Fracture Resistance Characteristics Research Articles

Structural design against brittle fracture: Optimizing energy release rate and experiment

Despite substantial advancements in optimizing structural designs for stiffness, the field of design against fracture is still in its early stages. This paper introduces a fundamental and standardized paradigm for structural design against brittle fracture, achieved through the minimization of the energy release rate G within the framework of linear elastic fracture mechanics (LEFM). By leveraging the Griffith criterion expression and the total potential energy in LEFM, we propose an efficient approach for structural optimization that enhances the toughness of architected materials. The energy release rate G is evaluated a synergistic application of finite element analysis and finite difference methods, yielding a precision of 0.6% compared to benchmarks in published handbooks. We demonstrate significantly reduced G values compared to standard stiffness and stress-oriented topology optimization, which directly contributes to increased toughness. To comprehensively analyze the fracture process encompassing damage, crack initiation, propagation, and failure, we employ post-processing phase field fracture modeling on the optimally designed architected materials. By performing multi-objective optimization of the stiffness and energy release rate G, the toughness and extreme load-bearing capacity can be simultaneously improved. The resulting perforated architecture effectively outperforms homogeneous structures in both toughness and peak load. Additionally, we extend our analysis to various configurations, such as non-center cracks, pure shear loading, and adherence to the standard 3D compact tension ASTM E-399-72. The designed structures are additively manufactured and experimentally validated, demonstrating a toughness increase of over 10 times compared to stress-based design. These contributions offer promising prospects for advancing the design of future engineering structures and materials with a favorable balance of critical fracture resistance characteristics.

Wear characteristics of flat die in flat die pellet mills based on Glycyrrhiza uralensis

During granulation, a serious wear problem may be found in flat die as a key component of a flat die pellet mill. Specific to this problem, Glycyrrhiza uralensis was selected as the wear-causing material to investigate the wear mechanism of the flat die. Additionally, carburizing steel (20Cr and 20CrMnTi) and stainless steel (4Cr13) commonly used in flat die were adopted to conduct wear tests. To explore the influence of Glycyrrhiza uralensis powder and rods on friction and wear properties of the above three types of steel materials, a CFT-I general-purpose tester for surfaces was applied under dry friction conditions. Moreover, x-ray diffractometer (XRD), three-dimensional profilometry, scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) were used to analyze the phase compositions, surface morphologies, and elementary compositions of the samples. As demonstrated by relevant results, the influence of Glycyrrhiza uralensis on the flat die is primarily embodied in abrasive, adhesive, and fatigue wear, and a thermal oxidation reaction occurs on the surface of the flat die. By comparing the wear conditions of the three steel materials between the powder and rods of Glycyrrhiza uralensis, it is found that flat die damages caused by glycyrrhiza rods are more severe than those of its powder. Additionally, the lowest friction coefficients are generated by 20CrMnTi, which are 0.40 and 0.88, respectively. In terms of the mean wear depth, its values are 1.2 and 2 μm, which are below those of 20Cr and 4Cr13. The results herein reveal that flat die made of 20CrMnTi have excellent wear and ductile fracture resistance characteristics. Hence, this study may provide a theoretical guide for selecting flat die materials.

On the influence of the adhesive and the adherend ductility on mode I fracture characterization of thick adhesively-bonded joints

Thicker bondlines along with manufacturing-tolerant and fracture-resistant adhesives are trends visible across different industries, especially maritime. In this work, two contrasting adhesives: an elastic-brittle epoxy-based, and a nonlinear-ductile methyl methacrylate (MMA) are characterized and compared via tensile, compact tension (CT) and double cantilever beam (DCB) testing, for steel-to-steel adherends. Significant differences are captured between the two bonding materials in terms of the energy required for crack growth: in the MMA “ductile” adhesive is ∼4 and 10 times more than for the epoxy “relatively brittle” adhesive for CT and DCB testing, respectively. While epoxy bondlines fail due to a symmetric in-plane crack, the MMA bondlines experience multiple cracking originating from high deformations and Poisson's effects. Moreover, in the case of MMA adhesive, the DCB testing led to plastic deformation of steel adherends. The existing evaluation protocols are adopted for data reduction and the effect of plastic dissipation is theoretically addressed. Despite adherend plasticity, it is concluded that the crack growth is driven by the elastic energy release, and thus, after small correction taking into account initial adherend plasticity, the existing simple models can still be used. This study highlights the potential use of ductile adhesive instead of the commonly used brittle ones to significantly improve the adhesively bonded joints in maritime applications in which thick bondlines, manufacturing-tolerant and fracture-resistance characteristics are required.

Fracture resistance of thin wall endodontically treated teeth without ferrules restored with various techniques.

To evaluate the fracture resistance and failure characteristics of simulated thin wall endodontically treated teeth without ferrules restored with various techniques. Forty-eight human mandibular single-root canal premolars were decoronated and endodontically treated. The 1 mm thick remaining root canal dentin was prepared. The roots were randomly divided into four groups of 12 roots according to the following post and core reconstruction techniques: direct resin composite post and core (CP), multiple fiber posts and resin composite core (FP), CAD/CAM anatomical post and core (AP), and metal cast post and core (MP). Full metal crowns were cemented to the cores. All specimens were subjected to thermocycling for 5000 cycles and submitted to axial compression until failure at a 45°angle using a universal testing machine. The failures were classified into one of the followings: post and/or core fractures, root fractures, and root fractures combined with post and/or core fractures. Average failure loads of groups CP, FP, AP, and MP were 360.0, 655.2, 402.7, and 856.1N, respectively. MP provided the highest failure load, which was significantly higher than those of the other groups (p < 0.05). FP was second, being inferior to MP with a significance level of p=0.039. CP exhibited the least failure load, and it was not significantly different from the AP group (p > 0.05). Root fractures were the major failure mode for most of the specimens except the CP group, in which composite fractures at the cervical level were commonly observed. Metal cast post and core provided the highest fracture resistance for reconstruction of a thin wall in endodontically treated teeth without ferrules, followed by multiple fiber posts and resin composite core. The milled anatomical post and core and a direct resin composite post and core provided significantly lower fracture resistance. Metal cast posts and core and multiple fiber posts with resin composite core techniques were effective for restoring severely compromised endodontically treated teeth.

Statistical assessment on relationship between fracture parameters of plain and fiber reinforced polymer concrete materials

Polymer concrete is a relatively new concrete in which a matrix made of a polymeric resin material is used to bind the ingredients. In this paper, 288 specimens made of 72 different plain and fiber-reinforced polymer concrete mixtures (PC and FRPC) are prepared and tested to assess the fracture behavior under pure mode I and pure mode II conditions. The main purpose of this research is to determine the relationships between fracture load and work of fracture as two important fracture mechanics parameters using statistical clustering or trends analysis. The weight percentages of the ingredients were varied as 17–25% resin, 75–81% fine and coarse aggregates, and 0–2% glass fibers. A general comparison of results obtained from the PC and FRPC materials show that for a given mix-design, addition of glass fiber increases the work of fracture by about 10%. The assessment shows a good correlation between fracture load and work of fracture. Results also show that the relation between the fracture load and work of fracture obeys the dominantly linear curve. The scatter of results obtained for the FRPC material were higher than the data of PC mixture for both modes I and II. In addition, the fracture resistance characteristics of both PC and FRPC mixtures tested under mode II loading conditions are greater than the corresponding values of mode I case.

Fracture resistance characteristics of mild steel under mixed mode I-II loading

The fracture resistance of elasto-plastic materials varies significantly depending on the mode mixities, i.e., the loading combinations. This paper aims to experimentally investigate the fracture resistance and behaviour of two grades of mild steel under various in-plane loading combinations. A loading fixture with high loading capacity and modified compact tension shear (CTS) specimen are designed to conduct fracture tests on elasto-plastic materials under various mode mixities. A digital image correlation (DIC) technique-based method is developed and verified to detect the fracture initiation. It is found in the paper that the sensitivity of the fracture resistance of steel to mode mixity is attributed to the strain hardening capacity and the impurities in chemical composition of the steel. It is also found that the plastic strain concentration, crack tip blunting and fracture mechanism lead to different fracture resistance of both types of steel under various mixed mode loading combinations. The contribution of the paper is that an additional method to determine the fracture initiation under non-mode I loading is developed. The test results show the necessity of considering the mode mixity effect under the mode II loading dominance in practical engineering applications.

Effect of Impact Toughness Anisotropy on Brittle Fracture Resistance Characteristics of High-Strength Steels Subjected to Thermomechanical Treatment

The structure and mechanical properties under tension and impact bending of eleven batches of high-strength manganese-containing steels (Mn-steels) containing 0.09 to 0.14 wt.% Ti subjected to thermomechanical rolling were studied in the temperature range from –60 to +20 °С. It was found that the values of the coefficient of impact toughness anisotropy in the range of Ka = 2.0–4.9 increase at higher titanium content and decrease at higher aluminum content. The difference between ductile-to-brittle transition temperatures T50 and T34 for longitudinal and transverse KCV samples increases at higher contents of titanium, aluminum, sulfur, and carbon. This effect is caused by an earlier nucleation and growth of large dimples of ductile fracture around sizable inclusions preferentially located in the direction of rolling.

Local Fracture of Nanolaminates: Edge Chipping Test

The fracture resistance of domestic and foreign nanolaminate ceramics was studied by the EF (edge fracture) method. This method provides for indentor chipping of rectangular specimen edges, which permits evaluating such fracture resistance characteristics, as chipping resistance and edge toughness. There is no way of experimental determining the stress intensity factor effected as the penetration of a Vickers indentor into the polished specimen surface and measurement of crack sizes that are formed near the angles of its imprint. The influence of stress concentrations in the indentor–specimen surface contact zone on the fracture resistance of ceramics was assessed. Different test stress concentrations were produced with conical diamond indentors of different tip radii. Studies on domestic titanoaluminous carbide Ti3AlC2 specimens demonstrated that with a reduction in stress concentration levels (indentors with increasingly larger tip radii), its edge toughness grew to a smaller extent than that of Y2O3 and TS Mg-PSZ ceramics. It is indicative of the limited sensitivity of an examined material to stress concentrations on local fracture. The ratio of edge toughness determined with the indentors of maximum and minimum tip radii (in this case, 400 and 11 μm) can serve as a measure of its sensitivity (in comparison to this characteristic for examined materials). Note that the edge toughness of Ti3AlC2 ceramics is almost one-third as large than, e.g., that of Y2O3 ceramics and 1.6 times smaller than that of TS nonlinearly elastic zirconia Mg-PSZ.

Low-cycle bending fatigue and electrical conductivity of high-strength Cu/Nb nanocomposite wires

The comparative low-cycle fatigue tests of the Cu/Nb nanocomposite wires obtained by the “melt-and-deform” method and pure copper samples were carried out using a dynamic mechanical analyzer (DMA). The fatigue tests were carried out using transverse bending scheme. It has been established that the fatigue fracture resistance characteristics of the Cu/Nb composites significantly higher as compared to that of pure copper samples. It has been found that the fatigue crack propagation in the Cu/Nb composites occurs at two scale levels. The effect of fatigue damage accumulation on the change in the electrical resistance of the Cu/Nb composites was studied.

Structural Viability of Steel with Stress Concentrations under Uniaxial Tension

Abstract—Two types of mechanical characteristics of structural steel in uniform and nonuniform force fields are presented. In the science of metals and alloys, assignment by type is a fundamental concept. An analytical apparatus is developed for finding relations between the fracture resistance and basic mechanical characteristics of the metal, so as to assess the structural viability of steel in nonuniform force fields with annular stress concentrators, under uniaxial tension. The structural viability of steel with regular stress concentrators is assessed, and their low-temperature embrittlement is estimated.

Microstructure and brittle fracture resistance of layered steel composites produced by explosion welding and pack rolling followed by heat treatment

In the present paper, the microstructure and fracture resistance characteristics of 7-layered composites based on Fe-2Mn-1Si low carbon low alloyed steel and Fe-11Cr-9Ni-2Mo-1Ti maraging steel obtained by two different methods such as explosion welding and hot pack rolling with subsequent heat treatment were investigated. It was shown that an important microstructural features of Fe-2Mn-1Si steel layers are associated with the formation of a fragmentation zone ~10 μm wide with a size of structural elements 0.5-1.0 μm near the interface in the welded composites and the appearance of decarburized ferrite zone ~50 μm wide in the hot-rolled composites. Aсcording to local energy dispersive X-ray microanalysis, at the interface of welded and hot-rolled composites, the most active diffusion processes near of Fe-2Mn-1Si and Fe-11Cr-9Ni-2Mo-1Ti steel interlayer borders occur during the composites production by pack rolling. It was established that explosion welding makes it possible to retain the initial microstructure of steel blanks, with the exception of a narrow near-weld zone of grain fragmentation. After the subsequent heat treatment of explosively welded and hot-rolled composites, Fe-2Mn-1Si steel layers are characterized by a viscous ferrite(sorbitol)-pearlite microstructure, and Fe-11Cr-9Ni-2Mo-1Ti steel layers possess a martensitic microstructure with strengthening intermetallic particles. From the results of impact tests at temperatures from +20°C to −60°C, it was found that the impact strength KCV and energy of impact loading A of the hot-rolled composites are 2 and 3.5 – 5.4 times higher than the ones of the welded composites, respectively.

Implication of Electrode Material Choice on Failure Characteristics of Lithium-Ion Batteries

Thermo-mechanical failure of electrode material in lithium battery system is a cause of concern for battery health and safety. With the advent of high energy storage materials and faster charging mechanisms, consideration towards the risk of failure is a substantial component in the selection of battery materials. In this work, we present a novel approach towards characterization and selection of thermally stable and mechanically favorable electrode materials using material indices. The selection process is based on a coupled thermo-mechanical multiphysics model, which solves for the deformation in the electrode during lithiation/delithiation considering the possibility of plastic deformation under high rates of charging. The thermal generation in electrode material is considered from four different mechanisms including, polarization heating due to surface charge accumulation and over potential, entropic heating due to free energy variation during lithiation/delithiation process, joule heating due to internal resistance offered by the electrode material and heat generation due to dislocation movement and phase transformation in the case of plastic deformation. Several material indices are developed for comparison of electrode materials based on their mechanical strength, fracture resistance, thermal generation and thermal diffusion characteristics. The mechanical based indices compare the electrode materials based on their capacity to generate stress during operation, resistance towards crack propagation under fatigue loading, ability to handle plastic deformation and stability under the conditions of fast charging. The thermal indices equate the thermal performance of the electrode materials based on the ability to generate less and diffuse more heat during operation. Three commonly used cathode and anode materials are compared using the above-mentioned indices and the results are verified against prior experimental data. In conclusion, these material indices provide a basis for comparison of newer high energy electrode materials against the industrially used materials, and provide crucial information regarding key material properties which affect the thermal and mechanical stability and performance of these novel materials.

Формирование комплекса механических свойств и характеристик сопротивления разрушению сэндвич-композитов на основе стали 09Г2С и высокопрочной стали ЭП678 различной дисперсности

Формирование комплекса механических свойств и характеристик сопротивления разрушению сэндвич-композитов на основе стали 09Г2С и высокопрочной стали ЭП678 различной дисперсности

Phase Effect on Deformation Anisotropy of Strength and Fracture Resistance Characteristics of Titanium Alloys

UDC 539.37:669.15 Comparative analysis of anisotropy of mechanical characteristics of titanium and aluminum alloys as well as austenitic steel in the formation of structural and crystallographic texture on rolling and in biaxial tension was carried out. The effect of increasing the -phase content in titanium alloys on the suppression rate of “reverse anisotropy” of fracture resistance and texture strengthening was examined. The mechanisms of a similar strengthening effect of a plane stress state on the plastic deformation resistance of -titanium alloys and austenitic steel with the metastable structure were discussed.

대형배관의 Curved CT 시편을 이용한 파괴저항특성평가에 관한 연구

The LBB (Leak Before Break) concept is based on evaluating the fracture toughness. NUREG 1061, Vol.3 announced that the specimen for evaluating fracture resistance needs to have same thickness or thicker than pipe. Therefore, it is difficult to collect specimen from pipe which has same thickness as a pipe. So, ASTM standard suggested the use of standard specimen with 1 inch thickness. However, it has been known that an application of LBB by test results of standard specimen is conservative compare with that by real pipe. In this study, to supplement such conservatism, the evaluation of fracture resistance characteristics was performed with curved CT specimen, which has same thickness and curvature as a pipe. In addition, fracture resistance characteristics of curved CT specimen were compared with those of CT specimen. For this, shape factor F, hpl and g were obtained from FEM analysis using the limit load method.

The elastic and plastic constraint parameters for three-dimensional problems

Fracture toughness and the in-plane and out-of-plane constraint effects are studied through experiments and computations for high-strength carbon steel 34ХН3МА. The subjects for the studies are single-edge-notched bend specimens under three-point bending and compact specimens under tension. Both types of specimens are of non-standard configuration because the specimen thickness-to-width ratio was varied in the range of 0.1–1.0, and the relative crack length was changed in the range of 0.24–0.64. Characterization of the constraint effects was performed using the non-singular T-stresses, the local triaxiality parameter h, and the TZ and TZZ, factors of the stress-state in a 3D cracked body. For the particular geometries of the specimens considered, the numerical constant of the plastic stress field In and the plastic stress intensity factor distributions along the crack front are obtained as a function of the dimensionless crack length and the specimen thickness. It is further demonstrated that the plastic stress intensity factor accounting for the in-plane and out-of-plane constraint effects can be used to characterize the fracture resistance characteristics as a unified single parameter for a variety of specimen geometries.

Unified Characterization of Crack Growth Parameters based on Plastic Stress Intensity Factor

The aim of this work is to study and represent the combined in-plane and out-of-plane constraint effect on the material fracture resistance characteristics under static and fatigue loading. Subjects for numerical and experimental studies are three-point bending and compact specimens under static loading as well as cruciform specimens under cyclic biaxial and mixed mode loading. For the static tests experimental specimen geometries considered (SENB and CS), the elastic constraint parameters and the parameter governing of the plastic stress field In distributions are obtained as a function of both the specimen thickness, the dimensionless crack length and crack length. For the fatigue tests specimen configurations (CCS) the T-stress and the numerical constant In are calculated with the variation of biaxial stress ratio and full range mode mixity. A method is also suggested for calculating the plastic stress intensity factor for mixed-mode I/II loading based on the T-stress and power law solutions. It is found that the plastic stress intensity factor accounting for the in-plane and out-of-plane constraint effect can be applied to characterize the fracture toughness and the multiaxial crack growth rate for a variety specimen geometries.

Relationship between fracture resistance and structural transformations in welding 1412 aluminium–lithium alloy

The dependence of fracture resistance characteristics in the nucleation and propagation of cracks on the structural state of individual zones of a welded joint is determined. It is shown that superheating the metal during pulsed arc welding results in the development of a heterogeneity of the alloying elements and impurities in the structure as a result of segregation of these elements along the grain boundaries and the formation of brittle intergranular interlayers from these phases, especially at the fusion boundary.

Anisotropy Patterns of Fracture Resistance Characteristics Stemming from a Deformation Texture Type in Structural Alloys

Strength and fracture resistance anisotropy patterns, different for aluminum and α- and pseudo-α- titanium alloys (with structural and crystal rolling texture, respectively), in relation to the technical deformation on the change in loading and mode I crack propagation directions are substantiated. Classification of titanium alloys, common for the two types of rolling texture, was carried out on nominal crystal slip systems, determining different fracture resistance levels. The mechanism of texture strengthening of sheet rolling at the plane stress state is examined.

Molecular mechanics of mineralized collagen fibrils in bone

Bone is a natural composite of collagen protein and the mineral hydroxyapatite. The structure of bone is known to be important to its load-bearing characteristics, but relatively little is known about this structure or the mechanism that govern deformation at the molecular scale. Here we perform full-atomistic calculations of the three-dimensional molecular structure of a mineralized collagen protein matrix to try to better understand its mechanical characteristics under tensile loading at various mineral densities. We find that as the mineral density increases, the tensile modulus of the network increases monotonically and well beyond that of pure collagen fibrils. Our results suggest that the mineral crystals within this network bears up to four times the stress of the collagen fibrils, whereas the collagen is predominantly responsible for the material’s deformation response. These findings reveal the mechanism by which bone is able to achieve superior energy dissipation and fracture resistance characteristics beyond its individual constituents.