Monotonic Tests Research Articles

Experimental study and numerical simulation on shear behavior of steel and concrete composite beam with molybdenum tailing

To improve the flexural performance of steel–concrete composite beams and alleviate the problem of sand depletion caused by the application of concrete structures, this paper proposes a new type of steel-molybdenum tailings concrete composite beam. In order to further study the shear performance of the new type of steel-molybdenum tailings concrete composite beam, this paper couples molybdenum tailings replacement ratio (0%, 50%, and 100%) and shear span ratio (1 and 2) as research parameters, designs a total of six 1:2 scaled composite beam models, and conducts monotonic loading tests to study the failure process, failure mode, ultimate bearing capacity, deformation, and local strain of some typical measuring points of the new composite beam. The steel and concrete composite beam with the molybdenum tailing has the similar mechanical behavior for each ratio of the shear span to the effective depth with that of the steel and concrete composite beam. In addition, they have a little difference in the failure processes for each ratio of the shear span to the effective depth, whereas they show typical diagonal compression failure mode for the ratio of the shear span to the effective depth is equal to 1 and the representative shear-compression failure mode for the ratio of shear span to effective depth is 2, and have no obvious difference in failure mode for each ratio of the shear span to the effective depth. Their shear resistance mechanism is basically the same. Furthermore, based on the validated finite element model, this paper conducted a parameter extension analysis. The finite element results show that: The ultimate load bearing capacity of the steel and concrete composite beam with molybdenum tailing varies significantly with the beam section size (beam section width and beam depth), reinforcement ratio, and the ratio of the shear span to the effective depth; Whereas it has little relation to the steel plate thickness. This provides the necessity and feasibility to use the steel and concrete composite beam with the molybdenum tailing in engineering practice. The proposed equation in this study is based on the previous researches and the simulated and test results. The proposed equation is rigorous and thorough and the predicted results are highly accurate and effective.

Appropriateness of hydrostatic pressure-based modeling for strength differential effect in advanced high strength steel

Although numerous models have been proposed to describe the strength differential (SD) effect, their appropriateness and efficiency in the case of advanced high strength steel (AHSSs) have not been investigated. To this end, this study investigates the SD effect in AHSS using a hydrostatic-pressure-dependent plasticity theory. Although pressure model can effectively predict the SD effect in AHSSs with only one coefficient, the original formulation is experimentally inconsistent in the first quadrant of a yield surface. Hence, this study developed a new formulation to remove the inconsistency in a simple manner and validated the pressure model using new experimental data reported for two recently developed AHSSs: DP980 and MART1500Y. The SD effect is characterized based on monotonic compression and tension tests in three different directions with respect to the rolling direction to obtain the stress–strain curves and r-values. Next, the pressure model is used to predict the plastic behavior of both steel sheets. The parallel transition of flow stress and similarity in r-values between the tension and compression states supports the appropriateness of the proposed pressure-based modeling. Furthermore, these insights substantiate the fact that deformation mechanisms cannot explain the SD effect in both steel sheets. Therefore, complex yield functions that describe the SD effect in general materials are not necessary in the case of AHSS. Additionally, the pressure model is incorporated into a distortional plasticity model for applying it to springback in the bending process. The distortional plasticity model with and without the pressure model is calibrated using tension–compression curves, thereby revealing that the SD significantly affects the calibration. Finally, a U-draw bending experiment and the corresponding finite element simulation are conducted to compare the springback; the results show that considering the SD effect improves the springback simulation accuracy.

Experimental behavior of concrete-filled double-skin tubular columns with outer galvanized corrugated steel tubes under axial compression

Twelve lightweight and corrosion-resistant concrete-filled double-skin tubular (CFDST) columns with outer galvanized corrugated steel tubes (CSTs) and inner flat carbon steel tubes were subjected to monotonic axial compression tests. Compared to a traditional CFDST column, a CFDST column with a CST as the outer tube can reduce the longitudinal stress transmitted by the steel and better provide hoop confinement for the sandwiched concrete. The key parameters were the hollow ratio (χ) and inner tube thickness (ti). The failure mode, axial load capacity, strain and ductility of specimens with different parameters were analysed. There was noticeable slippage at the lock seam of the CST under axial loading, which releases the CST and results in the relatively low strength and ductility of the specimens. Keeping other parameters constant, an increase in χ and a decrease in ti led to a reduction in the peak load (Nu), strength index (SI) and ultimate strain (εcc). On the other hand, the ductility index (DI) increased as χ and ti increased. The strain development of the outer CST in one corrugation period was nonuniform. The hoop strain (εho) dominated at the crest of the CST, while the vertical strain (εvo) dominated at the trough. εvo gradually decreased from the trough to the crest, whereas εho increased from the trough to the crest. The applicability of the current standard design code formulae and axial load capacity equations for circular CFDST columns was evaluated using a newly expanded database, and a satisfactory axial load capacity model for circular CFDST columns with outer CSTs was proposed.

Compression performance of FRP-steel composite tube-confined ultrahigh-performance concrete (UHPC) columns

A new ultrahigh-performance concrete (UHPC)-filled fibre-reinforced polymer (FRP)-steel composite tube column (UHPCFSCT) was designed. This structure uses not only UHPC with high strength and durability to reduce the section size and improve the stiffness of the column but also FRP–steel composite tubes as confinement tubes to reduce the brittleness of the UHPC. Thirty-two UHPCFSCTs were subjected to monotonic axial compression tests. The key parameters include the number of FRP layers, FRP type, FRP hybrid condition and loading mode. The full-section-loaded specimens mainly exhibit shear failure, while the core-loaded specimens mainly exhibit middle expansion deformation. The stress–strain curves of UHPCFSCTs represent three types of columns with different numbers of FRP layers and FRP types: columns with weak, medium and strong confinements. The weak and medium confinement curves exhibit a softening section after the elastic–plastic stage, and the strong confinement curve shows a bilinear response. With the increase in the number of FRP layers, compared with those of the unconfined UHPC column, the ratios of the increases in peak stress, ultimate stress, and ultimate strain are 1.436∼2.794, 2.046∼4.822 and 0.778∼2.315, respectively. The bearing capacity of the CFRP-confined specimens is stronger, while the deformation capacity of the BFRP-confined specimens is stronger. The ultimate stresses of the core-loaded specimens are 19.6%∼30.6% higher than those of the full-section-loaded specimens. Existing strength models were used to evaluate the test data of UHPCFSCTs, and the Hu et al. model was used to predict the strength of UHPCFSCTs under core loading. Finally, through database regression analysis, a strength model that can be used to predict steel tube-confined UHPC, FRP-confined UHPC and UHPCFSCT strength under full-section loading was proposed.

An experimental and numerical study on the coupling effect of CLT wall-to-floor angle bracket connections

Cross-laminated timber (CLT) wall panels are commonly connected to the floor or foundation using metal connections, which play a critical role in determining the seismic performance and energy dissipation of the CLT shear walls. In this study, to comprehend the tension–shear coupling effect of the CLT wall-to-floor angle bracket connections under seismic loads, both monotonic and cyclic shear tests were conducted on the angle brackets that were also simultaneously applied with different levels of prescribed vertical axial tension. The influence of the co-existent axial tension on the horizontal shear performance of the angle brackets was analyzed. Furthermore, a numerical model of the angle brackets was developed and validated with the experimental results, which could predict the tension–shear coupling effect based on the monotonic loading scenario. Based on the numerical model, parametric analysis was conducted, and an analytical tension–shear interaction diagram representing the coupling effect of the angle brackets under seismic loads was established. It is found that with an increase of the axial tension from 0 to 30 kN, the shear resisting capacity of the angle brackets is diminished by 33.29%, and the pinching effect of their hysteretic load–displacement curves is mitigated. When the number of the connection-to-floor screws of the angle brackets was increased from 10 to 14, the shear resisting capacity of the angle brackets can be enhanced by 6.43%, and their shear strength degradation can be relieved by 12.85–56.25%. For the CLT wall-to-floor angle brackets, the analytical interaction diagram can be described using one bilinear function, which consists of the ratio between the shear to the shear resistance and the ratio between the tension to the pull-out resistance.

Ultra-lightweight low-carbon LC3 cement composites: Uniaxial mechanical behaviour and constitutive models

The present study aims to characterize the constitutive models of a novel ultra-lightweight low-carbon LC3 cement composite (ULCC-LC3) under monotonic uniaxial compression and tension tests. The compressive stress–strain curves of ULCC-LC3 were obtained based on axial compressive tests. The curve characteristics were analyzed and the data was fitted with the existing concrete compression constitutive model. Modified axial compression constitutive model for ULCC-LC3 was proposed and verified using the independent test data and related data of ULCC in other literatures. The characteristics of tensile stress–strain curves of ULCC-LC3 were also analyzed and studied. Based on existing experimental data, the applicability of the Tetsushi et. al.’s model to this composite was verified. The experimental results show that use of PE fibers can improve the ductility of ULCC-LC3. As compared with normal concrete, ULCC-LC3 exhibits a higher compressive peak strain (over 0.3% for fiber reinforced specimens and over 0.5% for non-fiber reinforced specimens). These findings contribute to the understanding of the mechanical behavior of ULCC-LC3 and provide constitutive models that can be used in numerical simulations and engineering applications to promote the use of this novel ultra-lightweight low-carbon material.

Ductile fracture of LYP225 steel: Effects of stress states and loading histories

This paper presents the experimental and modeling studies of the ductile fracture initiation of LYP225 steel, considering the stress state and loading history dependency. The monotonic material tests, including the notched round bars (NRBs), flat grooved plates (FGPs), and the shear plates (SPs), confirm the prominent stress state dependency of the ductile fracture. The increased stress triaxiality will significantly reduce the fracture strain, and the shear effect quantified by the Lode angle parameter will degrade the deformability under similar triaxiality. The Hosford-Coulomb fracture criterion can well characterize the relationship between fracture strain and stress state variables. Regarding the cyclic loading, a generalized expression of the cut-off region is proposed to consider the temporarily frozen damage accumulation under compression applied. In addition, the premature cyclic fracture initiation predicted by the monotonic fracture criterion highlights the necessity of considering the loading history effect. Based on the plastic strain memory surface, a reduced factor is introduced for the lower damage accumulation rate under cyclic loading. By comparing the testing and predicted plastic deformation corresponding to fracture initiation, the proposed fracture model is validated under different stress states and loading protocols, as indicated by the low average percentage errors of 4.02% for monotonic loading and 16.7% for cyclic loading.

Formulation and implementation of a hypoplastic constitutive model for interface behavior of mechanical joints

The effects of the contact interface must be considered during the design process of the assembly structures connected by mechanical joints. An advanced three-dimensional (3D) constitutive model is needed to describe the complex behavior of the contact interface in a detailed finite element (FE) model. However, the simplified Coulomb friction law, which is a bilinear model without considering the microslip behavior and stiffness degradation, is often applied to the surface-surface contact element for modeling the interface in commercial FE programs. In this paper, a new 3D hypoplastic constitutive model for the nonlinear interface behavior is presented. This model is built on the framework of hypoplasticity developed by Kolymbas and the hypothesis of continuous media. First, the general hypoplastic model is derived based on the kernel formula and several restrictions and simplified according to the characteristics of the contact interface. Then, the coefficients of the model are associated with the widely used physical parameters by combining the model with the initial stiffness ratio, normal contact law and Coulomb law. Benefiting from the hypoplastic theorem, the deduced constitutive model has a simple mathematical formulation in which only five parameters are contained. Simulations of several monotonic and cyclic shear tests show that the model can represent the salient characteristics of the joint interface (e.g. stick/microslip/macroslip behaviors, motion coupling and pressure-dependency). Thus, it can be used to predict the response of the joint interface from arbitrary multi-axial load histories more precisely. The constitutive model is then implemented in a commercial FE program via analysis of a double-beam structure subjected to harmonic excitation. And vibration experiments on several preload levels are performed to validate the effectiveness and the applicability of the proposed model to the real joints. The results calculated from the FE model with the improved reduction techniques are in good agreement with the experimental data.

Single- and double-wythe brick masonry walls subjected to four-point bending tests under different support conditions: Simply supported, rigid, non-rigid

Out-of-plane actions cause confined unreinforced masonry walls (URM) to develop what is known as an arching action. The role of arching is central in the resisting mechanisms of a wall; it contributes significantly to its loadbearing capacity as long as the wall’s deflections are minor, but gradually loses effect with increasing deflections, until collapse occurs. To date, limited experimental data is available on how arching develops in relation to the out-of-plane behaviour of the wall. This study brings new experimental evidence to this aspect. Quasi-static monotonic four-point bending tests were conducted on eleven brick wall strips, with reinforced concrete (RC) slabs affixed below and over the walls to simulate contact conditions of a typical construction system. The walls were tested vis-à-vis three different support conditions: simply supported, rigid, and non-rigid. The influence of these support conditions on the out-of-plane behaviour of the walls was studied on specimens with varying thickness – single and double wythe – and subjected to different levels of axial compression (or overload). While the former support condition was designed not to yield any arching inside the wall (unconfined masonry), the intermediate and latter solutions generated an arching action that was proportional respectively to the elongation of the wall (partially confined masonry), and its deflection (confined masonry). The walls were tested inside a bi-axial test setup that allowed not only the out-of-plane force but also the arching action to be measured, corroborating its central role in the development of the out-of-plane capacity of the walls. To support the observations, deformation characteristics and crack distributions were determined using two optical measurement systems placed in front and to the side of the walls, making use of the Digital Image Correlation (DIC) technique. The results of the tests are discussed in terms of failure mechanism as well as force and displacement capacity of the walls in relation to the investigated parameters. The test data is collected and made available to help with future research on the out-of-plane capacity of URM walls.

Modelling of rate-dependent inelasticity and damage in semi-crystalline polymers using an Eulerian framework

The present paper concerns the mechanical response of semi-crystalline polymers during cyclic loading, and it includes both modelling and experimental testing. The model is Eulerian in the sense that it is independent of measures of total deformation and plastic/inelastic deformations. It is able to account for such essential phenomena as strain-rate dependence, work hardening, and damage. The model was applied to uniaxial tension tests performed on high-density polyethylene (HDPE), which is a semi-crystalline polymer widely used in the industry. Two types of tests were conducted: monotonic tests, and loading–unloading tests. The model was able to reproduce the experimental results very well. The proposed model was also implemented as a UMAT in Abaqus, including an analytic tangent. The UMAT was used for simulating two 3D geometries. The implementation seems to be robust, and no convergence problems were observed.

Off-axis response and shear characterization of unidirectional ply-level hybrid carbon-fiber-reinforced polymer materials

Composite materials, among them Carbon Fiber Reinforced Polymers (CFRP), have become a key material in structural applications for lightweight structures such as spacecraft and aircraft. CFRP can be found under various quality grades and their mechanical performances increase with their cost and quality grade. In order to limit the costs of the material without degrading technical performances, hybridization could be of interest. However, assessing the conservation of quality standards of hybridized CFRP is crucial. This paper investigates the off-axis mechanical response of ply-level hybrid carbon composites, with varying thickness and material quality. Two types of carbon fiber prepregs were combined in the same laminate using symmetric and asymmetric stacking sequences. Monotonic quasi-static off-axis tests were performed to evaluate the non-linear stress-strain behavior of the laminates, with Digital Image Correlation used to measure strain. The apparent elastic modulus and the in-plane shear modulus were evaluated from the tensile tests at three off-axis angles. The results indicate that the hybrid laminates exhibit higher failure stress levels compared to simple laminates, with an intermediate failure strain. Overall, this study provides insights into the off-axis mechanical behavior of ply-level hybrid carbon fiber composites, with potential applications in the design of composite structures.

A triaxiality‐dependent fracture model for hot‐rolled sections made of S355 steel

AbstractFracture at net areas of steel sections often leads to premature failures of steel members, especially in the region of joints (bolted connections). This study develops a fracture model for hot rolled S355 steel for enabling a better understanding of the ultimate behaviour of steel sections through numerical simulations using the general‐purpose finite element software ABAQUS. Monotonic tensile tests are conducted on traditional dog‐bone plate specimens with a uniform cross‐section and notched plate specimens extracted from hot‐rolled I‐beams. Two material thicknesses and three notch radii per thickness are considered thus obtaining equivalent plastic strains at fracture over a wide range of stress triaxialities. The experimental fracture displacement is used as a threshold for the determination of the average stress triaxiality – equivalent strain history at the critical location (fracture initiation) of each plate model. Using regression analysis, an exponential approximation of the fracture locus is proposed to correlate the average stress triaxiality for a given equivalent plastic strain at fracture. The proposed model is then used to predict fracture initiation of unnotched tensile coupons and steel plates with a bolt hole in their centre extracted from the same steel sections. The test results are in good agreement with the numerical predictions thus demonstrating the efficiency of the proposed method.

Static and cyclic liquefaction of granular materials considering grain morphology

In this study, a series of undrained monotonic and cyclic triaxial shear tests were performed on glass sands to evaluate the effect of grain morphology on the static and cyclic undrained response of granular materials. The grain morphology of five test materials prepared with two glass sands with significant shape discrepancy was quantified with an image-based method. The test results show that as the overall regularity decreases, the peak and steady state stress ratios increase, and the dilatancy is suppressed. The development of excess pore water pressure and accumulated axial strain as well as the rate of stiffness degradation are lowered as the overall regularity decreases. The results also reveal that excess pore water pressure is correlated well with the cyclic stiffness degradation index. The liquefaction resistance decreases with the increase of the overall regularity.

Full‐Scale Composite Moment‐Resisting Frame with Dissipative Bolted Connections under Monotonic Loads: Experimental versus Numerical Results

AbstractThe detailing of typical semi‐rigid beam‐to‐column joints in Germany was based on the assumption of low seismic actions, thus design could be covered by wind and gravity actions. Given the recent seismic hazard assessment of the national territory, in which the seismic risk was proved to be higher than formerly considered, questions have been raised about the approach to steel and composite joint design and detailing. Answers to the effect of increased seismic demands on semi‐rigid connections and to joint performance are provided in new studies of the authors. The performance (insufficient bending resistance and stiffness, brittle failures) and detailing deficiencies (small weld sizes, weak web panel) require improvements in order for joints to transfer higher bending moments and to conform to prEN 1998‐1‐2. Pre‐test analyses showed that, in comparison with current typical joints, improved solutions have 40% / 70% higher sagging / hogging bending resistance and sustain plastic deformations within connections prior to failure. Thus, the performance of joints designed for moderate‐low seismicity is experimentally assessed through monotonic and cyclic tests on composite frame specimens. The focus of the paper is on the monotonic response.

Rotating bending fatigue behaviour and quasi‐static tensile properties of Wire Arc Additively Manufactured 308L stainless steel

AbstractWire Arc Additive Manufacturing (WAAM) is a direct energy deposition method used to manufacture steel components by using an electric arc as a heat source to melt a metal wire and deposit it layer by layer. In this study, monotonic tensile tests, standardized Charpy impact tests, and rotating bending fatigue tests are executed to characterize the mechanical properties of WAAM 308L stainless steel using specimens extracted from additively manufactured plates. In particular, monotonic tensile properties are investigated in three directions: that is 0, 90, and 45 degrees with respect to the plane of deposition, whereas the fatigue strength is quantified for one direction only, i.e. 90 degrees since this is deemed to be the weakest.The mechanical characterization highlights that WAAM 308L SS shows an anisotropic behaviour, an enhanced strain‐rate sensitivity, and an overall reduced yield strength as compared to the base material 308L. The anisotropic material behaviour is explained by the microstructure morphology since the austenite grains form anisotropic columnar zones due to an uneven heat profile during production. During the fatigue tests, the relatively high strain rate sensitivity causes susceptibility to self‐heating at relatively low loading frequencies, i.e. below 100Hz.

Effect of Moisture Content on the Permanent Strain of Yellow River Alluvial Silt under Long-Term Cyclic Loading

The Yellow River alluvial silt has unique engineering properties and is unstable when encountering moisture. The mechanical properties of silt subgrade can be impaired by the increase in moisture content due to rainwater infiltration, which has a negative effect on traffic safety. To further reveal the influence of moisture content on the deformation characteristics of silt, a series of monotonic and cyclic triaxial tests were conducted on the alluvial silt with different moisture contents. The development law of cyclic accumulative permanent strain and the effects of moisture content, cyclic deviator stress and confining pressure on the axial permanent strain of silt were explored. The study shows that the static strength of silt decreases with the increase in moisture content, and the attenuation of static strength is mainly caused by the decrease in cohesion due to the reduction in matric suction. The permanent strain rises linearly with the increase in moisture content and cyclic deviator stress, and decreases with the increase in confining pressure. An empirical model for predicting the permanent strain of silt under long-term cyclic loading considering the effect of moisture content was established. Compared with the test data and other existing models, the established model has easier obtained parameters, higher prediction accuracy and better applicability.

Effect of Openings on the Torsional Behavior of SCC Box Beams Under Monotonic and Repeated Loading

Repeated Torsional loading occurs in many concrete structures, such as offshore structures, freeways, multistory parking garages, and other structures; however, repeated torsional loading is still poorly understood. This study aims to investigate the effect of openings on the ultimate and cracking torques, angle of twist, and modes of failure of self-compacted R.C. box beams under monotonic and repeated loading. Two groups of eight half-scale box beams with different numbers of circular openings in the web with a diameter of about 30% of the hollow box dimension were investigated. The first group (I) included four beams: one was the control box beam without openings, whereas the rest of the beams were hollow with one, two, or three openings in the web tested under monotonic loading. The second group (II) consisted of the same details as the first one tested under repeated loading. The range of the repeated loading was about 30% and 60% of the ultimate load of the monotonic tests. The study showed that the cracking and ultimate torques and the angle of twist of the tested beams were significantly reduced due to openings in the web. Results revealed a more pronounced effect for monotonic loading, with a maximum reduction of 20% and 26.8% in cracking and ultimate torsional strength, respectively, compared to monotonic loading. Moreover, results revealed that repeated loading causes inelastic deformations in proportion to the number of loading cycles. Doi: 10.28991/CEJ-2023-09-09-015 Full Text: PDF

Full‐Scale Steel Moment‐Resisting Frame with Dissipative Bolted Connections under Monotonic Loads: Experimental versus Numerical Results

AbstractIn the light of the new National Annex in Germany (DIN‐EN‐1998‐1/NA), in which extended seismic areas and higher spectral accelerations are specified, dissipative design of steel structures gains significance for moderate seismic regions as well. The use of the inherent ductility of steel can lead to an effective and safe design. Thus, a series of beam‐to‐column joints with dissipative bolted connections for Moment‐Resisting Frames were developed within an ongoing German‐funded project. The aim is to develop joint typologies, which can dissipate energy through a ductile response of the connection. Joints from the German catalogue of typical connections were used as a starting point. They were investigated and improved using FE numerical simulations to exclude brittle failure and provide dissipative, semi‐rigid and partial‐strength beam‐to‐column joints, which could allow for the use of behaviour factors in the range 1.5÷3. The optimized joints were used within full‐scale frame specimens (10.0 m length, 3.0 m height) and tested under monotonic and cyclic loads. The paper provides an overview of the: ▪ experimental program; ▪ monotonic test results; ▪ numerical results of the calibrated numerical model, as well as the response of the beam‐to‐column joints; ▪ main conclusions.

Textile Reinforced Mortar/masonry joints under reverse cyclic in-plane shear

This study investigates for the first time the effect of reverse cyclic loading on the shear bond capacity of Textile Reinforced Mortar (TRM)/masonry joints. The single-lap/single-prism set-up was adopted for monotonic tests, whereas a modified version thereof was developed for reverse cyclic tests making use of a single piston. Specimens comprised wallettes reinforced with glass fiber TRM overlays of various bond lengths (BL = 250–50 mm, step = 50 mm). Reverse cyclic loading: (i) bore no effect on the joints’ failure modes; (ii) resulted in a reduction of the shear bond strength by <20%.

Mechanical Properties and Microstructure of Dissimilar S355/AA6061-T6 FSW Butt Joints.

The aim of this paper is to analyse the mechanical properties of butt joints between S355 steel and 6061-T6 aluminium alloy, as well as their relationship to changes in the structure of the material caused by welding. The effect of the tool offset was analysed in particular. For the analysis, tensile tests were carried out using macro- and mini-specimens taken from S355/AA6061-T6 joints and base materials. In addition, the macro- and microstructure of the joints was determined, the hardness profiles in the joints were analysed, and fractographic analysis of the fractures of the specimens was carried out. Based on the results of the macro- and microstructure examinations, typical friction stir welding (FSW) joint zones were characterised. The microstructure was observed in the interface line of the materials on the root side, the negative effect of which on the quality of the joint was confirmed by digital image correlation (DIC) strain analysis during the monotonic tensile test. The highest average value of su = 141 MPa for the entire joint was obtained for a 0.4 mm tool offset. The highest average value of su = 185 MPa for the selected joint layer was obtained for a 0.3 mm tool offset. Fracturing of the joint in the selected layer for the tool offset values of 0.3 mm and 0.4 mm occurred in the weld nugget zone (WNZ) where the lowest hardness was recorded.