failure process. Through mining process innovation, mining method innovation and improvement, research was undertaken on new processes and technologies for phosphorus mining under complex conditions. The relevant research results not only have important economic value and academic significance for Yunnan Phosphate Group Co. Ltd. but also have important guidance and impetus to the exploitation of a large number of similar phosphate resources in China.

Deflection Laws of Gas Drainage Boreholes in Interbedded Soft and Hard Seams: A Case Study at Xinzheng Coal Mine, China

Coal and gas outbursts can lead to serious disasters in coal mines. The drilling of boreholes to predrain the gas is an effective measure for preventing such accidents. However, due to the complexity of the geological situation, the drilling trajectory often deviates from the design trajectory, resulting in poor gas extraction. To solve the problem of gas drainage borehole deflection, an analytic hierarchy process (AHP) model is established based on geological factors, technical factors, and human factors. The AHP model is used to rank the weights of various influencing factors, and the analysis is combined with a drilling model and engineering examples. Finally, the results show that soft and hard interlayers are the most important factors affecting the deflection of the borehole. The rock drilling model is mainly affected by the formation forces. The regularity of the change in the azimuth angle during drilling is not obvious when the angle of the encountered layer is less than some critical value. When the borehole is skewed downward, the deflection angle ranges from 0 to 4°, and the deflection of the borehole occurs mainly at the interface of the rock layers. When the angle of the encountered layer is greater than the critical value, the borehole is skewed upward, with a deflection angle of 0–6°, and the deflection occurs at the rock interface. The trajectory curve obtained by theoretical predictions from field data is found to be consistent with that of an actual project.

Roof Failure Mechanism and Control Technology of Large Section Open‐Off Cut in Soft Rock Strata with Thin Thickness

The open‐off cut is used for equipment installation of working face before underground mining, and its sectional size is larger than that of the mining roadway. Therefore, the stability of open‐off cut surrounding rock determines whether the panel can be put into operation. To solve the roof instability of open‐off cut in the Wanli No.1 coal mine, the roof failure mechanism of open‐off cut under weak composite rock strata with thin thickness was studied by field monitoring, theoretical analysis, and numerical simulation. First, the characteristics of surrounding rock and the basic law of strata behaviors were obtained by detailed field monitoring. Afterward, FLAC3D numerical simulation and mechanical analysis were used to obtain the main mechanical control parameters of surrounding rock instability, and the existence of a soft interlayer above the roof is the main cause of roof instability. Based on this, the supporting parameters of the open‐off cut were optimized and adjusted. The optimized parameters were applied to the adjacent 31207 open‐off cut. The engineering practice showed that the optimized supporting parameters have an ideal control effect on roof stability.

Theoretical and experimental study on identification of the soft interlayer in coal mine roadway roof

Theoretical and experimental study on identification of the soft interlayer in coal mine roadway roof

Flash Sintering of 3YSZ and In-Situ Joining with 304 Stainless Steel Using Copper as an Interlayer

We demonstrated the feasibility of flash sintering of 3 mol% yttria-stabilized zirconia (3YSZ) and its in-situ joining with metal by applying an electric field. Herein, rapid densification of 3YSZ and its robust joining with 304 stainless-steel by using copper as a soft interlayer were achieved under a preset alternating current/direct current (AC/DC) field within only 1 min at 950 °C. Nevertheless, defects were present in the microstructures of the joints under the application of a single AC or DC field. The sintering-joining mechanisms were addressed in view of electric field-induced Joule heating and internal electrochemical reaction.

Stability analysis of an expansive soil-embankment slope with a soft interlayer

The soft interlayer in the foundation is one of the most important factors that induce landslide in the expansive soil-embankment slope. The existence of large soft layers significantly reduces the overall stability of the slope, and they have the tendency to further develop into a sliding surface. To investigate the influence of the soft interlayer on expansive soil slopes, taking the high-fill embankment slope with a soft interlayer in the Baoshan area of Yunnan Province as an example, the causes and strength effects of the soft interlayer are analyzed via landslide investigation, laboratory test, and numerical simulation, and the stability and instability mode of the slope are studied. Results indicate the following: ① The soft interlayer is located at the bottom of the weathering layer within the depth of the atmosphere. Its strength is less than that of the expansive soil on both sides. ② The overall stability of the slope and the shape of the sliding surface are controlled by weak interlayers, and its strength greatly impacts the damage scope of the slope. When the strength is high, it appears as a collapse of the fill area, and when the strength is extremely low, it appears as the overall sliding of the slope. Using the residual strength as the calculation parameter of the weak layer reflects well the actual stability and failure mode of the slope. ③ Results of soil layer parameter sensitivity analysis indicate that the internal friction angle of the soft interlayers has the most significant effect on slope stability. Using the lightweight embankment fill can effectively improve the stability factor of embankments.

Statistical Simplification and Discrete Element Analysis of Seepage Model for Complex Fracture Network of Dam Foundation Rock Mass

In this paper, a model of seepage in a fracture network is analyzed by taking the rock mass of the dam foundation of Datengxia Hydropower Station, the No. 1 Project of the Ministry of Water Resources, as an example. Complex discontinuity systems are present in the rock mass of the Datengxia Hydropower Station dam foundation, and faults, soft interlayers, and structural fracture systems intersect with one another. A multi scalar structural analytical scheme that combines the deterministic analysis of large scale geological structures (i.e., faults and weak interlayers) with the statistical simulation of random discontinuities (i.e., structural fractures) is proposed in this paper to reduce the difficulty and uncertainty of the analysis of rock masses with complex structures. In particular, a chain analytical method from dominant group definition to statistical parameters (i.e., spacing and occurrence) is formed for the structural fracture system. In this way, the analysis of rock masses with complex structures is simplified to a regular and feasible scientific problem that could be solved by rock mass simulation. We then establish a seepage model of the rock mass in dam section 29# in UDEC by adopting the above structural simplification scheme. The quantitative analysis of seepage in complex structured rock masses under normal water storage and dynamic conditions is then realized. Results show that the statistical simplification of the rock mass structure and discrete element simulation can efficiently solve the seepage analysis of complex rock masses. The negative influence of pore pressure caused by seepage on the rock mass, especially under dynamic conditions, should be emphasized for safety assurance in the stability analysis of dam foundations.

Microstructure and Mechanical Properties of Ti-6Al-4V Alloy/Interstitial Free Steel Joint Diffusion Bonded with Application of Copper and Nickel Interlayers

The application of interlayers in solid-state diffusion bonding is considered for facilitating improved joint strength as well as optimizing the bonding parameters. In case of dissimilar metals, the interlayers are preferred to promote diffusivity by reducing the metallurgical incompatibility. In the present work, the effect of formation of intermetallics at interfaces of the dissimilar joints between Ti-6Al-4V (Ti64) alloy and interstitial free (IF) steel, produced by direct diffusion bonding as well as by using the interlayers of copper and nickel, was evaluated. The diffusion bonding experiments were performed in a temperature range of 1023 K to 1223 K, under a constant pressure of 10 MPa for 10 minutes, in high vacuum conditions. It was observed that diffusion of interlayer(s) into the base metals increased with bonding temperature, which led to the increase in intermetallic layers at the joint interface. At 1223 K, the influence of interlayer on microstructure of interfaces was reduced by complete diffusion of interlayers and subsequently led to the interdiffusion of base metals. The maximum shear strength of ~ 186 MPa was recorded for the bonding performed using a nickel interlayer at 1023 K. Detailed microstructure analysis, nanoindentation measurements and shear tests suggest that the presence of a thin layer of hard TiFe intermetallic at the interface has no adverse effect, but a soft remnant interlayer can deteriorate the shear properties of the diffusion-bonded joints.

Numerically investigation on blast-induced wave propagation in catastrophic large-scale bedding rockslide

Large-scale landslides as a common geological hazard can be easily triggered by natural factors, while it is extremely difficult to be activated by anthropolical blasting operations. The paper presents a comprehensive analysis of characteristics of stress wave propagation in a blasting-triggered large-scale rockslide, termed Wangshan–Zhuakousi Landslide, to investigate the effect of blasting wave on multi-layer interface condition. A detailed analysis of the propagation of P wave in the filling joints was conducted to verify the reliability of the analytical model and the deterioration characteristics of the weak interlayer. The results indicate that the reflection tensile wave can be formed when P wave propagates from the basalt across the tuff interlayer. The theoretical equation for damage assessment of soft rock interlayers is proposed, which can be adopted in calculating the additional stress of soft rock mass in blasting operation. It is found that the material density is the most influential factor in attenuation rate. Besides, the longitudinal wave velocity of materials and the period of incident waves perform the identical effect on the attenuation rate. It is demonstrated that the cumulative failure of tuff layer plays a crucial role in triggering successive sliding. According to the modelling, the tuff interlayer appears to be in a compressed state before the complete damage under P-wave propagation. The locally tensile behaviour can be observed after the complete damage of the tuff. The underlying tuff interlayer forms a discontinuous cumulative damage zone, which significantly triggered major ruptures and destabilized the original bedding rock slope. This paper could prove new insight towards the enforcement of risk assessments and mitigation countermeasures for blasting-induced landslide.

Blast loads and nonlinear vibrations of laminated glass plates in an enhanced shear deformation theory

The nonlinear dynamic response of a laminated glass plate under the pressure generated by a blast wave, described via the Friedlander’s model, is investigated. In order to account for the heterogeneity of the laminated package, composed by two glass plies sandwiching a thin and soft polymeric interlayer, a geometrically nonlinear, third-order shear deformation theory with rotary inertia is used. Within the quasi-elastic approximation, the constitutive response of the polymer is described by its secant elastic moduli for short-term loading at room temperature, while the dissipation associated with its viscosity is taken into account through an equivalent effective damping. The problem is discretized by a reduced-order model retaining 40 degrees of freedom and the first four vibration modes, which are the ones receiving most of the energy from the blast. A geometrically nonlinear damping model is introduced to simulate the increase in damping associated with large-amplitude oscillations of the plate, which results from the interaction between the large deflections of the glass plies and the viscosity of the interlayer. Forced nonlinear vibrations around the frequency of the fundamental mode are also investigated, to complete the study of the nonlinear dynamics. The results highlight the importance of the nonlinear effects of damping, which can almost halve the deformations and stresses in laminated glass with respect the linear case at high levels of excitation, while still remaining within the limits of material strengths.

Buckling Failure Mechanism of a Rock Dam Foundation Fractured by Gentle Through-Going and Steep Structural Discontinuities

The failure mechanism analysis of dam foundations is key for designing hydropower stations. This study analyses the rock masses in a sluice section, which is an important part of the main dam of the Datengxia Hydropower Station currently built in China. The stability of the sluice rock masses is predominantly affected by gentle through-going soft interlayers and steep structural fractures. Its foundation failure mechanism is investigated by means of a numerical method, i.e., Universal Distinct Element Code (UDEC) and the geomechanical model method. The modeling principle and process, and results for the rock dam foundation are introduced and generated by using the abovementioned two methods. The results indicate that the failure mechanism of the foundation rock masses, as characterized by gentle through-going and steep structural discontinuities, is not a conventional type of shear failure mechanism but a buckling one. This type of failure mechanism is verified by analyzing the deformation features resulting from the overloading of both methods and strength reduction of the numerical method.

Оценка степени контактного упрочнения сварных соединений трубных сталей

The metal welding is accompanied by the formation of mechanically non-homogenous sections of welded connection. The pipeline welded connections also have sections, which are different in structure, chemical composition and mechanical properties. The mechanical inhomogeneity affects the load bearing capacity of welded connection and the structure as a whole, which is necessary to take into consideration when performing calculation analysis. So far, the specialists have established the dependencies in assessment of welded connection strength with various types of heterogeneous sections. However, this phenomenon has received little attention in case of pipeline welded connections made of low carbon steels. The existing theoretical models do not reflect actual anisotropy of mechanical properties of the welded connections and weld adjacent zone. The present study considers the model of welded connections of K56 pipe steels with various strength characteristics of sections of welded seam and weld adjacent zone, without defects. The assessment of mechanical inhomogeneity influence on load bearing capacity of welded connections was performed by applying the finite-element modelling of its stress-strain state. The developed numerical model helps to determine and optimize the criteria of testing of full scale samples of pipe steel welded connections with regards to the implementation of local strengthening effect. The research results demonstrated that the degree of contact strengthening in welded connections with X-shape grooving is higher than in welded connections with V-shaped grooving by 8 % at similar relative thickness of soft interlayer. The suggested numerical model can be applied for detailed calculations of pipelines with regards to the mechanical inhomogeneity of its welded connections.

Instability Mechanism of a Multi-Layer Gangue Roof and Determination of Support Resistance Under Inclination and Gravity

A multi-layer gangue roof of a steeply dipping coal seam with a large mining height face area was analyzed using physical simulation, numerical simulation, theoretical analysis, and field measurement methods to evaluate the roof deformation and the mechanisms associated with the instability of the hard gangue and soft coal interlayer. The results indicated that the first weighting step of the multi-gangue roof was larger than that of a non-gangue roof, but periodic weighting steps were similar. The overburden collapse height was lower in the multi-gangue roof than in the non-gangue roof due to the buffering and supporting function of the collapsed gangue. Moreover, the failure of the coal interlayer was the key factor in the collapse of the multi-layer gangue. A mechanical model was established for the hard gangue and soft coal interlayer based on a revised Prandtl squeezing theory. The limited load of the interlayer and maximum resistance of the shield support was thus modeled. The maximum resistance of the support increased with the dip angle of the seam and burial depth. It also increased with the interlayer thickness at thicknesses below 2.75 m. It reached a peak when the interlayer thickness was between 2.75 and 3 m and exhibited a decreasing trend when the thickness was greater than 3 m. The results were confirmed using physical simulation and a field test. Certain measures were proposed to control the stability of the gangue roof, including zoning control of the mining height and resistance and advancing the support while maintaining roof contact, thus ensuring the integrity of the support and surrounding rock system.

Effect of Ti interlayer thickness on mechanical properties and wear resistance of TiZrN coatings on AISI D2 steel

In the tool industry, adding a soft metallic interlayer to enhance the adhesion of hard coatings is a common practice. This study investigated the effect of Ti interlayer thickness on the residual stress, adhesion strength and wear resistance of TiZrN coatings. The feasibility of using stored elastic energy as an index of wear resistance of the coatings was also studied. The effect of Ti interlayer thickness was evaluated by comparing the mechanical properties of TiZrN films with different Ti interlayer thickness, ranging from 50 to 250 nm. The results showed that the increase of interlayer thickness from 50 to 250 nm reduced the stress of the TiZrN coatings from −5.67 to −3.75 GPa. The optimal Ti interlayer thickness to enhance the adhesion strength of the TiZrN coatings with about 2 μm thickness on D2 steel was 150 nm; however, the adhesion was insignificantly improved compared with the specimen without interlayer. Introducing 250 nm Ti interlayer could slightly increase the wear resistance of the TiZrN coating about 16%, but the adhesion strength of the coating decreased about 6%. The insignificant improvement on mechanical properties and wear resistance of the TiZrN coatings by the Ti interlayer were mainly attributed to the high residual stress of TiZrN top layer. For the coatings with high residual stress (>−4.0 GPa), the stress relief by adding a metal interlayer is limited and insufficient to enhance adhesion strength or wear resistance. Other approaches that can directly lower the intrinsic growth stress in hard coatings may be more effective.

Increase of Weld Joint Efficiency of the Combined Band of a High-Speed Rotor of an Electric Machine by Local Strengthening

The research shows the possibility of increasing the structural strength of the weld joints of EP517 steel and 36NKhTYu iron-nickel alloy as applied to the combined bandage of the high-speed rotor of an electric machine, due to the effect of local strengthening of the soft interlayer. The technology of electron-beam welding of 36NKhTYu alloy to EP517 steel with free root formation, which allows to obtain narrow welds, is described. The results of metallographic researches and mechanical tests of weld joints with different weld widths are presented, which showed that the structure and properties of the weld metal on samples with different weld widths are almost identical. The tension test results of weld joints demonstrate a significantly greater ultimate tensile stress, compared to the ultimate tensile stress of the weld metal. Also, it was established that, due to the local strengthening phenomena the smaller the weld width, the stronger the welded joint is. In addition, the use of heat treatment after welding allows us to increase the strength properties of the weld metal and the heat-affected zone of the 36NKhTYu alloy, due to the formation of the hardening γ’-phase. The possibility of increasing the ultimate tensile strength of the weld up to 98% of the ultimate tensile stress value of EP517 steel (as the less durable of both welded materials), due to heat treatment and reducing the weld width, is demonstrated.

Acoustic Emission Characteristics of Normal and Layered Concrete Blocks during Dilating/Static Fracture

Static fracturing technology is one of the most effective methods for localized breaking of rock and concrete. Layered concrete and rock structures are commonly seen in engineering applications such as breaking of concrete buildings, stone cutting, and excavation of rock in underground spaces. Therefore, it is essential to study the static fracturing characteristics of layered concrete to ensure the safety of engineering construction processes. In this paper, using acoustic emission (AE) technology and surface displacement monitoring, the deformation and fracturing of ordinary‐strength concrete, concrete with a soft interlayer, and layered concrete (with strength decreasing successively by layer) were studied under the effect of a static (or soundless) cracking agent (SCA). The experimental results indicated that (1) AE activity of the two layered concrete test blocks during static fracturing showed a gradually increasing trend, while that of the ordinary‐strength concrete tended to first increase and then decrease; (2) for the concrete test block with a soft interlayer sandwiched by high‐strength layers, the AE events reached a maximum in the transfer of expansion pressure stage, which accounted for 47.11% of the total value in static cracking; the macroscopic damage to layered concrete test blocks comprising multiple interlaid layers with different strengths mainly occurred in the fracturing stage, during which the AE events and AE energy accounted for 76.22% and 66.94%, respectively, of those in the whole static fracturing process; and (3) the duration of static fracturing prolonged with the increase of the overall strength of the concrete test blocks. The results provide a useful experimental reference for the application of static fracturing technology in the breaking of layered concrete and rock.