Brittle Point Research Articles

Ductile and brittle yielding of athermal amorphous solids: A mean-field paradigm beyond the random-field Ising model.

Amorphous solids can yield in either a ductile or brittle manner under strain: plastic deformation can set in gradually, or abruptly through a macroscopic stress drop. Developing a unified theory describing both ductile and brittle yielding constitutes a fundamental challenge of nonequilibrium statistical physics. Recently, it has been proposed that, in the absence of thermal effects, the nature of the yielding transition is controlled by physics akin to that of the quasistatically driven random field Ising model (RFIM), which has served as the paradigm for understanding the effect of quenched disorder in slowly driven systems with short-ranged interactions. However, this theoretical picture neglects both the dynamics of, and the elasticity-induced long-ranged interactions between, the mesoscopic material constituents. Here, we address these two aspects and provide a unified theory building on the Hébraud-Lequeux elastoplastic description. The first aspect is crucial to understanding the competition between the imposed deformation rate and the finite timescale of plastic rearrangements: We provide a dynamical description of the macroscopic stress drop, as well as predictions for the shifting of the brittle yield strain and the scaling of the peak susceptibility with inverse shear rate. The second is essential to capture properly the behavior in the limit of quasistatic driving, where avalanches of plasticity diverge with system size at any value of the strain. We fully characterise the avalanche behavior, which is radically different to that of the RFIM. In the quasistatic, infinite-size limit, we find that both models have mean-field Landau exponents, obscuring the effect of the interactions. We show, however, that the latter profoundly affect the behavior of finite systems approaching the spinodal-like brittle yield point, where we recover qualitatively the finite-size trends found in particle simulations. The interactions also modify the nature of the random critical point separating ductile and brittle yielding, where we predict critical behavior on top of the marginality present at any value of the strain. We finally discuss how all our predictions can be directly tested against particle simulations and eventually experiments, and make first steps in this direction.

Influence of Particle Size and Content of Agglomerated Polybutadiene on Mechanical and Rheological Properties of Acrylonitrile-Butadiene-Styrene Terpolymer

The particle size of polybutadiene (PB) particles can be effectively controlled through polymer agglomeration. However, up to now, the impact of the particle size and concentration of agglomerated PB on the mechanical properties and rheological behavior of ABS terpolymer remains unclear. Our research described here studied the effect of the particle size and content of agglomerated PB on the mechanical and rheological properties of ABS. It was found that the impact strength of ABS with a bimodal size distribution of PB (67/452 nm) exceeded that of ABS with a unimodal PB size distribution within the PB content range studied. Furthermore, the impact strength of the ABS containing 319 nm PB above the brittle-toughness transition point was greater than that of other ABS containing unimodal PB at the same PB content. For ABS with a unimodal PB distribution, the PB contents of ABS containing 220, 319, and 415 nm PB at the brittle ductile transition point were 14%, 12%, and 16%, respectively. The tensile strength and melting index of the ABS containing different particle sizes of agglomerated PB decreased linearly with the increase of PB content. Rheological tests showed the viscosity and dynamic viscoelastic properties of the ABS blends. All ABS exhibited shear-thinning behavior, and the addition of PB content resulted in more elastic than viscous behavior in the ABS blends. At the same angular frequency (ω), higher PB content corresponded to greater complex viscosity in the ABS blends. In addition, as the PB content in ABS was increased, it exhibited more solid-like behavior. This study, we suggest, provides a good insight into the effect of agglomerated PB on the ABS/PB blend properties and explores practical applications for the polymer agglomeration of polybutadiene latex (PBL).

Microscopic mechanism and effect analysis of polymer modifiers on embrittlement and viscosity behaviour of asphalt

To support the research and development of asphalt binder with low embrittlement point in cold areas, the microscopic mechanism and effect of polymer modifier on embrittlement and viscosity of asphalt were analysed by molecular dynamics method. The mixed molecular models of three polymer modified asphalt commonly used in cold areas and the interactive molecular models of each component of asphalt and modifier were established. The micromechanical properties of high-content polymer modified asphalt were studied by three important indices, namely brittleness point, shear viscosity and elastic modulus, and the interaction behaviour of each component of asphalt and modifier molecules was analysed by the layer model. The following conclusions were obtained: The brittleness point of modified asphalt can be decreased by increasing the polymer modifier content, with a notable reduction of 25.54 % observed when the content reaches 7.5 %. However, this is accompanied by a subsequent increase in shear viscosity at mixing temperatures, with the highest increase reaching 16.9 %. At low temperature environment, the diffusion rate of the modifier is closely related to its own type, temperature and the type of asphalt components, and in different modified asphalt, the law of the diffusion rate of each asphalt component is not completely consistent, so it is necessary to fully consider the influence of the proportion of asphalt components, and choose the modifier sensitive to the corresponding components. The above research results have an important guiding role in the scientific formulation of the design and test scheme of low-brittleness-point asphalt binder and the completion of the research and development of low-brittleness-point asphalt binder for cold areas.

A Data Mining Method for Constitutive Model of Hard Brittle Coal

Data mining is an effective way to solve various types of complex nonlinear problems. And the anisotropy of the mechanical characteristics of coal is a typical nonlinear problem. Hard coal seam are usually characterized by brittleness, which makes them difficult to be crushed efficiently. It is important to improve the efficiency of hard coal crushing by the brittleness characterization method of hard coal is clarified. So the constitutive model and damage mechanism of hard brittle coal was studied in this paper. Damage model of hard brittle coal based on Weibull distribution was established. The damage transition point concept was proposed based on the deformation stage characteristics of hard brittle coal. And effective damage intervals for hard brittle coals can be determined based on the damage transition point. Uniaxial compression experiments of hard brittle coal were simulated using EDEM. The characterization of the effect of discrete elemental eigenstructural parameters on the brittleness of coal was analyzed. And quantitative relationships between shear modulus and brittleness, brittleness and damage transition point were fitted by Matlab. A discrete elemental constitutive model for hard brittle coals was obtained. Finally, the correctness of discrete elemental constitutive model was verified by comparing uniaxial compression experiments with other specimens. The results of this paper were expected to provide a theoretical basis for the crushing technology of hard brittle coal. And the numerical theoretical basis for data mining of the intrinsic model of hard and brittle coal was provided.

Mid-ocean ridge unfaulting revealed by magmatic intrusions.

Mid-ocean ridges (MORs) are quintessential sites of tectonic extension1-4, at which divergence between lithospheric plates shapes abyssal hills that cover about two-thirds of the Earth's surface5,6. Here we show that tectonic extension at the ridge axis can be partially undone by tectonic shortening across the ridge flanks. This process is evidenced by recent sequences of reverse-faulting earthquakes about 15 km off-axis at the Mid-Atlantic Ridge and Carlsberg Ridge. Using mechanical models, we show that shallow compression of the ridge flanks up to the brittle failure point is a natural consequence of lithosphere unbending away from the axial relief. Intrusion of magma-filled fractures, which manifests as migrating swarms of extensional seismicity along the ridge axis, can provide the small increment of compressive stress that triggers reverse-faulting earthquakes. Through bathymetric analyses, we further find that reverse reactivation of MOR normal faults is a widely occurring process that can reduce the amplitude of abyssal hills by as much as 50%, shortly after they form at the ridge axis. This 'unfaulting' mechanism exerts a first-order influence on the fabric of the global ocean floor and provides a physical explanation for reverse-faulting earthquakes in an extensional environment.

Impact response of filament-wound structure with polymeric liner: Experimental and numerical investigation (Part-A)

Filament wound pipelines and Type IV composite pressure vessels (CPVs) constitute polymeric liners and are extensively used to transport and store petroleum products, hydrogen, and compressed natural gas (CNG). The polymeric liner does not share much pressure load; hence, the composite layers share most of the load. The situation gets worse under transverse impact loads on such structures. For the polymeric liner to be effectively used in pipelines and CPVs, it is crucial to study impact response through testing and computational methods. This article presents experimental and numerical investigations of the transverse low-velocity impact response of filament wound samples. High-density polyethylene (HDPE) liner was adopted, and carbon fiber (T700) continuous filaments with epoxy resin were wound over the liner with several layers. A drop-weight impact loading with 40 J energy has been applied to the fabricated samples. The development of impact damage was assessed using the finite element method, and the damage modes have been discussed. The specimen remains unperforated at the chosen energy level. Though HDPE is ductile, however at impact loads liner damage was encountered, displaying a brittle fracture. At higher strain rates, the material reaches its brittle fracture point sooner, leading to failure. The material breaks as brittle due to its inability to dissipate impact energy quickly, resulting in fracturing instead of deformation. Fiber damage was scarcely seen; however, matrix damage has been the dominant failure mode at the chosen impact energy. Comparisons between the simulation and test findings were made, and they agreed on force-time and force-displacement histories.

Study of the Viscoelastic and Rheological Properties of Rubber-Bitumen Binders Obtained from Rubber Waste.

According to scientific research from different countries, crumb rubber obtained from end-of-life tires (ELT) during processing can improve the properties of the asphalt mixture, thereby extending the service life of the road surface. This paper presents the modification of bitumen with industrial rubber waste. The modification of bitumen for roads is considered one of the most suitable and popular approaches. This research paper describes the details of using different types of crumb rubber as bitumen modifiers. The modified bitumen's main physical and mechanical characteristics were determined after conventional tests: penetration and ductility, softening point, and Fraas brittleness point. In order to obtain a rubber-asphalt concrete mixture with improved performance characteristics, the viscoelastic and rheological properties of rubber-bitumen binders and their comparison with polymer-bitumen binders were also studied. The research results show that with increasing temperature, the values of viscosity, shear stress and complex shear modulus of all studied bitumen systems decrease, the values of the phase shift angle increase, and the size of the rubber particles has a greater influence on the properties of bitumen systems.

INVESTIGATION OF MODIFICATION OF PETROLEUM BITUMEN BY RUBBER WASTE

According to scientific research in different countries, rubber granules obtained from rubber waste during recycling can improve the properties of the asphalt mixture, thereby extending the service life of the road surface. This paper presents the modification of bitumen with industrial rubber waste. Modification of bitumen for roads is considered one of the most suitable and popular approaches. This research paper describes the details of using different types of rubber granules as bitumen modifiers. The main physical and mechanical characteristics of the modified bitumen were determined after conventional tests, penetration and ductility, softening point, Fraas brittleness point. In order to obtain a rubber-asphalt concrete mixture with improved performance characteristics, the viscoelastic and rheological properties of rubber-bitumen binders and their comparison with polymerbitumen binders were also studied. The research results show that with increasing temperature, the values of viscosity, shear stress and complex shear modulus of all studied bitumen systems decrease, and the values of the phase shift angle increase, and that the size of the rubber particles has a greater influence on the properties of bitumen systems.

Differential Energy Criterion for Brittle Fracture: Conceptualization and Application to the Analysis of Axial and Lateral Deformation in Uniaxial Compression of Rocks.

This paper discusses modeling the behavior and prediction of fracture of brittle materials. Numerous publications show that progress in this area is characterized by the emergence of a number of new models that meet the requirements of the mining industry, construction and other engineering practices. The authors focus only on one class of models, paying special attention to the compromise between simplicity of solution and versatility of the model. A new version of the model is proposed, taking into account the advantages of previous models. We present a differential energy criterion for brittle fracture substantiated, according to which, fracture occurs at a certain ratio of dissipated and stored (elastic) energy. Fracture is considered as the end of the deformation process with a virtual transformation of the initial material almost without cracks into a real material with cracks. The highest and lowest elastic moduli are analytically determined, respectively, on the ascending and descending branches of the stress-strain curve. A graphical version of the algorithm for determining the brittle fracture point on the post-peak branch of the stress-strain curve is proposed. The modeling results are consistent with the experimental data known from the literature.

Effects of the ductility and brittle point of modified asphalt on the freeze-break behavior of asphalt concrete: A 3D-mesoscopic damage FE model

Hydraulic asphalt concrete is widely used in pumped storage power stations and other anti-seepage engineering. The low-temperature freeze-break of asphalt mixtures is a rather complex phenomenon significantly affected by the ductility (at 5℃) and the brittle point of asphalt binder. In order to achieve better crack resistance at low temperatures, the influence of ductility and brittle point on low-temperature fracture becomes a major problem. This paper firstly proposes an effective modulus equation of asphalt mortar, which accounts for ductility and brittle point of modified asphalts as dominant factors. Then, a three-dimensional (3D) mesoscale finite element (FE) model, which considers this equation and the damage evolution of the asphalt mixture from linear viscoelastic (LVE) to elastic-brittle due to cooling, is established through an aggregate random placement procedure to simulate the freeze-break behavior of asphalt concrete samples in the thermal stress restrained specimen test (TSRST). The numerical simulation results of thermal stress are in good agreement with the previously published TSRST thermal stress data, and this verifies that our model is effective. Furthermore, the proposed model can predict the freeze-break temperature of asphalt mixture with good accuracy, and well describe the mesoscale thermal stress, strain, and damage distributions.

Modelling of ductile fracture in pure iron considering the ductile–brittle transition at very high strain rate

At different deformation rates, a ductile material may fail by isothermal deformation fracture, thermoplastic shear instability, or even brittle fracture. The failure mode transition at sound speed deformation rate has not been well described. This paper aims to establish a new fracture model which considers the strain rate embrittlement effect (SREE) at the sound speed deformation rate, and can be used to predict the failure of the material in a large range of strain rate. Taking pure iron DT 8 as the experimental material, impact tests of pure iron specimens under different stress states, strain rates, and temperatures were carried out. Fracture strains under different stress states, strain rates, and temperatures were obtained. The strain rate was increased to 227450/s (5.36/s in log10) to obtain the ductile–brittle transition point. A new fracture model is proposed to describe the evolution of fracture strain over the wide range of strain rate. The new proposed model is experimentally validated and compared with the J-C failure model. It shows the new proposed fracture model can predict the ductile fracture behavior of a ductile material in the full strain rate range, and capture the failure mode transition at the sound speed deformation rate of a material.

Performance of asphalt mortar with recycled concrete powder under different filler-to-asphalt weight ratios

The feasibility of using recycled concrete powder (RCP) as fillers in asphalt mortar is investigated in this study, to achieve a sustainable and economical asphalt production. The differences in physical properties between limestone powder (LSP) and RCP are analyzed and compared. Moreover, the interactions of LSP and RCP with asphalt are studied as well. The properties of asphalt mortar studied include ductility, softening point, penetration, viscous and elastic behaviors of asphalt mortar. Compared to LSP, the RCP presented a rougher surface, additional pores, more complex pore structures, larger Brunauer, Emmett and Teller (BET) surface areas, and smaller particle size. At 0.6 and 0.9 of filler-to-asphalt weight ratio (F/A), the RCP is more effective for the performance enhancement of asphalt mortar compared with the LSP. When the F/A is 0.9 and LSP is completely replaced by RCP, the 15 °C penetration index (PI) and ductility of asphalt mortar decrease by 9.3% and 29.2% respectively. The softening point increases by 5.4%. By contrast, the RCP causes a considerable decrease in PI, equivalent brittle point (T1.2) and ductility when F/A ratio is 1.2. After RCP completely replace LSP, the PI, T1.2, and ductility of asphalt mortar decrease by 47.1%, 44.0%, and 29.0%, respectively. However, at F/A of 0.6, the asphalt mortar with 100% RCP replacement ratio presented both acceptable ductility and plasticity. Under the same temperature and F/A, the complex shear modulus G* and rutting resistance factor G* /sinδ of asphalt mortar raise with the increase of RCP replacement, which indicates that the RCP can better enhance the high-temperature rutting resistance of asphalt mortar than the counterpart LSP. It also implies that the modification of LSP and RCP in asphalt mortar mainly depends on the physical interactions rather than the chemical reactions.

Effect of bio-asphalt as additive on macro and micro properties of TLA modified asphalt and its modification mechanism

Trinidad Lake Asphalt (TLA) modified asphalt has excellent high temperature performance, but its low temperature performance is poor, which limits its engineering application. But bio-asphalt presents relatively excellent low temperature performance. In this paper, TLA and Bio-asphalt were used as additives to prepare composite modified asphalt with excellent properties both at high and low temperatures. The micro modification mechanism of asphalt was studied by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The macro mechanical behavior of asphalt binder was explored through routine physical property test and rheological property test. Finally, the mechanical properties of asphalt mixture were studied through the routine test of asphalt mixture, and the relationship between the macro and micro indexes of asphalt binder and the high and low temperature performance of asphalt mixture was established through grey correlation. The test shows that the mixing mode of TLA, bio-asphalt and base asphalt is physical blending. Modifiers affect the macro mechanical properties of asphalt by changing the distribution of asphalt components, the size of molecular weight, the interaction strength and arrangement of molecules. TLA improves the performance of asphalt binder at high temperature, but weakens the low-temperature performance. The low temperature performance of TLA modified asphalt was significantly improved by adding bio-asphalt at the cost of slightly reducing the high temperature performance. When the content of bio-asphalt is 9%–12%, the bio-asphalt/TLA modified asphalt and its mixture have better performance on high and low temperature properties than that of base asphalt. The micro indexes such as aromatic ring index and weight average molecular weight are good indicators of the high temperature performance of asphalt mixture. Creep rate (m), equivalent brittle point (T1.2) and stiffness modulus (S) can reflect the low-temperature performance of asphalt mixture.

Effects of the Ductility and Brittle Point of Modified Asphalt on the Freeze-Break Behavior of Asphalt Concrete: A 3d-Mesoscopic Damage Fe Model

Effects of the Ductility and Brittle Point of Modified Asphalt on the Freeze-Break Behavior of Asphalt Concrete: A 3d-Mesoscopic Damage Fe Model

COMPARATIVE EVALUATION OF BND 50/70 ROAD BITUMEN MODIFIED WITH SKEPT-60 AND SKN-26 ELASTOMERS

The article provides information on the physical and mechanical properties of polymer-bitumen compositions obtained by modifying road bitumen BND 50/70 with elastomers SKEPT-60 and SKN-26 and determination of the obtained polymer-bitumen composites. The properties of composite samples of various concentrations (2.5, 3.0, 5.0%, 6.5 and 7.0%) were determined: needle depth, softening, brittleness and flash point, stretching and adhesion. It was determined that the physical and mechanical characteristics of polymer-bitumen composite materials obtained at high concentrations (6.5, 7.0%) are improved

Production of Bitumen Modified with Low-Molecular Organic Compounds from Petroleum Residues. 3. Tar Modified with Formaldehyde

The chemical modification of tar with formaldehyde as 37% aqueous solutionhas been studied in the presence of the catalysts. Hydrochloric acid, sulfuric acid, sodium hydroxide and acid tar were used as the catalysts. The effect of the catalyst nature and amount, as well as temperature, process time and initial components ratio on the softening point, penetration, brittle point and adhesion to crushed stone has been determined. The structure of the modified tars was confirmed by IR spectroscopy. The structural-group composition was determined. Arene-formaldehyde resins have been synthesized on the basis of toluene and modified tars using hydrochloric acid as a catalyst. The synthesized resins were characterized using IR spectroscopy. The chemistry of the tar modification with formaldehyde has been proposed.

Performance of fine-grained W/Cu plate prepared by explosive welding with high wave impedance confinement at room temperature

Due to the brittleness and high melting point of tungsten (W), it remains a challenge to clad tungsten layers non-destructively by an explosive welding process at low temperatures. In this study, the tungsten foil was successfully welded to a copper plate by a high wave impedance constraint explosive welding method without cracks. Electron backscatter diffraction (EBSD) and energy dispersion spectroscopy (EDS) analyses detected that the tungsten clad characterized a lamellar structure of several hundred nanometers with homogeneous elemental distribution and smooth surface. The tungsten layer maintains continuity and high hardness regardless of the cross-sectional view, and exhibits a unique wave-like bond of high strength with copper. The tensile strength of the tungsten/copper composite plate is about 391 MPa and the elongation is more than 12%. The results show that the high wave impedance constrained explosive welding method is an effective process for producing nanoscale brittle material coatings at room temperature.

The role of hydrogen in the edge dislocation mobility and grain boundary-dislocation interaction in [formula omitted]-Fe

The atomistic mechanisms of dislocation mobility depending on the presence of hydrogen were investigated for two edge dislocation systems that are active in the plasticity of α-Fe, specifically ½<111>{110} and ½<111>{112}. In particular, the glide of the dislocation pile-ups through a single crystal, as well as transmission of the pile-ups across the grain boundary were evaluated in bcc iron crystals that contain hydrogen concentrations in different amounts. Additionally, the uniaxial tensile response under a constant strain rate was analyzed for the aforementioned structures. The results reveal that the presence of hydrogen decreases the velocity of the dislocations – in contrast to the commonly invoked HELP (Hydrogen-enhanced localized plasticity) mechanism -, although some localization was observed near the grain boundary where dislocations were pinned by elastic stress fields. In the presence of pre-exisiting dislocations, hydrogen-induced hardening was observed as a consequence of the restriction of the dislocation mobility under uniaxial tension. Furthermore, it was observed that hydrogen accumulation in the grain boundary suppresses the formation of new grains that leads to a hardening response in the stress-strain behaviour which can initiate brittle fracture points.

Review of Recent Developments and Understanding of Atterberg Limits Determinations

Among the most commonly specified tests in the geotechnical engineering industry, the liquid limit and plastic limit tests are principally used for (i) deducing useful design parameter values from existing correlations with these consistency limits and (ii) for classifying fine-grained soils, typically employing the Casagrande-style plasticity chart. This updated state-of-the-art review paper gives a comprehensive presentation of salient latest research and understanding of soil consistency limits determinations/measurement, elaborating concisely on the many standardized and proposed experimental testing approaches, their various fundamental aspects and possibly pitfalls, as well as some very recent alternative proposals for consistency limits determinations. Specific attention is given to fall cone testing methods advocated (but totally unsuitable) for plastic limit determination; that is, the water content at the plastic–brittle transition point, as defined using the hand rolling of threads method. A framework (utilizing strength-based fall cone-derived parameters) appropriate for correlating shear strength variation with water content over the conventional plastic range is presented. This paper then describes two new fine-grained soil classification system advancements (charts) that do not rely on the thread-rolling plastic limit test, known to have high operator variability, and concludes by discussing alternative and emerging proposals for consistency limits determinations and fine-grained soil classification.

Development of Auto-Searching Method of Brittle Fracture Initiation Point Based on River-Pattern and Tear Ridge

Development of Auto-Searching Method of Brittle Fracture Initiation Point Based on River-Pattern and Tear Ridge