Assessment Of Fracture Toughness Research Articles

Fracture toughness assessment of axial partially through cracks in X65 and X70 steel pipes

This paper presents analysis of fracture assessment methods of axial partially-through crack in X65 and X70 steel pipes with internal pressure. Two analytical methods Folin–Ciocalteu method (FC method) and Gauss–Seidel method (GS method)) are used to make assessment for two steel pipes (steel X65 and X70). Finite Element model of X65 and X70 steel full-scale pipes with axial part-through crack was established. In this work, a comparison is made between results obtained from FC and GS methods and finite element model with previous experimental results. The GS is more conservative assessment method as it provides smaller crack depth (a) corresponding to (Jcr). Finite Element model in case of steel X70 is more conservative than the analytical methods and its results close to the experimental values.

Effects of Portland Cement and Polymer Powder on the Properties of Cement-Bound Road Base Mixtures.

This article presents the test results for the physical and mechanical properties and fracture toughness of polymer-modified hydraulically-bound mixtures (HBM) produced with Portland cement for road base layers. The modifier used was a redispersible polymer powder (RPP) based on a vinyl ethylene acetate (EVA) copolymer obtained by spray drying. A three-level full factorial design with two factors was applied to determine the contents of Portland cement and polymer powder in the cement-bound mixture (CBM). Both Portland cement and polymer powder were added at three levels: 0%, 2%, and 4%. The assessment included basic physical properties (water absorption, density, and bulk density) and mechanical properties (stiffness modulus, axial compressive strength, and indirect tensile strength) of the CBM. Particular attention was paid to the assessment of fracture toughness in the semi-circular bending test. The results of the research show that polymer powder positively influenced the mechanical properties of CBM by improving its cohesion while maintaining its stiffness. Another benefit coming from the use of polymer powder was the CBM’s increased resistance to cracking, which is the desired characteristic from the perspective of pavement durability.

Mechanical Properties and Flexural Behavior of Sustainable Bamboo Fiber-Reinforced Mortar

In this study, a sustainable mortar mixture is developed using renewable by-products for the enhancement of mechanical properties and fracture behavior. A high-volume of fly ash—a by-product of coal combustion—is used to replace Portland cement while waste by-products from the production of engineered bamboo composite materials are used to obtain bamboo fibers and to improve the fracture toughness of the mixture. The bamboo process waste was ground and size-fractioned by sieving. Several mixes containing different amounts of fibers were prepared for mechanical and fracture toughness assessment, evaluated via bending tests. The addition of bamboo fibers showed insignificant losses of strength, resulting in mixtures with compressive strengths of 55 MPa and above. The bamboo fibers were able to control crack propagation and showed improved crack-bridging effects with higher fiber volumes, resulting in a strain-softening behavior and mixture with higher toughness. The results of this study show that the developed bamboo fiber-reinforced mortar mixture is a promising sustainable and affordable construction material with enhanced mechanical properties and fracture toughness with the potential to be used in different structural applications, especially in developing countries.

Sliding of a diamond sphere on fused silica under ramping load

A diamond sphere of radius 105 μm was used to slide on fused silica under ramping load from 5 mN to 5 N in order to investigate scratch-induced deformation and micro-cracking of brittle solids. Complete circular cracks were observed with elastic deformation playing the predominant role. Results show: initial cracking can be detected by acoustic emission; the valleys of horizontal mean contact pressure and the apparent friction coefficient together with the sudden rise of the ratio of vertical work over horizontal work indicate the beginning stage of circular cracks; micro-comminution is signified by the decrease in residual depth. Values of fracture toughness obtained by Vickers hardness techniques are larger than reasonable ones. Scratch-based approaches by linear elastic fracture mechanics and microscopic energetic size effect laws are found to be applicable to assess fracture toughness of brittle glass by scratch test with a spherical indenter under an appropriate range for curve fitting. Fracture toughness of fused silica measured by scratch test is 0.7 MPa• m1/2, which is compared favorably with the values obtained by conventional methods.

Fracture Toughness Assessment of the Susceptibility for Sulfide Stress Corrosion Cracking in High-Strength Carbon Steels: A Review

High-strength carbon steels typically used as oil country tubular goods (OCTG) made from high-strength carbon steels can be susceptible to sulfide stress cracking (SSC) when in service in environments that contain H2S. In the last 25 y, linear-elastic fracture mechanics has been used to understand both the mechanistic aspects of this form of cracking and to quantify the susceptibility to SSC of different OCTG steel grades. This paper presents a review on the evolution of the double cantilever beam method as a standard practice to assess the threshold stress intensity factor KISSC. The paper evaluates the capabilities and limitations of this testing method to describe the conditions associated with crack propagation. The review study indicates that new fracture parameters based on the energy required for crack propagation such as J-integral might be required to overcome the limitations of the static conditions implied in the stress intensity factor evaluation approach.

Fracture Toughness Assessment of Longitudinally Seam-Welded Gas Pipelines at Low Temperatures

AbstractAmerican Petroleum Institute (API) 5L X65 and X70 steel pipelines are employed widely for natural gas transportation and typically experience internal high transmission pressures and low te...

Assessing fracture toughness in sintered Al2O3–ZrO2(3Y)–SiC ceramic composites through indentation technique

Al2O3–ZrO2(3Y)–SiC ceramic composites were prepared by spark plasma sintering. The fracture toughness (K1C) of the material was evaluated by indentation technique using different types of empirical formulas between 29.4 N and 98 N. The calculated K1C values depend on the crack profile and the applied load. By analyzing the relationship between the indentation radius and the crack length and the crack profile, the crack form of the composite is determined as a Palmqvist crack. Raman spectra result shows that ZrO2 has a significant martensitic phase transformation when the applied load is 5 kg or higher. Additionally, the K1C value decreases slightly as the load increases. The equation based on the Palmqvist crack system and the curve fitting equation are more suitable for the calculation of the K1C value of the material. The composite exhibits a combination of various toughening mechanisms, such as crack deflection and bridging, thereby improving the fracture toughness of the material.

Mixed mode notch fracture toughness assessment of quasi-brittle polymeric specimens at different scales

In this study, the mixed mode I/II notch fracture toughness (NFT) of polymeric (PMMA and GPPS) specimens weakened by U- and key-hole notches is assessed experimentally and theoretically. For this aim, first, by performing experiments, the apparent fracture toughness values of cracked polymeric semi-circular bending (SCB) and Brazilian disk (BD) specimens with four different radii are specified. Next, multiple fracture experiments are conducted on the notched polymeric SCB and BD specimens at four different scales, from which the critical loads are measured and converted to the NFT values. Then, the critical radius of the fracture process zone (FPZ) for the notched polymeric specimens is acquired using two different equations already suggested in literature for cracks. A well-established stress-based failure model, namely the point stress (PS) criterion, is employed for anticipating the NFT values of the specimens tested at various scales, by taking advantages of two different critical distance formulas. The results show that at all of the four scales, the fracture toughness values of U- and key-hole notches achieved from PS criterion are in good agreement with the experimental results. Also, shown in this research is that the mixed mode NFT is considerably dependent on the nominal radius of the specimen, such that, as the specimen radius increases, the mixed mode NFT increases significantly. Moreover, it is exhibited that for the present specimens tested, both the critical distance formulas give almost the same predictions, proposing that each of them can be arbitrarily chosen for the NFT prediction.

Analysis of damage-tolerance of TRIP-assisted V10Cr10Fe45Co30Ni5 high-entropy alloy at room and cryogenic temperatures

A single-phase face-centered-cubic (FCC) high- or medium-entropy alloys (HEAs or MEAs) have attracted great attentions due to their novel damage-tolerance properties (strength, ductility, and fracture toughness) by generating nano-twins at cryogenic temperature. The fracture toughness assessment is essential for evaluating the reliability of high-performance materials for cryogenic applications; however, fracture studies on single-phase FCC HEAs showing transformation-induced plasticity (TRIP) have been hardly conducted. In this study, thus, damage-tolerance mechanisms of a V10Cr10Fe45Co30Ni5 HEA showing the FCC to body-centered-cubic (BCC) TRIP were investigated at room and cryogenic temperatures. At room temperature (298 K), the alloy shows the tensile strength of 731 MPa, elongation of 40%, and fracture toughness (KJIc) of 230 MPa m1/2. At cryogenic temperature (77 K), the strength and elongation improve to 1.2 GPa and 66%, respectively, while the KJIc remains almost constant at 237 MPa m1/2. Dislocation-mediated plasticity prevails at 298 K; however, the TRIP from FCC to BCC occurs at 77 K. Deformation and fracture mechanisms are analyzed by stacking fault energies and differences in Gibbs free energies between phases calculated by ab-initio methods, and are compared to those of CrMnFeCoNi, CrCoNi, Fe50Mn30Co10Cr10, and V10Cr10Fe45Co20Ni15 alloys. Despite the presence of a considerable amount of BCC which is intrinsically brittle at low temperature, the transformed BCC martensite shows ductile fracture after the fracture toughness test even in cryogenic environments. These results demonstrate that the FCC to BCC TRIP can be an attractive route in a field of HEA design to overcome the strength and toughness trade-off at cryogenic temperature.

Assessment of fracture toughness using EWF of IFHS steel

The aim of the present work is to experimentally investigate the essential work of fracture of 1 mm thick interstitial free high strength steels in cold rolled condition. Essential Work of Fracture (EWF) is done experimentally using Double edge notched tension (DENT) specimens of 140 mm in length and 25 mm in width along both rolling and transverse direction in tensile testing machine. Using a universal testing machine, the specimens were strained along their longitudinal direction until completion of cracking. Totally 23 samples with different ligament lengths are tested to obtain essential work of fracture. The specific essential work was determined by extrapolating the straight-line relationship between the specific work of fracture (wf) and ligament length (/) to zero ligament length. The magnitude of essential work of fracture (we) along rolling direction is 133.56 kJ/m2 and for transverse direction is 17.85 kJ/m2.

Effect of blend composition and related morphology on the quasi-static fracture performance of LLDPE/PP blends

In the present work, the effect of composition and related morphology on the fracture behavior of LLDPE/PP blends was thoroughly investigated. Fracture behaviors evaluated under quasi-static loading conditions and different fracture mechanics methodologies were applied to assess fracture toughness depending on the materials behavior. For pure PP and 2575 blend, J at instability was chosen whereas for blends which exhibited completely ductile behavior (such as LLDPE, 7525 and 5050), the EWF methodology was used. Fracture mechanisms were elucidated with the aid of scanning electron microscopy, and results correlated with blends morphology. It was observed that fracture properties are mostly dominated by the majority component properties. In addition, for the 5050 blend, the presence of a co-continuous morphology is responsible for the high scatter of experimental data obtained.

Quantitative fractography as a novel approach to measure fracture toughness of direct resin composites

Dental resin composites generally fail from small cracks. Large crack techniques are not representative of in vivo failures. Quantitative fractography relies on the observation of small “natural flaws”. This study investigates the effect of flaws that occur from fabrication and handling on the measurement of fracture toughness for four different direct resin composites. Microtensile dog-bone shaped specimens for each of four composites were fractured to measure the strength. In addition, we measured crack sizes of the fracture initiating cracks and determined the fracture toughness from these measurements using quantitative fractographic analysis on selected specimens. The characteristic strengths (28–51 MPa) and Weibull moduli (4.9–7.8) were also determined and related to the toughness values (0.5–0.9 MPa m1/2) obtained. The elastic moduli (5–10 GPa) were measured using an indentation technique that has not been used before for direct resin composites. The indentation technique offers an alternative method for small specimens. Quantitative fractographic analysis offers a useful technique to assess fracture toughness of resin composites from cracks of the same size as observed in practice. The toughness of the direct resin composites results from a balance between the size, number and shape of filler particles and the viscosity of the resin matrix.

Compressive transverse fracture behaviour of pultruded GFRP materials: Experimental study and numerical calibration

This paper presents a study on the transverse fracture behaviour of pultruded glass fibre reinforced polymer (GFRP) materials in compression, namely the assessment of transverse compressive fracture toughness (G2−) and transverse compressive residual strength (σr). These properties were assessed through experimental Compact Compression (CC) tests of six different GFRP materials, which were coupled with a data reduction method to determine experimental predictions of G2− and numerically calibrated as a function of the experimental load vs. displacement curves. Through this process, the expected experimental overestimation of G2−, attributed to contact stresses behind the notch tip, was evaluated and accurate numerical estimates of G2− were determined. The numerical calibration considered both G2− and σr, by considering a bi-linear cohesive law. Through the numerical calibration, the G2− results ranged between 36 and 67 N/mm and σr values varied from 9% to 16% of transverse compressive strength (7.6 and 16.9 MPa, in absolute values). Finally, the G2− results were analysed as a function of transverse fibre reinforcement percentage and compared to transverse tensile fracture toughness results (G2+) determined in a previous work. This study showed that G2− is generally higher than G2+ and that the compressive-to-tensile ratio is inversely proportional to the transverse reinforcement percentage.

J-evaluation on tensile testing (JETT) based fracture toughness assessment of Aluminium (6063) alloy using circumferentially notched round bar specimens

The J-evaluation on tensile testing (JETT) using circumferential notch round bar specimens has been proposed for rapid determination of fracture toughness of structural materials exhibiting substantial ductile mode fracture. However, very little has been reported on the effect of notch parameters (notch diameter and notch angle) on the JETT fracture toughness values determined. In this study, Al 6063 alloy was used as test material, and the dependence of the fracture properties on notch parameters, investigated. The Al6063 alloy samples were machined having a constant gauge length (D) of 10 mm, notch diameters (d) of 6, 7, and 8 mm, and notch angles of 45, 60, and 75°, and subjected to tensile loading to fracture. The results obtained showed that the notch strength of the alloy increased with decrease in notch diameter and increased slightly with increasing notch angle. The percent elongation of the notch samples increased with increase in notch diameter and slightly with increase in notch angle. The JETT-fracture toughness values were observed to be more convergent with Dd ratio within the range 1.25–1.7 and the use of notch angles of 60 and 75° with an average value of 328.33 ± 23.73 kJ/m2 obtained. Notch angle of 45°, is not recommended for the JETT basis for evaluation of fracture toughness of Al 6063 alloy.

In silico non-linear dynamic analysis reflecting in vitro physical properties of CAD/CAM resin composite blocks

PurposeThe aim of this study was to assess the validity of in silico models of three-point bending tests to reflect in vitro physical properties obtained from three commercially available computer-aided design/computer-aided manufacturing (CAD/CAM) resin composite blocks and demonstrate notchless triangular prism analysis with those properties. Material and methodsThree types of commercially available CAD/CAM resin composite blocks were used: Cerasmart 300 (CS300; GC, Tokyo, Japan), Katana Avencia P Block (AP; Kuraray Noritake Dental, Tokyo, Japan), and KZR CAD HR3 Gamma Theta (GT; Yamakin, Osaka, Japan). In vitro/in silico three-point bending tests were conducted to obtain elastic modulus and fracture strain for non-linear dynamic finite element analysis (n = 10/each). Fractured surfaces of specimens after in vitro NTP tests were observed, and the fracture toughness of each CAD/CAM resin composite was obtained by in silico NTP analysis. ResultsBoth in vitro and in silico load–displacement curves obtained from three-point bending tests were significantly correlated (p < 0.05). The elastic moduli of CS300, AP, and GT were 8.0 GPa, 10.0 GPa, and 9.0 GPa, respectively. The fracture toughness values obtained from in silico NTP analysis of CS300, AP, and GT were 5.057 MPa m1/2, 4.193 MPa m1/2, and 4.880 MPa m1/2, respectively. There was no significant difference in the length of the stable region among the three CAD/CAM resin composites (p = 0.09). ConclusionsThe in silico approach established in this study showed acceptable reflection of in vitro physical properties and will be useful for assessing fracture toughness related to the longevity of CAD/CAM resin composites without wastage of materials.

Investigation on the constraint effect on the fracture toughness assessment of stainless steel AISI 304L thin sheets

Investigation on the constraint effect on the fracture toughness assessment of stainless steel AISI 304L thin sheets

Sliding of a diamond sphere on K9 glass under progressive load

Micro-scratch tests have been carried out on borosilicate K9 glass using a Rockwell C diamond indenter with a spherical tip radius 105 μm in order to study deformation/damage regimes and microcracking patterns of K9 glass with increasing normal load. The abrupt changes of test data together with optical microscopy observation can be used to determine three transition loads corresponding to initiation of sub-surface median crack, onset of surface ring crack, and lateral cracks reaching the surface, respectively. Based on linear elastic fracture mechanics, fracture toughness obtained from scratch test under a low driving speed and a suitable fitting range of nominal size is found to be 0.85 MPa•m1/2 for K9 glass, which is close to 0.82 MPa•m1/2 obtained from Vickers hardness technique, making micro-scratch a powerful means to assess fracture toughness of material, and opening new application of scratch test as a quantitative method.

Assessment of Fracture Toughness in Bone Tissue Engineering

The fracture mechanisms affecting bone tissue can be described as a damage accumulation process due to the initiation and propagation of microcracks. Fracture risk does not solely depend on strength but also on fracture toughness. To replace damaged bone or cartilage tissues, hydrogels are required to provide appropriate stiffness or deformation properties as well as resistance to fracture. However, failure properties, such as the resistance to fracture, must be evaluated by fracture toughness techniques. Microindentation has emerged as a novel technique for the measurement of material properties of cortical bone. The application of this test for fracture toughness determination in these tissues can become widespread because of the simplicity of the test. The aims of this article are to discuss clinical application of fracture toughness analysis and to present a well tested and more realistic approach for estimating fracture toughness in bone. POLYM. ENG. SCI., 59:2402–2405, 2019. © 2019 Society of Plastics Engineers

Biomimetic fabrication, mechanical behavior and interrupted turning performance of the microscopic surface structures of Al2O3/TiC micro-nano-composite ceramic

The present work was conducted to study biomimetic fabrication, mechanical behavior and interrupted turning performance of the microscopic surface structures of Al2O3/TiC micro-nano-composite ceramic. A novel nondestructive method for fracture toughness assessment and two novel performance indicators with critical influencing factors integrated were proposed for the biomimetic microscopic structures. Laser surface texturing (LST) was employed to fabricate the biomimetic microscopic structures considering the structures on the cuticle of both catharsius molossus and carassius auratus. The fractal dimensions of the indentation-caused microscopic cracks and the laser-caused microscopic cracks were gained and analyzed. The external load in cutting process, the microscopic structure within the composite ceramic and the resistance to fracture of the composite ceramic were integrated in the proposed performance indicators I1 and I2. The number of scans and the angle of laser beam had substantial influences on the sloping characteristics of microscopic dimple and microscopic groove. The sloping characteristics of the microscopic dimple were more sensitive to the changes of the number of scans and the angle of laser beam. Higher degree of oxidation of the biomimetic microscopic structures corresponded to greater reduction of fracture toughness. The fractal dimensions of the indentation-caused microscopic cracks and the laser-caused microscopic cracks can be used to reflect fracture toughness. The fractal analysis of the laser-caused microscopic cracks can be used as a nondestructive method for the assessment of fracture toughness. The biomimetic microscopic structures on ceramic tool surface were found to be effective in postponing tool failure. The optimum interrupted turning performance of the biomimetic microscopic structures can be acquired when the number of scans was 2 and the angle of laser beam was 50°. Indicator I1 had a higher accuracy in the prediction of performance. Indicator I2 can be utilized to predict the performance of the biomimetic microscopic structures without destruction.

The Role of Substructural Features on the Deformation and Fracture Behavior of BCC and FCC High Entropy Alloys

The applicability of high entropy alloys (HEAs) as useful structural components is limited due to our lack of systematic understanding of the role of micro- and sub-structural features on their deformation and fracture behaviour. Synergistic assessment of fracture toughness (FT) and activation volume (V) for plastic deformation of typical BCC and FCC HEAs containing Al-Cr-Co-Cu-Fe-Ni by standard practices have been made to throw some light in this direction; these assessments are supplemented by micro- and sub-structural examinations using electron microscopy together with measurements of conventional mechanical properties. The major results indicate that the BCC alloy exhibits higher hardness and strength with inferior FT compared to the FCC alloy. This observation has been explained using the estimated magnitudes of V which is governed by the operative deformation mechanisms controlled by the nature of dislocations in the concerned microstructural constituents.