Evaluation Of Fracture Toughness Research Articles

A facile synthesis method and fracture toughness evaluation of catfish bones-derived hydroxyapatite

AbstractIn this study, biological hydroxyapatite (HAp) was synthesized from catfish (Pangasius hypophthalmus) bones. First, the as-received catfish bones were de-proteinized in open air, and then converted to HAp by a solid state heat treatment method at a temperature of 900 °C for a holding time of 2 h in a muffle furnace. X-ray diffraction (XRD) analysis confirmed that HAp with high crystallinity of 99.9% was formed matching the structural properties of flouro-apatite with crystallite sizes of approximately 37.1 nm. The morphology of the HAp prepared showed irregularly shaped particles and revealed the appearance of open pores with a less agglomerated structure and a Ca/P ratio of about 1.58. The specific mechanical properties: hardness, compressive strength and fracture toughness of the catfish derived scaffolds were recorded as 480 MPa, 1.92 MPa, and 5.72 Mpa.m1/2, respectively. The fracture toughness of the HAp derived scaffolds suggests that the produced biomaterial is promising for biomedical applications. These findings are useful for the production and application of the HAp powders prepared from catfish bones, and further suggests a possible low-cost route for producing inexpensive ceramics using natural catfish bones.

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.

Evaluation of fracture toughness and residual stress for both single GYbZ and double layered GYbZ/8YSZ coatings by modified indentation tests

Single (Gd0.9Yb0.1)2Zr2O7 (GYbZ) and double layered GYbZ/yttria partially stabilized zirconia coatings were prepared with supersonic plasma sprayed technique. The microstructure and texture of the two coatings were analyzed by scanning electron microscope and X-ray diffraction. The elastic modulus, hardness, fracture toughness and residual stress of both coating systems were measured in indentation tests. The influence of residual stress on fracture toughness measurements was discussed with different indentation models. It is interesting to find that the absolute value of residual stress on the cross section of the coating becomes smaller, while the corresponding fracture toughness gets larger when the indented point gradually moves to the interface. The present results would be helpful for understanding the design optimization and failure mechanisms of advanced ceramic coatings.

A novel evaluation of fracture toughness for random fibrous material

In this study, we perform three-point-bending tests for 3-dimensional random fibrous (3D RF) material specimens of two porosities (87% and 83%) with a crack. The crack with two different crack-length-to-specimen-width ratios (0.2 and 0.5) is considered. Using the tensile strength obtained from experiments and a characteristic average fiber spacing parameter from an equivalent orthotropic fiber network model, a simple theoretical model is developed to evaluate the fracture toughness of 3D RF material. This model gives the fracture toughness of 3D RF material, which is in good agreement with that from compact tension test, and better than the results calculated via the American Society for Testing Materials (ASTM) standard for three-point-bending test. This fact not only rationalizes the use of average fiber spacing size in the developed model, but also demonstrates the model efficiency in evaluating the fracture toughness of 3D RF material. Further, considering the temperature effect on the fracture strength of material, this theoretical model can be successfully used to predict fracture toughness of 3D RF materials at elevated temperatures (299 K~1073 K).

Mode I Fracture Toughness Evaluation of Adhesively Bonded Joints via J‐Integral and DIC

AbstractAmorphous polymers, such as epoxy resins, are commonly used in the realization of adhesively bonded joints. In this paper an evaluation of mode I fracture toughness of bonded joints is presented. Moreover, an identification of cohesive zone model parameters via Rice's J‐integral is described. Experimental tests are performed on double cantilever beam specimens and relative displacements between adherends are acquired by using the digital image correlation technique. The obtained interface law can be implemented in a finite element code for simulating the decohesion process of complex bonded structures.

Measurement of Fracture Toughness of Pure Tungsten Using a Small-Sized Compact Tension Specimen.

The evaluation of fracture toughness of pure tungsten is essential for the structural integrity analysis in a fusion reactor. Therefore, the accurate quantification of fracture toughness of tungsten alloys is needed. However, due to the inherent brittleness of tungsten, it is difficult to introduce a sharp fatigue pre-crack needed for the fracture toughness test. In this study, a novel fatigue pre-cracking method was developed and applied to the small-sized disc-type compact tension (DCT) specimens of double-forged pure tungsten. To overcome the brittleness and poor oxidation resistance, a low-frequency tensile fatigue pre-cracking was performed at 600 °C in Ar environment, which resulted in the introduction of a sharp pre-crack to DCT specimens. Then, fracture toughness tests were conducted at room temperature (RT), 400 °C, and 700 °C in air and Ar gas environments using as-machined and pre-cracked DCT specimens. At RT and 400 °C, the test environment and crack tip radius did not affect the fracture toughness measurement. However, at 700 °C, the Ar gas environment and the presence of a sharp fatigue pre-crack resulted in a decrease in the measured fracture toughness. Thus, it was suggested that, for the conservative fracture toughness measurement of pure tungsten, fatigue pre-cracking and fracture toughness test should be performed in an inert environment, especially for high-temperature tests.

Fracture toughness evaluation for thin-shell stainless steel weldment

Integrity of spent nuclear fuel (SNF) interim storage canisters are very important to the safety of the back-end nuclear fuel cycle. Stress corrosion cracking (SCC) potential of interim storage canister has been considered as a high priority. Because no post-weld heat treatment was required for forming these canisters, the high tensile residual stress existed within these canister welds. This can change the fracture resistance capacity significantly as well as increase SCC potential. Due to relative thin shell thickness of a canister weldment, the spiral notch torsion test (SNTT) method of small specimen approach was used to estimate the canister weldment fracture toughness. Most SNTT weldment samples fracture initiation sites are at heat-affected zone (HAZ) regions. The estimated fracture toughness JQ’ for the baseline SS304 steel is at 283 kJ/m2. The estimated JQ’ for the SS304/308 weld from HAZ and weld specimens are 126 kJ/m2 and 148.9 kJ/m2, respectively.

The Evaluation of Fracture Toughness on Mode I for Twill CFRP/GFRP Laminated Hybrid Composites

The Evaluation of Fracture Toughness on Mode I for Twill CFRP/GFRP Laminated Hybrid Composites

Comparative evaluation of fracture toughness and marginal adaptation of two restorative materials in nonendodontically and endodontically treated teeth: An in vitro study.

To evaluate and compare the fracture resistance and marginal adaptation of Zirconomer and bulk fill posterior restorative material (Surefil SDR) in nonendodontically and endodontically treated teeth. The sample consisted of 52 caries-free extracted human premolars which were individually mounted in polyvinyl chloride (PVC) ring filled with acrylic resin up to 1.0 mm below the cementoenamel junction. The teeth were then divided into four groups according to the restorative material used as group I: Zirconomer + Operative only, Group II: Zirconomer + Endodontic treatment, Group III: SDR + Operative, and Group IV: SDR + Endodontic treatment. Fracture strength was tested using a universal testing machine and was expressed in Newtons. The marginal gap was measured at its maximum using a scanning electron microscope and expressed in micrometers. One-way analysis of variance followed by Tukey's post hoc test was used to compare the mean fracture resistance (N) and marginal adaptation (μm) between the four groups. Statistical significance was determined at α = 0.05. Group 3 exhibited significantly highest mean fracture resistance than Group 1 (P < 0.001), Group 2 (P < 0.001), and Group 4 (P < 0.001). Group 4 had significantly higher mean fracture resistance than Group 1 (P = 0.008) and Group 2 (P < 0.001). Group 1 exhibited significantly highest mean marginal gap than Group 3 (P < 0.001) and Group 4 (P < 0.001). Group 2 had a significantly higher mean marginal gap than Group 3 (P < 0.001) and Group 4 (P < 0.001). The fracture resistance and marginal adaptation of Zirconomer are significantly lower than Surefil SDR in both nonendodontically and endodontically treated teeth.

A Comparative Evaluation of Fracture Toughness of Composite Resin vs Protemp 4 for Use in Strip Crowns: An In Vitro Study.

ABSTRACTAimThe aim of this study was to compare the fracture toughness of pedo shade packable composite resin (Z100, 3M ESPE, St. Paul, USA) vs Protemp 4 (3M ESPE, Seefeld, Germany) when used inside a strip crown to restore primary incisors.Materials and methodsThirty-six exfoliated noncarious human primary central and lateral incisors were randomly divided into two equal groups. The teeth were prepared to standardized dimensions to receive a strip crown. All the teeth were etched, rinsed, and dried following which bonding agent was applied and light cured. In group I, pedo shade packable composite resin (Z100, 3M ESPE, St. Paul, USA) was packed into strip crowns, placed on the prepared tooth, and light cured. In group II, the strip crowns were filled with Protemp 4 (3M ESPE, Seefeld, Germany), placed on the prepared tooth, and left to autopolymerize for 10 minutes. The strip crowns were removed, and the teeth were tested using the universal testing machine until fracture. Fracture toughness of the two groups was recorded and analyzed statistically using Student's “t” test.ResultsThe mean force required to fracture strip crowns restored with Protemp 4 (416.89 ± 124.58 N) was higher when compared with pedo shade packable composite resin (338.27 ± 130.99 N). However, statistical analysis did not show a significant difference in the fracture toughness between the two groups (p = 0.074), based on Student's “t” test results.ConclusionThe fracture toughness of teeth restored with Protemp 4 was comparable with pedo shade packable composite resin when used inside a strip crown.Clinical significanceThe use of Protemp 4 is a possible alternative to pedo shade packable composite resin in restoring the primary anterior teeth, when used inside the strip crowns. The data also showed that the fracture toughness of Protemp 4 was comparable with pedo shade packable composite resin.How to cite this articleVignesh KC, Kandaswamy E, Muthu MS. A Comparative Evaluation of Fracture Toughness of Composite Resin vs Protemp 4 for Use in Strip Crowns: An In Vitro Study. Int J Clin Pediatr Dent 2020;13(1):57–60.

Fracture toughness evaluation of axially-cracked tubular thin-walled specimens of Zircaloy-4 and its implications for integrity analysis of nuclear fuel clad

As nuclear fuel clad is a thin-walled and small diameter tube, it is not possible to machine standard ASTM specimens from these tubes in order to conduct the fracture tests. In this work, fracture experiments have been conducted using a different type of specimen (which is machined from the tubular clad of Zircaloy-4) and a test setup. Initial cracks in the axial direction have been machined in these tubular specimens and the cracked tubes have been loaded with a conical mandrel. The conical mandrel, when pushed into the cracked specimen, simulates the loading which is similar to that induced by the hourglass-shaped fuel pellet on fuel clad during the postulated reactivity-initiated-accident scenarios. By changing the mandrel angle as well as the specimen geometry, different magnitudes of crack-tip constraints are induced in the experiments and these, in turn, influence the crack initiation and propagation toughness of the axially-cracked fuel clad. In addition, simulations have been carried out using 3D elastic-plastic finite element model of the fuel clad, mandrel and their frictional contact to predict the load-displacement behavior. The crack-tip constraints of the axially-cracked specimens of different geometries have been evaluated from results of finite element analysis. The J-R curves as functions of different specimen geometry and loading conditions have been evaluated from experimental data and the differences of the fracture toughness data among the specimens have been explained in terms of variations in crack-tip constraint.

Applicability of compact tension specimens for evaluation of the plane-strain fracture toughness of steel

AbstractThe plane-strain fracture toughness test method enables the determination of the plane-strain fracture toughness (KIC) of metallic materials by tests using a variety of precracked specimens, such as bend, compact tension (CT), arc-shaped, disk-shaped specimens. In this study, to determine the effect of the heat treatment process on the specimen thickness required for a valid plane-strain test in accordance with the ASTM standard, fracture tests are performed by using CT specimens made of AISI 1040 carbon steel. Furthermore, by taking into consideration the effect of residual stress caused by heat treatment in the vicinity of the notch, additional fracture tests are also performed. The specimens are machined from rolled plates in the L-T rolling direction (crack plane is perpendicular to the rolling direction). Having performed experimental analyses, the applicability of the plane-strain fracture toughness tests using CT specimen made of AISI 1040 steel is investigated.

Load separability and ηpl factor determination for CT specimen of Zr-2.5Nb pressure tube material

For fracture testing of pressure tubes, specimens are machined directly from the pressure tube without disturbing its curvature. The compact tension (CT) specimens thus obtained are called curved compact tension (CCT) specimens. Apart from being curved, the CCT specimens do not satisfy width/thickness criteria as mentioned in ASTM E1820-15. In spite of these differences, CCT specimens use the same ηpl and χpl factors as that of standard CT specimens for fracture toughness evaluation. In this work, 17 mm wide blunt notched CT specimens of different crack length obtained from a Zr-2.5Nb pressure tube, which were not meeting the thickness criteria, were used to investigate load separation and to evaluate the ηpl factor experimentally. Load separation existed between a/W of 0.45 and 0.70. The ηpl factor had a constant value of 2.078 in this range when calculated using the load separation method by power law fit. The ηpl factor calculated using a third order polynomial fit passing through the origin showed linear increase with b/W similar to but marginally lower than standard CT specimen.

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.

Fracture Toughness Evaluation of a Cracked Au Thin Film by Applying a Finite Element Analysis and Bulge Test

This paper presents a finite element analysis of a pre-cracked freestanding gold thin film subjected to bulge test. These tests were conducted in order to determine the elasto-plastic properties and fracture toughness of the gold films. For the experimental tests, a pre-crack was introduced in the center of the film by focused ion beam (FIB) milling with a length of 10 and a width of 100nm. For the numerical fracture analysis, the problem was divided into two stages; the first stage was the development of the numerical model on the whole film without pre-crack (elasto-plastic analysis) and the second one was performed on a film portion that included the pre-crack (sub-modeling stage). Three different notches (rounded, sharp and V-sharp) were applied to calculate the stress intensity factor around the crack tip using path independent J-integral. The obtained results show that the load-deflection curves for non-cracked and pre-cracked film reproduced the experiments using the calculated elasto-plastic properties. This indicates that the proposed models presented a good correlation and robustness. Additionally, fracture toughness values were calculated between 0.288 and 0.303with J-integral values 1.037 J/m2 (elastic) and 1.136 J/m2 (elasto-plastic) which correspond with other calculations available in the literature.

Scratch and Sliding Wear Testing of Electroless Ni–B–W Coating

Abstract Electroless Ni–B–W coating is deposited on low carbon steel in an alkaline sodium borohydride-reduced electroless bath. The mechanical and tribological properties of such coatings are much necessary to be assessed to carry out application-based studies. The present work focuses mainly on the evaluation of hardness and fracture toughness of electroless Ni–B–W coatings using a scratch tester. Coating's response toward scratching is also studied thoroughly. The characteristic short-range order present in its lattice structure causes the generation of a specific behavioral pattern. Furthermore, a linear sliding wear test is carried out on coatings' surface to analyze the wear behavior at different loading conditions. The specific wear rate is observed to be minimum at a normal load of 22.5 N against Si3N4 counterbody. The patterns of tribological behavior of the coating at different load values are examined from the worn surface morphologies. But before embarking on the scratch and sliding wear tests, the synthesized coatings are characterized under field emission scanning electron microscope and X-ray diffraction in an exhaustive manner. The growth rates with respect to time and the changes in morphological aspects of the coating are also evaluated. The present study establishes electroless Ni–B–W deposits as a suitable option for protecting mechanical components against wear.

Irradiation tensile property and fracture toughness evaluation study of A508-3 steel based on multi-scale approach

In the framework of multi-scale modeling, a BCC crystal plasticity constitutive model based on the densities of dislocations and irradiation defects is numerically implemented and a Voronoi polycrystalline geometric model is established. Combining with the Beremin cleavage fracture local approach, a multi-scale fracture toughness evaluation method is proposed and the macroscopic tensile and fracture properties of A508-3 steel at different temperatures before and after irradiation are studied from microstructural information at the micro level. The simulation results indicate that the crystal plasticity model is able to take into account the effects of temperature and irradiation hardening. The fracture toughness calculated by the crystal plasticity model and local approach at different temperatures are in agreement with the experimental values, which shows obvious irradiation embrittlement.

Development of experimental methodology on fracture toughness of microscale polymer resins under in situ observation

The purpose of this study is to develop a method on fracture toughness test for single-digit micrometer scale polymeric materials, including shape design of the specimen and introduction of precrack. Acrylonitrile butadiene styrene (ABS) polymer resin is employed as test material for the development. The specimens are carefully manufactured by means of the focused ion beam (FIB), and a precracks are successfully introduced at the notch root by the asymmetric loading. After then, the specimens are reshaped, and the mode I load is applied for the evaluation of fracture toughness. The stress field around the crack tip is calculated by the finite element analysis, and the critical stress intensity factor KIC is found to be KIC = 0.145 to 0.175 MPa .

Investigation of fatigue and fracture behaviour of sensitized marine grade aluminium alloy AA 5754

AbstractIn the present study, fatigue and fracture characteristics of sensitized marine grade Al‐Mg (AA 5754) alloy are experimentally evaluated. Received alloy is sensitized at temperatures of 150°C (SENS50) and 175°C (SENS75) for 100 hours. Fracture parameters, KIc and JIc, are experimentally evaluated. Slow strain rate tensile tests at a crosshead speed of 0.004, 0.006, and 0.01 mm/min; fatigue crack growth tests at load ratios (R = Pmin/Pmax) of 0.1, 0.2, and 0.5; and low cycle fatigue tests at four strain amplitudes of (0.3‐0.6)% are performed for SENS50 and SENS75 alloys. Relatively lower magnitude of fracture toughness values are observed for SENS75 specimen. Severe degradation in tensile properties, fatigue crack growth characteristics, and low cycle fatigue lives are observed for SENS75 samples. Extended finite element method is adopted to simulate the elasto‐plastic crack growth during fracture toughness evaluation. Scanning electron microscopy (SEM) is used to understand the failure mechanism of sensitized alloys.

Evaluation of Interfacial Fracture Toughness and Interfacial Shear Strength of Typha Spp. Fiber/Polymer Composite by Double Shear Test Method.

The aim of this paper is to evaluate the Mode II interfacial fracture toughness and interfacial shear strength of Typha spp. fiber/PLLA and Typha spp. fiber/epoxy composite by using a double shear stress method with 3 fibers model composite. The surface condition of the fiber and crack propagation at the interface between the fiber and the matrix are observed by scanning electron microscope (SEM). Alkali treatment on Typha spp. fiber can make the fiber surface coarser, thus increasing the value of interfacial fracture toughness and interfacial shear strength. Typha spp. fiber/epoxy has a higher interfacial fracture value than that of Typha spp. fiber/PLLA. Interfacial fracture toughness on Typha spp. fiber/PLLA and Typha spp. fiber/epoxy composite model specimens were influenced by the matrix length, fiber spacing, fiber diameter and bonding area. Furthermore, the interfacial fracture toughness and the interfacial fracture shear stress of the composite model increased with the increasing duration of the surface treatment.