Reduction Of Material Strength Research Articles

Dynamic mechanical response, energy absorption capacity, and constitutive modeling of polypropylene fiber-reinforced foamed concrete under high temperature

This study utilized a modified split Hopkinson pressure bar apparatus to subject polypropylene fiber-reinforced foamed concrete (PPFRFC) to substantial deformation loading at high temperatures and strain rates. Based on experimental results, the study systematically investigated the coupled effects of temperature and strain rate on the dynamic mechanical behavior of PPFRFC across a broad range of strain rates (0.001 s−1 to 1300 s−1) and temperatures (25 °C–600 °C). The findings revealed that elevated temperatures significantly affected various mechanical parameters including peak stress, plateau stress, elastic modulus, densification strain, dynamic increase factor (DIF), and energy absorption. Notably, with increasing temperature, the strain rate amplified the peak stress, plateau stress, and energy absorption, whereas its influence on the elastic modulus diminished. Microstructural examination revealed the absence of notable cracks in the pore walls after high-temperatures exposure. However, degradation of the cement matrix results in a loose skeleton structure within the pore walls, leading to a considerable reduction in material strength. Finally, a constitutive model was developed, considering the coupling effects of temperature and strain rate. This model accurately describes the mechanical response of the PPFRFC across various stages, including the elastic, plateau, and densification stages, as well as the stress drop behavior in the transition stage. Moreover, it effectively reflects the influence of strain rate and temperature coupling effects on the material's mechanical properties.

Study on mechanism of radial long cracks propagation on sliding surface of wheel brake discs

A long radial crack with a length of more than 60 mm was observed near the bolt hole of the brake disc of high-speed railway vehicles. It is necessary to study its causes and propagation mechanism. In this study, the gradient change of grain size was studied by microscopic observation of the brake disc after service. Through a variety of tensile tests, a relationship describing the gradient distribution of mechanical properties of materials was established. The radial crack propagation at the bolt hole of the friction surface was analyzed by using the extended finite element model (XFEM). The final crack lengths at the initial speeds of 250 km/h and 350 km/h are 32 mm and 43 mm, respectively. The reduction of material strength on the sliding surface and the stress concentration near the bolt hole make the crack propagate rapidly. The crack length increases with the decrease of residual strength. Cracks may continue to expand to the core through fatigue propagation, eventually leading to fatigue failure. It is proposed that the hot spot area around the bolt hole should be the key area for checking cracks during operation and maintenance.

COMPARISON OF FLEXURAL PROPERTIES OF PINEWOOD WITH FEA SIMULATION FOR MARINE APPLICATION

Pine wood sourced from pellet packaging, being abundant, holds potential for utilization in creating bio composites, particularly as activated carbon for laminated coatings in structural applications. However, there is a current lack of research identifying its specific properties as a coating material for Fiber Reinforced Polymer (FRP) composites. Fiber Reinforced Polymer (FRP) composites provide a highly adaptable solution for reinforcing and revitalizing existing structures in challenging marine conditions. This study delves into investigating the flexural characteristics of FRP pine wood composites, comparing the findings with Finite Element Analysis (FEA) results. Furthermore, the activated carbon derived from pine wood exhibits potential for resisting barnacle attachment when immersed in saltwater. For the flexural analysis, samples were produced using a silicone rubber mold, incorporating varying weight percentages (wt.%) of activated FRP pine wood, ranging from 2 wt.% to 10 wt.%. The outcomes of the study reveal that the introduction of activated carbon from pine wood leads to an enhancement in ultimate strength, reaching a maximum of 2700 MPa. Nonetheless, the results also indicate a reduction in material strength as the proportion of activated carbon pine wood is increased.

Thermomechanical shakedown analysis considering temperature-dependent yield stress based on the primal-dual eigenstress-driven method

Many industrial structural components are loaded repeatedly in high-temperature environments. The shakedown limit under variable thermomechanical loads is a critical factor in thermomechanical elastoplastic structure design assessment. The shakedown limit is weakened due to material strength reduction at high-temperature conditions.This paper develops an efficient shakedown analysis Primal-dual Eigenstress-driven Method(PEM) algorithm for temperature-dependent yield condition, which overcomes the obstacle of the original PEM method [1] which can only deal with constant material properties. The developed temperature-dependent PEM algorithm proposes a two-level iteration algorithm to determine the shakedown limit and the time-independent residual stress field. At the inner level the theoretical framework tailored to the temperature dependence problem is derived to solve the Karush-Kuhn-Tucker (KKT) conditions of the extended temperature-dependent shakedown theorem and establish an increment algorithm for forming residual stress fields. Besides, the lower bound safe multipliers are computed to verify the residual stress field obtained by inner-level algorithm. At the outer level an efficient fixed-point algorithm is applied to search the shakedown multiplier, where the corresponding updating strategy for the yield stress with temperature is nested. For practicability, the proposed algorithm is seamlessly integrated into commercial platform ANSYS, which is applicable to industrial structures. Four numerical examples from multiple perspectives show the effectiveness of developed PEM method.

Analysis of dynamic strain aging in titanium alloys using CPFEM

Titanium alloys have been reported to exhibit Dynamic Strain Aging (DSA) at intermediate temperatures that strongly influence their workability and performance under various loading conditions. It has been experimentally well established that DSA in these alloys is due to the dislocation pinning and unpinning by the Cottrell atmosphere. In the present work, a model for DSA is developed which is an extension of Kubin–Estrin–McCormick (KEMC) model. The model takes into account the reduction in material strength due to thermal softening along with its implications on DSA. The one-dimensional DSA model developed in this work is further extended to the CPFEM framework. The results from this model show good agreement with the experimental findings for a wide range of temperatures.

Axial compression performance of UHPCFCST stub columns after exposure to high temperatures

In this study, axial compression tests were performed on thirty ultra-high performance concrete-filled circular steel tube (UHPCFCST) stub columns after high-temperature exposure. Temperature, fiber type, and steel tube thickness were varied to examine the damage process, damage characteristics, load–strain curve, and load–displacement curve of the columns, as well as the effects of changing each parameter on the peak load of the UHPCFCST stub columns after high-temperature exposure. The test results reveal that the restraining effect of the steel tube prevented the core ultra-high performance concrete (UHPC) from bursting at high temperatures. The specimens remained unchanged in shape between 25 °C and 400 °C but showed significant damage at 600 °C. The ductility of specimens with either polypropylene fibers or a mix of polypropylene and steel fibers were better, and the increase in the thickness of the steel tube could prevent shear damage of the specimens. As the temperature increased, the ultimate resistance of the cross-section of the specimen tended to first increase and then decrease, with the curve gradually flattening. The ductility of the specimen was greater after 800 °C. In addition, a finite element model (FEM) of the behavior of UHPCFCST stub columns under axial compression after high-temperature exposure was established, and the stress development of the UHPC and steel tubes was analyzed. A material strength reduction factor was introduced to modify the existing method of calculating the axial compression resistance of cross-section after high-temperature exposure, and the results showed that it could be better predicted using superposition-based calculations.

The effect of differential mineral shrinkage on crack formation and network geometry

Rock, concrete, and other engineered materials are often composed of several minerals that change volumetrically in response to variations in the moisture content of the local environment. Such differential shrinkage is caused by varying shrinkage rates between mineral compositions during dehydration. Using both 3D X-ray imaging of geo-architected samples and peridynamic (PD) numerical simulations, we show that the spatial distribution of the clay affects the crack network geometry with distributed clay particles yielding the most complex crack networks and percent damage (99.56%), along with a 60% reduction in material strength. We also demonstrate that crack formation, growth, coalescence, and distribution during dehydration, are controlled by the differential shrinkage rates between a highly shrinkable clay and a homogeneous mortar matrix. Sensitivity tests performed with the PD models show a clay shrinkage parameter of 0.4 yields considerable damage, and reductions in the parameter can result in a significant reduction in fracturing and an increase in material strength. Additionally, isolated clay inclusions induced localized fracturing predominantly due to debonding between the clay and matrix. These insights indicate differential shrinkage is a source of potential failure in natural and engineered barriers used to sequester anthropogenic waste.

Thermal Effects on Mechanical Strength of Additive Manufactured CFRP Composites at Stable and Cyclic Temperature.

Additive manufacturing (AM) techniques can be applied to produce carbon-fiber-reinforced polymer (CFRP) elements. Such elements can be exposed to different environmental factors, e.g., temperature, moisture, and UV radiation, related to their operational conditions. From a variety of environmental factors, the temperature is one of the most typical. Temperature strongly influences matrix material joining together CFRP components, resulting in material strength reduction. Therefore, it is important to understand processes in the composite material caused by temperature. This experimental work investigated the thermal effects on the performances of AM CFRP composites. Specimens with unidirectional (UD) alignments of the fiber reinforcement were printed using the fused deposition modeling (FDM) technique. The printed specimens were subjected to two different thermal conditions: stable continuous at 65 °C and cyclic temperature between 50 and 70 °C. Tensile testing was performed to study the mechanical strength and Young's modulus of AM UD-CFRPs. In order to investigate the morphological structure on the surface of AM specimens, an optical microscope, scanning electron microscope (SEM), and digital microscope were utilized. Untreated (intact) samples attained the highest average tensile strength value of 226.14 MPa and Young's modulus of 28.65 GPa. The ultimate tensile strength of the sample group subjected to stable heat treatment decreased to 217.99 MPa, while the thermal cycling group reduced to 204.41 MPa. The Young's modulus of the sample group subjected to stable thermal exposure was decreased to 25.39 GPa, while for the thermal cycling group, it was reduced to 20.75 GPa. The visual investigations revealed that the intact or untreated specimen group exhibited lateral damage in top failure mode (LAT), the thermally stable group underwent edge delamination in the middle (DGM) as the nominated failure mode, and the explosive breakage at gauge in the middle (XGM) failure mode occurred in the sample from the thermal cycling group. Based on morphological observations at the microscale, the delamination, fiber pull-out, and matrix cracking were the dominant damages in the 3D-printed tensile-tested specimens. The molecular chains of the polymer changed their structure into an amorphous one, and only local motions of stretching occurred when the specimens were exposed to stable heating (prolonged). In the case of thermal cycling, the strain gradients were accumulated in the matrix material, and the local stresses increased as a result of the reheating and re-cooling exposure of the polymeric composites; the molecular motion of the long-range polymer structure was reactivated several times. Micro-cracking occurred as a result of internal stresses, which led to material failure and a reduction of the mechanical properties.

Characterization and Analysis of the Cedar Pass Landslide Complex, Badlands National Park

ABSTRACT The Cedar Pass Landslide Complex is located in Badlands National Park, South Dakota, and has created the need for regular maintenance and repair of Badlands Loop Road (South Dakota State Highway 240), the main highway traversing the park. Although there have been previous studies done in small portions of the complex, there has not been a comprehensive study to evaluate the interactions between smaller landslides and the sensitivity of the landslides within the complex to changing conditions. This study used extensive field mapping and slope stability modeling to delineate the boundaries of landslides within the complex, assess the stability, and investigate the sensitivity to fluctuations in groundwater, reduction in material strength, and erosion within the landslide mass. Results show that highway surface damage in the complex is related to the interaction of movement in both smaller and larger landslides. For instance, damage to the Cliff Shelf parking lot is related to small, destabilized blocks above the head scarp of the larger Prairie Island Landslide located to the southeast. In the Upper and Lower Wedge areas, previously mapped landslides were not confirmed, but highway damage may relate to settlement and erosion of an embankment fill and continued deformation of the massive Cliff Shelf paleo-landslide, which was thought to be dormant until the late 1990s. The overall slow and episodic movement of the landslides observed over the past 30 years may be attributed to dilatant strengthening.

Evaluations of Aluminum Tri-Hydroxide and Pristine Montmorillonite in Glass Fiber Reinforced Polymer for Vehicle Components

One of the safety requirements for the vehicle components is in terms of the flammability factor. Generally, the polymer material used for vehicle components is Unsaturated Polyester (UP). Unfortunately, this material is highly flammable. The addition of Aluminum Tri-Hydroxide (ATH) to UP is known to improve its flame retardancy, but its material strength is compromised. Moreover, the use of pristine Montmorillonite (MMT) rather than the commonly used organomodified MMT as a mixture to the ATH results in different material characteristics that could potentially minimise such a reduction of material strength. This manuscript discusses the combination of ATH and MMT in Glass Fiber Reinforced Polymer (GFRP) composites, specifically in terms of mechanical properties and flame retardancy. The increase of ATH content to UP decreases the flexural strength of GFRP, ranging from 34.3% to 63.4% lower than the neat GFRP. A slight increase of flexural strength is found in samples with ATH and MMT combinations (CA45M15), indicating that the addition of MMT does not dramatically change the flexural strength of GFRP. However, the addition of filler ATH, MMT, or a combination of both could increase the flame retardancy of GFRP. The addition of ATH leads to a slight increase of the UP initial temperature of decomposition, while the addition of MMT shows almost no notable differences. The flammability test shows that the additions of ATH, MMT or their combinations tend to decrease the rate of linear burning. Therefore, it can be concluded that the ATH and MMT could effectively improve the flame retardancy of GFRP.

Insight into the nondestructive performance evaluation of fiber‐reinforced polymer composite laminate immersed in produced water using embedded fiber Bragg grating sensor

AbstractFiber‐reinforced polymer (FRP) composites are exposed to various corrosive media during their service life, which adversely affects their material properties. Here, a novel approach is developed to investigate the long‐term performance of glass FRP composite laminate immersed in produced water generated in oil fields. This is achieved by monitoring the internal hygroscopic strain developed over the aging time using embedded fiber Bragg grating sensor. Composite material strength reduction over the immersion time is evaluated by conducting destructive mechanical tests at regular intervals, and the mechanism of property degradation is established. It is observed that property degradation follows first‐order kinetics and absorption of produced water medium obeys dual‐sorption diffusion kinetics. Moreover, the strain developed within the composite laminate is formulated by considering the unified influence of swelling and chemical degradation. The predicted strain closely interprets the experimentally recorded strain. This work proves that the strain measurement is an effective nondestructive technique to estimate the property of FRP composite laminates on a real‐time basis.

Effect of Microstructure and Relative Humidity on Strength and Creep of Gypsum

The wide range of gypsum facies observed all over the world and the strong heterogeneity that may be present even within a single facies often cause an inhomogeneous mechanical response that, if neglected, may be particularly dangerous in the framework of underground excavations. In addition, gypsum is particularly sensible to the presence of water. The high relative humidity conditions often registered in underground gypsum quarries may imply an additional worsening of mechanical properties. In the present study, the strength and the creep response of a natural gypsum rock facies are investigated, considering the influence of material heterogeneity and relative humidity conditions. The heterogeneity of the material, quantified with MIP and SEM analyses, is observed to strongly affect the mechanical response. To this intrinsic mechanical variability, the influence of an external parameter as the relative humidity is observed to generate an additional reduction of material strength and to increase the creep strain rate in the long-term tests. The effect of all these elements in the underground quarry framework is discussed and a constitutive model of these experimental results is provided.

Effect of Bleaching with 15% Carbamide Peroxide on Flexural Strength of Three Resin-Based Restorative Materials.

Objectives:Considering the increasing use of vital bleaching procedures and the increased application of newly introduced resin-based materials for tooth restoration, this study was designed to evaluate the effect of 15% carbamide peroxide gel on the flexural strength of three resin-based restorative materials.Materials and Methods:Three different types of restorative materials namely Beautifil II giomer, Cention N, and Z250 micro-hybrid composite resin were evaluated in this in vitro, experimental study. Twenty-four bar-shaped specimens were prepared from each restorative material, totaling 72 specimens, and were randomly assigned to two subgroups with and without bleaching procedure (n=12). In the bleaching subgroups, 15% carbamide peroxide gel was applied on the specimen surface 8 h a day for 14 days. The flexural strength of the specimens was then measured. Two-way ANOVA was used to compare the flexural strength of the specimens.Results:There was a significant reduction in the flexural strength of materials following exposure to the bleaching agent (P<0.05). The flexural strength was significantly higher in the groups that did not undergo bleaching. However, the mean flexural strength of the restorative materials was not significantly different (P=0.12).Conclusion:The flexural strength of Beautifil II giomer, Cention N, and Z250 micro-hybrid composite resin could be compromised subsequent to bleaching with 15% carbamide peroxide gel. The three resin-based restorative materials exhibited similar flexural strength values irrespective of the use or no use of 15% carbamide peroxide gel.

Testing, finite element analysis and design of high strength steel RHS T-joints

This paper investigates the structural behaviour of high strength steel (HSS) rectangular hollow section (RHS) T-joints under brace axial compression. Seven fabricated RHS T-joints which were composed of built-up steel tubes with a measured yield stress of 907 MPa were tested. Extensive finite element simulations on the fabricated RHS T-joints covering a wide range of geometric parameters and steel grades ranging from S460 to S960 were conducted. The chord face plastification, chord side wall failure and a combination of these two failure modes in the fabricated RHS T-joints were examined. The effects of material softening in the heat affected zones (HAZ) on the joint behaviour and influences of the steel grade, brace to chord width ratio (β) and chord width to wall thickness (2γ) on the suitability of the CIDECT strength equations for the fabricated RHS T-joints were evaluated. The deformation capacity and ductility of test specimens are shown to be reasonably sufficient. The effect of HAZ on the initial stiffness of the fabricated RHS T-joints is insignificant. The HAZ can lower the joint strength more significantly for medium β ratio; however, the joint strength reduction is less pronounced than the material strength reduction. The CIDECT strength prediction for chord face plastification is more unconservative for higher steel grade, larger 2γ ratio and smaller β ratio and becomes unduly conservative for the combined failure modes and chord side wall failure. It is suggested that 0.4 ≤ β ≤ 0.85 and 2γ ≤ 60β-1 for chord face plastification to allow for more effective use of HSS and corresponding reasonably conservative strength equations were proposed. Simplified strength equations which are based on an analytical model of plate buckling were proposed for chord side wall failure in the fabricated RHS T-joints with β = 1.0 and are also applicable for cold-formed steel RHS T-joints. A linear interpolation approach using the proposed strength equations at β = 0.85 and β = 1.0 is recommended for the combined failure modes in the fabricated RHS T-joints with 0.85 < β < 1.0.

Effect of artificial aging on high translucent dental zirconia: simulation of early failure.

Higher yttria content enhances the translucency and appearance of dental zirconia materials. Alterations in material composition also affect mechanical properties. The aim of this study was to compare the fracture load after artificial short-term aging of monolithic, full-contour zirconia crowns with different amounts of yttria-stabilization. Sixty crowns (thirty super high translucent crowns (5Y-Z) and thirty high translucent crowns (3Y-Z)) were produced to fit a model of a premolar with a shallow chamfer preparation. The crowns were cemented with self-adhesive resin cement on composite abutments. For each zirconia type, three groups of crowns (n=10) were allocated to: (i) cyclic loading (200N, 1Hz, 30,000 cycles), (ii) hydrothermal aging (3×20min, 134°C 3.2bar), or (iii) no treatment (control). Surviving crowns from the aging process were quasistatically loaded until fracture. The 3Y-Z crowns had statistically significantly higher fracture values (3,449N) than the 5Y-Z crowns (1,938N). The aging procedures did not affect load at fracture. Fractographic analysis showed that fractures started either at the crown margin or at the occlusal intaglio area. Higher yttria content leads to a reduction in material strength and damage tolerance, and this should be reflected in recommendations for clinical use.

Study on the Mechanical Properties of 125S Casing for oil and gas wells

In the process of evaluating the quality of a batch of 125S casing for oil and gas wells, it was found that the mechanical properties of different casing bodies in the same batch were significantly different, and the fluctuation range of yield strength was up to 60 MPa. The steel pipe with the lowest yield strength was not satisfied according to the technical standards. In order to study the causes of the uneven tensile properties, the chemical composition analysis, tensile tests, Charpy impact tests, Rockwell hardness tests and metallographic analysis were investigated for the two casings of this batch. Through the analysis of the test results, it is found that the chemical composition and metallographic structure of this batch of casing were conforming to with the design requirements, and the materials possessed high toughness. The problem of non-uniform performance of this batch casing was generated from the heat treatment stage during the production process. The excessive tempering temperature caused the reduction of material strength.

Effectiveness of hybrid fibre-reinforced polymer retrofitting on behaviour of fire damaged RC columns under axial compression

Reinforced concrete (RC) members when subjected to elevated temperatures due to fire undergo a significant reduction in material strength, concrete cover damage, and loss of bond of reinforcing steel with concrete. In such cases, to ensure the safety of the structure and to allow its future use, it is essential to assess the performance of the fire-affected RC elements and strengthen them appropriately. The objective of this study is to understand the effectiveness of hybrid fibre reinforced polymer (FRP) retrofitting technique on the emergency repair of the severely damaged RC columns under combined fire and axial compression loads. The hybrid FRP retrofitting technique uses the combination of near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) reinforcement and externally bonded (EB) CFRP wrapping for lateral confinement. In total, eleven short RC columns were damaged under a combination of thermal and axial compression loading conditions. The damaged columns were then retrofitted using an innovative hybrid FRP retrofitting technique. Experimental results reveal that the hybrid FRP retrofitting technique restored 71%–116% of the original capacity of columns before the fire damage.

Experimental study on the behaviour and strength of high strength steel CHS T- and X-joints

This paper presents an experimental investigation on high strength steel circular hollow section (CHS) T- and X-joints. In total, seven T-joints and six X-joints were tested under axial compression in the braces and failed by chord plastification. The brace to chord diameter ratio (β) ranged from 0.60 to 0.93 and chord diameter to wall thickness ratio (2γ) varied from 42.8 to 54.3. The test specimens were composed of CHS tubes which were cold-formed from one parental steel plate with a nominal yield stress of 960 MPa. The steel plate was manufactured by the quenching and tempering (QT) technique. A robotic welding machine was employed to perform the gas metal arc welding for the fabrication of the test specimens in order to achieve consistent welding quality and a low heat input of approximately 0.38 kJ/mm. The material strength reduction of the heat affected zones (HAZ) in the CHS tube was investigated. The deformation capacity, ductility and strength of the test specimens were examined. The current CIDECT and Eurocode design rules for normal strength steel tubular joints were assessed against the obtained test results. It is shown that the material strength reduction of the HAZ was minor, and the deformation capacity and ductility of the test specimens could be considered as reasonably sufficient. The CIDECT and Eurocode mean strength predictions are unduly unconservative for the T- and X-joint specimens.

Magnetic Metal Memory in the Assessment of the Technical Condition of Crane Girders for the Needs of Safety

Abstract With the passage of time of exploitation of means of technological transport, their degradation takes place and the threat to operational safety increases. The source of development of fatigue damages of gantry crane girders are areas of stress concentration caused by loads. The subject of the publication is to determine the possibility of diagnosing potential damage sites of the overhead travelling crane (girders) by magnetic metal memory (MPM). As a result of the test with the use of the TSC-7M-16 ferrite magnetometer, stress concentration areas were determined in which processes leading to the reduction of material strength or damage to the material structure may take place. Residual tangential magnetic field distributions and normal components of their gradients were determined. A magnetogram database for the needs of girder diagnostics was created.

Structural behaviour and design of high strength steel RHS X-joints

This paper aims to investigate the structural behaviour and static strength of high strength steel rectangular hollow section (RHS) X-joints under axial compression in the braces through tests and numerical analysis. Eight RHS X-joints which were composed of fabricated steel tubes with a measured yield stress of 907 MPa were tested. Extensive numerical simulations on the fabricated RHS X-joints in S460, S690 and S960 steel were conducted using finite element (FE) analysis. The FE model was validated against the test results. The investigated failure modes are chord face plastification, chord side wall failure and a combination of these two failure modes. The effects of the heat affected zones (HAZ) and suitability of the strength equations adopted by the CIDECT design guide for the fabricated RHS X-joints were examined. The deformation capacity and ductility of test specimens which failed by chord face plastification could be considered as reasonably sufficient. The effects of material strength reduction in the HAZ on the joint initial stiffness are minor, but could significantly lower the joint strength. In general, the CIDECT strength prediction is increasingly unconservative with increasing steel grade for the RHS X-joints failing by chord face plastification. However, the CIDECT strength prediction is generally conservative for the combined failure modes, and becomes increasingly conservative with increasing chord side wall slenderness for chord side wall failure. The suggested ranges of brace to chord width ratio (β) and chord width to wall thickness ratio (2γ) are 0.4 ≤ β ≤ 0.85 and 2γ ≤ 60β − 1 for the RHS X-joints failing by chord face plastification to allow for more effective use of high strength steel, and corresponding strength equations were proposed. An analytical model of plate buckling was proposed and the deformation-based continuous strength method (CSM) originally developed for designing non-slender stainless steel cross-sections was adopted for the design of chord side wall failure in the RHS X-joints with β = 1.0 and 2γ up to 50. The proposed design method is also applicable for designing chord side wall failure in equal-width RHS X-joints using cold-formed and hot-finished carbon steel and cold-formed stainless steel. A linear interpolation approach using the proposed strength equations at β = 0.85 and β = 1.0 is suggested for the RHS X-joints with 0.85 < β < 1.0 and 2γ ≤ 50 which failed by the combined failure modes. The proposed strength equations can produce much more accurate and consistent strength prediction than the CIDECT design guide, and were converted to design strength equations for the design of high strength steel RHS X-joints.