Ultimate Strength Of Joints Research Articles

Ultimate strength of multi-ring-stiffened tube-gusset joints with dual-function stiffeners under combined bending and compressive loads

Tube-gusset (TG) joints play a crucial role in connecting crossarm chords to tower bodies in steel-pipe power transmission towers, bearing the highest loads in the entire tower structure. This study investigated TG joints with five-ring stiffeners under combined bending and compressive loads, using the middle stiffener plate as the connecting plate. Through experimental studies, numerical simulations, and theoretical analyses, insights were obtained into the failure mechanism and mechanical characteristics of TG joints. This study identifies the key factors influencing the ultimate strength of TG joints under combined bending and compressive loads and proposes a method for determining the joint bearing capacity. Notably, the mechanical performance of multi-ring-stiffened tube-gusset joints was minimally affected by the initial geometric defects under combined compression and bending moments. The load exerted on the gusset plate was primarily supported by the stiffeners, with the gusset plate demonstrating minimal bending deformation, owing to its substantial in-plane stiffness. Consequently, the gusset plate underwent an overall rotation or translation under the combined effects of compression and the bending moment. The proposed method accurately predicted the joint bearing capacity, ensuring the safety of TG joints. These findings provide valuable insights into the meticulous design of joints in steel-pipe transmission towers, thereby ensuring the safety and stability of transmission lines in the field of civil engineering.

Ultimate Strength of Internal Ring-Reinforced KT Joints Under Brace Axial Compression

Internal ring stiffeners are frequently used to improve the ultimate strength of tubular joints in offshore structures. However, there is a noticeable absence of specific design guidance regarding the assessment of their ultimate strengths in prominent offshore codes and design guides. No equations are available to determine the ultimate strength of internal ring-reinforced KT joints. This work developed equations to determine the ultimate strength and the strength ratio of internal ring-reinforced KT joints based on numerical models and parametric studies comprising ring parameters and joint parameters. Specifically, a finite element model and a response surface approach with eight parameters (λ, δ, ψ, ζ, θ, τ, γ, and β) as inputs and two outputs (ultimate strength and the strength ratio) were evaluated since efficient response surface methodology has been proven to give precise and comprehensive predictions. KT-joint with parameters λ=0.9111, δ=0.2, ψ=0.7030, ζ=0.3, θ=45°, τ=0.90, γ=16.25, and β=0.6 has the maximum ultimate strength, and the KT-joint with parameters: λ=1, δ=0.2, ψ=0.8, ζ=0.5697, θ=45°, τ=0.61, γ=24, and β=0.41 has the maximum strength ratio. The KT-joints with the optimized parameters were validated through finite element analysis. The percentage difference was less than 1.7%, indicating the applicability and high accuracy of the response surface methodology. Doi: 10.28991/CEJ-2024-010-05-012 Full Text: PDF

Shear Strength of Adhesively Bonded Joint with Toughened Epoxy Mussel Powder

Synthetic fillers were usually used to improve the shear strength of epoxy resin, but dependency on mineral-derived substances may increase the greenhouse effect. To surmount the problem, biofiller from household wastes mussel shells is proposed to improve the mechanical properties of epoxy due to its high calcium carbonate content. In this paper, the physical properties (X-ray diffraction test)and shear strength of toughened epoxy with mussel shell powder (TEMP) were investigated. Single lap joints (SLJ) specimens were tested for shear strength with incorporation of various TEMP volume fractions and over-lap length. The testing series includes TEMP volume fractions from 0% to 10% (by 2.5% increment) and overlap length ranging from 12.7 to 50.8 mm. The results demonstrated that the longest overlap length and 7.5% TEMP volume fractions exhibited a significant effect on the ultimate joint strength. From scanning electron microscopy (S EM), 10% TEMP was prone to particle agglomerations and gave less joint strength. The joint strength with 7.5% mussel shell powder was stronger compared with other volume fractions, with strength enhancement from 103.7% to 169.6% for the studied overlap lengths.

Effects of off‐axis load direction on tensile properties of pultruded fiber‐reinforced polymer bolted joints with multi‐directional fiber lay‐ups

AbstractThe limited joint performance of unidirectional (UD) pultruded fiber‐reinforced polymer (FRP) composites poses a critical issue that constrains their application in structural engineering. Moreover, UD pultruded FRP joints display a notable reduction in strength and stiffness as the load angle diverges from the fiber pultrusion direction. This paper presents a numerical study of bolted pultruded FRP joints with different off‐axis loading directions. Two types of fiber lay‐ups, including UD and multi‐directional (MD), were investigated. Static tensile tests were conducted with the loading direction parallel to the pultrusion. A finite element model was validated by the test results. Studied geometric parameters includes the end‐to‐diameter (e/d) ratio, width‐to‐diameter (w/d) ratio, and bolt arrangement. Compared to UD joints, MD joints exhibited significant advantages in strength and stiffness under off‐axis loading with an increasing of 78.3% at a loading angle of 90°. Compared to the end distance, plate width has a more significant impact on the off‐axis behaviors of MD joints, especially between 30° and 75°. Multi‐bolted joints were more susceptible to net‐tension failure than single‐bolted joints. Furthermore, classical laminate theory and Hashin failure criterion were employed to predict the resistance of single‐bolted FRP joints with different loading angles, achieving high accuracy.Highlights Under increased off‐axis loading angles, compared with unidirectional (UD) joints, multi‐directional (MD) joints display a less reduction in both strength and stiffness. At a 90° angle UD joints displayed only 21.7% of the joint resistance of MD joints. Compared to the end distance, plate width has a more significant impact on the off‐axis behaviors of MD joints, especially between 30° and 75°. Classical Laminate Theory, Hashin failure criterion were effectively utilized to predict the ultimate strength of pultruded joints under various tensile loading angles, yielding high accuracy. The error between theoretical and simulated values is within 20%.

Effect of Friction Coefficient in Friction Stir Welding of B4C Reinforced AA5083 Metal Matrix Composites and Use of Fuzzy Clustering Technique for Weld Strength Prediction

The friction stir welding (FSW) method was used to weld B4C reinforced AA 5083 metal matrix composites in this study. By coating titanium nitride (TiN), aluminium chromium nitride (AlCrN), and diamond-like carbon (DLC) to a thickness of 4 microns, three FSW tools with square pin profiles were developed and the friction coefficients of 0.69, 0.32, and 0.2 were maintained. At three levels, the process factors such as tool rotating speed, transverse feed, and axial force were examined. For each tool, 15 samples were made using the central composite design. The influence of the friction coefficient on ultimate tensile strength, microstructural features, and tool condition was studied, and the flower pollination algorithm (FPA) technique was used to find the best process parameters for obtaining maximum ultimate tensile strength of FSW joints. The improved tensile strength of FSW joints was verified using a validation test. The coating has a considerable influence on the ultimate tensile strength, microstructure, and tool condition, according to the results of the tool’s friction coefficient. The results on the prediction of strength using the fuzzy clustering technique showed that the technique is effective in predicting the tensile strength values, with the root mean square error (RSME) of TiN, AlCrN, and DLC being 0.0027, 0.0016, and 0.0015, respectively, and the low RSME indicating that the prediction based on the fuzzy subtractive clustering technique is perfect and effective.

In-situ rolling friction stir welding of aluminum alloys towards corrosion resistance

In-situ rolling friction stir welding (IRFSW) was proposed to improve corrosion resistance of 7075-T6 aluminum alloy joint via microstructural design and residual stress regulation. The residual stress at the weld edge was changed from +58.3 MPa to –25.7 MPa. The dissolution of precipitates and narrowing of precipitate-free zones reduced corrosion potential difference between the precipitates and the matrices. The active corrosion path was cut off by discontinuous distribution of fine precipitates in grain boundary. The ultimate tensile strength and elongation of IRFSW joints were increased by 24.1 % and 100.0 % compared to conventional FSW joints after constant load stress corrosion.

Cyclic behavior of UHPC corner beam-column joints under bi-directional bending

Design codes contain special provisions for anchorage lengths of flexural reinforcement and amount of transverse reinforcement in beam-column joints, to safeguard against joint failure and possible structural collapse. However, those stipulations could lead to congested joints with construction problems such as segregation. This study leverages experimental testing of eight corner beam-column joints under constant axial and cyclic bi-directional bending loads. In addition to being one of few on corner joints under a complex and practical loading, the study’s main aim is to evaluate the effectiveness of ultra-high-performance concrete (UHPC) as a joint fill in lieu of normal strength concrete (NSC). Brittle failure, either by pure shear or shear combined with yielding of beam reinforcement occurred in all NSC joints and varied in shape and intensity depending on the column depth-to-beam longitudinal bar diameter (hc ⁄db) ratio and spacing of transverse beam/column reinforcement. Ductile failure characterized by the yielding of beam reinforcement and plastic hinge at the beam-joint interface occurred in all UHPC joints and was independent of the two aforementioned variables. The application of UHPC in the joint region resulted in increasing the joint ultimate strength by 27.6–54.8%, energy dissipation by 24–163%, and stiffness by 20 to 50%, compared to NSC joints. Such results were obtained when no transverse reinforcement is used in the joint, and only half transverse reinforcement is used in the beam/column members, and with hc ⁄db relaxed to 38% of the code recommended ratio, highlighting the advantages of UHPC joints. Predictions of ACI-ASCE 352R code were found to be overly unconservative and in need of future improvement.

Effect of in-situ ZrB2 nanoparticles on microstructure and mechanical properties of friction stir welding joints in 7N01 matrix composites

In this paper, in-situ nanoparticles ZrB2 were introduced to improve the mechanical properties of Friction Stir Welding (FSW) joints in 7N01 matrix composites. The recrystallization driving force was increased induced by ZrB2 particles. Modified by ZrB2 nanoparticles, the grains in the SZ (stir zone) were refined from 4.8 μm (7N01) to 3.7 μm (ZrB2/7N01), and the recrystallization proportion was increased from 75.1% (7N01) to 85.4% (ZrB2/7N01). Compared with the 7N01 matrix, the ultimate tensile strength (UTS) of friction stir welding joints in ZrB2/7N01 composites was enhanced from 283.3 to 395.6 MPa, the yield strength (YS) was enhanced from 250.8 to 361.4 MPa, elongation was enhanced from 12.7% to 16.2%. The strengthening effect was mainly achieved through the Orowan mechanism. The MgZn2 precipitates grew up under the influence of heat input, the inhibiting effect of precipitates on dislocations movement was weakened. Nanosized ZrB2 particles with superior coarsening resistance can still maintain its morphology and size at high temperature, playing a good strengthening role during the FSW.

Residual strength prediction of single lug and yoke joints based on the J-A2 method

To examine the effect of fatigue cracks on the residual ultimate strength of 30CrMnSiA steel single lug and yoke joints for pontoons, we developed a residual ultimate strength J-A2 model. This model was constructed by applying fracture mechanics principles, and the law of decay of the residual ultimate strength of aging single lug and yoke joints with crack propagation was obtained. Using this model, the empirical relationships of the remaining ultimate strength engineering applications of a certain equipment joint were determined, and the rationality and practicality of the method were verified by combining fatigue tests and finite-element simulations. The results provide a foundation for further analysis of the influence of crack propagation on the ultimate strength of single lug and yoke joint structures.

Static performance of multi-planar CFST chord-CHS brace KK joints

This paper investigates the static performance of jacket joints to promote the application of CFST jacket foundations for offshore wind power. An experimental and numerical study of the influence of loading patterns, concrete filling in the chord, geometric parameters, and material strength is examined. In total, five 1:6 scale tests and twenty-eight FEAs are described. The novelty is that a limit device is introduced to consider the interaction among the braces by connecting four braces. The experimental results indicate that, compared to symmetrical loading joints, the bearing capacity of CHS-KK joints decreased by 14% under anti-symmetric loading. Concrete filling in the chord alters the failure mode, enhancing the ultimate bearing capacity of the KK joint. However, its effect on the punching shear failure strength of the joint is limited. An FEA model incorporating the modified Mohr-Coulomb criterion (MMC) was established to explore the ultimate strength of CFST-KK joints, following validation through experiments. Through parameter analysis, it was found that the punching shear capacity of CFST-KK joints is significantly influenced by the diameter ratio of the brace to chord (β), the chord diameter to thickness ratio (2γ), the angle between the brace and chord axis (θ), and the chord steel strength. In addition, the recommended formula in GB50017–2017 for CHS-KK joint punching shear capacity conservatively predicted CFST-KK joint performance.

Identification of the most suitable probability distributions for ultimate strength of FRP-strengthened X-shaped tubular joints under axial loads

This paper focuses on identifying the most appropriate probability distributions for characterizing the ultimate strength of FRP-strengthened X-shaped tubular joints under axial loads. The study begins by verifying the accuracy of finite element (FE) models through a comparison with experimental results. Subsequently, 218 FE nonlinear static analyses are conducted to generate two reliable datasets for strength ratios. To determine the most suitable probability distribution models, 16 different distributions are fitted to the data, and their accuracy is evaluated using Kolmogorov-Smirnov and Chi-squared goodness-of-fit tests. The findings reveal that the Generalized Extreme Value distribution provides the best fit for describing the ultimate strength under compressive axial load, while the Burr distribution is identified as the most suitable model for tensile axial load. The analysis of probability differences revealed that the proposed probability distribution models for compressive and tensile loads exhibit minimal disparities, with a slight difference of 5.24% and 4.80%, respectively. The identified probability distribution models enhance the reliability and confidence in predicting the behavior and performance of these joints, contributing valuable insights to the field of structural engineering.

Parametric investigation into the mechanical characteristics of dissimilar steel joints produced using SMHH-based joining technology

Selective microwave hybrid heating (SMHH)-based joining technology was utilized to fabricate dissimilar joints between SS2205 and SS304. The joining process involved exposing the materials to a 2.45 GHz frequency and 900 W of power for 720 s under atmospheric conditions, with SS304 powder used as the filler material. SMHH principles were employed to melt and fuse the filler powder with the interfaces of the joining specimens. To assess the joint properties, various characterizations were conducted, including X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), microhardness and tensile testing. XRD revealed the presence of carbides and intermetallics in the joint region. SEM revealed that the complete melting of powdered particles with the joining interface resulted in good metallurgical bonding between the joining specimens. The Vicker’s microhardness measured in the joint region was determined to be 515.2 HV, indicating a substantial increase as compared to the microhardness value of the joining specimens. The average measured ultimate tensile strength of dissimilar joints was 584.15 MPa, with an elongation of 20.27%. The SMHH-induced dissimilar welds between SS2205 and SS304 demonstrated promising microstructural and mechanical properties, indicating the effectiveness of this joining method in industrial applications.

Impact of standard and unexpected bolt-hole-washer tolerances on the performance of pinned and torqued joints in CFRP composites

This study aimed to investigate the impact of some practical assembly errors on the performance of composite joints with M6 bolts in quasi-isotropic CFRP laminates with stacking sequence of [±45/0/90]2S, which are increasingly used in aerospace and automotive industries. The detailed experimental explanations of the behaviors of the bolted joints in CFRP composites with standard and unexpected joining parameters, exhibited a vital impact on the bearing and ultimate joint strength, stiffness, energy absorption, and failure mechanisms. The joining parameters include tightening torque (0-16Nm), bolt-hole clearance (0–240 μm), and washer-to-bolt hole clearance (0–500 μm) with different offset arrangements. The bolt axial force is monitored during the testing of double-lap bolted composite joints. The maximum performance of the bolted joints was observed at tightening torque of 12Nm, bolt-hole clearance up to 60 μm, washer-to-bolt hole neat-fit or with negative clearance arrangement. The first peak, 2 % offset, and ultimate strengths are increased, respectively, by 55.9 %, 56.4 % and 52.4 % compared to those of the pinned joints. The 2 % offset strength and stiffness of bolted joints with negative washer-to-bolt hole clearance arrangements is improved by 26.8 % and 57 % respectively compared to those having positive arrangements. Energy absorption increase almost linearly with bearing load with correlation coefficient of 0.982.

Effect of asynchronized and synchronized laser shock peening on microstructure and mechanical properties of the Ti–6Al–4V laser joint

Welding processing is an important method to connect precision component, but the internal stress and crystal anisotropy reduce its performance, which are difficult to solve due to the specific demand on regional post-treatment. In the present research, the asynchronized laser shock peening (ALSP) and synchronized laser shock peening (SLSP) processing technologies were applied to treat the laser joined Ti–6Al–4V thin plates. The microstructure and mechanical properties of the as-welded joint, ALSP and SLSP processed joint were investigated. The results revealed that the as-welded joint presents obvious anisotropic characteristics, and high strain level exists on the prior β grain boundary, which causes stress concentration. The ultimate tensile strength (UTS) and elongation (EL) values of as-welded joint just reach the 92.18% and 72.33% of as-received plate, respectively. ALSP processing could result in the deformation with the depth more than ten microns and introduce compress stress in the top layer, but has little effect on decreasing the anisotropy. The grain boundary becomes obscure and the strain distribution is relatively uniform, accompanying with some dynamic recrystallized laths exist along the grain boundary. Its values of UTS and EL are 5.23% and 5.59% higher than as-welded joint, respectively. With the SLSP processing, the deformation depth exceeds twenty microns, and the crystal isotropy could be greatly promoted. Moreover, higher compressive stress is introduced from top layer to center area of joint. The grain boundary becomes obviously obscure, which is completely replaced by recrystallized lath structures. The residual strain in the top layer is partly eliminated, and the stress concentration phenomenon along grain boundary is dramatically decreased. The UTS and EL values are 6.16% and 20.58% higher than as-welded joint, and reach 97.86% and 87.22% of as-received plate, respectively.

Ultimate strength of CFST-gusset plate joints with ring stiffener plates under tension

Tube-gusset plate joints are increasingly adopted in large lattice towers for wind power, due to the advantages of simple fabrication and clear force transmission path. To investigate the mechanical performance of CFST-gusset plate joints with ring stiffener plates, tensile bearing capacity tests of three tube-gusset plate joints were performed in this study. The test results showed that setting ring stiffener plates and filling concrete could effectively improve the stiffness and tensile bearing capacity of tube-gusset plate joints. In addition, the finite element (FE) models were established in this study, and the accuracy of the FE models was verified by comparing it with the test results. Parameter analysis showed that the increase of the width ratio (R/D) and thickness ratio (tr/t) of the ring stiffener plate and the width ratio (LGP/D) of the gusset plate was a significant method to improve the ultimate strength of tube-gusset plate joints under tension. But when the width ratio and thickness ratio of ring stiffener plates exceeded the limit relationship, the ultimate strength of joints would not be further improved, which was easy to cause waste of materials. Finally, to simplify the calculation of CFST-gusset plate joints with the ring stiffener plates, an equivalent interaction method (EIM) was proposed in this study, which could accurately predict the ultimate strength of CFST-gusset plate joints with ring stiffener plates under tension.

Microstructure and fracture analysis on MIG welding of Nimonic alloys

Advanced alloy has an essential role in welding process to enhance the performance characteristics. Nimonic alloy has outstanding welding characteristics. The purpose of this work is to analyze the microstructure and fracture analysis of the welded Nimonic alloy joints by employing metal inert gas welding (MIG) welding. In this work, Taguchi analyze was effectively utilized to anticipate the ideal parameters of the input variables such as voltage, welding speed, welding current towards the maximized optimal value of the welded specimen's ultimate tensile strength. In this study, a L9 orthogonal array was employed, and the ultimate tensile strength for the specimen were estimated. The findings reveal that at maximum welding speed and voltage, the specimen has a satisfactory strength bonded joint. Microstructure and fracture analysis were also discussed. The objective of the work is to enhance the ultimate tensile strength of the nimonic welded joints. The optimal welding strength was attained at welding current of 110A, speed of 20 m/s and voltage of 155 V.

EFFECT OF CHORD PRELOADING AND BRACE INCLINATION ON AXIAL RESISTANCE OF FULL-WIDTH RHS X-JOINT

According to current representative design standards, the influence of brace angle on the axial resistance of rectangular hollow section (RHS) X-joints is assumed to be independent of the chord preloading state. To investigate the appropriateness of this assumption, extensive test-validated finite element (FE) analyses are performed on full-width RHS X-joints with varying brace angles and chord preloads. The analyses showed that an appreciable coupling effect between the brace angle and chord preload exists on the joint resistances. The most adverse coupling effect occurs under the condition of high brace inclination and large compressive chord preload, leading to the concern that the current design resistance formula may overestimate the ultimate joint strength. Consequently, a revised chord stress function is sought for inclined full-width RHS X-joints that accounts for the coupling effect between chord preload and brace angle. In the FE analyses, high strength steel joints are included as well as conventional mild steel joints. The chord stress effect in high strength steel joints is found to be more detrimental compared to geometrically identical mild steel joints, implying that the chord stress effect may be influenced by the class (slenderness) of the chord cross-section. Therefore, a proper limitation on the chord section slenderness, such as the Class 2 requirement in design codes, appears essential.

Prediction of ultimate tensile strength of friction stir welding joint using deep learning-based-multilayer perceptron and long short term memory networks

Friction stir welding (FSW) is a solid-state joining technique where the joint strength is mainly influenced by three process parameters, namely, spindle speed (N), welding speed (V), and plunge force (Fz). The modelling of complex relationships between the process parameters and joint strength requires many experiments, which is a challenging, time-consuming, and non-economical affair. To tackle this problem, computational mathematical models such as deep learning (DL) can be employed to predict the joint strength reliably. In this paper, DL techniques, namely, deep multilayer perceptron (DMLP) and long short-term memory (LSTM) networks have been proposed for such a purpose. The DL networks were first trained with the FSW experimental data and then, the pre-trained models were used for predicting the weld strength. It was found that the DMLP and LSTM models provided lower prediction errors, which are RMSE of 3.30 and 7.63, respectively, and can be effectively utilized for determining weld quality. The proposed DL-based techniques were further compared with the traditional models – the shallow artificial neural network (SANN) model having an RMSE of 27.11 and the ANFIS model having an RMSE of 5.31. DMLP was found to be superior in determining the weld strength most accurately.

Analytical models for characterizing coupling effects of loading state and loading rate on ultimate strength and yield strength of riveted joints

An electromagnetic split Hopkinson tensile bar system was employed to determine the dynamic mechanical behaviors of riveted joints under different shear/tension combinations. Combining with results obtained from quasi-static tests, the effects of loading state and loading rate on both ultimate strength and yield strength of riveted joints are analyzed. An obvious elevation for the levels of yield force and ultimate force when increasing the loading speed is observed, meanwhile, such strengthening effects are sensitive to the loading state. On the basis of detailed load analysis, two analytical models considering both the loading rate effect and loading state effect were proposed to predict the ultimate strength and yield strength under different loading conditions. The theoretical calculations by applying such two analytical models agree well with the experimental results under five different loading states over a wide range of loading speeds (5 × 10-6 m/s ∼ 17 m/s), indicating the coupling effect of loading angle and loading speed on both ultimate strength and yield strength of riveted joint is reasonable defined.

Influence of Heat Input on Microstructure and Mechanical Properties of Laser Welding GH4169 Bolt Assembly—Numerical and Experimental Analysis

By conducting the numerical and experimental analysis, the influence of heat input on the microstructures and mechanical properties of laser welding GH4169 bolt assembly is systematically investigated. The weld formation, temperature field, and residual stress distribution during laser welding by using the finite element modeling are consistent with experimental results. The numerical simulation results show that the increase of heat input imparts lower residual stresses and higher temperature gradient. During the process of laser welding, the steepest temperature gradient and the peak residual stress arise in the fusion zone (FZ). In addition, the dissolution of γ″ and γ′ toward the fusion line increases in heat affected zone (HAZ), but only Laves phase is observed in FZ. With increasing heat input from 24 to 48 J mm−1, the ultimate tensile strength of welded joints decreases. Both the lowest microhardness values and tensile failure of GH4169 alloy laser welded joint are in FZ. Herein, it is that the relationship among the heat input, microstructures, and mechanical properties of GH4196 bolt assembly in laser welding is systematically established, which will be of guiding significance for the selection of welding parameters in aerospace.