Fracture Of Materials Research Articles

Strain hardening of acid-induced sodium caseinate gels as a function of pH and temperature

Strain hardening is a type of rheological behaviour that can be observed in large deformation tests of various materials. In oscillatory shear rheometry, it is characterised by an increase in storage and loss modulus ( and ) with increasing oscillation amplitude (i.e, shear strain) until the material fractures and the moduli drop again. Acid-induced caseinate gels were previously shown to exhibit such a strain hardening behaviour. However, it has not been studied in much detailed how the extent of strain hardening is affected by pH and acidification temperature. In this work, the strain hardening of acid-induced caseinate gels was characterised as a function of pH by starting strain sweeps at various time points during acidification with glucono-delta-lactone, and the experiments were conducted at either 20, 30 or 40 °C to investigate the impact of temperature. The results demonstrate that the strain at fracture and the extent by which increases with the strain amplitude change throughout acid-induced gelation of sodium caseinate in a complex manner with characteristic minima and maxima being barely related to the parameters observed in small strain experiments. The findings demonstrate the importance of considering the pH and temperature when characterising the strain hardening of caseinate gels as previous work showed that the strain hardening properties are related to water expression in forced syneresis experiments.

Tensile strength of MgO-graphite based refractories: effect of anisotropy and specimen size

Oxide-graphite refractories represent the new paradigm of materials for extreme environments since 1970´s: materials that resist thanks to "in situ" microstructural changes. The analysis of post-mortem linings necessitates the use of small specimens because main microstructural changes occur within the matrix, exhibiting zonal distributions relatively small compared to maximum aggregate sizes. In this paper the minimized tensile strength of discs (diameter=18 mm, width=8 mm) tested in diametral compression is addressed for commercial materials representative of the typical microstructures. Effects of aggregate and graphite sizes, graphite anisotropy and size of the specimens on the quasi-brittle fracture of these heterogeneous materials are discussed.

A phase field finite element study and evaluation of sulfide stress cracking in DCB specimen testing

The challenges presented by sour environments rich in hydrogen sulfide (H2S) underscore the necessity for a comprehensive understanding of material behavior under such conditions. The cracking susceptibility of metals and alloys used for subsurface equipment in downhole oil and gas exploration operations is particularly concerning. The NACE Double Cantilever Beam (DCB) test has emerged as a widely used quality assurance tool in the petroleum industry, leveraging fracture mechanics principles to assess the environment-assisted cracking (EAC) resistance of metals and alloys. The DCB test evaluates the fracture toughness KISSC of materials in H2S-containing environments via assessment of the crack arrest, which serves as a vital parameter in structural integrity assessments to mitigate the risk of service-related failures from sulfide stress cracking (SSC). However, various studies suggest that different test parameters, such as arm displacement and initial notch, significantly influence KISSC. This work presents a detailed numerical investigation on a comprehensive simulation of the DCB test, examining the effects of different test parameters on KISSC prediction. A coupled deformation-diffusion phase field framework is adopted to simulate SSC in DCB specimens arising from a complex interplay between material deformation, hydrogen diffusion, and fracture. The numerical results show good agreement with experimental results reported in the literature and provide deeper insights into the factors affecting crack growth and arrest in DCB testing.

Porous silicon/carbon composites as anodes for high-performance lithium-ion batteries

Silicon anodes are promising for use in lithium-ion batteries. However, their practical application is severely limited by their large volume expansion leading to irreversible material fracture and electrical disconnects. This study proposes a new top-down strategy for preparing microsize porous silicon and introduces polyacrylonitrile (PAN) for a nitrogen-doped carbon coating, which is designed to maintain the internal pore volume and lower the expansion of the anode during lithiation and delithiation. We then explore the effect of temperature on the evolution of the structure of PAN and the electrochemical behavior of the composite electrode. After treatment at 400 -, the PAN coating retains a high nitrogen content of 11.35%, confirming the presence of C―N and C―O bonds that improve the ionic-electronic transport properties. This treatment not only results in a more intact carbon layer structure, but also introduces carbon defects, and produces a material that has remarkable stable cycling even at high rates. When cycled at 4 A g−1, the anode had a specific capacity of 857.6 mAh g−1 even after 200 cycles, demonstrating great potential for high-capacity energy storage applications.

On Microplasticity-induced Fatigue Fracture and its Relation to Entropy

Abstract The study delves into the intricate effects of microplasticity on fracture formation in testing specimens under axial cyclic loading. The primary aim is to pinpoint the juncture at which microplasticity becomes discernible across the stress cycle. Fatigue tests are conducted on varied specimens until failure using a fatigue testing machine, while recording parameters such as frequency, stress amplitude, applied power, and tensile strain. The investigation seeks to ascertain whether cracks must attain a specific size before manifesting these subtle alterations. A conjectured relationship is proposed between the number of cycles and entropy throughout the process. Additionally, a hypothesis is posited suggesting that microplasticity emerges only once the crack surpasses a certain threshold, such as grain size. This research provides insights into material fracture mechanisms and their implications for product durability and safety. Such discernments into the product life cycle under analogous conditions hold promise for delineating operational limits.

A lattice modelling framework for fracture-induced acoustic emission wave propagation in concrete

To date, there is no comprehensive approach available that can explicitly model the complete transient waveforms of acoustic emissions (AE) induced by fracture processes in brittle and quasi-brittle materials like concrete. The complexity of AE modelling arises from the intricate coupling between the local discontinuity of material fracturing and the global continuity of elastic wave propagation in solids. Among others, the lattice type models are promising approaches, as they are known to be a matured modelling approach to simulate the fracturing process in concrete-like materials. Nevertheless, like other discrete element methods (DEM), they are currently limited to describing the number and rate of AE events (broken elements) in the fracture process and cannot explicitly model wave generation and propagation. In this study, we propose a lattice modeling framework to simulate the propagation of complete waveforms of fracture-induced AE signals in concrete. A proportional-integral-derivative (PID) control algorithm is incorporated in an explicit time integration procedure to reduce dynamic noise from spurious oscillations. Additionally, a Rayleigh damping-based calculation method and corresponding calibration procedure are proposed to model the attenuation of AE signals due to material damping. Using the developed approach, we systematically investigate the feasibility of lattice models for elastic wave propagation simulation, the dependence of lattice mesh sizes and the choice of numerical damping parameters. These results lead to a systematic framework which can be employed in simulating wave propagation with attenuation using DEM models in general including lattice models.

The cruciality of particle size and shape on fracture mechanism of aluminum matrix composites

Metal matrix composites are generally believed to achieve better performance with spherical reinforcements than irregular ones. In this work, through experiments and computational simulations, we have demonstrated that spherical reinforcements do not necessarily enhance the tensile ductility of composites. There exists a critical size for spherical particles. Using an Al2O3-Al2024 composite as an example, we found that when the size of spherical Al2O3 particles is less than 3 µm, they are not fractured during deformation, resulting in enhanced ductility. We elucidated the competitive mechanism between particle and matrix fracture under various reinforcement sizes and volume fractions, and constructed a deformation map that can be utilized to determine fracture mechanisms. This work clarifies the micro-mechanical mechanisms of reinforcements on material fracture behavior, providing guidance for the design and fabrication of strong and ductile metal matrix composites.

Linear polydichlorophosphazene and Ti3C2Tx MXene nanohybrids: Synthesis and application to epoxy resin to improve the fire safety and mechanical properties

Enhancing the fire safety of epoxy resins (EPs) typically requires a significant amount of flame retardants, which often results in considerable degradation of their mechanical properties. To address this issue, a novel flame retardant known as PDCP@DPA@MXene was synthesized and integrated into EP to achieve notable improvements in flame retardancy, smoke suppression, and mechanical strength. By incorporating 1.5 wt% PDCP@DPA@MXene, the impact strength, tensile strength, and elongation at break of the resulting PDM-1.5 %/EP composite reached 12.1 kJ/m2, 57.4 MPa, and 13.0, respectively, reflecting enhancements of 63.5 %, 18.4 %, and 17.1 % compared to the pure EP. The enhancement in tensile strength may be attributed to the high rigidity of Ti3C2Tx MXene, which reinforces the EP matrix. Additionally, the intertwined structure of PDCP@DPA@MXene chains effectively mitigates material fracturing and absorbs impact forces, thus toughening the EP. The presence of phosphorus, nitrogen, and titanate in PDCP@DPA@MXene contributes to the formation of a more compact char layer. The PDM-1.5 %/EP sample achieved a V-0 rating in the vertical UL-94 test and exhibited a high limiting oxygen index of 32.0. Furthermore, the sample containing 2 wt% PDCP@DPA@MXene showed a significant reduction in peak heat release rate (p-HRR) and total heat release (THR), recording values of 689 kW/m2 and 71.9 MJ/m2, which are decreases of 45.1 % and 26.9 %, respectively, compared to pure EP. Additionally, the incorporation of PDCP@DPA@MXene led to a reduction in CO production. These flame-retarded EPs demonstrate strong potential for various applications due to their elevated glass transition temperature and robust thermal stability.

Microstructure evolution in laser powder bed fusion melted 2205 duplex stainless steel using in-situ EBSD during uniaxial tensile testing

Compared to duplex stainless steels (DSSs) prepared by traditional methods, specimens produced through laser powder bed fusion (LPBF) exhibit excellent yield strength but lower elongation. To improve elongation, understanding microstructure evolution during uniaxial tensile testing is crucial. This study investigates the slip behavior, grain boundary evolution, and phase transformation of LPBF 2205 duplex stainless steel during tensile deformation using in-situ electron backscatter diffraction (EBSD). Results show the formation of slip bands, which increase in number as loading stress rises. The primary slip systems activated are {110}<111> in ferrite and {111}<110> in austenite. In the ferrite phase, slip dislocations accumulate and generate low-angle grain boundaries (LAGBs), which evolve into high-angle grain boundaries (HAGBs), refining the grain structure. Numerous Σ3 annealing twins form in the austenite phase, but detwinning and twinning reduce Σ3 content as deformation processes. Ferrite and austenite exhibit good stability during the initial stages of tensile deformation. However, some austenite transforms into martensite through the transformation-induced plasticity (TRIP) effect at the final stages of deformation, which helps relieve stress concentration and delays material fracture. This study provides valuable insights for optimizing microstructure to improve the mechanical properties of LPBF materials.

Record statistics of fracture in the random spring network model.

We study the role of record statistics of damage avalanches in predicting the fracture of a heterogeneous material under tensile loading. The material is modeled using a two-dimensional random spring network where disorder is introduced through randomness in the breakage threshold strains of the springs. It is shown that the waiting strain interval between successive records of avalanches has a maximum for moderate disorder, thus showing an acceleration in occurrence of records when approaching final fracture. Such a signature is absent for low disorder when the fracture is nucleation-dominated, as well as for high disorder when the fracture is percolation type. We examine the correlation between the record with the maximum waiting strain interval and the crossover record at which the avalanche statistics change from off-critical to critical. Compared to the avalanche exponent crossover based prediction for failure, we show that the record statistics have the advantage of both being real-time as well as being a precursor significantly prior to final fracture. We also find that in the avalanche-dominated regime, the failure strain is at best weakly correlated with the strain at the maximum waiting strain interval. A stronger correlation is observed between the index of the largest record and the index of the record at the maximum waiting strain interval.

Translaminar fracture toughness characterisation for a glass fibre/polyamide 6 laminated composite by a novel approach based on fictitious material concept

This paper proposes a novel approach for the characterisation of the material fracture toughness associated with translaminar tensile failure, consisting in the application of the Fictitious Material Concept (FMC) by using the testing configuration of the Modified Two Parameter Model (MTPM). The main advantage of such an approach is to avoid the use of nonlinear fracture mechanics for material fracture toughness characterisation. The novel approach is applied to compute the translaminar fracture toughness of a unidirectional glass fibre (GF)/polyamide 6 (PA6) laminated composite. Moreover, the experimental campaign carried out is numerically simulated by means of a micromechanical finite element model, and the fracture toughness is computed by employing two different approaches, that is, the novel one and the MTPM. The present study proves, for the first time, that the Fictitious Material Concept can be applied by considering both experimental and numerical structural responses since it provides, in both cases, quite satisfactory accuracy in term of laminated composite fracture toughness. Therefore, the great advantage is that, when a validated numerical model is available, experimental campaigns may be avoided, saving time and money. Moreover, it is proved that the FMC can be used to investigate specimen size effect on fracture toughness.

Hydraulic fracturing in cement mortar subjected to seepage-sulfate coupled attack under varying pH levels

Cement-based structures are prone to hydraulic fracturing in acidic sulfate and seepage environments, posing a significant safety threat to engineering projects. To investigate the impact of pH levels on hydraulic fracturing in cement-based materials under seepage-sulfate coupled attack, hydraulic fracturing test and splitting tensile strength test have been conducted on cement mortar specimens permeated with Na2SO4 solution. A mathematical model is developed to establish the relationship between the critical water pressure of hydraulic fracturing and the splitting tensile strength at varying pH levels. The results show that the critical water pressure and splitting tensile strength initially increase and then decrease with the increase in erosion duration under pH levels of 7 and 3, while they continuously decrease with the increase in erosion duration under pH level of 1. Furthermore, the peak values of the critical water pressure and splitting tensile strength gradually diminish, which indicates an increased deterioration in hydraulic fracturing resistance with the decrease in pH value. The relationship between critical water pressure damage coefficient and erosion duration can be accurately described by a quadratic polynomial. Overall, the findings of this study can serve as a useful reference for enhancing the structural performance of cement mortar subjected to seepage-sulfate coupled attack at varying pH levels.

Efficient BFGS quasi-Newton method for large deformation phase-field modeling of fracture in hyperelastic materials

The prediction of crack propagation in materials is a crucial problem in solid mechanics, with many practical applications ranging from structural integrity assessment to the design of advanced materials. The phase-field method has emerged as a powerful tool for modeling crack propagation in materials, due to its ability to accurately capture the propagation of cracks. However, current phase-field algorithms suffer from the elevated computational cost associated with the so-called staggered solution scheme, which requires extremely small time increments to advance the crack due to its inherent conditional stability. In this paper, we present, for the first time, a quantitative analysis detailing the numerical implementation and comparison of two common solution strategies for the coupled large-deformation solid-mechanics-phase-field problem, namely the quasi-Newton based Broyden–Fletcher–Goldfarb–Shanno algorithm (BFGS) and the full Newton based alternating minimization (or staggered) (AM/staggered) algorithm. We demonstrate that the BFGS algorithm is a more efficient and advantageous alternative to the traditional AM/staggered approach for solving coupled large-deformation solid-mechanics-phase-field problems. Our results highlight the potential of the quasi-Newton BFGS algorithm to significantly reduce the computational cost of predicting crack propagation in hyperelastic materials while maintaining the accuracy and robustness of the phase-field method.

Microstructural behavior of CNT-PDMS thin-films for multifunctional systems

Heterogeneous ribbed and non-ribbed carbon nanotube (CNT)-PDMS thin-film systems manufactured by large-scale rolling exhibit large-strain and high strain-rate characteristics with favorable surface behaviors, such as superhydrophobicity and drag reduction. However, it is not well understood how the multi-phase microstructure and material properties of non-ribbed thin-films are related to the surface material behavior and fracture. Hence, the objective of this investigation is to characterize the large-strain mechanical behavior and the microstructure of various CNT-PDMS compositions to understand how the CNT loading, agglomeration, distribution, and orientation affect the mechanical behavior and fracture of CNT-PDMS unribbed systems. Non-ribbed thin tensile testing specimens were fabricated for neat PDMS and CNT-PDMS with different weight CNT distributions to understand non-ribbed behavior. The ultimate strain, strength, and global stress–strain behavior were obtained by uniaxial mechanical testing. Scanning electron microscopy (SEM) of the fracture surface was also obtained for each sample to analyze the microstructure and relate the damage mode to the different weight distributions. Based on these experimental measurements and observations, large-strain, hyperelastic and hyper-viscoelastic material models were used to characterize the material behavior. The hyper-viscoelastic material model was shown to provide the most accurate material description of the thin-film behavior of the viscoelastic PDMS with the high-strength CNTs.

{10-12} twinning transfer behavior in compressed high-purity hafnium

The interaction between twins and grain boundaries (GBs) significantly influences material deformation and fracture behavior. In the present study, high-purity hafnium (Hf) was subjected to compression at both room temperature and under liquid nitrogen cooling conditions. Twinning transfer (TT) behavior of {10–12} <−1011> extension twin was thoroughly and statistically investigated. Results show that compression temperature affects the misorientation angle (MA) for TT. Under room temperature compression, twins can transfer across GBs with MAs below 30° and partially transfer across GBs with MAs between 30° and 50°. When compressed under liquid nitrogen cooling, twins can traverse the GBs with MAs below 40° and partially traverse the GBs with MAs above 40° and with a maximum MA of 77°. The MA, Schmidt factor (SF) value, and geometrical compatibility parameter m’ of twinning systems in neighboring grains influence the TT. Favorable conditions for TT include low MAs, high SF and m’ values. Stress concentration caused by incoming twins can be alleviated through TT with high m’ at GBs with low MAs. For GBs with high MAs, stress concentration can also be alleviated through TT or twinning-slipping transfer with high m’. Extension and growth of outgoing twins contribute to further stress concentration relief.

Using fractal voids to understand Mode I compressive fracture in brittle materials – A two-dimensional analysis

Unlike cases of direct or indirect tensile loading, analysis of Mode I fracture in cases of compressive loading must necessarily consider two-dimensional flaw geometries. The consequent analytical complications have resulted in little theoretical evolution towards understanding Mode I fracture in compressive loading. Researchers have recently observed that the linear elastic (LE) stress fields surrounding two-dimensional flaws in compression appear to have indicative value regarding Mode I fracture, but no rational framework has yet been proposed for their interpretation. Herein it is demonstrated that by idealizing void surfaces as fractal, and using what will be called the “small flaw assumption,” LE stress fields can be interpreted to obtain significant insight regarding brittle Mode I compressive fracture. Using fractal voids, a rational and consistent explanation for the satisfaction of the stress and energy criteria at the surface of two-dimensional flaws is presented. The discussion resolves many typical theoretical issues in the literature in a manner consistent with fundamental Griffith theory, and accounts for size and shape effects. The framework further enables the computationally efficient prediction of peak KI values associated with the propagation of line cracks from two-dimensional flaws from a brittle medium subject to macroscopic uniaxial compression via LE stress fields.

High-performance bamboo-wood composite materials based on the natural structure and original form of bamboo: Fracture behavior and mechanical characterization

Reducing the destruction of bamboo's original structure to produce high-utilization and high-performance engineered bamboo products has long been a goal in the industry. This study developed a new natural arc-shaped laminated bamboo-wood lumber (NALBWL) based on the natural structure and original form of bamboo, using equal arc-shaped bamboo split (EASB) and poplar veneer. A multi-scale analysis of the bending performance and crack propagation dynamics of EASB and NALBWL was conducted. EASB's modulus of elasticity (MOE) and rupture (MOR) were 1.06 and 1.17 times higher than those of air-dried bamboo, respectively, exhibiting excellent mechanical properties. Additionally, its toughness in the full and elastic-plastic stages were 1.24 and 1.38 times higher than those of air-dried bamboo. NALBWL's MOE and MOR were 12.73 GPa and 174.41 MPa, fully meeting structural material requirements and even surpassing most engineered bamboo products. Moreover, NALBWL's radial bending load values were 2.29 and 2.24 times higher than that of EASB and air-dried bamboo, respectively, and it also demonstrated excellent water heat and drying resistance in impregnation and peeling performance. Real-time crack propagation analysis indicated that NALBWL's superior mechanical properties benefited from the respective advantages of bamboo and poplar veneer. This work showcased the application of "natural form-inspired design" in developing bamboo-wood composite materials, and the conclusion provided a reference for the sustainable development of engineered bamboo products and the study of biomass material fracture mechanisms.

Properties of true stress diagrams in the areas of necking and fracture of materials under tension

Properties of true stress diagrams in the areas of necking and fracture of materials under tension

Data-driven integration of synthetic representative volume elements and machine learning for improved microstructure-property linkage and material performance in ceramics

Ceramic materials, characterized by their heat resistance, dielectric properties, and mechanical performance, are often compromised by brittleness due to microstructural inclusions. These inclusions, such as defects, secondary phases, and pores, are critically analyzed for their impact on material strength and fracture properties. In this study, the linkage between microstructure and properties in ceramic materials is explored through a methodological approach that combines experimental observations with physics-based and machine learning models. A data-driven approach has been employed, utilizing synthetic Representative Volume Elements (RVEs) derived from X-ray computed tomography scans of ceramics. The methodology involves an automated finite element (FE) simulation process for progressive failure analysis under uniaxial compression and tension. The analysis is conducted using statistical, data-driven, and machine learning techniques, including principal component analysis and k-means clustering, to assess the microstructural features' impact on material performance. The study focuses on the use of RVEs for accurately capturing essential microstructural characteristics and addresses the challenges in developing synthetic models and the limitations of simulation capabilities. The study's findings reveal that less uniform inclusion distribution and a higher standard deviation in inclusion size correlate to lower mechanical performance. By applying data-driven methods, this research contributes to the optimization of material performance and the establishment of structure-property relationships, with a particular emphasis on the influence of inclusions and defects on the mechanical behavior of ceramic materials.

First‐Principle Calculation of the Hydrogen Adsorption and Diffusion Characteristics at an Ni3Al/Ni Interface

ABSTRACTThe occurrence of hydrogen embrittlement often leads to significant fracturing in materials. Thus, a comprehensive understanding of the interactions of hydrogen and its effects on material properties is essential. In this study, first‐principle calculations based on density functional theory are conducted to investigate the adsorption and diffusion characteristics of hydrogen at the Ni/Ni3Al(γ/γ') interface of a Ni‐based single‐crystal superalloy. The results show that hydrogen can stably adsorb onto the γ/γ′ interface, nearby octahedral interstitial sites, and tetrahedral interstitial sites in the γ‐phase. Analysis of the density of states and charge density confirms that the hydrogen atoms formed covalent bonds and ionic bonds with nearby Al atoms. A transition state structure search based on linear synchronous transit (LST) and quadratic synchronous transit (QST) models is utilized to calculate the diffusion paths and energy barriers of the hydrogen atoms between the stable adsorption sites near the interface. In addition, the permeation characteristics of hydrogen atoms at the interface are analyzed. Furthermore, it is confirmed that hydrogen atoms entering the matrix from the interface preferentially occupy the positions of the regular octahedral interstitial sites, diffuse towards adjacent regular 6Ni octahedral interstitial sites through the inclined octahedral interstitial sites between the atomic layers, and converge at the interface.