Notch Tensile Research Articles

Microstructure and mechanical assessment of Inconel 625 and AISI 904L dissimilar joints using high-density welding technique for pressure vessels

The dissimilar bimetallic joints of 5 mm thick Inconel 625 and AISI 904L were accomplished through the high-density fiber laser welding (LBW) process. The metallurgical investigation ensured the micro-segregation of Mo and Nb in the dendritic and inter-dendritic regions along with the formation of secondary topologically closed packed (TCP) phases. In addition to the metallurgical studies the Kernal average misorientation (KAM), Schmid factor (SF), and nucleation of the new grains were investigated through Electron backscattered diffraction (EBSD) analysis. The tensile strength opined the occurrence of failure on the 904L side, away from the weld seam ensuring that the joints have a higher strength. The notch tensile showed a higher strength of 678 ± 4 MPa in the weld zone than that of the 904L base alloy. The Charpy V notch studies showed a drastic decrease in the impact toughness with 38 ± 2 J as compared to the base alloys under sudden impact loading at room temperature (RT).

A shear modified GTN model based on stress degradation method for predicting ductile fracture

The Gurson–Tvergaard–Needleman (GTN) model has provided a powerful description of the nucleation growth and coalescence of micro voids, but it has limitations in simulating shear fracture due to the absence of a description of shear localization behavior. A shear improvement method is proposed for simulating the ductile fracture of materials under different stress states. The modified model not only allows for strain hardening of the matrix material, but also accounts for the stress degradation caused by shear. The strength equation of the material is described by both the shear stress state function and a decay function, making it easier for materials under shear stress state to experience material softening and further inducing shear fracture. The modified GTN model is developed by incorporating the shear stress degradation factor into the yield function, while taking into account both void growth and shear failure mechanisms. By carefully calibrating the model’s parameters, the deformation and fracture processes of tensile, plane strain, notch tensile, and compression specimens in the 7A52 aluminum alloy are simulated. The damage evolution behavior of the material under different stress states is analyzed. The results indicate that the damage include void growth mechanism and void shear mechanism. The proportions of these two mechanisms vary under different levels of stress triaxiality. Upon localizing material deformation, the shear stress state intensifies, and the shear damage mechanism assumes a critical role in fracture. The modified GTN model accurately predicts the load-displacement response and fracture path of the 7A52 aluminum alloy under a wide range of stress states.

Optimization on the mechanical parameters and impact of welding parameters of pulsed TIG welding of Aluminium-Zinc-Magnesium alloy

As a function of pulsed Tungsten Inert Gas (TIG) weld processing factor, authors have studied the relationship between dilution and mechanical qualities including impact toughness, notch tensile strength, hardness in the as-welded condition. Welds made with a pulsed TIG torch have a minimum notch tensile strength and impact toughness than the base metal (BM) because of the grains of the inter-dendritic network formed during the welding process. Weldments made from heat-treatable (Al-Zn-Mg) Aluminium alloys have their process parameters for pulsed TIG welding optimized employing the Taguchi analysis to get the best possible mechanical qualities. Notch tensile strength is shown to be inversely proportional to impact toughness.

Investigating the failure behavior of cast Al-11Ce-0.4Mg alloys using in-situ scanning electron microscopy tensile testing

Within the last decade, research on Al-Ce-Mg alloys has reported promising results for use in cast part applications. In this paper, the failure behavior of cast Al-11Ce-0.4Mg (wt%) was investigated experimentally with focus on the effect the matrix and intermetallic phases have on the fracture propagation behavior at failure. For the first time, in-situ SEM tensile testing was used to study the failure behavior of cast Al-Ce alloys, reporting results for uniaxial, DIC, and single edge notch tensile tests. The results of the in-situ SEM tensile testing were compared with the materials characterization experiments, which included serial sectioning, EBSD, EDS, and fractography. Analysis of EBSD and EDS mapping of cast Al-11Ce-0.4Mg showed that the cast microstructure was a hypereutectic two phase Al-Ce alloy with grains encompassing large complex colonies of laminar eutectic Al11Ce3 intermetallic. The uniaxial tensile results reported the effect casting defects have on the strength and ductility of the alloy, and DIC in-situ testing showed that the eutectic colonies plastically deform less than the matrix phase. In-situ SEM single edge notch tensile testing displayed how the strength of an individual phase affected the crack propagation direction in the alloy. The results of both the materials characterization and in-situ tensile testing experiments on the failure of this alloy revealed further directions for future alloy development that can improve both the strength and fracture toughness of Al-Ce-Mg alloys.

Identification of micro‐failure processes of HDPE‐henequen fiber composite material by using acoustic emission monitoring: Effect of fiber surface modification

AbstractIt is well known that fiber‐matrix interface region is crucial to ensure an efficient stress transfer between matrix and reinforcement and that it controls the composite behavior when subjected to external loads. In this experimental study, micro‐damage mechanisms of HDPE/surface modified henequen fiber reinforced composites are investigated in tensile quasi‐static mode. Two essential parameters of the materials composition were taken as main indicators: fiber length and quality of the fiber matrix adhesion. Essential Work of Fracture theory (EWF) was applied on double edge notch tensile (DENT) specimen geometry. Acoustic Emission (AE) technique was coupled to composite samples to obtain the characteristics of stress waves signals to monitor in real time damage evolution and failure mechanisms detection. Results demonstrated the substantial effect of chemical bonds interaction in the interface area on the composite mechanical properties. The total fracture work (Wf) exhibited an increasing value in both components, We and Wp, in chemically treated fiber composites. Likewise, mechanical properties are reported to be higher by 37% in maximum load in such materials. Elastic waves detected by AE were identified and correlated to micromechanical events during composite damage sequence. Most of the signals corresponded to microcracks (signals of low amplitude, short duration), propagation of microcracks (signals of medium amplitude), fracture of fibers and matrix (signals of long duration and high amplitude). AE signals detected exhibiting higher energy were associated to an enhanced fiber/matrix interface.

Effect of retrogression and reaging (RRA) on pitting and stress corrosion cracking (SCC) resistance of stir zone of high strength AA7075-T651 alloy joined by friction stir welding

The main purpose of this study is to investigate the influence of retrogression and re-aging post weld heat treatment (RRA-PWHT) on potentiodynamic corrosion (PC) and stress corrosion cracking resistance (SCC) of stir zone (SZ) of AA7075-T651 alloy butt joints developed using friction stir welding (FSW). FSW was employed to overcome the problems in fusion welding of AA7075-T651 alloy such as solidification cracking, heat affected zone (HAZ) softening, grain coarsening, dissolution of strengthening precipitates and inferior mechanical performance. The SZ of joints were subjected to potentiodynamic corrosion test in 3.56 wt% NaCl solution. The circumferential notch tensile (CNT) specimens were subjected to SCC test at various conditions of axial stress level in 3.56 wt% NaCl solution. The microstructural features of butt joints SZ were characterized using optical (OM), scanning electron (SEM) and transmission electron microscope (TEM). The results disclosed that RRA-PWHT joints exhibited greater PC and SCC resistance compared to as-welded joints. The threshold stress level for the failure of CNT specimens of parent metal, as-welded joints and RRA-PWHT joints was 242 MPa, 175 MPa and 198 MPa, respectively. The threshold stress level of RRA-PWHT joints and as-welded joints is 81.81% and 72.31% of parent metal threshold stress level. It is correlated to increase in vol% and coarsening of grain boundary precipitates with enrichment of copper at the grain boundaries.

Abnormal notch brittleness induced by short-range ordering in low-cobalt iron-cobalt alloys under tensile and impact loading: A combined experimental and molecular dynamics simulation study

According to the binary Fe-Co phase diagram, Fe-21.5/23 wt% Co alloys undergo an order-disorder transition in the temperature range of 430–470 °C. Above the order-disorder temperature, Fe-21.5/23 wt% Co alloys are generally considered as disordered solid solutions with excellent ductility and toughness. In this work, short-range ordered (SRO) structures in Fe-21.5 wt% Co alloy quenched from α phase region were directly observed via scanning transmission electron microscope (STEM). SROs are mainly the B2 structure, with a very small amount of L60 Fe3Co structure. The mechanisms of SRO-induced notch brittleness were systematically investigated by experiments and molecular dynamics (MD) simulations. Under tensile loading, SROs change slip mode from cross slip to planar slip, which significantly leads to the strengthening effects and large work hardening rates. For the notch tensile tests, different notch depths were set to investigate the effects of SROs on the notch brittleness. The Fe-23 wt% Co samples quenched from 550 °C were surprisingly found to exhibit the notch brittleness induced by SROs. Under impact loading, SROs significantly lead to impact brittleness with the cleavage fracture. MD results of notch tensile and impact tests showed that SRO-induced poor dislocation and twinning plasticity leads to larger concentrated stresses and stress concentration factor near the notch, directly resulting in the easier nucleation and rapid propagation of intergranular and intracrystalline microcracks. Our findings suggest that SRO-induced notch brittleness must be considered in engineering applications for the low-cobalt iron-cobalt alloys.

A Deterministic Methodology to Calibrate Pressure-Independent Anisotropic Yield Criteria in Plane Strain Tension Using Finite-Element Analysis

The yield strength of materials under plane strain deformation is often not characterized experimentally due to difficulties that arise in interpreting the results of plane strain tensile tests. The strain and stress fields in the gauge region of these tests are inhomogeneous, making it challenging to extract the constitutive response from experimental measurements. Consequently, the plane strain yield stress is instead predicted using phenomenological plasticity models calibrated using uniaxial and biaxial tension data. To remove this uncertainty, a simple finite-element based inverse technique is proposed to determine the arc of the associated yield locus from uniaxial-to-plane strain tension using a constrained form of Vegter’s anisotropic yield criterion to analyze a notch tensile test. The inverse problem is formulated under associated deviatoric plasticity and constrained such that only a single parameter, the major principal yield stress under plane strain deformation, needs to be identified from the finite-element simulations. The methodology was applied to two different automotive steel grades, an ultra-high strength DP1180 and a DC04 mild steel. The predictive accuracy of the constitutive models was then evaluated using an alternate notch geometry that provides an intermediate stress state between uniaxial and plane strain tension. By performing notch tensile tests in three sheet orientations, three arcs of the yield surface were obtained and employed to calibrate the widely used Yld2000 yield function. The study shows that for DP1180, the normalized plane strain yield stress was in the range of 1.10 to 1.14 whereas for DDQ steel, the normalized plane strain yield stress was notably stronger, with values ranging from 1.22 to 1.27, depending on the orientation. The proposed methodology allows for a wealth of anisotropic plasticity data to be obtained from simple notch tests while ensuring the plane strain state is accurately characterized, since it governs localization and fracture in many forming operations.

Notch tensile and dry sliding wear studies on Mg-Nd-Gd-Zn alloy

This main purpose of the present research is to investigate the properties of wear and tensile in smooth and notch conditions of the heat-treated Mg-Nd-Gd-Zn alloy. The material applications such as complex helicopter gear box casing, piston and brake actuating components demands tensile data in notch conditions and wear characterizations. The alloy was characterized for microstructure, hardness, tensile properties in smooth and notch conditions and tribological properties such as wear resistance and friction coefficient. The microstructure examination revealed equiaxed grain structure with the size of about 42 μm. The XRD results confirms the presence of Mg3 (Nd) precipitates. Smooth and notched samples were evaluated to determine the effect of notch radii and ductile-brittle transition. Notched samples show 25.31% improvements in strength compared to the smooth sample with the marginal reduction in ductility (1.3%–1.8%). The fractography results for notched specimens exhibited cleavage, intergranular mode whereas the smooth specimens exhibited quasi cleavage, inter and transgranular modes. At 10N, the wear rate and friction coefficient change from 8.83 × 10–5 mm3 min−1 to 7.11 × 10–5 mm3 min−1 (24.2%) and to 0.29 and 0.26 (11.5%) respectively when the sliding velocity increases from 1 to 5 m s−1. Similarly, at 20N, the wear rate and friction coefficient change from 9.11 × 10–5 mm3 min−1 to 0.75 × 10–6 mm3 min−1 (12.7%) and 0.29 to 0.23 (26.1%) respectively when the sliding velocity increases from 1 to 5 m s−1. With the increase of load, plastic deformation is dominant controlling the wear rate. With the increase of sliding speed, oxidation is dominant controlling the wear rate and friction coefficient. Mixed modes of wear mechanisms such as abrasion, oxidation, delamination, third body assisted wear and melt wear were observed.

Counterexample-trained neural network model of rate and temperature dependent hardening with dynamic strain aging

Constitutive models dealing with the thermal and visco-plasticity of metals have seen wide applications in the automotive industry. A basic plasticity and fracture characterization of a 1.5 mm thick DP780 dual phase steel sheet based on uniaxial tensile (UT) experiments with seven distinct material orientations is complemented by low (∼0.001/s), intermediate (∼1/s) and high (∼150/s) strain rate experiments on notched tensile (NT) and shear (SH) specimens at temperatures ranging from 20 °C to 500 °C. At low strain rates, we observe a non-monotonic effect of the temperature on the force-displacement curves, with the highest curve obtained at 300 °C. Contrasting low speed tests, a monotonic effect of temperature is observed for intermediate and high strain rate experiments, with the highest curves obtained at 20 °C for both cases. Strain rate jump tests are performed proving the positive strain rate sensitivity of the steel. A machine-learning based plasticity model is developed to capture the observed complex strain rate- and temperature effect. The material is modeled as elasto-plastic, with a Hill’48 yield surface and a non-associated flow rule. The flow resistance is decoupled into a reference strain hardening term and a neural network term, which is a function of the plastic strain, strain rate, temperature, and an additional dynamic strain aging variable. The plasticity model is implemented into a material user subroutine and identified using a counterexample-guided hybrid experimental-numerical approach. The extracted loading paths reveal a complex rate and temperature effect on the ductility of DP780. A neural network based fracture initiation model is therefore adopted to describe the fracture onset across various stress states, strain rates and temperatures considered.

Experimental investigation on aluminium alloy AA6082 and AA2014 using the friction stir welding

Friction stir welding is a solid-state welding method that involves bonding two similar or dissimilar metals utilizing a rotating tool. Traverse speed, rotating speed, axial force, and the angle of the tool are different variables used in this method. Mechanical characterization, similar and dissimilar metals, structural characterization, and the Influences of tool pin profiles for FSW processes square measure a number of the vital areas of analysis. In this project work the mechanical, metallurgical properties and analysis in friction stir welding. In the present work, aluminium alloy AA6082 and aluminium alloy AA2014 plates of 6 mm thickness are welded together using the friction stir welding process. The base material and welded joints are then tested for their mechanical properties and metallurgical properties by conducting tests such as tensile test, notch tensile, impact, hardness tests, SEM Fractrography, and the results are evaluated.

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.

Distinct Advantages of Circumferential Notch Tensile (CNT) Testing in the Determination of a Threshold for Stress Corrosion Cracking (KISCC).

Stress corrosion cracking (SCC) is a vexing problem for load-bearing equipment operating in a corrosive environment in various industries, such as aerospace, chemical and mineral processing, civil structures, bioimplants, energy generation etc. For safe operation, effective maintenance and life prediction of such equipment, reliable design data on SCC (such as threshold stress intensity for SCC, i.e., KISCC) are invaluable. Generating reliable KISCC data invariably requires a large number of tests. Traditional techniques can be prohibitively expensive. This article reviews the determination of KISCC using the circumferential notch tensile (CNT) technique, the validation of the technique and its application to a few industrially relevant scenarios. The CNT technique is a relatively recent and considerably inexpensive approach for the determination of KISCC when compared to traditional techniques, viz., double-cantilever beam (DCB) and compact tension (CT) that may be fraught with prohibitive complexities. As established through this article, the CNT technique circumvents some critical limitations of the traditional techniques.

Stress-state-dependent deformation and fracture behaviors in a cold-rolled 7Mn steel

Tensile tests were conducted on a series of specially designed specimens to understand how the stress state affected the deformation and fracture characteristics of a recently developed 7Mn steel containing a high fraction of retained austenite (RA). The digital image correlation (DIC) method was utilized to measure the strain and displacements applied to the specimen shoulders. The results show that the fracture strain was sensitive to the stress state that changed from pure shear (PS) with a stress triaxiality of zero to plane strain with stress triaxiality of approximately 0.58. Microstructural observations indicate that the uniaxial tensile (UT) specimens exhibited more rapid transformation kinetics from austenite to martensite compared with those in-plane PS and notched tensile (NT) specimens. This was primarily related to the difference in the stability of RA resulting from the change in austenite grain morphologies with the imposed stress state. Finally, special attention was drawn to the characteristics of the microscopic deformation behaviors related to the austenite-to-martensite transformation through the detailed microstructural evolution mechanism diagrams under three typical stress states.

Modified Johnson–Cook model of SWRH82B steel under different manufacturing and cold-drawing conditions

In this study, the parameters of the Johnson-Cook model of SWRH82B steel are determined to describe the dynamic mechanical properties and fracture behaviors of steel wires. A total of 299 specimens are tested to determine the parameters. Quasi-static tensile tests at varying temperatures (20–700 °C) and different strain rates (10−4–10 −2 s −1) and split Hopkinson pressure bar tests are conducted to identify the parameters of the Johnson-Cook model. Notch tensile tests are conducted to calibrate the Johnson-Cook fracture criterion model. The wires made from SWRH82B high-strength steel with different diameters and shapes have different material performance due to different manufacturing and cold-drawing process. Therefore, two cross-section types (circular and Z shapes) and seven diameters of high-strength steel wires are considered for the material characteristic tests. The strain rate hardening effect is not significant at low loading rates but has a remarkable effect at loads exceeding. Analysis of the stress-strain curves at elevated temperatures shows that the thermal softening effect of the two types of wires is evident and that the temperature sensitivity varies in different temperature ranges. In addition, the mechanical performance of circular wires with diameters ranging from 4.0 to 5.2 mm and Z-shaped wires with diameters from 4 to 6 mm are compared. Fractography of SWRH82B high-strength steel is conducted to investigate the failure mechanism at various temperatures and strain loading rates. Finally, an improved Johnson-Cook model is proposed considering the strain hardening of SWRH82B steel wires based on different shapes and diameters.

Enhancing the Notch Tensile Strength of GMAW welded AISI 1013 Low Carbon steel with Taguchi Optimization

There is currently no exact dynamic model which predicts hysteresis and creeps in a piezoelectric actuator under varying operating conditions (increasing frequency and amplitude of input, time of operation, temperature effects), and is stable against uncertainties. Thus, research needs to be carried out to predict the hysteresis and creep on the modeling and identification of the non-linear dynamics of a piezoelectric actuator. It would aid the implementation of a model-based control algorithm such as the precise positioning of a nano-positioning.

Fatigue Crack Growth of Natural Rubber/Butadiene Rubber Blend Containing Waste Tyre Rubber Powders

Fatigue crack growth in NR/BR compound and the effect of two different types of recycled rubber powder (RRP) i.e. micronized cryo-ground 74 μm and ambient-ground 400 μm were studied using fracture mechanics approach. Absolute and relative hysteresis losses using single-edge notch tensile (SENT) specimens were determined with a displacement-controlled strain compensating for permanent set of the samples throughout the Fatigue Crack Growth (FCG) experiments. Results indicated a correlation between absolute/relative hysteresis loss and fatigue crack growth rate under specific dynamic strain amplitudes. Differences in relative hysteresis loss showed that additional energy dissipation, due to multiple new crack surfaces at the crack tip, contributes to the FCG of the RRP compounds. At higher tearing energy, beside other factors affecting the FCG performance of the RRP compounds, both higher absolute and relative hysteresis loss are slightly detrimental to the crack growth rates.

Uticaj orijentacije vlakana na žilavost loma kod Z/HDPE kompozita ojačanih svilenim vlaknima

The aim of this work is to investigate the fracture toughness and deformation of silk fiber (SF)-reinforced zeolite (Z)/high density polyathylene (HDPE) composites. The chopped SFs are arranged in the thickness middle of the dry mixture of Z/HDPE powder that has been prepared in a mold. Composites were produced by the compression molding to produce double-edge notch tensile (DENT). The fracture toughness characterization was carried out based on essential work of fracture method. The results show that the presence of SF increased the essential fracture work even though the non-essential fracture work for Z/HDPE was higher than S-Z/HDPE. The evolution of plastic zone growth coincides with the growth of the fracture process zone (FPZ) whose height has no effect on energy consumption.

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.