Notch Strength Ratio Research Articles

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.

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.

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.

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.

Notch-tensile behavior of Al0.1CrFeCoNi high entropy alloy

Notch-tensile behavior of an Al0.1CrFeCoNi high entropy alloy (Al0.1-HEA) was studied using V-notch geometry and with local strain mapping using digital image correlation (DIC). A notch-strength ratio of 1.51 indicated notch strengthening. Further analysis of stress-strain response supplemented with microstructural analysis revealed that, while the presence of notch results in strengthening due to work hardening by twinning induced plasticity, the notch also contributes strongly to geometrical softening in the non-uniform ductility regime, and accounts for the onset of failure. The strain localization behavior of Al0.1-HEA due to the presence of V-notch was compared with three conventional alloys: Inconel 625 nickel-based superalloy, 304 stainless steel and Ti–6Al–4V titanium alloy. The study revealed that the nature of notch widening with increasing strain was dependent on material characteristics. The extent of notch widening impacted the local strain field and stress distribution, thereby influencing the propensity for crack initiation and growth. The experimental results were verified by finite element analysis.

Mechanical behaviors and texture evolution of CoCrFeNi high-entropy alloy under shear-tension deformation

The shear-tension deformation behaviors of CoCrFeNi high-entropy alloy (HEA) were investigated by introducing five groups of different inclined notches, and mainly focus on mechanical response and texture evolution. The results show that CoCrFeNi HEA exhibits significant structural sensitivity and high notch strength ratio (NSR), and the stress concentration factor Kt of specimens and stress distribution at the notch roots were acquired by finite element method (FEM). In addition, the notch strengthening effect of HEA is more obvious with the increase of shear stress component. When the shear stress component increases, the E {111}<110>, F {111}<112> and γ-fiber textures are the main texture components after deformation. The evolution characteristics of Cu-type and Brass-type textures under the shear-tension stress states are significantly different from those under the rolled state. Moreover, complex stress states have no obvious effect on Cu texture under shear-tension deformation, but a large one on CuT texture.

Notch Tensile Behavior of the Mg-Zn-Gd-Zr Alloy

The Mg-Zn-Gd-Zr alloy is one of the important aerospace alloys in the aircraft gearbox applications. The complex geometry of the gearbox introduces several stress concentration points with various intensities. These regions are susceptible to catastrophic failure under mixed loading condition. Therefore, it is important to understand the deformation and failure mode of this alloy for various plastic constraint conditions. In the present work, Mg-4%Zn-1.5%Gd-0.5%Zr alloys were prepared with four different increasing notch root radii (1, 2, 4 and 8 mm). These samples were tested for tensile properties and compared with the smooth condition. In addition, notch sensitivity was determined analytically. The microstructure and fracture samples of the alloy were characterized with the aid of an optical/scanning electron microscope. Tensile test results show that the alloy is notch sensitive and shows notch-strengthening effects. The notch strength ratio increases with the decrease in the notch root radius due to the strong plastic constraint. The predicted and experimental results of the fracture strain with the notch root radius are in qualitative agreement. The void growth rate prediction is qualitatively in agreement with the tensile and fractography results and suggests that the notch geometry has a significant influence on the plastic strain of the alloy. The microstructure of the alloy has equiaxed grains of 74 ± 24 µm with the grain boundary eutectic. The eutectic is composed of Gd-rich Mg phase. The fracture surface has a distinct change from mixed mode to complete cleavage with the increasing notch root radius. The fractography results show that the fracture mode is predominantly intergranular for all the cases.

Experimental and finite element analysis of progressive failure in friction stir welded AA6061-AA7075 joints

In the present study, an in-situ analysis of crack initiation and propagation during tensile loading was captured using high speed camera for dissimilar friction stir weld joint of AA6061-T6 and AA7075-T651 prepared with plain cylindrical (CYL) and threaded with three intermittent flat faces (TIF) tool pins. To study notch sensitivity, experiment was also carried out for notch tensile sample creating notch at weld center. Joint failures were further predicted by finite element (FE) method. Results indicate that for joints obtained with CYL tool pin, crack initiated from vicinity of tunnel region however, propagated through the boundary of stir zone (SZ) and thermo-mechanically affected zone. FE results also indicate that the stresses and strain were confined near tunnel region which act as crack initiation site. For joints obtained with TIF tool pin, no tunnel/ void was noticed in the SZ and the sample failed from the heat affected zone on the advancing side (AA6061-T6) of the joints. For notch tensile specimen, the specimen exhibited minimum elongation when compared with tensile specimen and notch strength ratio > 1 indicated that the joint was notch insensitive or in other words, notch strengthened. FE result indicated that the higher stresses were confined near the notch root from where crack initiated and propagated through the SZ. Fractographic analysis showed the presence of dimples, micro-voids with some shear failure marks for all joints indicating the ductile fracture.

Studies on the structural property, mechanical relationships and corrosion behaviour of Inconel 718 and SS 316L dissimilar joints by TIG welding without using activated flux

This research article addresses about the joining of 4mm thick plates of Inconel 718 and ferritic stainless steel (S.S) 316L by Tungsten Inert Gas (TIG) welding process without using the activated flux. Trial experiments were conducted to find the influence of welding current on the depth of penetration and depth to width (D/W) ratio. The studies proved that a complete penetration could be achieved in multi pass. Microstructure examination using optical and Scanning Electron Microscope (SEM) clearly exposed the development of unmixed zone and also the Heat Affected Zone (HAZ) of Inconel 718. The chemical components of the Inconel 718 and SS316L were determined using Energy Dispersive Analysis (EDAX). Tensile and bend failures were observed at the parent metal of Inconel 718, SS316L and Inconel 718 & SS316L dissimilar joints. It was indicated from the notch tensile studies that the notch strength ratio was better than unity, which established that the weldments were ductile in all circumstances. The corrosion studies were carried out in the Nacl solution and it was found that Inconel 718 and SS316L dissimilar joint possess less corrosion resistance than similar SS316L weldment. It was inferred from the current study that the ultimate tensile strength of dissimilar weldments was better compared to similar weldments and the failure was observed in the parent metal for all the cases. Bend test results portrayed that dissimilar weldments possess better strength compared to SS316L weldments.

Investigations on the microstructure, tensile strength and high temperature corrosion behaviour of Inconel 625 and Inconel 718 dissimilar joints

In this article, an attempt has been made to investigate the effect of fillers on the pulsed current gas tungsten arc welding (PCGTAW) of Inconel 625 and Inconel 718. Two different Ni-Mo rich fillers namely ERNiCrMo-4 and ERNiCrMo-10 were employed for joining 5mm thick plates of Ni based super alloys. The deleterious Laves phase was completely suppressed, while using these fillers. Mo rich segregation was observed in the fusion zones for both the fillers without much depletion of Mo in the fusion matrix. Tensile failures were observed at the parent metal of Inconel 718 in both the cases. It was attested from the notch tensile studies that the notch strength ratio was greater than unity, which attested that the weldments were ductile in all conditions. Impact studies showed that the weldments employing ERNiCrMo-10 exhibited better impact toughness at room temperature conditions. Hot corrosion studies were performed on the coupons exposed in the synthetic molten salt environment of 60%Na2SO4–40%V2O5 at 900°C. Studies showed that both the parent metal Inconel 625 followed by the fusion zone of ERNiCrMo-10 exhibited better corrosion resistance in the high temperature environment. Surface analytical techniques were adopted to investigate the hot corroded species.

Creep failure prediction of brazing joints with double notches

This paper predicts the creep ductile failure of brazing joints with three different types of double notches by continuum damage mechanics simulation, and the effects of distance between the double notches (notch distance) and inside notch radius have been discussed. The results show that the different double notches have different creep failure lives and notch sensitivity effects due to the different notch strength ratios. For the notches in the surface of base metal and filler metal, the creep failure time decreases with the notch distance increases. Compared with single notch, the smaller notch distance shows a strengthening effect because of the larger notch strength ratio, otherwise it is a weakening effect. For the notches in the surface and center of filler metal, the creep failure time increases firstly then decreases with the increase of inside notch radius. Opposite to the notch distance effect, the smaller inside notch radius shows a weakening effect, while the bigger inside notch radius shows a strengthening effect. As the notch radius increases, the strengthening effect becomes not obvious. For the notches in the center of filler metal and the surface of base metal, the creep failure location moves from base metal to filler metal, and the failure time decreases with the increase of inside notch radius. The creep life of smaller inside notch radius is the same as single base notch, showing an insensitive effect. Nevertheless, it is a weakening effect for the bigger inside notch radius.

Influence of Notch on Mechanical Properties of Cf/Mg Composite Fabricated by LSEVI

Cf/Mg composite was fabricated by liquid-solid extrusion following vacuum infiltration technique and uniaxial tensile tests were conducted on the notched and unnotched specimens to investigate the mechanical properties of Cf/Mg composite. The effects of circular notch on the notched strength, net tensile strength, tensile modulus, and fracture strain of Cf/Mg composite were investigated. The notch sensitivity of Cf/Mg composite was elucidated through the notch strength ratio (NSR), fracture surface, and fracture mechanism. By comparing the experimental and theoretical NSR, the influences of notch size and stress concentration factor on notch sensitivity of Cf/Mg composite were investigated. The results showed that the fracture strain of the notched specimens increased with increasing the notch size. Meanwhile, net tensile strength, notched strength, and tensile moduli had opposite trends. The NSR had a functional relationship with the notch size and stress concentration factor caused by the notch had no influence on the NSR.

A size effect law for notched tensile strength of woven carbon/epoxy laminates

Specimen-size effect and notch-size effect on the tensile strength of woven fabric carbon/epoxy laminates are evaluated and modeled. For two different layups of [(0/90)12] and [(±45)2/(0/90)5]S, respectively, static tension tests were performed on two-dimensional geometrically similar unnotched and double-edge notched specimens scaled to three different sizes. Experimental results demonstrate that the notched strength of the woven CFRP laminates depend on the size of specimen as well as the size of notch. The ratio of notched strength to unnotched strength decreases as the length of notch increases, regardless of the size of specimen. For a given size of notch, the notch strength ratio becomes larger with decreasing size of specimen. A notch-size effect law is derived by means of the Neuber interpolation method. A specimen-size effect is embedded into the notch sensitivity parameter involved by the notch-size effect law to establish a size effect law that can cope with these two kinds of size effect. The engineering size effect law proposed can adequately describe the specimen-size effect as well as notch-size effect on the tensile strength of the woven CFRP laminates. It is also demonstrated that the size effect law allows determining the size independent fracture toughness on the basis of notched strengths of small specimens that fail in a quasi-brittle manner.

Notched strength prediction of glass fiber reinforced composite based on fracture toughness analysis

The notched strength prediction of normal glass mat composite and needle punched glass mat composite based on fracture mechanics was carried out in this study. The prediction constitutes of three parts including establishing the relation between characteristic distance and notch strength ratio (a ratio of notch strength to unnotched strength), modulus calculation in thickness direction and fracture toughness measurement. The characteristic distance was determined by point stress criterion and calculated from finite element analysis. After contrastive analysis from a mass of tensile results on notched specimens with an open hole, a relation between characteristic distance and notch sensitivity was established. Modulus calculation was calculated according to the classic theory of “Rule of Mixtures” and “Reuss Model”. After that, the results of modulus calculation together with fracture toughness results were employed to establish the relation between notch strength and characteristic distance according to elastic fracture mechanics. The characteristic distance was used in this part as a parameter of a crack. Finally, from the two equations between notch strength and characteristic distance, the notched strength of composite with an open hole can be predicted. The predicting results were compared and analyzed with experiment results.

Notch Effect of Materials: Strengthening or Weakening?

Notch is a very important geometry with widespread applications in engineering structural components. Finding a universal equation to predict the effect of notch on strength of materials is of much significance for structural design and materials selection. In the present work, we tried to find this universal equation from experimental results of metallic glasses (MGs) and other materials as well as theoretical derivations based on a universal fracture criterion (Qu and Zhang, Sci. Rep. 3 (2013) 1117). Experimental results showed that the notch effect of the studied MG was affected by the notch geometry characterized by the stress concentration factor Kt. As Kt becomes smaller, the notch strength ratio (NSR, which is the ratio of nominal ultimate tensile strength (UTS) of the notched sample to UTS of the unnotched sample) increases. By comparing MGs with other materials like brittle ceramics and ductile crystalline metals, we find that when Kt is same, the NSR is larger for ductile metals but smaller for brittle ceramics. Theoretically, we derived a universal equation for notch effect on strength of materials: NSR = M/Kt, where M is a constant related to materials. This universal equation was found to be consistent with the experimental results.

Comparison of mechanical properties of pure copper welded using friction stir welding and tungsten inert gas welding

The objective of this research is to investigate the mechanical properties including bonding, tensile strength, and impact resistance of pure copper welded using friction stir welding (FSW) method and compare them with that of tungsten inert gas (TIG) welding. Micro-hardness tests are performed on pure copper, TIG welded copper and FSW welded copper to determine the effect of heat on the hardness of welded coppers. Tensile strength tests and notch tensile strength tests are performed to determine the mechanical properties of different weld process.In this experiment, it is found that the notch tensile strength and the notch strength ratio for FSW (212MPa, 1.10) are significantly higher than those (190MPa, 1.02) of TIG welding. For the impact tests, the weld zone and heat-affected zone energy absorption values for FSW (2.87J, 2.25J) are higher than those (1.32J, 0J) of TIG welding. XRD tests are performed to determine components of copper before and after welding process for TIG and FSW.