Notch Strength Research Articles

Comparison of SMAW and GTAW Welding Properties

Low carbon steel is a type of welding with good formability, machinability, hardenability, and weldability. It can be welded without preheating or postheating processes. Notch strength and sensitivity to weld cracking are the factors that influence the weldability of low carbon steel. SMAW and GTAW welding techniques were applied in this study. In addition to its mechanical properties, parameters and the type of welding process also affected the corrosion of the welded joint. Local corrosion attacks were easier to occur on one than the other welded joint due to significant differences in chemical composition and microstructure. Welded joints in a chlorine-rich environment have a high corrosion rate. In comparison to base metal, low-weld metal triggers high corrosion.

Notch strength evaluation for highly ductile Al/Cu bi-metal fabricated by the roll-bonding technique under pure mode I and pure mode II loading conditions

In this work, the aluminum alloy AA1050 and copper sheets are cladded together using the roll-bonding technique to make rectangular bi-metallic joints. To examine the notch strength of this bi-metal under quasi-static loading, central slits with two U-shaped ends are introduced into the bi-metal. The slit orientation angle is adopted such that for horizontal slit, the notched rectangular specimen experiences pure mode I loading. However, when the slit orientation angle changes to about 67 degrees, which is obtained by the finite element (FE) analysis, the U-ends of the slit are subjected to pure mode II loading. Considering three different notch tip radii, two loading conditions, and three replicates for each test configuration, totally 18 U-notched specimens are produced and tested with the goal to measure the notch strength of bi-metal experimentally. According to the experimental observations, the bi-metal joint is perfect such that crack initiates from the notch in the whole thickness, proposing that the whole bi-metal joint can be considered as a single bulk material. Based on these observations and thanks to the virtual isotropic material concept (VIMC), the AA1050/Cu bi-metal is firstly equated with a virtual bulk material having homogeneous and isotropic behavior. Secondly, due to highly ductile behavior of the bi-metal joint proven by the associated tensile stress–strain curve, the fictitious material concept (FMC) is used to equate the virtual isotropic material obtained from the previous step having elastoplastic behavior with a fictitious material having perfectly linear elastic behavior. Finally, the VIMC and FMC are linked to the U-notch maximum tangential stress (UMTS), U-notch mean stress (UMS), and U-notch strain energy density (USED) criteria to predict the notch strengths of the bi-metal joint experimentally measured. With always higher than 92% accuracy for all VIMC-FMC-UMTS, VIMC-FMC-UMS, and VIMC-FMC-USED combined criteria, it is shown that the two-level strategy of material simplification, i.e., VIMC-FMC, is quite successful to be combined with different brittle fracture criteria for predicting the notch strength of AA1050-Cu bimetals under both pure tensile and pure in-plane shear modes of loading.

Experimental and computational meso-scale investigation on the deformation and failure behaviors of plain woven SiC/SiC with intrinsic and manufactured defect

For plain woven SiC/SiC composites used in aerospace thermal-structural applications, not only the pristine material properties but the open-hole performance are of critical concern for the components in service. This study investigated the influence of intrinsic pores induced during SiC matrix preparation and manufactured holes on the macro mechanical properties of plain woven SiC/SiC through experimental and numerical methods. Tensile tests at room temperature were conducted on SiC/SiC specimens with different hole apertures and configurations, and the digital image correlation (DIC) method was employed for full-field strain measurement. Moreover, micro-computed tomography (μ-CT) was utilized to characterize the internal microstructure, original defects, and failure fractures. Based on the reconstructed mesoscale model, the tensile strength and failure mechanisms of pristine and open-hole specimens were predicted and analyzed, with the models validated against the experimental results. The results showed that the inter-tow defects play an important role on the deformation and failure of pristine SiC/SiC specimens during tensile loading. The notch strength results indicated that SiC/SiC exhibits weak notch sensitivity, and the local mesoscopic deformation of the notch is affected by the combination of macroscopic stress gradients and mesoscopic structures. The mesoscale simulation results showed that the position of the hole has a significant impact on the strength of the single layer SiC/SiC composite. The more the notch invades the warp, the greater the decrease in load-bearing capacity, and the relative position of the weft mainly determines the crack propagation path. The failure mode in the simulation results is consistent with the experimental findings, indicating that the simulation model, which considers the weave architecture, can better explain the notch failure behavior of Ceramic Matrix Composites (CMCs).

Microstructural Engineering of Mn-Alloyed Austenitic Steel for Hydrogen Storage and Delivery

Austenitic stainless steels are commonly used for hydrogen storage and transportation. These alloys have a high nickel (Ni) content, which increases alloy cost. In this study, high manganese (Mn) austenitic alloys were evaluated as potential lower cost alternatives. Two heats of high Mn alloys with different stacking fault energies (SFE) of ~29 mJ·m-2 and 49 mJ·m-2 were acquired. Additionally, a new vanadium (V)-microalloyed high Mn alloy was designed to achieve a SFE of 47 mJ·m-2 to minimize planar slip deformation mechanisms. Post-processing via cold working in conjunction with aging was also performed on the V-microalloyed high Mn steel. Hydrogen embrittlement sensitivity was investigated using circumferential notch tensile specimens cathodically charged with hydrogen in a 0.05M NaOH electrolytic solution. The alloys were compared to a cold-worked 316L stainless steel, which exhibited no strength loss due to hydrogen. The high Mn alloys with SFE of ~29 mJ·m2 and 49 mJ·m-2 had notch strength losses of 11 and 6 pct, respectively. The V-microalloyed high Mn steel in the as-hot-rolled condition had a notch strength loss of 17 pct. The V-microalloyed high Mn steel in the cold worked and aged condition indicated no notch strength loss in hydrogen, which was comparable to the performance of the 316L stainless steel.

Effect of friction pressure on microstructure and tensile properties of linear friction welded Ti–6Al–4V alloy joints

This investigation aims to study the influence of friction pressure (FRNP) on the evolution of microstructure and tensile properties of Ti6Al4V alloy joints developed using linear friction welding (LFW) for aeroengine applications. The Ti6Al4V alloy plates of 6 mm thickness were joined using different levels of FRNP from 10 MPa to 30 MPa. The weld joint quality was analyzed employing stereo-zoom microscope. The microstructure of LFW joints was studied using optical (OM), scanning electron (SEM) and transmission electron microscope (TEM). The hardness and tensile properties were evaluated and correlated to the microstructure of joints. The fractographs were studied using SEM and correlated to the hardness. The LF welded Ti6Al4V joints made using the optimum level of FRNP of 20 MPa exhibited greater tensile strength (UTS) of 993 MPa, and elongation (EL) of 8%. It showed notch tensile strength (NTS) of 1073 MPa and notch strength ratio (NSR) of 1.041 revealing ductile fracture. The LF welded Ti6Al4V joints revealed 96.41%, 104.10% and 66.67% of UTS, NTS and EL of base metal. The greater smooth and notch tensile properties of joints are principally imputed to maximum refinement of alpha + beta grains at interface of joint.

A fast procedure to predict the notch strength with the coupled criterion

An efficient procedure is described for applying the Coupled Criterion in order to estimate the notch strength of a structure made of a brittle material. It is based on the representation of the size effect law, which gives the notch strength as a function of a characteristic structure length. A new analytical formulation of this function, which depends on only three parameters, is provided. Three parameters must be identified, requiring only three finite element calculations. The accuracy of the approach is verified by analyzing various notched structures.

Optimization of process parameters of rotary friction welding of low alloy steel tubes using response surface methodology

Rotary Friction Welding (RFW) is a solid-state welding process that is becoming increasingly popular due to advantages such as low weld heat input, high production efficiency, ease of manufacture, and environmental friendliness. Rotary friction welding can weld materials that are difficult to fuse using fusion welding techniques. The main objective of this study is to join SA 213 T12 and SA 213 F12 low alloy steel (LAS) tubes using a rotary friction welding process and to optimise welding parameters such as friction pressure, forging pressure, and rotating speed. To optimise the welding conditions, the response surface method (RSM) was applied. Empirical relationships were developed to predict tensile properties such as tensile strength (TS), yield strength (YS), elongation (EL), notch tensile strength (NTS), and notch strength ratio (NSR). Using the test results, the tensile properties of the rotary friction-welded low alloy steel (LAS) tubes were determined. The optimum process parameters for better tensile properties of the rotary friction welded joint are found to be rotation speed (N) 60 rps, friction pressure (FF) 0.851 MPa/s, and forging pressure (FOF) 0.851 MPa/s.

Burst speed prediction and reliability assessment of turbine disks: Experiments and probabilistic aspects

Under harsh and stochastic environmental conditions, turbine disks may exceed their maximum allowable speed and then burst. Aeroengine certification requires demonstrating its integrity at higher rotation speeds than the designed steady-state speed. In particular, testing the burst speed of turbine disk is an essential part of this procedure. In this work, based on the average stress approach, a novel model for turbine disk burst speed assessment is proposed, in which the notch strength ratio and the stress triaxiality parameter are introduced to characterize the inhomogeneous stress field and multiaxial stress state, respectively. Disk overspeed test data are utilized for model validation and comparison, and results show that the proposed model matches the experimental evidences well. Furthermore, a probabilistic framework is built to characterize the influence of material property dispersion on burst speed, and the proposed model is extended to a probabilistic one. Finally, the relationship between the safety margin and the reliability index is established, which provides a reference for reliability-based design and evaluation of turbine disk.

Notch effect in 20% short carbon fibre-PA reinforced composites under quasi-static tensile loads

In this work the static behaviour of notched specimens made of a polyamide-6 thermoplastic material reinforced with 20% of short carbon fibres was investigated. In more details, U and V-shaped notched specimens were manufactured by a wire cutting process from injected plates and tested under tensile quasi static loadings. All in all, 42 new experimental data have been provided, related to different notch root radii and notch opening angles, investigating the effect of the local geometry on the notch strength. Taking advantage of the scanning electron microscopy, a detailed damage analysis was also carried out on the fractured specimens, identifying the main damaging mechanisms occurring in the highly stressed regions close to the notch tip. Eventually, all the experimental data from the notched specimens have been reconverted in terms Generalised Notch Stress Intensity Factors, GSIFs, and summarised in a single scatter band.

Providing a virtual material for simple estimation of fracture in U-notched highly orthotropic specimens with nonlinear behavior under mixed mode I/II loading

This research investigates the fracture toughness of U-notched Russian pine specimens with highly orthotropic nonlinear behavior under mixed mode I/II loading conditions theoretically and experimentally. The notch strength of orthotropic specimens is successfully predicted by introducing a novel two-step model of material simplification. Adopting this model, the nonlinear orthotropic material is equated with a virtual linear elastic isotropic material by coupling the Virtual Isotropic Material Concept and the Equivalent Material Concept. Therefore, the linear elastic notch fracture mechanics criteria, such as the mean stress and point stress models, can be basically employed to predict the notch fracture toughness of U-notched specimens made of nonlinear orthotropic material. Accordingly, the experimentally obtained notch strength of nonlinear orthotropic samples is predicted in the form of fracture limit curves and the curves of fracture initiation angle. It is shown that the two-step model proposed can be successfully applied for mixed mode I/II fracture estimation of notched orthotropic specimens with nonlinear behavior.

Effect of notch severity and crystallographic texture on local deformation and damage in commercially pure titanium

The evolution of local deformation and damage in commercially pure titanium was studied for flat un-notched, U-notch and V-notch tensile specimens with two distinct initial textures namely off-basal (BA) and prismatic-pyramidal (PP) orientations to establish the micro-mechanisms of anisotropic deformation and damage in titanium for different notch severity. BA orientation showed higher apparent yield stress, greater plastic deformation, better notch strength ratio (NSR) value than PP orientation for all the cases. Electron backscatter diffraction investigation showed an increase in the number of twins per grain and the thickness of twins with notch severity irrespective of orientation with BA samples showing higher twin activity than corresponding PP samples. In addition, extensive slip activity was observed within twins and parent grains in BA orientation unlike PP orientation that showed slip activity near grain boundaries. These microstructural observations correlated well with strain measurement from digital image correlation which also showed that the local maximum longitudinal strain for BA orientation increased with notch severity unlike PP orientation. Viscoplastic self-consistent crystal plasticity simulations at the mesoscale indicated that the activity of basal, pyramidal <c+a> slip systems and twinning increased at the expense of prismatic slip with an increase in notch severity for both the orientations. The experimental observations show extensive diffuse necking in BA orientation, while higher fraction of fluted voids with c-axis aligned along the major axis of the void are observed in the PP orientation. Prismatic slip promotes nucleation and growth of voids in the prism plane which is perpendicular to the tensile axis for PP orientation contributing to void growth along c-axis forming fluted voids, while higher twinning in BA orientation leads to fewer fluted voids, thus highlighting the significant role of crystallographic texture in controlling anisotropic deformation and damage mechanisms in titanium.

Notch strength and notch fracture mechanisms of a cast Mg-Gd-Y alloy

This study aims to elucidate the mechanical properties and fracture mechanisms of cast Mg-6Gd-3Y-0.4Zr (wt.%) (GW63) alloy in the presence of geometrical discontinuities induced by notches. Notch strength is evaluated by room-temperature tensile tests using circumferentially notched bars of different notch acuity. Finite element calculations suggest that notch fracture is controlled by the von Mises stress and effective plastic strain at the notch tip. Through fractographic observations and EBSD analysis on samples subjected to interrupted tests, a cleavage micro-cracking behavior uncommon for conventional Mg alloys is found to dominate notch fracture. Grain-sized cleavage microcracks tend to occur along the basal plane of grains favorably oriented for basal slip, which is explained by crack nucleation at co-planar slip bands blocked by the grain boundary according to Smith and Barnby's theory. Failure is initiated by the accumulation and coalescence of such microcracks in the notch vicinity. The unexpected cleavage micro-cracking behavior is mainly ascribed to the RE solutes that suppress {10–12} twinning, and is responsible for the limited deformation capacity and notch strength of the cast-T6 GW63 alloy with coarse grains and significant strengthening due to precipitation.

Tensile and water absorption properties of notched glass fiber/polypropylene and glass fiber/polyoxymethylene injection-molded composites

In this work, the tensile properties and hydrothermal aging behavior of notched glass fiber/polypropylene (GF/PP) and glass fiber/polyoxymethylene (GF/POM) prepared by injection molding were investigated. It is shown that the notch strength ratio (NSR) of GF/PP was higher than that of GF/POM with the same fiber mass fraction. With the increase of the fiber mass fraction, the NSR decreased. After 30 times cyclic loading–unloading tensile process, the decrease rate of tensile strength was not evident at 55% level cyclic loading, whereas the decrease rate was over 15% when cyclic loading reached 85% level. The specimens were exposed to 80 °C hot water to investigate the hydrothermal aging behavior. For the water absorption properties, the weight gain and weight loss of GF/PP barely changed after 1600 h. The weight of GF/POM increased within 25 h, and then reached equilibrium. After 1600 h, the weight loss of GF/POM was below 0.4%. The effect of immersion time on the tensile strength of notched GF/POM was noticeable. The decrease rate of tensile strength of GF/POM reached 21% after 1600 h, owing to the hydrolysis of matrix and the weakened interface between matrix and glass fibers.

Effect of welding consumables on shielded metal arc welded ultra high hard armour steel joints

Abstract Materials with high hardness are usually preferred in armour applications and are difficult to weld due to high Carbon Equivalent (C.E). In this investigation, an attempt was made to weld Ultra-high Hard Armour (UHA) steel (having C.E of 0.91) by Shielded Metal Arc Welding (SMAW) process using three electrodes (i) austenitic stainless steel (ASS- E307-16), (ii) super duplex stainless steel (SDSS-E2594-16) (iii) low hydrogen ferritic (LHF-E12018M-low-alloy steel electrode). The mechanical properties (tensile, impact toughness, and microhardness) were evaluated and correlated with microstructural features along with Cr eq /Ni eq ratio of weld metal. The joints fabricated using LHF electrodes showed superior strength of 962 MPa and hardness of 341 HV. The joints made using ASS electrode showed superior impact toughness of 72 J and Notch Strength Ratio (NSR) of 1.32 due to the higher energy absorption capability of the austenitic phase. At the weld interface, joints fabricated using ASS and SDSS electrodes show the unmixed zone (UMZ) and martensitic band (MB) due to sudden change of crystal structure (Face Centred Cubic (FCC) / Body Centred Tetragonal (BCT)). It is also found that the strength property increases (651 MPa to 856 MPa) with an increase in Cr eq /Ni eq ratio (1.87 to 3.2) of weld metal and with a decrease in ductility.

Study on notch tensile properties of Magnetically Impelled Arc Butt (MIAB) welded carbon steel tubes

Magnetically Impelled Arc Butt (MIAB) welding is a pressure welding process that uses the circumferential rotating arc to cause uniform heating of the faying surfaces. In this work, notched tensile testing of MIAB welded Carbon steel was carried out to determine the notch sensitivity of Thermo-Mechanically Affected Zones (TMAZ) and to compare the notch tensile property of these zones with the base metal property. In MIAB welding, after sufficient melting of the faying surface, a short pulse of high current is applied to expel the molten metal and impurities from the interface before welding. Insufficient expulsion and formation of Light Band (LB) zone at weld interface resulted in lower Notch Tensile Strength (NTS). Incomplete expulsion with lower upset current at the weld interface contributes to lower Normalized Notch Strength Ratio. Instead higher upset current contributed to higher NTS due to complete expulsion and stronger acicular ferrite formation. Other TMAZs away from the weld interface showed higher notch tensile strength with Notch Strength Ratio (NSR) and Normalized Notch Tensile Strength Ratio (NTSN) greater than unity.

Notch tensile properties of Magnetically Impelled Arc Butt (MIAB) welded T11 steel tubes

The Magnetically Impelled Arc Butt (MIAB) welding process uses a rotating arc as its heat source and is known as an efficient method for tube welding. Interaction of external magnetic field and induced magnetic flux results in the creation of Lorentz force along peripheral edges of tubes. The circumferential arc rotation helps in the uniform heating of faying surfaces. After sufficient melting, faying surfaces are pressed against each other for weld formation. This paper aims at studying the notch tensile properties of T11 tubes welded by MIAB welding. In MIAB welded T11 steel tubes various Thermo-Mechanically Affected Zones (TMAZ) are formed as an effect of heat and pressure during welding. Tensile properties of all these TMAZs are different due to varying microstructures. Therefore notched tension testing was carried out to compare the properties of various zones in welded T11 tubes. All TMAZs show higher notch ductility with Notch Strength Ratio (NSR) greater than one. In comparison to the base metal, all TMAZs except TMAZ III display no loss in notch strength. The presence of granular bainite in TMAZ III causes lower notch strength with a Normalized Notch strength (NTSN) ratio less than unity.

Tensile Notch Sensitivity of Additively Manufactured IN 625 Superalloy

The notch sensitivity of additively manufactured IN 625 superalloy produces by laser powder bed fusion (LPBF) has been investigated by tensile testing of cylindrical test pieces. Smooth and V-notched test pieces with four different radii were tested both in as-built state and after a stress relief heat treatment for 1 h at 900 °C. Regardless of the notch root radius, the investigated alloy exhibits notch strength ratios higher than unity in both as-built and in stress-relieved states, showing that the additive manufactured IN 625 alloy is not prone to brittleness induced by the presence of V-notches. Higher values of notch strength ratios were recorded for the as-built material as a result of the higher internal stress level induced by the manufacturing process. Due to the higher triaxiality of stresses induced by notches, for both as-built and stress-relieved states, the proof strength of the notched test pieces is even higher than the tensile strength of the smooth test pieces tested in the same conditions. SEM fractographic analysis revealed a mixed mode of ductile and brittle fracture morphology of the V-notched specimens regardless the notch root radius. A more dominant ductile mode of fracture was encountered for stress-relieved test pieces than in the case of the as-built state. However, future research is needed to better understand the influence of notches on additive manufactured IN 625 alloy behaviour under more complex stresses.

Characterizing and predicting the tensile mechanical behavior and failure mechanisms of notched FMLs—Combined with DIC and numerical techniques

This paper mainly extensively investigates the effects of layer direction, notch shape and notch size on the tensile mechanical behavior and failure mechanisms of notched fiber metal laminates (FMLs) by numerical and experimental methods. In virtue of Digital image correlation (DIC) technique, tensile tests are implemented to measure tensile stress-strain responses, displacement distributions and localized strain fields of different notched FMLs. Subsequently, the progressive damage analysis considering thermal residual stress is conducted to characterize failure modes and progressive damage evolution of notched FMLs, which contains the intra-laminar damage in composite laminates and the interfacial delamination between aluminum sheets/composite laminates simultaneously. Results demonstrate that the ultimate notch strength is more sensitive to layer direction and notch size in comparison with notch shape. FMLs with smaller notches exhibit more prominent directional dependence than those with larger notches. Additionally, regarding to fracture morphologies, notched FMLs present typical brittle fracture for on-axis case, while they manifest as initial transverse fracture following tilted cracking along fiber directions for off-axis case. Consequently, with the increase of layer direction, the final failure mode of notched FMLs results from fiber-driven to aluminum-driven, and the critical damage mechanism gradually transfers from tension dominated to tension-shear dominated.

Mechanical response and critical failure mechanism characterization of notched carbon fiber reinforced polymer laminate subjected to tensile loading

AbstractThe purpose of this article is to investigate the mechanical responses and critical failure mechanisms of notched composite laminates with the aid of numerical and experimental approaches, considering the effect of notch geometry, notch size and off‐axis angle. Quasi‐static tensile tests are implemented to study the influence of design variables on the mechanical response, during which the relationship of force vs displacement and strain distributions are collected by means of digital image correlation technique. Subsequently, the numerical simulation is implemented in ABAQUS/Explicit through a progressive damage model integrated with a VUMAT subroutine. Meanwhile, the initiation and propagation of damage are explored through the damage morphologies, combining with the logarithmic strain components from numerical predictions. Results show that notch strength and failure strain are more closely associated with off‐axis angle and notch size compared with notch geometry. In addition, with the increase of off‐axis angle, the contribution of fiber is increasingly weakened, the damage mode gradually varies from fiber fracture to pull out accompanied with the damage near the notch changing from fiber fracture to delamination. Meanwhile, the critical failure mechanism varies from tension dominated to tension‐shear/shear dominated as the off‐axis angle grows larger.

Seismic fracture evaluation of diaphragm joints in welded beam‐to‐box column moment connections

SummarySteel box columns are widely used in steel building structures in Taiwan due to their dual strong axes. To transfer the beam‐end moment to the column, diaphragm plates of the same thickness and elevations as the beam flanges are usually welded inside the box column. The electro‐slag welding (ESW) process is widely used to connect the diaphragms to the column flanges in Taiwan because of its convenience and efficiency. However, ESW may increase the hardness of the welds and heat‐affected zones (HAZs), while reducing the Charpy‐V notch strength in the HAZ. This situation can cause premature fracture of the diaphragm‐to‐column flange welds before a large plastic rotation is developed in the beam‐to‐box column joints. To quantify the critical eccentricity and the effectiveness of fracture prediction, this study uses fracture prediction models and finite element model (FEM) analysis to correlate the test results. In this study, two beam‐to‐box column connection subassembly tests are conducted with different loading protocols and ESW chamber shapes. To implement a fracture prediction model, the material parameters are established from circumferential notched tensile tests and FEM analysis. Test results indicate that the fracture instances can be predicted on the basis of the cumulative plastic deformation in the HAZs. Analytical results indicate that fracture instances and locations are sensitive to the relative locations of the ESW joints and beam flange. Tests also confirm that the possible fracture of the diaphragm‐to‐column flange joints can be mitigated by enlarging the chamber of the ESW joint.