Fracture Of Materials Research Articles

A mixed three‐field total Lagrangian material point method for phase‐field fracture modeling of nearly incompressible rubber‐like solids

AbstractThe rubber‐like solids, as commonly observed materials in nature and engineering areas, often show high extensibility and weak compressibility, which lead to difficulties for modeling the fracture behavior of these materials. In this paper, we propose a mixed three‐field total Lagrangian material point method (TLMPM) to deal with the fracture of nearly incompressible rubber‐like solids. In this method, the phase‐field method combining with perturbed Lagrangian approach is developed to describe the fracture of nearly incompressible materials. Based on the Lagrangian equation, the governing equations of the displacement, pressure and phase fields are derived for the system considering dynamic effect. Then, a mixed three‐field TLMPM discrete formulation with a remapping strategy is then built to solve the problem involving large deformation. Besides, a staggered solving scheme with explicit time integration is developed for the three‐field problem. The accuracy and capabilities of the proposed method for dealing with the fracture of incompressible materials are demonstrated by modeling several quasi‐static and dynamic numerical problems and comparing the results with other numerical methods and experiments. Moreover, the applicability of the method is further proved by an out‐of‐plane tearing case.

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A dislocation-based model for shear cracks in arbitrary orientations under contact loading

Mechanical transmission components are generally under the risk of contact fatigue, resulting in cracks initiated from the subsurface. When subject to compressive stress, these cracks might be forced to be closed, thus their faces are in partial slip contact. Under such conditions, the interactions of stick and slip zones cannot be directly determined, which is one of the greatest challenges of contact fatigue problems. In this study, the distributed dislocation technique is adopted to investigate the stick–slip friction along the alignment of shear cracks in arbitrary orientations in a half-plane under contact loading. The unknown dislocation density describing the crack face displacement is iteratively calculated based on the stress conditions and then introduced to update the surface gap between contacting bodies. The complex expressions of the influence coefficients used to determine the stress and displacement induced by the dislocations are derived and the FORTRAN codes are provided in the Supplementary Materials. A step-by-step loading method is proposed to progressively capture the slip history of crack faces. The model is also capable of simulating rolling contact problems. The results are comparable to those predicted using the finite element method with more robust convergence properties. The effects of friction coefficient, crack alignment, and locations of crack faces are discussed in detail. The model paves the foundation for further studies on competing mechanisms of crack propagation and crack face wear, and provides insights into the frictional fracture of materials under contact loading.

A novel SiC composite material infiltrated by basalt glass-ceramic with a high hardness

New high-performance materials for environments with high abrasive and erosive loads resistant are in a great demand for the modern industry. For the first time, a composite material obtained by infiltration of SiC porous oxide bonded preform with a basalt rock melt at a temperature of 1400 °C in air was proposed. The produced composite material significantly reduces porosity from 31.0 to 1.2%. Interestingly, an aluminosilicate phases crystallizes on the surface of SiC grains meanwhile the migration of Ca and Fe to the melt basalt volume due to atomic radii mismatch with the forming phases. The crystallinity of the basalt glass matrix obtained by petrurgical method is 66.9%. All together allows to improve hardness of the obtained composite material SiC/basalt glass-ceramics from 2.6 (preform) and 6.8 (basalt glass ceramics) to >9.6 GPa. The composite material fracture toughness (K1c ∼ 0.85 MPa·m1/2) also increases in comparison to a highly fragile basalt glass ceramics matrix. Thermal expansion coefficient value of the produced composite material is close to the dense polycrystalline SiC one and no sample destruction was observed caused by materials TEC mismatch.

Effect of the withdrawal rate on the microstructure and creep behavior of the directionally solidified nickel-based superalloy

The effect of the withdrawal rate on the microstructure and creep behavior of a directionally solidified nickel-based superalloy DZ125L is investigated in this study. A directionally solidified nickel-based superalloy is directionally solidified using the high rate directional solidification (HRS) process at various withdrawal rates. The results show that the closely packed dendrite arms and well distributed γ′ phase can significantly enhance the creep rupture life of the alloys, while the carbides and γ/γ′ eutectics affect the strength failure and fracture of materials. A series creep tests are performed on the nickel-based directionally solidified superalloy after different withdrawal rates. With an increasing withdrawal rate, the creep life of the alloy first increases and then decreases. The K–R creep damage model is established, which can reflect the quantitative relation between the withdrawal rate and creep life. The model simulation results are in good agreement with the tests.

Patients´ satisfaction concerning direct anterior dental restoration.

The objective of this study was to observe patients' satisfaction with their in-service direct anterior dental restorations and to compare it with clinical evaluation using FDI (Federation Dental International) criteria. Patients scored their own anterior dental restorations regarding satisfaction (satisfactory /dissatisfactory). If dissatisfaction was mentioned, then, they would be interviewed about the complaint. In the same session, the dental restorations were clinically evaluated by two dentists using FDI criteria (1-5 score) concerning esthetic, functional, and biological domains. Descriptive statistics were used for frequencies of scores attributed by patients and clinicians. In order to compare patients' to clinicians' frequencies, the Chi-square test was applied (p ≤ 0.05). A total of 106 restorations were evaluated by patients and clinicians. Patients reported 52.8% of restorations satisfactory and 47.8% dissatisfactory. Overall, clinicians reported the same restorations as 82,3% satisfactory and 17,6% dissatisfactory. Patients' most frequent complaints referred to color, followed by anatomical form, fracture of material and retention, and approximal anatomical form. Comparing patients' satisfaction and dissatisfaction rates to clinicians' evaluation per criteria, there was no difference regarding esthetics. The frequency of dissatisfactory restorations by clinicians was significantly lower when functional and biological properties were compared with patients' opinions. Direct anterior dental restorations were more frequently reported as satisfactory by patients and clinicians, being the main complaints related to esthetic issues. When clinicians and patients' evaluations were compared, it was observed that the frequencies of satisfactory restoration by patients and clinicians were similar regarding esthetic properties, and significantly different regarding functional and biological properties.

ENERGY MODEL OF SOILS AND ROCKS CUTTING DURING WELL DRILLING

The article deals with the process of cutting soils and rocks. Experimental studies show that a coneshaped wedge is formed on the cutting surface. The compacted core of the deformed material contributes to the formation of tensile forces, under the action of which the material is destroyed along the sliding surfaces at a shear angle. An energy model for cutting soils and rocks while drilling wells, consisting of four parts, is proposed. The model is aimed at minimizing the energy consumption of the cutting process during well drilling. It is proposed to determine the chisel rotation speed by the length of the crack that occurs during brittle fracture of materials.

Simulation of crack nucleation in materials with regularly arranged spherical pores under multiaxial loading conditions

A numerical study of the initial stage of crack growth in a material containing spherical pores under multiaxial compression (constrained conditions) has been carried out using the finite element method. The influence of the pore spacing and the mechanical properties of the material on the fracture localization and the direction of crack growth has been analyzed. Both brittle and ductile materials were studied. It has been established that material properties and the mutual arrangement of defects have a significant influence on the direction of propagation of cracks arising on the stress concentrators (structure defects), up to mutually perpendicular directions (for uniaxial of the characteristic sizes of the region of influence of spherical pores on each other, beyond which the stress fields of the neighboring elements of the structure do not overlap. The dependences of the sizes of this area on the elastic characteristics of the matrix material are shown. The obtained results are relevant for obtaining numerical estimates of the duration of the initial stages of quasi- brittle fracture of ceramic-based heterophase materials, refractories in particular. Ill. 6. Ref. 26. Tab. 1.

On the evaluation of entropy threshold for debonding during crack prorogation using DIC technique

The accumulated entropy at the crack tip of a semi-circular bending (SCB) specimen is investigated to obtain a threshold for material fracture and interatomic debonding. The presented approach uses the experimental data obtained from the Digital Image Correlation (DIC) technique and strain maps superposed to SCB specimens to measure the plastic flow at the crack tip. The Swift strain hardening model is utilized to calculate the stress domain at the crack tip and, consequently, the plastic strain energy and entropy accumulation. Results show that the crack surface propagates when the generated entropy at the crack tip reaches a critical limit. This critical value can be considered as the material capacity beyond which bond breakage occurs.

Deformation, Fracture and Microstructure of Metallic Materials

Metallic materials are mostly a combination of metallic elements, such as iron, aluminum, magnesium, titanium and manganese, which may also include small amounts of non-metallic elements, such as carbon, nitrogen and oxygen [...]

(103) 3-Piece Inflatable Penile Implant Pump Malfunction: Management using Pump Replacement Alone

Abstract Introduction Expert opinion is that when an implant malfunctions after 2 years it should be replaced in its entirety, despite the fact that reservoir removal is associated with serious potential complications. Furthermore, modern reservoir construction is such that material fracture and leak is rare. Objective In this time we reviewed our experience with replacing only the reservoir in patients with malfunctioning 3-piece inflatable implants resulting from pump breakdown. Methods The study population consisted of (i) men who had had 3-piece inflatable penile implant surgery (ii) with device malfunction (iii) resulting from pump malfunction (iv) who had all other components functional (v) who underwent pump replacement alone and (vi) had ≥5 years follow-up after device repair (clinic visit, telephone call, letter). Only patients who had undergone a single prior implant operation were included. At the time of the repair, the pump was removed and replaced with a new pump, making sure that both cylinders and reservoir were filled fully intraoperatively and retained all fluid that was instilled. At the postoperative appointment, all patients were retrained in the correct means of device inflation, specially focused on avoidance of pump torqueing. Results 88 patients had pump tubing blow-out upon delivery of the pump at a mean duration post-primary implant of 9 ± 11 (2-16) years. Mean age 62 ±14 years. All patients had either a Mentor Alpha-1 or a Coloplast Titan devices placed. Tubing disruption was present ≤1cm from pump itself in 66 (75%) or >1cm from the pump in 22 (20%) patients. 25% had a blow out of the pump-reservoir tubing, while 66 (75%) had a tear in the pump-cylinder tubing (46 frayed tubing, 20 compete transection), evenly distributed between right and left-sided tubing. With a mean follow-up of 7±2.5 years, none of the devices had failed again. Conclusions In patients with a malfunctioning penile implant with proven pump-only failure, replacing the pump is a viable repair option, thus, circumventing the need for reservoir placement. Disclosure No

Phase Field Modeling of Crack Growth with Viscoplasticity

The fracture of viscoplastic materials is a complex process due to its time-dependent and plastic responses. Numerical simulation for fractures plays a significant role in crack prediction and failure analysis. In recent years, the phase field model has become a competitive approach to predict crack growth and has been extended to inelastic materials, such as elasto-plastic, viscoelastic and viscoplastic materials, etc. However, the contribution of inelastic energy to crack growth is seldom studied. For this reason, we implement the fracture phase field model coupled with a viscoplastic constitutive in a finite element framework, in which the elastic energy and inelastic energy are used as crack driving forces. The implicit algorithm for a viscoplastic constitutive is presented; this procedure is suitable for other viscoplastic constitutive relations. The strain rate effect, creep effect, stress relaxation effect and cyclic loading responses are tested using a single-element model with different inelastic energy contributions. A titanium alloy plate specimen and a stainless-steel plate specimen under tension are studied and compared with the experimental observations in the existing literature. The results show that the above typical damage phenomenon and fracture process can be well reproduced. The inelastic energy significantly accelerates the evolution of the phase field of viscoplastic materials. For cyclic loadings, the acceleration effect for low frequency is more significant than for high frequency. The influence of the weight factor of inelastic energy β on the force-displacement curve mainly occurs after reaching the maximum force point. With the increase of β, the force drops faster in the force-displacement curve. The inelastic energy has a slight effect on the crack growth paths.

Size effect and scaling in quasi‐static and fatigue fracture of graphene polymer nanocomposites

AbstractThis work investigated how the structure size affects the quasi‐static and fatigue behaviors of graphene polymer nanocomposites, a topic that has been often overlooked. The results showed that both quasi‐static and fatigue failure of these materials scale nonlinearly with the structure size due to the presence of a significant fracture process zone (FPZ) ahead of the crack tip induced by graphene nanomodification. Such a complicated size effect and scaling in either quasi‐static or fatigue scenario cannot be described by the linear elastic fracture mechanics, but can be well captured by the size effect law (SEL) which considers the FPZ. Thanks to the SEL, the enhanced quasi‐static and fatigue fracture properties were properly characterized and shown to be independent of the structure size. In addition, the differences on the morphological and mechanical behaviors between quasi‐static fracture and fatigue fracture were also identified and clarified in this work. The experimental data and analytical analyses reported in this article are important to deeply understand the mechanics of polymer‐based nanocomposites and even other quasi‐brittle materials (e.g., fiber‐reinforced polymers or their hybrid with nanoparticles, and so forth), and further advance the development of computational models capable of capturing size‐dependent fracture of materials under various loads.

A Study on the Fracture of Cementitious Materials in Terms of the Rate of Acoustic Emissions in the Natural Time Domain

A novel approach for describing the acoustic activity in brittle structural materials while they are loaded mechanically at levels close to those causing macroscopic fracture is proposed. It is based on the analysis of the rate of acoustic emissions in terms of the Natural Time concept. Experimental data from protocols with either intact or notched beams, made of cementitious materials, subjected to three-point bending are analyzed. It is concluded that in case the acoustic activity is described with the aid of the F-function in the Natural Time domain, its evolution is governed by a power law, independently of geometrical details and the type of the loading scheme. It appears that the onset of validity of this law provides an interesting pre-failure indicator.

Hydrogel-Assisted Double Molding Enables Rapid Replication of Stereolithographic 3D Prints for Engineered Tissue Design.

Tissue-engineered in vitro models are an essential tool in biomedical research. Tissue geometry is a key determinant of function, but controlling the geometry of microscale tissues remains challenging. Additive manufacturing approaches have emerged as a promising means for rapid and iterative changes in the geometry of microdevices. However, it has been shown that poly(dimethylsiloxane) (PDMS) cross-linking is often inhibited at the interface of materials printed with stereolithography. While approaches to replica mold stereolithographic three-dimensional (3D) prints have been described, these methods are inconsistent and often lead to print destruction when unsuccessful. Additionally, 3D-printed materials often leach toxic chemicals into directly molded PDMS. Here, we developed a double molding approach that allows precise replication of high-resolution stereolithographic prints into poly(dimethylsiloxane) (PDMS) elastomer, facilitating rapid design iterations and highly parallelized sample production. Inspired by lost wax casting, we used hydrogels as intermediary molds to transfer high-resolution features from high-resolution 3D prints into PDMS, while previously published work focused on enabling direct molding of PDMS onto 3D prints through the use of coatings and post-cross-linking treatments of the 3D print itself. Hydrogel mechanical properties, including cross-link density, predict replication fidelity. We demonstrate the ability of this approach to replicate a variety of shapes that would be impossible to create using photolithography techniques traditionally used to create engineered tissue designs. This method also enabled the replication of 3D-printed features into PDMS that would not be possible with direct molding as the stiffness of these materials leads to material fracture when unmolding, while the increased toughness in the hydrogels can elastically deform around complex features and maintain replication fidelity. Finally, we highlight the ability of this method to minimize the potential for toxic materials to transfer from the original 3D print into the PDMS replica, enhancing its use for biological applications. This minimization of the transfer of toxic materials has not been reported in other previously reported methods describing replication of 3D prints into PDMS, and we demonstrate its use through the creation of stem cell-derived microheart muscles. This method can also be used in future studies to understand the effects of geometry on engineered tissues and their constitutive cells.

A hybrid phase-field method for modeling mixed-mode fractures in elastoplastic rock-like materials

The phase-field method has been proven to be a powerful tool for predicting complex crack patterns and widely utilized in many fields. To effectively characterize and depict the complex cracking behaviors of rock-like materials, however, is still a challenge. In this study, a modified phase field model for mixed-mode fractures in rock-like materials is proposed. The effect of plastic free energy on damage is taken into consideration by developing a new phase field evolution equation. A non-associative Drucker–Prager constitutive model is coupled within the framework to capture more accurate stiffness and plastic strain in rock-like materials. To solve the coupled problem more efficiently, an accelerated monolithic iteration method has been developed. Several numerical results are presented to examine the viability of the established phase field model. Additionally, the investigation of the local stress field is done to identify the main driving forces of the different fracture modes.

Aggregate size effects on fracture behavior of concrete SCB specimens

Fracture in concrete and rock-like materials is the result of applying external loads, initiation, and propagation of the cracks, and finally, creating the failure surface in the material. The most common type of fractures in solid materials are usually formed under combined tensile/shear loading conditions. The stress intensity factors KI and KII, corresponding to opening and sliding modes (I and II), are the main fracture parameters, and their critical values (i.e., fracture toughness) show the material's resistance against the initiation and propagation of cracks. In this paper, the fracture toughness of concrete specimens is determined by considering different aggregate sizes and using the three-point bending test on semi-circular bend (SCB) specimen. The fracture toughness parameters have been determined by different fracture criteria and compared with the values obtained in the laboratory on concrete specimens. The effect of aggregate size on fracture parameters and crack propagation path has been evaluated. To predict thecrack initiation angle and fracture toughness values, themodified maximum tangential stress (MMTS) and extended maximum tangential strain (EMTSN) criteria along with conventional fracture criteriawere used. The results showed, that with the increase in aggregate size, the fracture toughness value under mode I, II, and mixed-mode (I-II) has increased. The laboratory results showed that specimens with aggregate sizes of 0–19 mm have the highest fracture load, and specimens with the aggregate sizes of 0–5 mm have the lowest fracture load

Strain orthogonal decomposition implemented within the phase field method with interfacial damage to model fracture in multi-phase heterogeneous materials

In recent times, the phase field method is a robust simulation tool that can predict crack formation and propagation in structures. In brittle and quasi-brittle materials, the strain tensor is decomposed into negative and positive parts corresponding to the compression and tension behaviors when the structure is loaded. In the previous studies related to the phase field method, the strain tensor decompositions do not satisfy the orthogonal condition of these two parts, even if the elastic stiffness tensor is isotropic. This problem leads to inaccuracies in the mechanical behavior of the materials. In this paper, the strain tensor orthogonal condition is applied to the bulk strain tensor parts representing the internal strain of the component phases. This orthogonal condition is implemented into the phase field method with interfacial damage to simulate crack propagation in a sample containing multi-phase heterogeneous materials. Furthermore, the shape and area fraction of these phases are recognized by a supplemental sub-function which was studied in our recent paper from image formats. Through several examples, the obtained results are compared with the relevant numerical ones to demonstrate the correctness and effectiveness of the proposed method.

Advances in Fracture, Fatigue and Structural Integrity Analyses of Metals

Given the good response of the scientific and technical communities to our previous Special Issue in Metals, titled “Fracture, Fatigue and Structural Integrity of Metallic Materials” (2019), and given that research in these fields is continuously increasing in qualitative and quantitative terms, this new Special Issue intends to provide a forum for the dissemination of the latest significant advances in fracture, fatigue and structural integrity analyses [...]

Effect of Lode angle and projectile diameter on the ballistic resistance of 6061-T651 aluminum alloy plates struck by hemispherical nosed projectile

Aluminum alloy has been gradually applied to the field of armor protection because of its excellent material properties. The research on its ballistic resistance has important theoretical and engineering application value. In order to study the ballistic resistance of 6061-T651 aluminum alloy plate, the impact tests of 6061-T651 aluminum alloy plate against hemispherical nosed projectile with a diameter of 12.66 mm were carried out with a light gas gun system and the ballistic limit velocity and failure mode of the target plate were obtained. Subsequently, the numerical simulations corresponding to the tests were carried out by using the Lode dependent and independent fracture criteria, and the effect mechanism of the Lode angle on the numerical simulation results were analyzed. Finally, the effect of projectile diameter on the ballistic resistance of the target plate was analyzed by the expansion of numerical simulation. The research results show that the numerical simulation will be quite different from the test results if the effect of the Lode angle on the material fracture strain is not considered. As the diameter of the projectile increases, the armor-piercing efficiency of the hemispherical nosed projectile is improved since the energy dissipation mechanism of the target plate gradually changes from ductile hole enlargement to shear plugging.