Stainless Steel Connections Research Articles

A proposal for a simple characterization of stainless steel connections through an equivalent yield strength

Notwithstanding some recent contributions, there still appears to be a gap in the literature regarding the express evaluation of the moment–rotation performance of some connections fabricated from austenitic, duplex, or ferritic stainless steel, such as flush end-plate connections (FEP). In the present work, moving from a previous proposal, the authors investigate a simple approach for the practical characterization of these connections. The results from industry standard software, which is dedicated to the analysis of connections based on the component method and widely used in engineering practice, are compared with the results from a more refined numerical model. It is found that, by using conventional carbon steel procedures with an ad hoc ideal material model, the results can be made in line with some experimentally validated numerical simulations for stainless steel. The findings are discussed in detail and may turn useful from both a design and an assessment standpoint.

Experimental investigation on double-lap shear behavior of 3D printed austenitic stainless steel bolted connections

This paper presents a comprehensive experimental investigation into the double-lap shear behavior of 3D printed austenitic stainless steel bolted connections, manufactured using wire arc additive manufacturing (WAAM) and ER316L feedstock wire. A total of 43 double shear bolted connections were tested, considering variations in end and edge distances, surface conditions (milled and as-built) and test orientations. Details regarding the manufacturing process, geometric measurements using 3D laser scanning, and tensile connection tests are provided. The key test results, encompassing failure modes, load-deformation curves, and resistances with and without consideration of bolt hole deformation, are reported and discussed. The test results were compared with resistances predicted by existing design rules documented in current American Specifications (AISC 360–22, AISC 370–21 and ASCE 8–22) and the Active Shear Plane-based Method from relevant literature, originally calibrated for conventionally fabricated steel lap-shear connections, in order to to assess their applicability for WAAM austenitic stainless steel connections. The comparison results indicated that the resistance predictions by the aforementioned American Specifications are generally conservative for WAAM 316 L austenitic stainless steel double shear bolted connections when considering bolt hole deformation, with AISC 360–22 being the most accurate. When bolt hole deformation is not a design concern, the Active Shear Plane-based Method was shown to provide the most accurate resistance predictions.

Effects of material property and thickness on block shear strength in lean duplex stainless steel welded connections

Recently, studies have been carried out to apply lean duplex stainless steels, with less than 1.5% nickel, which provides higher material strength and lower cost compared with austenitic stainless steel for building structures. This study compared with existing experimental and finite element analysis results on the structural behaviours of cold-formed lean duplex stainless steel welded connections with different tensile strength (tensile strength-to-yield stress ratio) and plate thickness despite identical steel grade. The main variables are plate thickness and weld lengths. The material tensile strength of a 3.0 mm thick plate was 22% lower than that of a 1.5 mm thick plate. All specimens showed block shear facture in the base metal. Block shear strengths predicted by current design codes and the proposed equations from previous studies were compared with test strengths. KDS 41 31 00-19/AISC2016 and EC3 design specifications underestimated block shear capacity by on average 24%, 43%, respectively for 1.5 mm and 3.0 mm thick specimens, and equations suggested in previous studies of stainless steel welded connections did not sufficiently account for the influence of stress triaxiality by material property and plate thickness difference on the block shear strength of lean duplex stainless steel specimens. Therefore, thickness-dependent modified strength equations were recommended based on experimental and numerical studies of lean duplex stainless steel welded connections and comparison of carbon steel and other stainless steel connections.

Preparation of a modified multi-component phosphate adhesive for connection of 316L stainless steel and its reinforcement mechanism

In this paper, a novel phosphate-based adhesive with excellent high-temperature bonding strength was prepared by using phosphate as the matrix and modified B4C, modified TiO2 as well as low-temperature fused Zn–B–Si–Al-R glass materials as fillers. The effects of heat treatment temperature and filler compositions on the high-temperature bonding strength of the adhesive were investigated. The results indicated that the aluminum phosphate in the adhesive was transformed from orthorhombic to cubic crystalline at 210 ± 5 °C, which increased the cell stacking density from 2.19 g/cm3 to 2.74 g/cm3 and made the binder dense. After calcination at 500 °C, a large number of pyrophosphates were generated inside the adhesive, and the chemical bonds such as P–O–Si and P–O–Cu in these pyrophosphates formed reticulated skeletal macromolecules, which improved the network structure of the transition zone between the adhesive and stainless steel. Meanwhile, the difference in potential resulted in the exchange of Fe and Cu2+, H+ at the bonding interface to enhance the high-temperature resistance and bonding strength of the specimen. When the additions of La2O3, Fe2O3, ZrO2, CuO were1.2%, 5%, 10%, and 15%, the maximum tensile strength of the specimen reached 8.73 MPa at 500 °C. The phosphate binder prepared in this work could be widely used in the field of high-temperature material repair such as aerospace and energy.

Some Considerations on the Behaviour of Bolted Stainless-Steel Beam-to-Column Connections: A Simplified Analytical Approach

Stainless-steel has proven to be a first-class material with unique mechanical properties for a variety of applications in the building and construction industry. High ductility, strain hardening, durability and aesthetic appeal are only a few of them. From a specific point of view, its nonlinear stress–strain behaviour appears capable of providing a significant increase in the rotational capacity of stainless-steel connections. This, in turn, may provide significant benefits for the overall response of a structure in terms of capacity and ductility. However, the bulk of the research on stainless-steel that has been published so far has mostly ignored the analysis of the deformation capabilities of the stainless-steel connections and has mostly focused on the structural response of individual members, such as beams or columns. For such a reason, the present study aims to contribute to the general understanding of the behaviour of stainless-steel connections from a conceptual, numerical and design standpoint. After a brief review of the available literature, the influence of the use of stainless-steel for column–beam connections is discussed from a theoretical standpoint. As a novel contribution, a different approach to compute the pseudo-plastic moment resistance that takes into account the post-elastic secant stiffness of the stainless-steel is proposed. Successively, a refined finite element model is employed to study the failure of stainless-steel column–beam connections. Finally, a critical assessment of the employment of carbon-steel-based design guidelines for stainless-steel connections provided by the Eurocode 3 design (EN 1993-1-8) is performed. The findings prove the need for the development of novel design approaches and more precise capacity models capable of capturing the actual stainless-steel joint response and their impact on the overall ductility and capacity of the whole structure.

Experimental investigation and design of slip resistant aluminium alloy–stainless​ steel connections

An experimental investigation into the structural response and slip resistance of aluminium alloy–stainless steel connections fastened by means of high-strength stainless steel swage-locking pins is presented herein. Thirty-seven friction tests on aluminium alloy–stainless steel shear connections featuring different surface treatments and material grades were carried out. Complementary material tests were also performed, while the roughness and hardness of the connected surfaces were measured. The failure modes, load–slip responses, friction coefficients and preloading behaviour of all specimens are fully reported, while the test setup, specimen dimensions, configurations of fasteners, and positions of displacement measurements, are explained. The slip factors corresponding to the different surface treatments are presented, while the key parameters affecting the preload losses of the swage-locking pins and the friction coefficients are described. Finally, the suitability of various surface treatments for aluminium alloy–stainless steel connections is evaluated, while design slip factors, as well as correction coefficients accounting for the influence of different material grades and preload levels on the response of the examined connections, are set out.

Influence of bearing coefficient in cold‐formed stainless steel bolted connection

AbstractThe connections play an important role in the overall behaviour of the structures. Therefore an adequate structural design taking into account both safe and economic criterion is necessary. The structural design of stainless steel bolted connections using actual codes can provide inadequate design capacity mainly due to the use of similar rules based on analogies from mild carbon structures. Thus, the purpose of this paper is to evaluate the structural response of stainless bolted connections considering the steel grade austenitic 304. Experimental and numerical analyses have been carried out considering bolted connection under bearing failure. In details, the study cases were subjected to two shear planes with thin‐plate and thick‐plate. In these cases, the occurrence of curling failures is possible. A detailed study involving the geometric parameters adopted by design equations of bolted stainless steel connections was made. The outcomes showed a reduction of the ultimate capacity characterised by out‐plane deformation. In addition, the current codes led to significant difference when compared to both experimental and numerical results.

Experimental study on stainless steel blind bolted T-stub to square hollow section connections

This paper presents an experimental study on blind bolted T-stub to square hollow section (SHS) connections made by stainless steel. Experiments were conducted to investigate the structural behaviour (e.g., failure mode, load–displacement curve and load-carrying capacity) of T-to-SHS connections and their basic components, including bolts, T-stubs and SHSs. The effects of key parameters, such as bolt types, bolt layouts, tube thicknesses and specimen configurations, on the performance of T-to-SHS connections and the components were identified. Design formulas were proposed to estimate the load-carrying capacities of T-stubs and SHSs, which agree well with the experimental results. The experimental results on connections between T-stub and steel hollow sections will provide a basis for verifying numerical simulations and theoretical analysis to derive design equations for such stainless-steel connections.

Low cycle fatigue capacity of shell-to-base connections in stainless steel thin-walled tanks

Strong ground motion during earthquakes can induce the uplift of part of the base of partially anchored or unanchored steel tanks for liquid storage. This partial uplift may induce large inelastic rotation demands at the shell-to-base connections and possible low-cycle fatigue failure. Current tank design guidelines limit the rotation at this connection to 0.2 rad. Nevertheless, recent studies have shown that this limit may be overly conservative for shell-to-base connections of tanks made of carbon steel and thicknesses of the base plate between 6 mm and 10 mm. To the best of the authors’ knowledge, no investigation has been reported on the shell-to-base connection rotation capacity of stainless steel liquid storage tanks. Aside from the material differences, the shell-to-base connections on stainless steel tanks have typical thicknesses between 2 mm and 6 mm and the connection geometries differs from the ones used for carbon steel tanks. Therefore, in this paper, a numerical study is carried out in order to evaluate the rotation capacity of shell-to-base connections in stainless steel storage tanks. First, modelling methods and a low cycle fatigue criterion are validated using experimental data from carbon steel tank connection tests. Then, stainless steel connections with thickness of 2 mm, 4 mm and 6 mm are evaluated. Results from this study are presented as plots of rotation amplitude vs. number of cycles to failure (i.e., R-N curves). These results show that a stainless steel tank connection could reach about 180 cycles at 0.2 rad which may represent rotation capacities larger than those established by current design standards.

Effect of Heat Input on Dilution, Hardness, and Microstructure in DMW Stainless Steel and Carbon Steel

The success of Dissimilar Metal Welding (DMW) occurred in optimal Heat-input (HI) parameters. The quality of welding joints was affected by dilution, hardness value, and intermetallic microstructure. DMW quality research was carried out on stainless steel SA SS312-TP304 and SA 53GrB carbon steel using the GTAW (Gas Tungsten Arc Welding) process with Heat-input of 1866.6 to 2362.2 J/mm. Visual observation on weld joints was not found weld defects. The optimal dilution area in the Schaeffler Diagram was obtained 35.35% austenitic area and without ferrite content. The lowest hardness value on carbon steel was 145 HV. The highest hardness value of 197 HV occurred in filler-metal dilution on carbon steel, so the difference in the value of hardness was high. The hardness value on stainless steel was 184 HV and in filler-metal stainless steel dilution was 172– 90 HV, so the difference in hardness value was low. Microstructure filler-metal dilution on stainless steel was austenite-dendritic, filler-metal dilution on carbon steel was fine-grained dendritic, and on allweld metal coarse-grained dendritic metal. HAZ stainless steel austenite microstructure and ferrite-pearlite carbon steel with an indication of a ferrite net. Observation of dilution, hardness value, and microstructure in DMW did not have a significant effect. This welded joint could be used as a reference in the DMW fabrication process for stainless steel and carbon steel pipe connections.

Interlayer Effect on Connection of Mild Steel ST37 and Stainless Steel 201 on Rotary Friction Welding

Friction welding is a type of solid state welding where the welding process is carried out in a solid phase to combine various types of ferrous and non-ferrous metals that cannot be welded by the fusion welding method but for welding different metals the welding results are less than optimal due to cracks on the surface of the welding results and differences in mechanical properties that cause the welding result to be brittle, therefore an interlayer is used. In this study, observations were made on the process and results of the joint friction welding using dissimilar metal material between mild steel ST37 and stainless steel 201 with copper interlayer. The results of the test will be a tensile test to see the maximum tensile strength and a hardness test to see the hardness value of the interlayer variation of 0.3 mm, 0.5 mm, 1 mm and without an interlayer. The conclusions obtained are: (1) The effect of the addition of an interlayer on the rotary friction welding process includes the friction phase, the forging phase and the results of welding parameters in the form of motor power, motor angular speed, the change in specimen length is greater without using an interlayer compared to using an interlayer while the duration of welding time is greater using an interlayer than without using an interlayer. (2) The maximum tensile test results were obtained at the 1 mm interlayer at 482.43 MPa and the maximum hardness test results obtained at the 1 mm interlayer were 321.34 VHN.

Cyclic behaviour and hysteretic model of austenitic stainless steel bolted T-stubs

The aim of this paper is to investigate the hysteretic behaviour of stainless steel bolted T-stub connections. A total of 22 bolted T-stubs in austenitic grade EN 1.4301 were tested under monotonic loading and cyclic loading under both variable and constant amplitudes. The tested T-stubs were carefully designed with two different bolt configurations and were fabricated with two types of stainless steel bolts – A4–70 and A4–80 thus allowing different failure modes to be obtained. Three additional bolted T-stubs in carbon steel grade Q345B were used as benchmark specimens to facilitate a direct comparison of the performance of carbon and stainless steel T-stubs under cyclic loads. Monotonic loading tests were conducted to acquire basic parameters of the cyclic loading protocols employed in the cyclic loading tests. The hysteretic responses of the tested T-stubs under two variable amplitude loading histories and three proportional constant amplitude loading histories were recorded and were further analysed in terms of failure characteristic, hysteresis response, skeleton curve, energy dissipation and strength degradation. Based on the evolution of the hysteresis curves, standard hysteresis loops were acquired and were used to develop a novel hysteretic model able to simulate the initial loading branch, the unloading branch and reloading branch of the hysteretic response. It has been demonstrated that the developed hysteretic models provide a close agreement with the obtained experimental results and can thus be used to estimate the expected energy dissipation of bolted stainless steel connections subjected to cyclic loads.

Experimental study on stainless steel high-strength bolted slip-resistant connections

Stainless steel structures have broad application prospects owing to their excellent corrosion resistance and mechanical properties. Current studies on stainless steel structures mainly focus on material properties and member behaviors. Several studies have reported on the performance of stainless steel joints and connections. In this study, a series of tests were performed on two fundamental parts of the stainless steel high-strength bolted slip-resistant connection, that is the stainless steel high-strength bolts and stainless steel faying surface treatment. For the stainless steel high-strength bolts, the tests were conducted on six types of bolts, including a new type of high-strength bolt made of S17400. The chemical compositions and full-range stress-strain curves were reported. The friction coefficients of the bolts with and without lubrication were measured. It was concluded that thread galling would probably occur during the application of the preload for bolts without lubrication. Lubricants would smoothen the tightening process and reduce the friction coefficient considerably. With regard to the stainless steel faying surface treatments, a total of eight types of treatment methods categorized into four groups were investigated. The surface roughness and slip factor were measured. It was concluded that under the commonly used steel structure faying surface treatments, the slip factor of the stainless steel plate was much lower than that of the carbon steel plate. The methods of clamping soft metal plates between the grit blasted stainless steel surfaces could improve the slip factor to approximately 0.30; a higher slip factor with a comparatively lower surface roughness would be obtained with the coating method. The proposed heavy brushing and mechanical scoring methods could considerably increase the surface roughness and slip factor. In addition, the slip factor was positively correlated with the surface roughness for most of the faying surfaces. The results of this study could benefit the development of related design codes.

The effect of laser scanning array structural on metal-plastic connection strength

The circular array structure is fabricated on the 304 stainless steel surface by fiber laser, and it is connected with the plastic under the condition of heating and pressurizing. The effects of heating temperature, connection pressure and coverage rate on the interfacial strength of the 304 stainless steel and plastics were studied, and the optimum process parameters of heating temperature and bonding pressure are obtained. The results show that the shear force of 304 stainless steel and plastic is the strongest when the heating temperature is 400 C. The strength of the connection joint is enhanced with the increase of the connection pressure, and the shear force of the 304 stainless steel and plastic connection joint is the strongest when the pressure is 70 kN. After laser treatment, the height and quantity of burr in the circular array structure have an important influence on the connection strength between stainless steel and plastic. The number of burrs in the height range of 10–20 μm is defined as Hm, which is main factor controlling the shear strength. When the Hm value corresponding to the burr height of 10–20 μm is less than 14.82%, the metal and plastic damage from the connection joint, and the connection strength increases with the increase of Hm. When the Hm is greater than 14.82%, the connection strength between stainless steel and plastic is more than that fracture strength of the plastic. And the shear force floats between 893N and 962 N, this is consistent with the average shear fracture force of plastics 946 N. The coverage rate of laser processing area has influences on the connection strength and machining efficiency. The results show that the corresponding minimum coverage rate is 38.5% when the stainless steel and plastic connection joint is damaged at the plastic, at which time the shear force is 901 ± 14.18 N.

Tensile strength Characteristics on Dissimilar Metal Friction Welding of Ti-6Al-4V & SS304L

In this research, the method of friction welding joints in Titanium and Stainless Steel with aluminium interlayer coating is created. The friction welding process is a solid-state joining process of dissimilar or similar materials. This friction welding process needs high rotational speed and high forging pressure. Titanium and stainless steel materials melting temperatures are around 1600OC. Welding process which needed high-pressure, temperature and good velocity regions. Titanium and stainless steels are coated 300OC ranges to applied aluminium spray coating method with constant pressure. The source of the aluminium coating is strong titanium and stainless steel adhesive strength. In this experimental project, four different trials of titanium and stainless steel joints have been performed at different speeds and constant forging pressures. Trial 4 connections of titanium and stainless steel made of 2100OC temperature and forging pressure of 60 MPa, friction time of 5 sec and friction pressure of 70 MPa. Friction welding experiments were completed with the help of friction time, forging pressure, rotational speed and friction pressure. Tensile load stress results are calculated by the UTM machine and evaluated the results of design experts with ANOVA table and RSM.

Behaviour of stainless steel beam-to-column bolted connections–Part 1: Simplified FE model

Most of the studies in the area of stainless steel structures concentrated on the structural performance of separate members, while the response of stainless steel connections (especially beam-to-column ones) still has not been well-researched. Some numerical investigations were conducted on these connections, however, in addition to their very limited number, they were all undertaken depending on computationally-demanding three-dimensional (3D) solid models. This paper presents for the first time a simplified finite element model able to simulate the behaviour of stainless steel beam-to-column bolted joints, whilst in the companion paper the suggested model is employed to carry out the first exhaustive parametric study on end-plate connections produced from stainless steel. The proposed model has been constructed using 3D shell elements, taking into account the complex interactions between connection components, as well as the geometric and material nonlinearities (including the considerable strain-hardening of austenitic stainless steel grades). The model was then verified against full-scale tests on stainless steel beam-to-column connections, and very good agreement between the experimental and numerical results (i.e. initial stiffness; ultimate moment capacity; overall moment-rotation response; and failure patterns) was achieved. With regard to computational time, the developed shell model demonstrated apparent superiority, consuming less than 20% of the CPU time of its 3D solid counterpart. Given its efficiency and high accuracy, the suggested model can pave the way for comprehensive systematic studies on beam-to-column connections made of stainless steel.

Tests of CHS-to-SHS tubular connections in stainless steel

A test program was conducted in this study on hybrid tubular T-, Y- and X-connections made of circular hollow section (CHS) braces and square hollow section (SHS) chord in stainless steel. A total of 18 specimens including 4 T-, 5 Y- and 9 X-connections were tested by applying axial compression to the end of circular brace. The failure modes, failure strengths and deformation curves of all specimens were obtained from experimental investigation. The influences of the key geometrical parameters including the brace diameter/chord width ratio (β), the brace/chord thickness ratio (τ), the chord width/thickness ratio (2γ) and the inclined angle (θ) between brace and chord on the load-carrying capacities of CHS-to-SHS tubular connections in stainless steel were carefully evaluated. Experimental results show that the initial stiffnesses and the failure strengths of hybrid tubular T-, Y- and X-connections increased with the increment of the β value, and increased with the decrement of the θ value. However, the influences of other geometrical parameters of τ and 2γ on the initial stiffnesses and the failure strengths are insignificant. Furthermore, the test strengths are compared with the nominal design strengths calculated using the design formulae of the current design specifications including CIDECT, Eurocode 3 (EC3), Australian/New Zealand Standard (AS/NZS) and Chinese Code, in which AS/NZS is the only design guideline for stainless steel structures. The comparison indicates that the design formulae of CIDECT, EC3 and Chinese Code are all conservative, in which the design formulae of EC3 are most conservative with the largest scatter of predictions. While, the design formulae of AS/NZS are generally appropriate for CHS-to-SHS tubular connections in stainless steel.

Validation of cyanide copper electrodeposited layer on test coupons for anti-seizing and outgassing in Tokamak vacuum vessel

A vacuum vessel which is the first confinement barrier of Tokamak fusion reactor should have numerous in-vessel components. Since those components are to be exposed to the plasma under ultrahigh vacuum condition and should be maintained during Tokamak operation, a threaded connection of vacuum vessel and in-vessel components is necessary. The threaded connection of stainless steel with the components causes difficulties during assembly or disassembly due to the large friction coefficient of stainless steel. To resolve this issue, anti-seize coating that does not affect the mechanical property, thermal stability, and outgassing rate of the threaded insert needs to be developed. In this study, adhesion, porosity, outgassing, and friction wear tests for a cyanide copper electrodeposited surface on 316 L austenitic stainless steel test coupons were performed to validate the high level of confidence in the performance of a cyanide copper electrodeposited threaded insert. The validation tests results showed that cyanide copper electrodeposition for anti-seizing could be applied to the 316 L stainless steel threaded insert in the vacuum vessel and in-vessel components of the Tokamak fusion reactor.

Carbon steel and stainless steel bolted connections undergoing unloading and re-loading processes

ABSTRACT A total of 50 bolted connections of carbon steel and stainless steel subjected to monotonic loading and cyclic loading conditions were investigated. The connection specimens were fabricated from carbon steel grades 1.20 mm G500 and 1.90 mm G450, as well as cold-formed stainless steel types EN 1.4301 and EN 1.4162 with nominal thickness 1.50 mm. In the monotonic tests, the specimens were tested under a constant loading rate by the displacement control test method, while in the cyclic tests, the specimens having the same dimensions as those in the monotonic tests were subjected to loading, unloading and re-loading processes, where displacement control and load control test methods were used. The results obtained from the cyclic tests were compared with those obtained from the monotonic tests. It was found that the ultimate loads obtained from the cyclic tests were, on average, larger than those obtained from the monotonic tests for carbon steel bolted connections; this was in contrast with the compared results for stainless steel bolted connections. The elongations corresponding to the ultimate loads obtained from the cyclic tests were, on average, larger than those obtained from the monotonic tests for both carbon steel and stainless steel, which may indicate that the loading processes in the cyclic tests generally delayed the bolted connection specimens from reaching the ultimate loads. Generally, the failure modes in the cyclic tests were consistent with those in the monotonic tests for the same specimen series, where the specimens mainly failed in the connection plate bearing.

Behaviour of top-seat double web angle connection produced from austenitic stainless steel

Beam-to-column connections are regarded as one of the critical elements in structures, especially in the case of bare metallic frame construction, as the overall structural performance is highly influenced by the connection behaviour. Significant research on stainless steel members has been reported in the recent past, but research on beam-to-column connections is still scarce. This paper presents an experimental and numerical investigation on the moment-rotation (M-φ) behaviour of a top-seat with double web angle (DWA) connection produced from austenitic stainless steel. A comprehensive investigation on the elasto-plastic deformation patterns observed in individual connection elements has been reported to gain in-depth knowledge in assessing overall stiffness, strength and rotational capacity of the considered connection type. Beam and column sections, as well as the connecting angles and fasteners used in the experiment, were produced from austenitic stainless steel AISI 316 L (equivalent to EN 1.4301). Significant strain hardening, as characterised by stainless steel, was observed throughout with the top angle experiencing most significant deformations. 3D finite element (FE) model was developed to replicate the observed experimental behaviour, and good agreement was observed between numerically obtained results and experimental observations. Based on the experimental and numerical results, semi-rigid connection behaviour was recognized for stainless steel alloy to lay a foundation for the development of the top-seat DWA connection. The observed behaviour for the considered stainless steel connections was compared with those obtained analytically for equivalent carbon steel connections; this comparison demonstrated enhanced ductility and significantly higher plastic moment for stainless steel connections.