Mechanical Properties Of Joints Research Articles

Experimental study on mechanical behavior of the skew joints of shield tunnels under large eccentric compressive loading

The existence of joints in shield tunnel lining rings contributes to various deformation problems, such as leakage, joint opening, cracking and dislocation, which will severely impair the safety and durability of tunnel structures. Laborious experiments having tried to work out the mechanical properties of joints, none have drawn attention to two special segmental joints existing in Shanghai metro shield tunnels, which are obliquely intersecting the frontal plane of the lining ring and thus appear askew compared with the rest. The study investigated segmental specimens with the K-shaped top block and its two adjacent segments, including two skew joints connected using straight bolts. Given two groups of experiments, their mechanical behaviors throughout the failure process when subject to a positive and a negative bending moment showed that the bending moment’s impact on bolt strain, joint opening and segmental rotation could be illustrated by two stages when the bending moment was positive and four when negative. Besides, the joint compression height slightly decreased under both conditions and tended to be stable after bolts yielded when subject to a negative moment. The joint opening angle was proved equal to the sum of the segmental rotation angles from both sides of the joint, indicating the individual segment could be regarded as a rigid body. Moreover, the maximum joint opening width increased linearly with the joint opening angle, so did the deflection at the joint position with the segmental rotation. Above all, the skew joints examined behaved similarly to but differently from those of straight joints as there happened strain advance of the bolt and the concrete at one side and strain lag at the other side, which would probably become more obvious as steeper the oblique angle of the skew joints grew.

Predicting the shear strength of saw-tooth jointed rocks using genetic programming

The geometrical and mechanical properties of joints play an important role in the determination of shear strength of jointed rocks. In this research, we propose a nonlinear model to estimate the shear strength of jointed rocks with unfilled saw-tooth triangular asperities using the basic friction angle φb, the tensile strength of intact rock σt, and the joint inclination angle i under various normal stress σn conditions. In order to propose the new shear strength model, firstly, a rock database of saw-tooth jointed rocks containing experimental and numerical data is established. The experimental data are collected from publications. The numerical data are generated by the particle flow code (PFC) model. Then, the genetic programming (GP) is used to analyze the database to propose the GP shear strength model. The prediction performance of the proposed GP model is tested and compared with that of the Patton model and the Ladanyi and Archambault (LA) model. Comparison results show that the proposed GP model has the best prediction performance compared with the Patton model and the LA model. The proposed GP model can capture the nonlinear shear strength behavior of saw-tooth jointed rocks and its input parameters can be easily estimated.

Contribution of ultrasonic to microstructure and mechanical properties of tilt probe penetrating friction stir welded joint

Tilt probe penetrating friction stir welding (PFSW) was an innovative technology proposed in recent years to avoid the formation of kissing bond in the root of joint. However, with the heat input decreasing, “S” line or zigzag line was easily introduced in the PFSW joint. In this study, ultrasonic enhanced tilt probe penetrating friction stir welding (U-PFSW) was developed to solve this problem and achieve improved joint mechanical properties. The experimental results confirmed that U-PFSW was a potent technology to completely clear the original butt surface, providing a crucial prerequisite for the achievement of high-strength joint. The application of ultrasonic improves the joint tensile strength and fracture elongation from 336 MPa and 4.3% to 359 MPa and 6.8 %, respectively. Furthermore, the strength of stir zone was also increased from 391 MPa in PFSW to 420 MPa in U-PFSW. Analyses of texture and precipitate indicated that the dynamic recrystallization (DRX) and precipitation strengthening were both enhanced by the ultrasonic. Ultrasonic-enhanced DRX enabled a complete elimination of the “S” line; the enhanced precipitation strengthening by vacancy-induced mechanism in U-PFSW was the intrinsic reason for the significantly improved mechanical properties.

Dependence of the microstructure and properties of joints on acoustic intensity during the ultrasonic soldering of 7075 Al alloys

• Acoustic intensity of solder remarkably affects the microstructure and mechanical properties of joints. • High acoustic intensity was produced by applying a small lap width without increasing input ultrasonic power. • The melting point of Zn increased by 73.8 °C under the high pressure caused by bubble collapse. • Zn grains were significantly refined due to undercooling–induced direct solidification caused by cavitation. • Shear strength and hardness respectively increased by 24% and 17% when lap clearance decreased by 50%. In this work, 7075 Al alloys were ultrasonically soldered by pure Zn solder in air under different acoustic intensities. The dependence of the microstructure and mechanical properties of joints on acoustic intensity was revealed. Acoustic intensity is innovatively controlled by applying different lap widths without increasing the input ultrasonic power. The acoustic pressure inside the solder was simulated by finite element simulation, and results showed that the acoustic intensity increased by more than six times when the lap width decreased by 50 %. High acoustic intensity led to intense cavitation, thereby causing a pronounced erosion of substrate. The Al content inside the joint increased from 17.3%–24.5% when the clearance width decreased from 0.8 mm to 0.4 mm. The Clausius–Clapeyron equation helped explain that the melting point of Zn increased by approximately 73.8 °C under the high acoustic pressure caused by cavitation bubble collapse, which could cause the direct solidification of Zn and served as the main reason of grain refinement. Zn grains were refined from 6.9 μm to 4.2 μm when soldered at 0.8 mm and further to 3.5 μm when soldered at 0.4 mm because of the strong cavitation caused by high acoustic intensity. Acoustic intensity had a remarkable effect on the mechanical properties of joints. Joint shear strength and hardness increased from 117.3 MPa and 93.3 HV to 145.1 MPa and 109.4 HV, respectively, when the lap clearance width decreased from 0.8 to 0.4 mm. Particularly, the joint soldered at 0.4 mm failed through the substrate because of the high strength of the joint seam and the weakness of the substrate, which were explained through the Hall–Patch relationship, the Schmid factor, the dissolution of secondary phases, and the increase in high angle boundaries. This work provides a novel method by producing strong joints with fine grains without increasing input power.

Interface development and microstructure evolution during double-sided friction stir spot welding of magnesium alloy by adjustable probes and their effects on mechanical properties of the joint

The flat friction stir spot welding using double side adjustable tools (Flat DSAT FSSW) was successfully applied to the joining of magnesium alloys in our previous research. In this study, the in-situ X-ray radiography observations using a high-intensity X-ray transmission device were carried out to investigate the interface development. In addition, the microstructure evolution at different welding stages was also studied. The mechanical properties of the welded joints were significantly affected by the minimum plate thickness of the joint, which was the distance from the tip of the unwelded interface to the bottom of the lower plate. The welding interface was well welded during the stage of the holding of probes, and the minimum plate thickness was eventually determined by the stage of raising the lower probe, which is the key stage affecting the joint properties. The in-situ X-ray radiography technique shows a significant advantage to reveal the welding process. In the tip area of the unwelded interface at low rotation speed welding condition, the grain growth was suppressed due to the limited heat generation, giving rise to refined microstructure. Moreover, a randomized texture was obtained owing to the weak material flow during the welding process and the introduced mechanical twins during the stage of raising the lower probe. The refined microstructure resulting from limited heat generation and randomized texture resulting from weak material flow contributed to the high strength welded joint.

Hip passive stiffness is associated with midfoot passive stiffness

BackgroundHip motion in the transverse plane is coupled with foot motion in the frontal plane during closed kinematic activities, such as gait. Considering that movement patterns and bone alignment might influence passive mechanical properties of joints in the long term, it is possible that hip passive stiffness and foot complex stiffness and alignment are related to each other. ObjectivesTo investigate whether hip passive stiffness, midfoot passive stiffness and shank-forefoot alignment are related to each other. MethodThirty healthy adult individuals with a mean age of 25.4 years participated (18 women and 12 men). The Foot Torsimeter was used to measure midfoot stiffness, and hip stiffness and foot alignment were measured using clinical measures. Pearson and Spearman correlation coefficients were calculated to test the associations between each pair of variables, with α = 0.05. ResultsHip stiffness was positively correlated with midfoot absolute stiffness (r = 0.41, p = 0.02), indicating that increased hip stiffness is associated with increased midfoot stiffness. There were no associations between shank-forefoot alignment and the other variables. ConclusionsIn clinical settings, individuals with reduced hip passive stiffness may also have reduced midfoot passive stiffness, and vice versa. Shank-forefoot alignment is not linearly associated with hip or midfoot passive stiffness.

Microstructure and mechanical properties of joints prepared by vacuum brazing on TC4 titanium alloy with Ag as filler metal

Vacuum brazing on TC4 (Ti–6Al–4V) titanium alloy was performed by using Ag foil as the filler metal. Two steps were designed, in which the TC4/Ag/TC4 samples were brazed at 1000 °C for 10 min and followed by a diffusion process at 800 °C for 60–360 min. The microstructural characteristics and the mechanical properties of joints were analyzed. The results indicated that the reaction zones of the joints mainly consisted of α+β lamellar structures with the distributions of acicular and micron-sized particle phases of TiAg attached to Ti2Ag. As the diffusion time increased, the characteristics of the intermetallic compounds (IMCs) at the joints changed accordingly, as the morphology of IMCs became spherical from acicular, and the amount of IMCs was decreased. Furthermore, the microhardness test results indicated that the lowest hardness values were observed at the centers of the joints. A maximum tensile strength of 864.5 MPa was obtained for the joint diffused at 800 °C for 120 min, and its fracture path was more curved than those of the other joints. Based on the shear test results and fracture analysis, regardless of diffusion time, the joints were fractured at the region of the reaction zone along the IMCs.

Effect of deposited layer thickness on the microstructure and mechanical properties of IC10 single-crystal Ni3Al-based alloy electron beam-welded joint

IC10 single-crystal Ni3Al-based alloy has poor weldability by electron beam welding (EBW). However, a defect-free butt joint can be obtained when the Inconel 718 alloy single-crystal deposited layer is used in the IC10 alloy EBW joint as a sandwich structure with a controlled chemical composition. The experimental results show that the optimized IC10 butt joint's microstructure contains preferably orientated columnar grains with deformation twins in the intragranular region and many small NbC particles in the intergranular region. The grain size, misorientation angle, and local grain orientation in weld seam changed with the deposited layer thickness variation. The residual deposited layer was found to be the most fragile zone possessing the lowest microhardness and tensile performance in the optimized IC10 butt joint. The tensile strength of the optimized IC10 butt joints deteriorated with the increasing deposited layer thickness. The optimal design with a 0.4 mm-thick deposited layer significantly improved the EBW joint mechanical properties. In general, the deposited layer thickness strongly influenced the microstructure and mechanical properties of the optimized IC10 butt joint.

Microstructure and mechanical properties of flash butt welding joint of high nitrogen austenitic stainless steel

The microstructure and properties of high nitrogen stainless steel welded joints under different flash currents were studied by flash butt welding. The results show that, the flash welding parameters have obvious influence on the joint structure and mechanical properties. The joint is organized into symmetrical distribution, and the grains obtained in the interface area are small, mostly pearlite and ferrite. With the increase of flash current, grain coarsening in overheated zone (OZ) and welding zone (WZ) of joint, which was mainly attributed to the increase of welding heat input. Martensite exists on both sides of the weld, in which the hardness reaches the peak. The tensile strength of welded parts can reach up to 97% of the base material, and the fracture is in the form of ductile fracture.

Microstructure and mechanical properties of CuAgZn/GH909 diffusion bonded joint fabricated by hot isostatic pressing

The hot isostatic pressing-diffusion bonding (HIP-DB) was proposed to achieve the joining of CuAgZn and GH909 directly without an interlayer. The microstructure of joint was characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The microhardness and shear strength were tested to investigate the mechanical properties of joint. The results showed that the interface was complete, and the joint was compact, uniform and free of unbonded defects. The maximum microhardness of joint was HV 443, higher than that of two base alloys, and the average shear strength of joint reached 172 MPa. It is concluded that a good metallurgical bonding between CuAgZn and GH909 can be obtained by HIP-DB with the process parameters of 700 °C,150 MPa and 3 h.

Effect of tool travel speed on tensile strength of friction stir welded dissimilar joint of aluminium AA6061 T6 alloy and maraging M250 steel

Friction stir welding (FSW) is a promising welding method to produce dissimilar joints between steel and aluminium. The formation of the intermetallic compound layer at the dissimilar joint interface affects the joint mechanical properties, which are also influenced by the FSW process parameters. In the present research work, M250 Maraging steel and AA6061 T6 aluminium alloy were joined by FSW. The joints were prepared with five different tool travel speeds ranging from 0.33 mm s−1 to 1 mm s−1 using a tapered tool pin made by tungsten carbide material, keeping tool rotational speed constant. The welded joints were analyzed for their tensile behaviour and microstructural change, including hardness measurement. The failed samples are analyzed using a scanning electron microscopy device for their mode of failure. In the Energy Dispersive X-Ray Spectroscopy (EDS) analysis, the formation of intermetallic compound (IMC) layers of Fe3Al, Fe4Al13, and Fe2Al5 are observed. When the thickness of the IMC layer increases, the joint strength decreases. It is found that the welding speed influences the thickness of the IMC layer formed, causing variation in the strength of the dissimilar joint. Better joint efficiency is obtained at a tool travel speed of 0.67 mm s−1.

Influence of Carbon Nanoparticles Additives on Nanosilver Joints in LTJT Technology

Abstract Ninety percent of high temperature electronic devices operate in temperatures in the range of 150 to 300 °C, and for such temperature needs, technologies typical for the military range might be adapted. To make it possible, new joining techniques are developed, one of them is use of pastes with silver nanoparticles sintered with low temperature joining technique. Silver sintered joints have three times higher thermal conductivity and five times lower electrical resistivity than typical solders, while being able to operate in temperatures reaching 350 °C. In this paper, the authors show the impact of additions of carbon nanoparticles on joints prepared in low temperature joining technology (LTJT). The authors prove that an addition of few percent of graphene nanoplatelets (GNPs) or carbon nanotubes (CNTs) improves joints mechanical, thermal, and electrical properties, while ensuring proper rheology of pastes.

Research on Mechanical Properties of Angle Beam-column Joint with Gusset plate

There is wide use of beam-column joint with gusset plate angle connection in engineering, however, the mechanical properties of these joints are still lack of complete theoretical and experimental research. This kind of joint is often simplified as an articulated connection or other types of connections in the design. In this paper, experimental study and finite element analysis are carried out to study the flexural behavior of the beam-column joint with gusset plate angle connection. The finite element analysis is used to analyze the differences between the beam-column joint with gusset plate and other joints. The moments-rotation curves and failure modes of the three kinds of beam-column joints were obtained by the static test which were carried out. A more reasonable design of beam-column joint with angle plate of gusset plate is put forward through the research of this paper: the deformation of the column flange is restricted after adding the stiffener, which can avoid the premature yield of the column flange and making the joint have good energy dissipation capacity.

Interface characteristics and formation mechanism of plasma arc welding-brazing aluminum alloy/ultrahigh-strength steel joint

A butt welding-brazing joint of 5A06 aluminum alloy and DP1180 ultrahigh-strength steel was carried out by using plasma arc welding (PAW) with Al-Si welding wire. Interface characteristics, formation mechanism and mechanical properties of the joint were investigated. The results showed that the dissimilar joint contained bond zone, weld zone and Al/steel interface zone. During PAW, the inter-diffusion of Fe and Al and the interfacial reaction occurred, and the double-layer structure intemtallics (IMCs) composed of Fe4Al13 layer and Fe2Al5 layer were produced in the interface zone. The thickness and morphology of both IMC layers depended on different positions in the interface zone. The Fe2Al5 layer thickness decreased obviously and its morphology changed from continuous layer to discontinuous layer with the decrease of welding heat input. The average tensile strength of the joint was 88 MPa and the joint fractured at the Al/steel interface zone with the highest hardness (524 HV). The interface zone IMCs were the main factor of affecting the mechanical properties of aluminum alloy and ultrahigh-strength steel PAW joint.

A strain-rate-dependent analytical model for composite bolted joints

In the present research, a novel analytical approach was developed to predict the bearing chord stiffness and the damage initiation bearing-load of single-lap composite bolted joints under medium strain rate loading. First, the elastic moduli, Poisson's ratio, and strength of a unidirectional composite ply at an arbitrary strain rate were predicted by available micromechanical equations. Then, the bearing chord stiffness of the joint at any arbitrary strain rate was predicted. For this purpose, the available spring-based model was modified. The strain-rate-dependent damage initiation bearing-load of the joint was predicted by using the moduli and the stress concentration factor of a pin-loaded unidirectional ply. Four types of single-lap joints with [-45/0/+45/90]s and [90/-452/+45]s layups with and without carbon nanofibers were tested at the strain rates of 0.0048 s-1, 0.36 s-1, and 0.89 s-1. The results of experiments showed that mechanical properties of single-lap composite bolted joints increased with increasing the strain rate. Also, employing carbon nanofibers has a significant effect on the mechanical properties of the joints. The predicted results in comparison with the conducted experimental data show good agreements.

Experimental analysis of rotary friction joining process by EN1A bright mild steel under normal air and wet environment condition

Rotary friction welding is a solid state metal joining process and it has many applications in future upcoming days because of its advantages like without fumes and smokeless operation. In this process heat generates through mechanical friction between one continuously rotating component and one stationary component. After heat generation phase an additional forging force is applied which completes coalescence. Since no melting of material occurs during friction welding, but metal gets deform after heat generation at welding zone. The main advantages of friction welding include low distortion, absence of weld related defects, high joint strength, ease of automation, ability to weld alloys and metals which are not weldable by conventional welding methods. In this research work weld specimens were prepared on all geared lathe conventional machine by consideration of parameters like rpm of rotating specimen, friction and forging force applied. This study includes that joining of metal initially carried out under normal atmospheric conditions i.e. air environment and secondly, continuous stream of water under the wet environment. The materials were used EN1A bright mild steel and only similar combinations were used for study purpose. An experimental setup was prepared for force measurement on all geared lathe machine. Mechanical properties of joints were evaluated utilizing tensile test and hardness at heat affected zone.

Activated flux TIG welding of dissimilar SS202 and SS304 alloys: Effect of oxide and chloride fluxes on microstructure and mechanical properties of joints

Low depth of penetration limits the use of favored tungsten inert gas (TIG) welding process for joining of ferrous and non-ferrous metals, demanding weld bead profile of high quality. This article aims to study the effect of chloride and oxide fluxes viz. calcium chloride (CaCl2) and ferric oxide (Fe2O3) on micro-structural and mechanical properties of TIG welded joints of dissimilar SS304 and SS202 steels. Results reflected that use of oxide and chloride fluxes significantly affects the weld bead geometry, bead dimensions and penetration. The use of oxide flux resulted in complete penetration and approximately linear root of weld with good fusion of both the base metals. Fusion zone showed columnar dendritic cast grain structure while coarse grain structure was obtained in heat-affected zone. Fusion zone hardness was higher than SS304 base metal and an opposite trend observed for SS202 irrespective of welding condition. Fine grained heat affected zone hardness was higher than coarse rain for all welding conditions.

A New Statistical Parameter for Determining Joint Roughness Coefficient (JRC) considering the Shear Direction and Contribution of Different Protrusions

The mechanical properties of joints are important factors affecting the safety and stability of rock mass. The joint roughness coefficient (JRC) is a parameter for describing the roughness morphology of the joint surface, and its accurate quantification is very important to predict the shear strength. In the current statistical parameter methods for the estimation of joint roughness, the size of different protrusions on the joint surface was completely ignored, which did not correspond to the real failure mechanism of rock joint during the shear process. In this study, a new statistical parameter WPA was proposed for the estimation of JRC considering the shear direction and the contributions of different protrusions. First, the 10 standard roughness joint profiles were digitized based on image processing technology, and the obtained coordinate data were proved to be reliable by the calculation results of existing parameters. Secondly, the WPA value of 10 standard roughness joint profiles was calculated at a 0.5 mm sampling interval in two directions. The functional relationship between WPA and JRC indicated that they should be established in the same shear direction to maintain a high correlation. The JRC values of 10 standard roughness joint profiles in direction 2 were obtained based on the functional relationship established between WPA and JRC in direction 1, and the roughness of these 10 joint profiles was confirmed to be influenced by direction. Next, the effect of sampling interval on WPA was investigated. As the sampling interval increases, the WPA values gradually decreased and the correlation between them and JRC gradually declined. In practical application, a smaller sampling interval was recommended for more accurate prediction. Finally, the geometric coordinate data of 21 joint profiles given in the literature and 4 natural joint surfaces were obtained by graphics processing technology and 3D scanning technology, respectively. The JRC values of them were separately estimated by WPA in different directions. The results showed that the new statistical parameter WPA proposed in this paper can well describe the joint roughness considering the shear direction and the contribution of different protrusions.

Mechanical properties of joints of stainless steel and titanium brazed with silver filler material

Mechanical properties of joints of stainless steel and titanium brazed with silver filler material

Mechanical properties of joints of 1460 aluminium alloy, produced by electron beam welding using filler material from 1201 alloy

The Paton Welding Journal, 2020, №12. International Scientific-Technical and Production Journal «The Paton Welding Journal» «The Paton Welding Journal» has been published monthly since 2000 in English, ISSN 0957-798X. «The Paton Welding Journal» is a cover-to-cover English translation of the «Avtomaticheskaya Svarka» (Automatic Welding) journal. The «Avtomaticheskaya Svarka» journal has been published monthly since 1948 in Russian, ISSN 005-111X.