ASTM E1820 Research Articles

A Proposal of the Crack Tip Opening Displacement Calculation Formula and Its Conversion Factor to J-Integral in C(T) Specimens

The crack tip opening displacement (CTOD) concept describing cleavage embrittlement failure proposed by Wells is an important technology supporting the reliability of steel structures around the world. In 2002, ASTM E1290, Standard Test Method for Crack-Tip Opening Displacement (CTOD) Fracture Toughness Measurement, proposed a CTOD calculation formula based on a J-integral different from the previous integral that reflected the work-hardening characteristics and was triggered by the appearance of a case where evaluation values significantly different from the conventional British Standard (BS) formula are given. The authors attempted to construct an accurate CTOD calculation formula by performing actual measurements in CTOD experiments and systematic numerical analyses. Detailed observation of the plastic deformation mode in the ligament demonstrates the validity of the plastic hinge model that BS has adopted to date. In 2016, it was possible to propose a highly accurate formula that considers the work-hardening characteristics for edge-cracked bending test piece specimens and is adopted into the Japanese and ISO standard. Here, the outline of the CTOD calculation formula for the compact specimen (denoted as C(T)) constructed in the same manner will be described. The authors also suggested that the CTOD and J-integral conversion factor can be expressed in a simpler form than the form indicated by ASTM E1820, Test Method for Measurement of Fracture Toughness. In this study, we discovered that the same conversion factor can be applied to a compact specimen, which is quite reasonable considering the energy release rate of the J value.

Estimation of the fracture toughness of tungsten fibre-reinforced tungsten composites

Tungsten fibre-reinforced tungsten composites (Wf/W) have been developed to overcome the inherent brittleness of tungsten, which is a promising candidate for the plasma-facing material in a future fusion power plant. As the development of Wf/W evolves, the fracture toughness of the composite is in the focus of interest for further component design. In this contribution fracture mechanical tests on two different types of chemical vapour deposited (CVD) Wf/W are presented. Three-point bending tests according to ASTM E399 as a standard method for brittle materials were used to get a first estimation of the toughness. A provisional fracture toughness value of up to 241 MPa m1/2 was calculated for the as-fabricated and of up to 20.5 MPa m1/2 for a heat-treated and thus embrittled state. As the material does not show a brittle fracture in the as-fabricated state, the J-Integral approach based on the ASTM E1820 was additionally applied for this state. A maximum value of the J-integral of 7.5 kJ/m2 (57.6 MPa m1/2) was determined. A detailed post mortem investigations was used to obtain the active mechanisms.

Mechanical Properties and Microstructure, in welded joints of Low and Medium Carbon Steels, Applying Rotary Friction

The effect of friction welding (FRW) in joints of medium and low carbon steels on its mechanical properties and microstructure was studied. AISI 1020 and 1045 steel bars of 12 mm diameter were used. Welding was carried out on a lathe with coupling to control the process parameters. For 1045/1045 joint, the following parameters were used: n = 1400 rpm, Friction pressure Pf = (0.8 - 1.0) MPa; Friction time (Tf) = 8 sec; Upsetting pressure (Pr) = 5 MPa; Upsetting time (Tr) = 5 sec, were used. For 1020/1045 joints the parameters that only varied were: n = (1000 - 1400) rpm; Pf = (0.7-0.8-1.0) MPa. Tensile tests were carried out on the IMSTRON UNIVERSAL machine under ASTM E8 standard. Microhardness tests were carried out on (HV) 0.5 scale, making a longitudinal and transverse scanning profile. Microscopy at the optical (OM) and electronic SEM levels, with analysis (EDS) was revealed. It was found for similar joints: a higher value of (Pf) increases the mechanical resistance (σrm), but for dissimilar joints decreases it. Welding efficiency of similar joints was 94% and for dissimilar joints 97.5% with regard to 1020 and 74% with regard to 1045. For dissimilar joints, a higher speed “n” increases σy, and σrm, with little effect on “ɛ”. In similar joints the microhardness is maximum in the center, and for the dissimilar ones it is not. Longitudinal and transverse microhardness profiles do not follow a defined pattern with respect to Pf. For both types of joints, the microstructure shows, that FDRZ joint zone, has variable thickness and has a fully recrystallized fine-grain structure. TMAZ deformation zone, a structure of deformed grains and dark grains is observed, the latter, due to the excess carbon produced by diffusion. In both cases, no intermetallic compounds have been produced, and perlite colonies is not observed in these two zones.

Evaluation of impact and hardness properties of Al 6063-AgNPs composites produced by stir cast technique

The effect of silver nanoparticles (AgNPs) on the mechanical and microstructural properties of aluminium 6063 alloy was investigated. Aluminium 6063 matrix was homogenously mixed with AgNPs impregnated with calcium carbonate at 2, 4 and 6% weight fractions. The mixture was used to produce refined samples through stir casting method. Measurement of impact strength and hardness property of the produced samples at ambient temperature was done by using Charpy impact and Brinell hardness testing machine in accordance with ASTM E23 and ASTM E384 respectively. The impact energy values (234-247 J) of all the samples with AgNPs/CaCO3 reinforcements were higher than the as-cast Al alloy (228 J) while the sample with 6% AgNp has the highest energy impact (247 J). Similarly, the hardness values (56.49-183.70 BHN) of all the samples with AgNPs/CaCO3 reinforcements were higher than the as-cast Al alloy (38.05 BHN) while the sample with 6% AgNPs has the highest (183.70 BHN). The magnitude of impact and hardness increased evidently with increase in percentage weight fraction of the AgNPs. The fracture images of the impact test samples revealed that the surface of AgNPs (CaCO3)-Al6063 composites were with dimples and there was a micro-void formation in CaCO3-Al6063 composite. The use of stir-casting technique influenced the homogeneity and microstructure of the AgNPs composites positively. The Al 6063-Ag nanocomposites possess better qualities in terms of impact energy and hardness, likewise can replace conventional aluminium alloy based on its performance.

Design-dependent shrinkage compensation modeling and mechanical property targeting of metal FFF

Metal-fused filament fabrication is gaining traction due to its low cost and high availability compared to metal powder bed fusion. However, the achievable mechanical properties and effects of shrinkage of this process should be understood thoroughly before it can be implemented as a direct digital manufacturing technology. This study investigates the influence of infill levels and different build orientations on the mechanical properties and shrinkage behavior of 3D-printed, debinded, and sintered components made from BASF Ultrafuse 316LX. The final objective of the work is to define a function for multi-directional shrinkage prediction for any given part geometry to achieve parts with a high degree of dimensional conformity by modifying the original designs accordingly. The Design of Experiment includes tensile and compression testing according to ASTM E8 M-04 and ASTM D695-15, respectively. Tensile testing samples are manufactured in three different build directions and compression testing pins are made with six infill levels. Furthermore, a complex part is printed and its dimensional shrinkage analyzed using 3D scanning. Finally, the multi-directional shrinkage behavior is measured for all samples to establish a shrinkage predictability function by applying linear regression models. Results show that material infill levels have no effect on the shrinkage behavior of printed components. Compressive strength increases with infill level and ultimate tensile strength of parts printed flat indicates the highest tensile testing results, followed by flipped and vertically printed parts. A complex part was manufactured successfully for spare part production, which helped to establish a function with moderate confidence levels for shrinkage predictability.

Quantitative comparison of the predictions of fracture toughness temperature dependence using ASTM E1921 master curve and stress distribution T-scaling methods

The fracture toughness temperature dependence of ferritic steels in the ductile-to-brittle transition temperature region, predicted using the ASTM E1921 master curve (MC) and stress distribution T-scaling (CDS) methods, is presented in this paper. A total of 34 cases (i.e., combination of material heats and specimen types) including 661 fracture toughness test data were considered. First, the direct correlation between fracture toughness and yield stress—as suggested by the CDS method—was validated using machine learning techniques. Subsequently, the accuracy of the predictions obtained by each method was quantitatively evaluated using a coefficient of determination. In 25 out of the 34 cases, the CDS method showed better prediction ability than the MC method. In the other 9 cases, the difference between the two methods was small, if considered from an engineering perspective.

Low-Cycle Fatigue Behavior of Thin-Sheet Extruded Aluminum Alloy

In this work, we investigate a novel testing method for fatigue testing of a thin sheet under fully reversed conditions. Specifically, the fatigue behavior of thin-plate AA6082-T6 was characterized by laminating multiple thin gage specimens together to form a thicker specimen to prevent buckling under low-cycle fatigue testing. In this unique technique, ASTM E606 fatigue specimens were bonded together with a structural adhesive in double and triple laminates, and fatigue behavior was compared against monolithic control specimens. To quantify the fatigue behavior of the laminated AA6082, strain-controlled experiments were conducted, where the fatigue life experimental results exhibited comparable fatigue performance to the published literature. Postmortem analysis of the laminated AA6082 revealed a similar fatigue nucleation and crack growth damage mechanisms compared to the monolithic fatigue specimens. Lastly, a microstructure-sensitive fatigue life model was utilized to elucidate structure–property fatigue mechanism relations of the monolithic, double-, and triple-laminate specimens. The fatigue behavior of laminated specimens exhibits good correlation to wrought AA6082-T6 mechanical properties and thus suggests that laminating sheets together can be used to quantify fully reversed fatigue behavior of thin sheets that would otherwise buckle under compression loading.

Fatigue of Tungsten Fiber/Copper Matrix Composite—An Interlaboratory Study

Abstract Seven laboratories participated in an interlaboratory study to assess the applicability of ASTM E606, Test Method for Strain-Controlled Fatigue Testing, to strain-controlled fatigue of a tungsten fiber/copper matrix composite (Battelle Columbus, University of Iowa, IITRI, MCL, MarTest, Rockwell International Science Center and University of Twente). Because of the material and specimen fabrication methods, the number of fibers in the 9, 25, and 36 % fiber volume fraction specimens is approximately the same and the strain-life data are nearly identical for each of the volume fractions. Although the specimen aspect ratio is within the nominal range, the specimen diameter is less than the nominal value specified in ASTM E606. Laboratories reporting data noted that a small specimen diameter and a large gage section aspect ratio made specimen alignment difficult. Thus, specimen buckling was problematic at high strain ranges. The study data are reported and analyzed with nonparametric and semiparametric statistical methods to assess the effect of study covariates on fatigue life. The median fatigue life, median absolute deviation from the median, and interquartile range are reported as measures of central tendency and variability. ASTM E606 may be used as a guide to evaluate the fatigue response of this type of composite material if the length-to-diameter aspect ratio, specimen alignment in the fatigue machine, and specimen surface finish are closely monitored to ensure valid data.

Characterization of Low Cycle Fatigue Parameters of Rotor Steel using Sub-sized Specimens

The paper is dealing with strain controlled cyclic testing method employing a novel strain-control technique based on digital image correlation (DIC) in low-cycle fatigue (LCF) region. The cyclic behaviour of 22CrMoNiWV 8-8 rotor steel was investigated on sub-sized round specimens with a diameter of 2 mm in gage length and total length of 20 mm. These results were compared with results obtained using conventional specimens designed in accordance with the ASTM E606 standard. The attention was paid to confirm the suitability of the proposed sub-sized geometry, testing set up and procedure. The test procedure and results obtained enabled to record hysteresis loops, construct Manson-Coffin curves and obtain cyclic material properties in LCF region.

The Effect of Artificial Aging Treatment on Microstructure and Morphology of AlMgSi Alloy

This research aimed to explore the effect of artificial aging temperature variations on toughness, hardness, microstructure, and fault morphology in AlMgSi. 120°C, 150°C, and 180°C with 6 hours of holding time were used as the variations. Impact tests used the ASTM E23 standard, and showed an increase in specimen toughness given artificial aging that peaked at 180°C with 0.0649 kg/mm2. Microstructure exhibited a sparse precipitate in the specimen with artificial aging. The fault morphology showed that specimens with artificial aging had brittle and ductile fractures.

Novel Specimen Design for Measurement of In-Plane Fracture Toughness of Metals

AbstractStandard-compliant measurement of the in-plane fracture toughness of metals is often challenging due to insufficient material in the through-thickness direction to extract a full single edge bending (SEB) or compact tension (CT) fracture specimen. In the present work, we propose a new specimen design methodology to overcome this challenge. A W-shaped SEB specimen (called W-SEB) was developed, and its topology was optimized using finite element simulations. The new specimen design was validated numerically and experimentally on a case study showing excellent agreement with standard ASTM E1820 actual SEB specimen geometry. In view assessing the anisotropy of the fracture toughness (KQ and crack tip opening displacement (CTOD)) of pipeline steels susceptible to hydrogen-induced cracking (HIC), the W-SEB specimen was tested on X65 and X42 pipeline steel samples taken from the field. Experimental results show an increase in the maximum CTOD along the in-plane direction as compared to the transverse direction for both steel grades. Such experimental results could lead to important considerations with respect to accurate fitness for service assessment of HIC-damaged assets.

Out-of-plane constraint loss in three point bend specimens with notches

This paper presents an experimental and numerical study of the effect of specimen thickness on the effective notch toughness Kmatρ for cleavage fracture measured using Single Edge Notch Bend (SENB) specimens containing a U-notch instead of a fatigue pre-crack. These specimens are typically used to measure a material's effective notch toughness Kmatρ and to assess failure of a structure containing a non-sharp defect using the Notch Failure Assessment Diagram (NFAD). Both the experimental data and the Finite Element (FE) failure predictions show a significant influence of specimen thickness on Kmatρ, over and above the microstructural weakest link effect arising from differences in the volume of the plastic zone. Kmatρ is a function of not only the in-plane effect of the notch radius, but also an out-of-plane constraint loss which itself is enhanced by the presence of the notch radius. Significant out-of-plane constraint loss occurred for notched specimens with a ratio of thickness B to width W of 0.5, a geometry that if pre-cracked would have met the minimum thickness requirement mandated by ASTM E1820. Doubling the thickness to B/W = 1.0 was sufficient to eliminate the out-of-plane constraint loss. The use of experimentally measured Kmatρ values in an NFAD assessment of a structure may therefore be non-conservative if B/W<1.0.

Evaluation of Quasi-Static and Dynamic Fracture Toughness on the Low-Alloy Reactor Pressure Vessel Steel JRQ in the Transition Region

Three point bending and impact tests with sub-sized Charpy specimens were performed on the JRQ reference steel for reactor pressure vessels. Quasi-static and dynamic fracture toughness data were calculated and the fracture behavior in the ductile to brittle transition region was evaluated within the frame of the master curve method (ASTM E1921). Specimens with shallow and deep cracks were studied and the respective influence of crack length and loading rate on the reference transition temperature was determined. The force-time curves of specimens with shallow cracks presented significantly smaller oscillations with respect to the absolute force, making the fracture toughness evaluation more accurate.

Additive Manufacturing of 316L Stainless Steel

Additive manufacturing (AM) is a process of making parts by adding ultrathin layers of materials such as liquid, powder or sheet material layer by layer using 3D printing machine with the aid of a computer-aided design (CAD) software from 3D model data. Intricate, complex parts with graded material can be fabricated with ease. However, additively manufactured parts can vary in physical and mechanical properties with conventionally manufactured parts. In this final year project, AM was done using metal powder of 316L stainless steel alloy owing to good corrosion resistance, ductility and strength. The main objectives for this project are to fabricate 316L stainless steel using AM and to study the physical and mechanical properties of the addictively manufactured specimens compared with electrical discharge machining (EDM) wire cut specimens. A standard specimen bone shaped were manufactured in accordance with ASTM E8 and followed by physical and mechanical testing. From the testing and analysis, 316L stainless steel samples manufactured via AM route have the ultimate tensile strength ranged from 514 to 520 MPa while EDM specimens ranged from 574 to 576 MPa, the yield strength of AM specimens ranged from 385 to 390 MPa while EDM specimens ranged from 350 to 355 MPa, and the average elongation at failure of AM specimens are 45% while EDM specimens are 66%. From this project, it shows that AM specimens have comparable physical and mechanical properties with EDM specimens.

Fracture Toughness of Cold Sprayed Pure Metals

The study of fracture toughness of pure Al, Cu, Ni and Ti deposited by cold spray was performed in order to obtain a fundamental understanding of the damage process and quantify the material performance. Rectangular specimens cut from self-standing deposits with fatigue pre-cracks were tested in three-point bending. The KIC values were obtained from J-R curves following the ASTM E1820 standard. The stress–strain behavior of the tested material was obtained from supplementary four-point bending. The cold spray deposits exhibited significantly lower fracture toughness than the corresponding wrought materials. The reduction was more pronounced for coatings with limited ductility (Ti and Cu), where the fracture toughness reached less than 12% of the wrought counterpart only. The higher ductility coatings of Al and Ni possessed fracture toughness of 18–25% of the wrought reference materials. The performed fractographic analysis revealed inter-particular decohesion as the major failure mode.

Fracture toughness of railway for higher speed rail corridors in Malaysia

When Keretapi Tanah Melayu Berhad (KTMB) introduced the High Speed Electrical Train System (ETS) in 2013, the fracture toughness of the railway rail remains relatively unknown. The aim of this study was to evaluate the fracture toughness of rail steel. The rail steel specimen was prepared according to ASTM E1820 and cut using electrical discharge machining (EDM) wire cut process. The specimen was pre-cracked using Biss Fatigue Machine to obtain a relatively accurate results followed by three point bend testing under Universal Testing Machine (UTM), in accordance to the standard of ASTM E1820. The fractured crack tip was then observed using an optical microscope. From the three point bend test, the fracture toughness was calculated and the behaviour of the steel failing was then studied and compared to previous studies. The fracture toughness of the steel was found to be 44.009 MPa√m, which is within the range of the various rail steels used around the world..

Fatigue Precracking Time Estimates for Three-Point Bending Specimens

Specimens containing sharp cracks are needed in certain types of mechanical tests, first and foremost for fracture toughness measurement of materials. Their use, however, is not just limited to this type of test. Another category of experiments deals with characterizing nonlinear vibrations of beams containing breathing cracks. To produce cracked beam specimens, fatigue cracks can be grown ahead of sharp notches under controlled loading. ASTM E399 and ASTM E1820 standards provide guidance on such procedures for preparation of fracture toughness test specimens. However, certain issues which might become important in testing of vibrations of cracked beams, such as the time required for specimen preparation is not addressed in these standards. In this article, both low cycle fatigue methods and linear elastic fracture mechanics methods are used to estimate the number of loading cycles required to have a crack of desired length at the notch tip. Calculation results are compared with experimental ones, and the effects of various factors influencing the required number of loading cycles for a certain crack size are discussed.

Parametric Optimization of Dissimilar TIG Welding of AISI 304L and 430 Steel Using Taguchi Analysis

Dissimilar welding of 3mm thickness of AISI 304L austenitic stainless steel plate and AISI 430 ferritic stainless steel plates were performed by Tungsten Inert Gas welding without any filler material by using argon as shielding gas. Welding is carried out according to set of combinations of welding parameters such as welding current (levels of 135,140,145 Ampere), welding speed (levels of 105, 110, 115 mm/min) and shielding gas flow rate (of levels 5,10,15 Litre/min) obtained through Taguchi L9 orthogonal approach for maximizing the ultimate tensile strength by using MiniTab software . Radiography test was performed to know the soundness of the welds. Tensile specimens are fabricated as per ASTM E8 standard for tensile testing. Microstructural observations of the weld are performed. Correlations have been obtained to know the effect of welding speed, welding current and shielding gas flow rate on tensile strength and an optimum level of parameter is obtained at welding current of 145 Ampere, welding speed of 115 mm/min and shielding gas flow rate of 5 Litre/min.

Bioinspired designs for shock absorption, based upon nacre and Bouligand structures

Biological materials such as nacre, found in mollusk shells and Bouligand structures, found in the armor of many arthropods, exhibit values of toughness that are much higher than their constituent materials. This is achieved via specific arrangements and combinations of natural materials. In all biomimetic studies seen in literature so far, any one type of material alone is chosen for mimicry. The present work aims to create a set of biomimetic designs that incorporate macroscopic features of both nacre and Bouligand structures, so as to achieve toughness amplification in the given material. Finite element analysis (FEA) of relevant geometric designs are initially performed using ABAQUS software and experimental validation of the most promising model (which was found to show a 46.15% improvement over the reference model) is done. The testing method selected for both simulations as well as experiment is the Charpy impact test (ASTM E23).

Fracture toughness properties of HIC susceptible carbon steels in sour service conditions

Hydrogen Induced Cracking (HIC) in carbon steels is a well-studied mechanism, where diffusing hydrogen atoms accumulates at the steel imperfections/laminations to create gaseous hydrogen with very high pressure, leading to initiation and growth of internal cavities, so-called HIC. Measurements of relevant fracture toughness properties of non-HIC resistant steels in hydrogen environment is critical to predict and assess the initiation and growth of HIC. The present work attempts to quantify the effect of hydrogen on the fracture toughness properties (KQ and CTOD) of an API X42 pipeline steel under simulated H2S in-service conditions. The fracture toughness properties are measured in TL and SL directions: perpendicular and parallel to the pipeline wall thickness, respectively, following ASTM E1820, standard. Since the X42 is a non-HIC resistant steel, the measurement of the fracture toughness properties in the SL direction is more relevant in terms of HIC initiation and growth than fracture toughness properties in the TL direction. Indeed, parallel to the thickness of the pipeline wall, X42 steel shows microstructural features prone to HIC formation and growth. Steady state H2S in-service conditions were simulated by charging the specimen for 48 h using a special electrolytic solution and then tested (ex-situ) to evaluate the fracture toughness properties. The steady state H2S environment was obtained by measuring the Hydrogen Concentration (CH) in the bulk of the specimen, using Thermal desorption Spectroscopy at three levels of CH. It was observed that the KQ was not affected in the SL direction, while it was reduced in the TL direction for 1.5 ppmw of CH. The CTOD showed mixed results in the TL direction while it was significantly reduced in the SL direction reaching a saturation at 1 ppmw of CH. Besides, microstructural analyses showed that the presence of inclusions coalescence in form of dimples promote the early failure, which is more pronounced in the hydrogen environment especially at higher levels of CH.