Fracture Toughness Characteristics Research Articles

Fracture toughness of the stomatopod dactyl club is enhanced by plastic dissipation: A fracture micromechanics study

The dactyl club of stomatopods is a biological hammer used to strike on hard-shell preys. To serve its function, the club must be imparted with a high tolerance against both contact stresses and fracture. While the contact mechanics of the club has been established, fracture toughness characterization has so far remained more elusive and semi-quantitative using nanoindentation fracture methods. Here, we used microcantilever fracture specimens with a chevron-notched crack geometry to quantitatively evaluate the fracture response of the impact region of dactyl clubs. The chevron-notched geometry was selected as it minimizes surface-related artefacts due to ion milling, and further allows to carry out fracture tests on samples free of pre-cracks with stable crack propagation even for brittle materials. Both linear elastic as well as elastic-plastic fracture mechanics methods, together with finite element modelling, were employed to analyse the fracture data. We find that crack-tip plastic dissipation is the main mechanism contributing to the fracture properties of the dactyl club material. Our study also suggests that the chevron-notched crack geometry is a suitable method to quantitatively assess the fracture toughness of hard biological materials. Statement of significanceCharacterizing the fracture resistance of biomineralized structures is essential to draw their structure-properties relationships. Yet measuring the fracture properties of such materials is often hampered by their small size and irregular shape. Indentation fracture is used to circumvent these issues but does not discriminate between the elastic and elastic-plastic contributions to the fracture resistance. The dactyl club “hammer” of mantis shrimps is a biological material whose fracture properties are central to its function. A microfracture study was conducted using microcantilever specimens with chevron-notched crack geometry to assess the fracture toughness. Adopting linear elastic and elastic-plastic fracture mechanics protocols, we find that plastic dissipation is the major contribution to the fracture response of the hypermineralized impact region of the dactyl club.

Characterization of debonding between two different materials with beam like geometries

Expressions for the energy release rate and compliance are defined for some asymmetric beam like specimens. The expressions are derived taking into account the Timoshenko beam theory with elastic foundation. The energy release rate is expressed by the applied loads or by a combination of loads and rotation angles, the latter allows to characterize bonded interfaces without taking into account the elastic foundation properties. The condition of stability under displacement controlled test is analysed for typical specimens. The results presented are useful for the characterization of fracture toughness of bimaterial interfaces.

Application of New Materials to Increase the Reliability of Centrifugal Separators

The urgent task of increasing the durability and reliability of centrifugal separators under the corrosion and erosion impacts of the processed media with a high content of chlorine ions and abrasive inclusions predetermined the transition to the manufacture of rotor parts from corrosion-resistant high-plastic steels of the austenitic and austenitic-ferritic class instead of previously used high-strength low-plastic steels of austenitic-martensitic class. Application of high-plastic corrosion-resistant steels with high fracture toughness characteristics excludes the possibility of brittle fracture of rotors. However, these steels have a low yield point, which makes it necessary to conduct hardening for highly loaded body parts of rotors in the field of centrifugal forces. Hardening ensures the elastic work of the rotor parts during operation, creates residual stress fields, partially compensating for the stresses arising in the operating mode. Based on the results of the study, steels of the austenitic-ferritic class are recommended for the manufacture of separator rotors with the provision of the necessary structural safety margins.

Weibull Modulus of Cleavage Fracture Toughness of Ferritic Steels

The ordinary Weibull distribution function has been commonly accepted for empirical characterization of cleavage fracture toughness of nuclear reactor and containment pressure vessel steels. However, this method lacks a fundamental basis. This work adopts the standardized Weibull distribution function to analyze cleavage fracture toughness of ferritic steels measured from different sized fracture mechanics specimens at different temperatures to estimate the Weibull modulus. The toughness data of five different nuclear reactor and containment vessel steels are analyzed. The estimations obtained the Weibull modulus (m) in the range of 1.83 to 2.55 and strong temperature dependence of the threshold cleavage fracture toughness Kmin, as opposed to the constant values of mK = 4 and Kmin = 20 MPam1/2 given in ASTM E1921-19. The goodness of fit test by the one-sample Kolmogorov–Smirnov (K–S) test validated Weibull distribution function for describing the toughness distribution.

Reliability prediction of a microwave sintered Si3N4-based composite ceramic tool

The wear life reliability prediction model of microwave sintered Si3N4/(W,Ti)C/Y2O3/MgO/Al2O3 composite ceramic tools based on the random distribution characteristics of hardness and fracture toughness of ceramic tool material was established. It showed that the Vickers hardness of ceramic tool materials followed a normal distribution and the fracture toughness followed a lognormal distribution. Distribution law of wear life can be determined by the joint distribution of hardness and fracture toughness. Experimental research on tool reliability of continuous dry cutting quenched high quality carbon steel T10A was carried out and the applicability of the tool reliability prediction model was verified. The results showed that the error between the theoretical reliable life and the actual life of the ceramic tool was less than 5% under the same reliability when the reliability was above 0.5.

Improvements of commercial chromium coatings wear resistance by means of electro-co-deposition with Graphite, TiN, and w-BN

Composite coatings were obtained by electro-co-deposition of chromium with Graphite, TiN or wurtzite-like BN (w-BN). The content (vol.%) of the dispersed phase in the electrodeposits was equal to: Cr–Graphite – 10, Cr–TiN – 4, Cr–w-BN – 1. Cr-Graphite coatings showed no increase in the microhardness (HV), while their fracture toughness (K1c) and wear characteristics were better as compared to Cr deposits. The coefficient of friction in the tribopair “coating–steel” decreased from 0.32 (Cr) to 0.19 (Cr–Graphite) under conditions of dry friction and from 0.05 (Cr) to 0.03 (Cr–Graphite) in the presence of a lubricant. The inclusion of TiN particles into a Cr-matrix resulted in an improvement in both HV and wear resistance (WR) of the coatings. A significant increase in WR (70–170%) was obtained for Cr–w-BN coatings with small content of the dispersed phase. Therefore, Cr–Graphite, Cr–TiN, Cr–w-BN electrodeposits may be considered as promising wear-resistant materials.

Applicability of focused Ion beam (FIB) milling with gallium, neon, and xenon to the fracture toughness characterization of gold thin films

Focused ion beam (FIB) milling is an increasingly popular technique for fabricating micro-sized samples for nanomechanical characterization. Previous investigations have cautioned that exposure to a gallium ion beam can significantly alter the mechanical behavior of materials. In the present study, the effects of gallium, neon, and xenon ions are scrutinized. We demonstrate that fracture toughness measurements on freestanding gold thin films are unaffected by the choice of the ion species and milling parameters. This is likely because the crack initiation is controlled by the local microstructure and grain boundaries at the notch, rather than by the damaged area introduced by FIB milling. Additionally, gold is not susceptible to chemical embrittlement by common FIB ion species. This confirms the validity of microscale fracture measurements based on similar experimental designs.Graphical abstract

Structural, mechanical and corrosion evaluations of Cu/Zn/Al multilayered composites subjected to CARB process

In this research, the structure, tensile, wear, fracture toughness, and corrosion characteristics of Cu/Zn/Al multilayered composites fabricated by cross accumulative roll bonding (CARB) were determined. X-ray diffraction and scanning electron microscopy were used for structural analyses. Results showed that the crystallite size of the Cu matrix is reduced to about 50 nm at the ninth cycle of CARB, while the plastic instability and shear bands appeared in the layers after the third cycle. The tensile strength of the composites increased up to the third CARB cycle and then decreased to the ninth CARB cycle gradually. Typically, the maximum strength of about 330 MPa and elongation of almost 31.5% were obtained at the third and first cycles, respectively. A similar trend was found for the fracture toughness of the samples, so that the maximum fracture toughness of about 31 MPa.m1/2 was obtained at the third cycle. It was also shown that the wear mechanism of the composite samples changes by increasing the cycles, a compromise of abrasion and delamination wear. The accommodation of Al and Zn layers toward the surface of the composites by increasing the CARB cycles was also recognized to be responsible for the decrease of the corrosion resistance determined by polarization experiments.

Fracture Toughness and Fatigue Crack Growth Characteristics of UFG Microalloyed and IF Steels Processed by Critical Phase Control Multiaxial Forging

The aim of the current study is to design multiaxial forging (MAF) schedules in order to achieve submicron-grained (<1μm) structure in a microalloyed (MA) steel as well as an interstitial-free (IF) steel, which could impart a good combination of yield strength and tensile ductility. At the same time, an effort has been made to evaluate the fracture toughness characteristics by conducting 3-point bend tests and computing the KQ, Kee and J-integral values of ultrafine grained (UFG) samples and correlating them with the microstructure, besides evaluating the other mechanical properties. Fatigue strength in the high cycle fatigue (HCF) regime were also investigated and fracture mechanisms analyzed and comparison established between differently processed samples. The microstructural analysis was performed using transmission electron microscopy (TEM) and Electron backscatter diffraction (EBSD) and results corroborated with the mechanical properties. Superior combinations of yield strength (YS), ductility (% El.), fracture toughness (Kee) and high cycle fatigue strength (σf) were obtained under certain conditions, i.e., i) MA steel: intercritical (α+γ) phase regime (~Ar1) controlled and 15-cycle multiaxially forged (MAFed) (YS=1027MPa, %El.=8.3%, σf=355MPa and Kee=90MPa√m), and ii) IF steel: ferritic region (<Ar1) controlled 18-cycle MAFed (YS=881MPa, %El.=11.2%, σf=255MPa and Kee=97MPa√m). In the case of MA steel, an enhancement of the fatigue and fracture toughness properties can be ascertained following the formation of uniformly distributed nanosized fragmented cementite (Fe3C) particles (~35nm size) present in the submicron sized (average ~280nm size) ferritic microstructure. In contrast, in the case of IF steel, this is ascribed to the development of submicron sized ferrite grains (average ~320nm) along with a high density of dislocation substructures. These fine dislocation cells/substructures along with the nanosized Fe3C particles could effectively block the initiation and propagation of cracks and thereby enhance the fatigue endurance and fracture toughness of the steel. Superior fracture toughness along with high mechanical properties in submicron-grained condition render the two steels highly useful for high-strength structural applications.

Fracture toughness properties and characteristics of Friction stir welded high strength aluminium alloy by post weld heat treatment (PWHT)

Abstract This paper presents the PWHTed effects on fracture toughness properties on stir-welded AA7075 aluminum alloy joints. 12-mm thick rolled AA7075-T651 plates were joined. The joints were given post-weld heat treated by STA and AA. Compact tension (CT) specimens were prepared to evaluate the plane strain fracture toughness of the welded joints. The fracture toughness properties were evaluated under uniaxial tensile loading conditions (stress ratio = 0.1, Frequency = 10 Hz) at room temperature using a servo-hydraulic controlled machine. The welded joints microstructures were examined by low magnification microscopy (OM) and high magnification microscopy (TEM) techniques. It is found that the joint treated with the solutionizing followed by artificial aging cycle exhibited superior fracture toughness properties compared to as-welded joint and artificially aged joints.

Use of instrumented charpy testing on the fracture toughness characterization of metallic materials

Use of instrumented charpy testing on the fracture toughness characterization of metallic materials

Dynamic shear fracture toughness and failure characteristics of Ti–6Al–4V alloy under high loading rates

A novel 2-bar/double-shear impact (2B/2SI) loading technique is used to study the dynamic mode II (shear) fracture characteristics of Ti–6Al–4V. The new specimen design, to be used in combination with a standard split Hopkinson pressure bar, circumvent classical limitations associated with conventional one-point impact methods. This paper presents a combined experimental-numerical approach to determining the mode II fracture toughness of Ti–6Al–4V for a broad range of loading rates between 1.10 × 10−2- 4.98 × 107 (MPa, m1/2s−1). Results showed only a slight initial increase in toughness, which increases abruptly with loading rates beyond 106 (MPa, m1/2s−1). Fractographic examination showed distinctively different mechanisms in operation at the microscale, depending on the rate of loading. Failure is through a brittle-ductile, mixed-mode fracture under quasi-static conditions; by contrast, the fracture surface exhibited fractographic features of adiabatic shear bands (ASB) and material melting/re-solidification under dynamic conditions. High-speed photography showed that both dynamic shear fracture (DSF) and ASB occurred during the same loading process. Interactions between DSF and ASB were observed to influence the dominant failure mechanism of the material at high loading rates.

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

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

Fracture Toughness of the Stomatopod Dactyl Club is Enhanced by Plastic Dissipation: A Fracture Micromechanics Study

The dactyl club of stomatopods is a biological hammer used to strike on hard-shell preys. To serve its function, the club must be imparted with a high tolerance against both contact stresses and fracture. While the contact mechanics of the club has been established, fracture toughness characterization has so far remained more elusive and semi-quantitative using nanoindentation fracture methods. Here, we used microcantilever fracture specimens with a chevron-notched crack geometry to quantitatively evaluate the fracture response of the impact region of dactyl clubs. The chevron-notched geometry was selected as it minimizes surface-related artefacts due to ion milling, and further allows to carry out fracture tests on samples free of pre-cracks with stable crack propagation even for brittle materials. Both linear elastic as well as elastic-plastic fracture mechanics methods, together with finite element modelling, were employed to analyse the fracture data. We find that crack-tip plastic dissipation is the main mechanism contributing to the fracture properties of the dactyl club material. Our study also suggests that the chevron-notched crack geometry is a suitable method to quantitatively assess the fracture toughness of hard biological materials.

Mode II Interlaminar Fracture Toughness of Flax/Glass/Epoxy Hybrid Composite Materials: An Experimental and Numerical Study

ABSTRACT The mode II interlaminar fracture toughness characteristics of flax/glass/epoxy hybrid laminates were experimentally and numerically examined. Three types of hybrid composites that are made of flax (F) and glass (G) and with different layup sequences (i.e., Hybrid I [0 G/0 F]8S, Hybrid II [04G/04F]S, and Hybrid III [04G/(90/0)2F]S) were investigated. The experimental results obtained from end notch flexural tests showed that both the mode II fracture toughness and flexural strength of Hybrid I composites were higher than those for Hybrid II & III composites. This was attributed to the presence of bridging in several interfaces of the flax plies and the glass plies in Hybrid I. A second delamination propagation between the flax/epoxy midplane plies was observed in Hybrid II and III and this helped to lower both the mode II fracture toughness and flexural strength. The finite element simulations employed the virtual crack closure technique and the cohesive zone model. The results showed that both methods successfully predicted mode II interlaminar fracture toughness characteristics of the Hybrid I composites, but significantly overpredicted the values for both Hybrid II & III due to the presence of a secondary delamination propagation.

Methods for forecasting and control of the phase composition and residual voltage in Al-Cu-Li alloys in friction mixing welding

One of the main directions for reducing the weight of structures of aerospace engineering products is the use of aluminum-lithium alloys, which have unique characteristics of strength, rigidity and fracture toughness [1–3]. Nevertheless, the manufacture of large-sized welded structures from high-strength aluminum-lithium alloys is associated with serious problems due to their softening under the influence of the thermal cycle of fusion welding, for which the joint strength coefficient (the ratio of the weld strength to the strength of the base material) is below 60% [4, 5]… It is possible to increase the operational characteristics of welded joints through the use of new effective technological processes, such as friction stir welding (FWW) [6].

Prediction of Fracture Toughness in the Shale Formation Based on Well Logging and Seismic Data: A Case Study of the Lower Silurian Longmaxi Formation in the Sichuan Basin, China

The rock physics experiments and fracture toughness tests of shales from the Lower Silurian Longmaxi Formation in the Sichuan Basin in China were carried out. Based on this, the calculation model of the fracture toughness was constructed, thus, the single well evaluation of the fracture toughness in shale formation would be obtained based on the well logging data, which can be used to summarize the spatial distribution characteristics of the fracture toughness in the shale formation. However, it is difficult to obtain transverse distribution characteristics of fracture toughness in shale formation based solely on the well logging data. Therefore, in order to investigate the spatial distribution of the fracture toughness, jointing well logging and seismic method could be adopted to quantitatively predict the fracture toughness in shale formation. The results show that fracture toughness of shales is sensitive to acoustic interval transit time and wave impedance. The prediction model of the fracture toughness of shales was constructed, which had a good prediction effect. The fracture toughness values of shales from the Upper Silurian Wufeng-Longmaxi Formation were larger, whereas those of shales from the Lower Silurian Wufeng-Longmaxi Formation were lower. The fracture toughness is mainly distributed in strips along the vertical direction while the distribution area is continuous in the lateral direction, indicating that it has obvious stratification characteristics.

Characterizing fracture toughness using machine learning

The existing models for fracture toughness characterization based on nanoindentations that account for the fracture length are limited to simple (ideal) geometries that are absent in shales. The present study proposes two conceptual models to estimate the fracture length created by nanoindentations in shales. It also presents a workflow to apply the conceptual models and uses machine learning, enabling a systematic and automated analysis. The conceptual models assume that the induced fracture is in the first mode to determine the fracture toughness. In this study, fracture toughness is also determined by the energy method that relates the load-displacement hysteresis to the fracture toughness without restricting the fracture mode. The present study sheds light on the complexities of characterizing fracture toughness using nanoindentations and has applications in the petroleum industry. The conceptual models are appealing for formation characterization using small pieces, such as drill cuttings, when large samples (~2.5 cm) required for conventional tests are unavailable. The conceptual models have applications in estimating fracture toughness when the induced fracture patterns become more complex.

Mechanical behavior and fracture toughness characterization of high strength fiber reinforced polymer textile composites

The mechanical and fracture behavior of polymer composites are the subject of great interest from many years and still interesting among the researchers. Composites are extremely used for their superior mechanical, thermal and fracture toughness properties in various sectors such as automobile, aerospace and defense applications. In this article, unidirectional and woven high strength glass, carbon and Kevlar fiber reinforced polymer textile composites are taken into consideration for the comprehensive review of mechanical behavior and fracture toughness characterization. Current review work began with the introduction to polymer textile composites with its manufacturing stages, processing techniques and factors affecting the performance under mechanical loading. The mechanical behavior of high strength fiber reinforced polymer (HSFRP) textile composites was discussed in tension, compression, flexural, low velocity and high velocity impact loading with the recent numerical and experimental characterization studies. Textile geometrical modeling and CAE tools are also described for numerical characterization. Under the influence of mechanical loading on composites, failure occurs actually due to the crack initiation and propagation, so it is also required to characterize. Significant elements of fracture mechanics are well described for the better understanding of fracture toughness characterization. Mode-I, Mode-II, Mode-III interlaminar and Mode-I intralaminar fracture toughness characterization are widely explained by considering the effect of filler content, fiber orientation and fiber volume fraction. Fracture toughness characterization techniques and research summery are uniquely presented by considering various factors under one umbrella for better understanding of fracture behavior. Statistical Weibull distribution is also presented for the failure prediction of composites.

A study on fracture toughness of nano-structured carbon black-filled epoxy composites

Carbon black (CB)-filled epoxy nanocomposites were produced by mixing the desired amount of nano-structured CB (CBNFs) from biomass waste (i.e., bagasse, bamboo, and oil palm shell) with the epoxy resin. The fracture toughness characteristics of epoxy nanocomposites with 1%, 3%, 5%, and 10% (based on wt.% of epoxy) filler loading were observed using the Vickers hardness test, and the surface morphology was analyzed using transmission electron microscopy and scanning electron microscope. The results showed a decrease in fracture toughness, mainly due to cracked bridging of CB nanograins formed onto the epoxy matrix. The size of the cleavage plane decreased after the infusion of the CBNFs. It implied that the path of the crack tip was distorted because of the CBNFs, making crack propagation more difficult. The physical and mechanical properties increased when the epoxy composites containing 1% to 5% CBNFs although it was decreased at 10% CBNFs filler loading. One key finding was the morphological interaction between the CNBFs and epoxy matrix shows that various types of fracture toughness were identified, such as voids, crack propagation paths, bridging effect, and branching effects of cracks.