Fracture Toughness Characteristics Research Articles

Fracture toughness characteristics of ultrafine grained Nb–Ti stabilized microalloyed and interstitial free steels processed by advanced multiphase control rolling

Aim of the current study is to analyze the fracture toughness values along with other mechanical properties and correlating the microstructures of ultrafine grained (UFG) microalloyed and interstitial free (IF) steels produced through advanced 3-steps control multiphase rolling. The analysis of fracture toughness was carried out through computing KQ (conditional fracture toughness), J-integral (crack initiation energy) and Kee (equivalent energy fracture toughness) values from 3-point bend test data of rolled specimens. Microstructural analysis was performed through transmission electron microscopy (TEM) along with selected area electron diffraction (SAED) and Electron backscatter diffraction (EBSD). The quantitative measurement of low and high angle grain boundaries and their distribution in the deformed state were determined through EBSD analysis. The good combinations of fracture toughness, yield strength (YS) and percent elongation (%El.) (i.e. ductility) were achieved through innovative 3-phase control rolling (microalloyed steel: Kee = 68.9MPa√m, J = 81.4 kJ/m2, YS = 923MPa, %El. = 13.6; IF steel: Kee = 72MPa√m, J = 87.7 kJ/m2, YS = 623Mpa and %El. = 19). This is ascribed to the development of homogeneously distributed submicron size (0.69μm) ferritic + martensitic structure in the microalloyed steel and submicron size (0.83μm) ferritic grains along with high density dislocation substructure in the IF steel. These dislocation cells and substructures could effectively block the crack initiation and propagation. The development of UFG microstructure has been analyzed in the light of deformation induced ferrite transformation (DIFT) and dynamic recrystallization (DRX) mechanisms. Superior fracture toughness of the UFG steels along with better combination of mechanical properties is very demanding for high strength structural applications.

Mode I Fracture Toughness Test and Fractal Character of Fracture Trajectory of Red Sandstone under Real-Time High Temperature

To evaluate the stability and compactness of high-temperature underground construction, it is necessary to test the fracture toughness of surrounding rock (red sandstone) under real-time high temperature. In this paper, SCB specimens recommended by the International Society for Rock Mechanics are used to measure the mode I fracture toughness of red sandstone at real-time high temperatures. Also, to reveal its fracture characteristics and fracture mechanism, the fracture morphology observation (SEM experiment), XRD experiment, mercury intrusion porosimetry testing, and fractal measurement of fracture trajectory are carried out on the red sandstone specimens at various temperatures. The results show that (1) temperature may have a significant impact on the fracture toughness and fracture characteristics of red sandstone. On the whole, the fracture toughness values decrease with the increase in temperature, while the fractal dimensions of fractal trajectories increase with the increase in temperature. (2) Temperature has a significant influence on the fracture mode of red sandstone. At relatively low temperatures (20°C–400°C), the main fracture mode is transgranular failure. At relatively high temperatures (400°C–700°C), the fracture mode is mainly intergranular failure. (3) The weakening mechanism of red sandstone is mainly due to the effect of thermal dehydration when the temperature is between 100°C and 400°C. When the temperature is between 400°C and 700°C, the weakening mechanism is mainly due to thermal cracking and theα-βphase transition of quartz.

Hydrogen Effect on Cumulation of Failure, Mechanical Properties, and Fracture Toughness of Ni-Cr Alloys

Influence of hydrogen pressure and internal hydrogen contents on short-term strength, plasticity, and plane-stress fracture toughness of 05Cr19Ni55 alloys at pressure up to 30 MPa was investigated. It was established that the crack resistance parameters Kc of alloys decrease with displacement rates decreasing similar to elongation (δ) and reduction of area (ψ) of smooth specimens. The maximum hydrogen influence is achieved at strain rate speeds less than 0.1 mm/min and hydrogen pressures above 15 MPa when δ and Kc of prehydrogenated samples are reduced by 3 times. The plane-strain conditions required for the evaluation of KІc were fulfilled on compact tension 05Cr19Ni55 alloy specimens with thickness above 20 mm under hydrogen pressure 30 MPa and preliminary dissolved hydrogen concentration above 20 wppm. Regardless of the test conditions, the value of the characteristics of plasticity (δ, ψ) and fracture toughness (Kс) of alloy (TO1) specimens oriented in the transverse direction (orientation TV) is significantly lower than that of specimens oriented in the longitudinal direction (LT). Alloy cleaning by vacuum arc remelting and optimization of heat treatment regime increase their hydrogen resistance.

The characteristics of dynamic fracture toughness and energy release rate of rock under impact

To investigate the characteristics of rock fracture toughness and dynamic energy release rate, impact experiments were conducted in large single cleavage semicircle compression (LSCSC) specimens. Fracture toughness and energy release rate of three sandstones were investigated and a drop-weight device was applied. Crack length and crack propagation velocity were corrected by fractal method, and fracture surface morphology was obtained by scanning electron microscope. The dynamic stress intensity factor (DSIF) was acquired from the finite element model established in the ABAQUS. The DSIF history was acquired, and the initiation and propagation toughness were determined according to the measuring result of fracture time. It shows that, for a material, propagation toughness is related to its Young’s modulus, and the higher the Young’s modulus or wave impedance is, the larger the propagation toughness is. For black sandstone, the energy release rate increases rapidly with crack length, whereas for green and red sandstones, it increases slightly under a same speed impact.

Characterization of phases, tensile properties, and fracture toughness in aircraft‐grade aluminum alloys

Characterization of phases, tensile properties, and fracture toughness in aircraft‐grade aluminum alloys

Formability Limits, Fractography and Fracture Toughness in Sheet Metal Forming.

This paper is focused on the utilisation of double edge notched tension, staggered and shear tests to determine fracture toughness and the formability limits by fracture in principal strain space. The experiments were performed in test specimens with different geometries and ligament angles, and the influence of strain hardening was taken into consideration by selecting two materials (aluminium AA1050-H111 and pure copper), with very different strain hardening exponents. Results are plotted in principal strain space, and the discussion is focused on the link between formability limits, fracture toughness and macroscopic fractography characteristics of the specimens that fail by mode I, mode II or mixed-mode.

Small-Scale Mechanical Testing of Cemented Carbides from the Micro- to the Nano-Level: A Review

In this overview, we summarize the results published to date concerning the small-scale mechanical testing of WC–Co cemented carbides and similar hardmetals, describing the clear trend in the research towards ever-smaller scales (currently at the nano-level). The load-size effect during micro/nanohardness testing of hardmetals and their constituents and the influence of the WC grain orientation on their deformation, hardness, indentation modulus, fracture toughness, and fatigue characteristics are discussed. The effect of the WC grain size/orientation, cobalt content, and testing environment on damage accumulation, wear mechanisms, and wear parameters are summarized. The deformation and fracture characteristics and mechanical properties, such as the yield and compression strength, of WC–Co composites and their individual WC grains at different orientations during micropillar compression tests are described. The mechanical and fracture properties of micro-cantilevers milled from WC–Co hardmetals, single WC grains, and cantilevers containing WC/WC boundaries with differently-oriented WC grains are discussed. The physical background of the deformation and damage mechanisms in cemented carbides at the micro/nano-levels is descri and potential directions for future research in this field are outlined.

Fracture Toughness Characterization of High-Performance Steel for Bridge Girder Applications

AbstractThe use of high-performance steel (HPS) in new bridge construction continues to increase as engineers and owners recognize the potential for cost savings and performance benefits. One inten...

The effect of SPS parameters on the production of yttria transparent ceramic

AbstractIn this work, the spark plasma sintering (SPS) of commercial yttria nanopowder is investigated. The SPS parameters such as sintering temperature, applied pressure, and dwell time are varied. Densification without grain growth occurring at occurred up to a sintering temperature of 1400°C and grain growth without further densification taking place at the higher temperature. The optimum sample was obtained at a temperature of 1400°C with a pressure of 70 MPa and dwelling time of 15 minutes. The highest relative density of 99.8% and the average grain size of 1.26 μm were obtained at 1400°C. The yttria ceramic annealed at 1200°C had the in‐line transmission of 5%‐70% and 70%‐82% in the visible and infrared wavelength region, respectively. The measurements of hardness and fracture toughness characteristics of the transparent yttria ceramic showed 9.2 GPa and 2.24 MPa.m1/2, respectively.

Development of investigations on fracture mechanics of materials and structural integrity: achievements and perspectives (review)

The main achievements of scientists at Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine (PhMI) on fracture mechanics of materials and structural integrity since the middle of the 20th century are analysed. The main attention is focused on the concepts of limiting-equilibrium state (strength) of deformed bodies with cracks and on experimental methods for determining the crack growth resistance of the material that is the characteristics of the material fracture toughness and the influence of working environment on these characteristics.

Assessment of Metal Cutting Tools using Cost Performance Ratio and Tool Life Analyses

Critical raw materials (CRM) are extensively used in tools for metal cutting, such as in cemented carbide tools (cobalt and tungsten), because they provide desired characteristics of high fracture toughness and wear resistance. Both academia and industry are examining CRM-free material alternatives, such as tools based on polycrystalline diamond (PCD) or ceramic materials. These materials are generally more cost intensive as compared to cemented carbide but could also provide higher efficiency in terms of material removal rate. Material removal rate and tool costs have a substantial influence on the final part cost. When deciding on tool material, the manufacturing industry is either looking for the most cost effective alternative or the alternative providing the highest productivity output. The purpose of this paper is to provide industry with decision support for selection of tool and cutting data that provide the financial most sound production set-up.This work aims to present a novel methodology combining the Colding tool life model and a previously presented model for cost performance ratio. A previous publication provided a method to assess technological solutions and investments based on final part cost. The developed methodology in this article combines cutting performance and production performance to allow a comprehensive cost assessment for a production process. The assessment includes cutting data, tool life and costs of tooling, quality rejections, process availability, equipment investment, personnel and facility. A case study based on experimental data is presented to verify the proposed methodology.

Fracture Toughness and Fatigue Crack Propagation Characteristics at Bonded Interface of Duplex Stainless-Clad Steel Plate for Chemical Tankers

Fracture Toughness and Fatigue Crack Propagation Characteristics at Bonded Interface of Duplex Stainless-Clad Steel Plate for Chemical Tankers

Effect of Aluminum Particles on the Fracture Toughness of Polyamide-based Parts Obtained by Selective Laser Sintering (SLS)

Numerous additive manufacturing technologies are currently used in industry and research: selective laser sintering, selective laser melting, electron beam melting, fused deposition modelling, laminated object manufacturing and stereolithography. Independently on the type of technology, a set of technological parameters have to be controlled in order to obtain good quality parts that also possesses acceptable mechanical properties. Selective laser sintering (SLS) is a multipurpose additive manufacturing technology that allows fabrication of good resolution parts with adequate mechanical properties. The versatility of the process refers to the limitless geometrical shapes that can be achieved and also to a variety of powders and mixtures that can be used.The uncontrollable process variables occurring along the sinterization process (heat transfer, humidity), together with the multitude of controllable technological factors, including raw materials, lead to inconsistencies in shape, size and mechanical properties of the parts. These inconsistencies appear not only in SLS but in all additive manufacturing technologies.The study proposes to underline the influence of the aluminum mixed polyamide on the fracture toughness and geometrical characteristics of parts manufactured using the same energy density but different orientations in the building environment. The findings can be used for part design and parameter setup, in order to prevent both mechanical and geometrical failures.

Hygrothermal effects on mode II interlaminar fracture toughness of co‐bonded and secondary bonded composites joints

Adhesive joints are being more extensively applied in the aeronautical industry, allowing for better integration between the structural parts and overall lower weight if compared with joints made with fasteners and rivets. However, a further evaluation of these new technologies is needed, once their critical fracture toughness under different environmental conditions is still unknown and this value is essential for design and certification of aircraft manufactured with these materials. Thus, this work focuses on the mode II fracture toughness characterization of carbon fiber composite laminates joined by co‐bonded (CB) and secondarily bonded (SB) techniques, using EA 9695 epoxy adhesive aged at different environmental conditions (room temperature ambient—RTA and elevated temperature wet—ETW). Dynamic mechanical analysis (DMA) was used to understand the effect of moisture absorption on the glass transition of materials and on the decreasing of Mode II fracture toughness after aging. The DMA results showed a reduction of 11% in Tg values for the GIIc values of ETW samples in comparison with specimens tested at RTA condition. Reductions about 92 and 94% in Mode II fracture toughnesses were obtained for CB and SB aged specimens, respectively when compared with the toughness values obtained for specimens tested at RTA. Further inspection of the fracture surfaces using scanning electron microscope proved that light fiber‐tear fracture occurred at both RTA and ETW conditions for CB joints, while fracture was mainly light‐fiber‐tear at RTA condition, becoming mostly cohesive after aging for SB joints. POLYM. COMPOS., 40:3220–3232, 2019. © 2018 Society of Plastics Engineers

Characterization of hardness, elastic modulus and fracture toughness of RB-SiC ceramics at elevated temperature by Vickers test

In this paper, mechanical properties of RB-SiC ceramics, such as hardness, elastic modulus and fracture toughness, are characterized through indentation technique using a Vickers indenter at elevated temperatures ranging from room temperature to1200 °C realized by laser heating. The indentation size effect, load-displacement curves and relationship between crack length and applied load are studied in order to determine hardness, elastic modulus and fracture toughness accurately. The results show that the Meyer’s index and Vickers hardness decrease with the increase temperature. It indicates that the permanent plastic deformation of RB-SiC ceramics is mainly responsible for the indentation size effect and the reduction of hardness at elevated temperature. Both material softening and plastic deformation will contribute to the indentation creep at elevated temperature as shown in the load-displacement curves. The elastic modulus decreases with the increase of temperature due to increase of contact depth as a result of less elastic recovery. In the indentation test for calculating fracture toughness, only radial-median cracks are identified by the relationship between crack length and applied load at all temperatures, although the fracture mode observed at the indent corner changes from transgranular at room temperature to intergranular at elevated temperature. As more energy is consumed by intergranular facture and cracking-healing takes place due to oxidation, only short crack length appears in the indentation test which implies an increase of fracture toughness with the increase of temperature. However, this tendency has an exception at the highest temperature of 1200 °C. This is because the free Si softening in RB-SiC specimen fails to resist crack propagation at extremely high temperature. Consequently, the crack length increases again which leads to the increase of the calculating fracture toughness at the highest temperature. These variations of hardness, elastic modulus and fracture toughness with temperatures will account for the possible change of material removal regimes occurred in some thermal-involved hybrid machining of RB-SiC ceramics.

Influence of the steel rolling direction on the mechanical properties and distribution of the local stress in front crack

In this article presented the results of studies of strength characteristics (yield strength-σy, ultimate strength σuts, power exponent-n) and fracture toughness (JR, JIC) determined on the specimens of steel S235 taken in the rolling and perpendicular direction. Standard strength characteristics are similar for the specimens in both directions. However, there occurs an essential difference in fracture toughness characteristics for the specimens from different directions. To determine (explain) factors that cause this phenomenon performed some metallographic studies and the analysis of local stress and strain distributions in front of the crack.

EXPERIMENTAL DETERMINATION OF CHARACTERISTICS OF CRACK-RESISTANCE OF DISPERSE-STRENGTHENED COMPOSITES BASED ON NON-SATUTATED POLYESTERS

Based on the series of tests for three-point bending of rectangular bars with central cuts on a universal test machine, using the compliance and K-methods, experimental values of the fracture toughness characteristics of the material under investigation were obtained. In this work, the characteristics of the fracture resistance of casting artificial stone (CAS) were determined. The obtained values of the mechanical characteristics of the material are comparable to those of the natural stone. As a result of the experiments, tension-compression diagrams for CAS and also the dependence of compliance from the relative length were obtained. Considering the substantial technological advantages of this composite, it is concluded that it is practical to use this material.

Characterization of elastic-plastic fracture toughness of AM60 Mg alloy under mixed-mode loading conditions

In this paper, an estimation of the elastic-plastic fracture of the AM60 alloy under pure mode-I, mixed-mode, and pure mode-II loading conditions has been investigated. For this purpose, a modified Arcan-type device and a butterfly specimen were used. Fracture tests were conducted according to ASTM standard E1820; however, due to the standard being limited to some specific geometries and the mode-I loading, the relationships and parameters presented in the standard, including the non-dimensional stress intensity factor, the geometric work factor, and other parameters were extracted and analyzed using finite element analysis for the butterfly specimens and under different loading conditions and relationships developed for them. In the following, the fracture tests for the butterfly specimen were carried out under mode-I, 45° mixed-mode, and mode-II loading conditions and the material resistance curves against crack growth (J-R) were extracted. As a result, the material fracture toughness was extracted for each. Also, for the verification of the fixture used in this study, a beam-shaped specimen test was arranged, and its results were compared with the values of mode-I obtained from the modified Arcan fixture. The results indicated that, by changing the loading angle from mode-I to mode-II, the critical values of the fracture took on a decreasing trend, which indicated the greater resistance of the material to crack growth under the conditions of mode-I (tension) compared to mode-II (shear). On the other hand, the difference between the results obtained from the fixture used and the beam-shaped specimen was less than 9%, which indicates the correct performance of the fixture. Finally, in order to get a deeper understanding of the material fracture mechanism under different loading conditions, the fracture surfaces were examined using scanning electron microscopy (SEM).

Development and fracture toughness characterization of a nylon nanomat epoxy adhesive reinforcement

The potential of an electrospun nylon nanofibrous mat as adhesive carrier and reinforcing web in adhesive bonding has been proven by the authors in a previous work. In that work, a pre-preg nanomat was developed using a low-viscosity epoxy resin for composite hand lay-up, in order to favour wetting of the nanofibres and to minimize air entrapment. However, the resin for hand lay-up exhibited a poor bonding performance when compared to the one typical of epoxy adhesives. The present work is therefore aimed at developing a laboratory route to add an electrospun polymeric nanomat to a two-part epoxy adhesive joint. Three different adhesives with increasing viscosity have been preliminarily evaluated regarding the entrapment of air after curing. The most promising one has been used to manufacture a small-size, Al-alloy double cantilever beam joint and compare the performance with and without the nanomat. Three different precracking procedures have also been developed and evaluated, namely fatigue precracking ...

Fracture toughness of ultra-high molecular weight polyethylene: A basis for defining the crack-initiation toughness in polymers

This paper presents a cohesive methodology for quantifying the fracture behavior of structural polymers. We accomplish this task by reviewing the complexities of polymer fracture mechanics and associated J-integral fracture toughness testing as well as by conducting appropriate nonlinear-elastic fracture mechanics measurements with comprehensive analysis. J-based crack-initiation and crack-growth fracture toughness testing is performed on ten clinically relevant formulations of ultra-high molecular weight polyethylene (UHMWPE). This polymer is chosen for its extensive literature base in terms of its mechanical properties and fracture toughness behavior, as well as its safety-critical importance and broad use in total joint replacements. One of the current limitations in the fracture toughness characterization of polymers is the use of “engineering” constitutive behavior to determine the crack-initiation toughness, as compared with the “true” constitutive properties. UHMWPE offers a plethora of true tensile stress-strain data that serves as a template and predicate base for fracture analysis. This paper aims to demonstrate why using true stress-strain behavior for polymer fracture mechanics is so important and why a justified comprehensive analysis method is needed in order to reliably measure the fracture toughness of polymeric materials.