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The heterogeneous structure of polymer and aluminum alloy is an effective way to meet the dual technical indicators of structural performance and lightweight design. Friction stir welding (FSW) is a solid-phase welding technology characterized by low temperature and large plastic deformation. It is basically not affected by the crystal structure and physical-chemical properties of materials and can realize polymer and aluminum alloy-specific materials quality connection. This paper presents a comprehensive review of the current advancements in FSW between polymers and aluminum alloys with a focus on optimizing welding parameters, joint formation, defect identification, and mitigation. The results showed that the most important details are that high rotation speed combined with low welding speed that is beneficial to increase welding heat input, improve joint forming and mechanical properties, and form aluminum riveting structure. Welding defects are the main reason for the low FSW performance of polymer and aluminum alloy heterogeneous structures. To improve the forming and load-bearing capacity of heterogeneous structures, welding tool structure design, surface pretreatment, and welding structure optimization can be utilized. [ABSTRACT FROM AUTHOR]

The fatigue response of additively manufactured (AM) specimens is mainly driven by manufacturing defects, like pores and lack of fusion defects, which are mainly responsible for the large variability of fatigue data in the S–N plot. The analysis of the results of AM tests can be therefore complex: for example, the influence of a specific factor, e.g. the building direction, can be concealed by the experimental variability. Accordingly, appropriate statistical methodologies should be employed to safely and properly analyze the results of fatigue tests on AM specimens. In the present paper, a statistical methodology for the analysis of the AM fatigue test results is proposed. The approach is based on shifting the experimental failures to a reference number of cycles starting from the estimated P–S–N curves. The experimental variability of the fatigue strength at the reference number of cycles is also considered by estimating the profile likelihood function. This methodology has been validated with literature datasets and has proven its effectiveness in dealing with the experimental scatter typical of AM fatigue test results. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is one of the most promising metal additive manufacturing technologies. SLMed Al-Si alloys have been widely used in the rail transport, aerospace, and automotive industries. Recently, the fatigue and fracture properties of SLMed Al-Si alloys have attracted considerable attention due to their application in critical load-bearing structures. This review aims to better understand the recent progress on the fatigue and fracture investigations of SLMed Al-Si alloys, especially AlSi10Mg, with emphasis on the effect of defects, heterogeneous microstructure, residual stress, and post-treatment methods. In addition, fatigue and fracture modeling methods are discussed. Finally, the challenges and future research opportunities are prospected. [ABSTRACT FROM AUTHOR]

The challenges of the 21st century require developing new materials combining attributes such as low cost, high strength and toughness, machinability, and recyclability. This is particularly true for alloys that are produced in mass, such as cast irons. Solution-strengthened ferritic ductile iron (SS-FDI) is a promising candidate to become a strategic material that summarizes the abovementioned attributes. The microstructure and static strength at room and low temperature (–25°C) of a 3.45 wt.% Si SS-FDI were investigated. The results showed that the analyzed cast iron is a promising material that, compared to traditional cast iron grades, shows a unique favorable combination of high strength and elongation at rupture. [ABSTRACT FROM AUTHOR]

This paper examines the potential of using additive manufacturing (AM) technology to create nature-inspired designs with decreased stress concentration factors, which are typically the source of fatigue damage. AM has advantages over conventional manufacturing processes, allowing for creation of complex and optimized geometries. Based on a real case study, this paper evaluates the possibility of bio-inspired optimization of a connection between a tubular profile and a steel plate through AM technology. The results reveal a significant decrease in the stress concentration factor for the optimized bio-inspired AM solution compared to traditional construction solutions. [ABSTRACT FROM AUTHOR]

Recently, the welding of dissimilar metals has attracted great interest due to its widespread use in engineering building applications. In this article, welding methods of dissimilar metal joints containing different metal types with different chemical compositions are examined and their fatigue behavior is evaluated. In dissimilar metal welds, the difference in chemical composition affects the weldability and mechanical properties of the joints. In this study, the factors affecting the fatigue strength of dissimilar welded joints are described. Since welded structures can be used in sensitive and risky places, welding quality and mechanical properties of the weld are extremely important. In the research, a detailed literature review was presented by evaluating the latest studies on the mechanical properties of dissimilar welded joints such as fatigue strength, tensile strength, hardness, and the latest developments in the welding of different metals were reviewed. This study, which deals with the latest developments in the joining of different metal alloy combinations, is expected to increase the interest of the researchers in the future. [ABSTRACT FROM AUTHOR]

Due to its high deterioration rate in the physiological environment, the clinical application of magnesium (Mg) in bone repair has been restricted. Graphene oxide (GO)-plasma electrolytic oxidation (PEO) coatings were effectively applied to Mg alloy to enhance corrosion resistance and biocompatibility. The structure, biocompatibility, electrochemical characteristics, and long-term corrosion performance of composite coatings were studied in the present paper. The incorporation of GO to the PEO layer decreased wettability of all samples, resulting in hydrophobic behavior. The amount of GO incorporated in the PEO layer had a minor effect on the film thickness, but the pore size of the PEO coating decreased as the amount of GO increased. PEO/GO coatings have better corrosion resistance than counterpart PEO coatings and bare samples, according to electrochemical tests. The results also demonstrated that corrosion resistance increases significantly as GO concentration increases, owing to the fact that GO nanosheets in the coating operate as a barrier to the electrolyte diffusion route, preventing aggressive electrolytes from accessing the substrate. Because of dramatically decreased Mg ion release and changes in pH value in the culture medium, all of the PEO and PEO/GO coatings could improve MG63 cell attachment and differentiation compared to the bare Mg alloy sample. The as-prepared PEO/GO coating on Mg alloy is attractive for medical applications due to its satisfactory corrosion resistance and biocompatibility. [ABSTRACT FROM AUTHOR]

Rainfall and change in reservoir water levels often lead to landslides, threatening the lives and properties of people in neighboring areas. Therefore, it is necessary to predict the landslide displacement. This paper proposes a novel coupling method of extreme gradient boosting (XGBoost) and Hodrick–Prescott (HP) filtering method to predict the landslide displacement. First, the HP filtering method is used to decompose the total landslide displacement into trend displacement and periodic displacement. The trend displacement is affected by the potential energy of landslide and the boundary constraints, and it is predicted by using the least square polynomial function. Rainfall and reservoir water level fluctuation are the main factors affecting the periodic displacement, and the extreme gradient boosting is used to predict the periodic displacement. The total displacement is obtained by adding the predicted trend displacement and the predicted periodic displacement. The Bazimen and Baishuihe landslides are taken as an example to verify the ability of this proposed model. Compared with other prediction methods (back propagation neural network (BP-NN), support vector machine regression (SVR)), this proposed method has the higher accuracy. Therefore, the proposed method can effectively predict the displacement of landslides. [ABSTRACT FROM AUTHOR]

Concrete, as one of the most widely used construction materials, has brittle behavior. Adding fiber to concrete affects the latter's ductility behavior as well as some of the mechanical properties. Hence, experimental research was conducted to study the effect of fiber type and content on the flexural performance of fiber-reinforced concrete. In this study, the concrete samples were made and evaluated in accordance with ASTM C1609, ASTM C1399 and ASTM C79 standards, with three different types of polymer fibers, including twisted, barchip and fibrillated, and three contents of 0.2, 0.4 and 0.6 volume percentages. The results showed that by adding fibers to concrete samples, the flexural strength and flexural toughness increased by 19.6–81.69% and 3.98–79.89%, respectively. Furthermore, adding the fibers to the concrete sample increased the postcracking flexural strength by 16.63–30.14%. The concrete containing twisted and broken fibers, despite their different fiber types, had similar flexural performance. [ABSTRACT FROM AUTHOR]

The additive manufacturing technology offers new and incredible opportunities in the design of components. Nowadays, structural integrity assessment of additively manufactured components is a formidable challenge that needs to be faced out in order to allow such components to be launched in the market. One of the major drawbacks of additive manufacturing is poor surface finish and loose geometrical tolerance of built parts. In this scenario, hybrid manufacturing, which takes advantage of both subtractive and additive manufacturing, can be considered as a solution worthy of investigation in view of possible applications to save costs and time in the component production. The present work is aimed at assessing microstructural properties of Co-Cr-Mo specimens manufactured by the hybrid subtractive/additive technology, when the additive part is built over the machined one. The results show an excellent metallurgical coupling at the interface between the two differently processed parts. [ABSTRACT FROM AUTHOR]

This study investigates the effects of tool traverse and rotational speeds in the friction stir back extrusion (FSBE) process on the microstructural and mechanical properties of brass wires produced. The microstructural properties were examined by microscopic tests and the mechanical properties of the wires by hardness and pressure tests. The material flow pattern, temperature history, and strain experienced by the materials were investigated using a numerical model to understand better the effects of tool traverse and rotational speed on the final properties of the wires. Numerical results showed that, on the one hand, the strain experienced by the material in the wire periphery is more than the center of the wire, and on the other hand, the material experiences a lower temperature in the wire periphery. The microstructural results showed that this more significant strain and lower temperature in the perimeter of the wires caused the grain size to be finer than the center of the wire. Moreover, a coarser microstructure is produced by a faster rotation speed or a slower traverse speed. Also, increasing the traverse speed or decreasing the rotational speed increased the hardness of wires produced, so that the sample made with a traverse and rotational speeds of 40 mm/min and 315 rpm had the highest hardness, and the wire made with a rotational speed of 800 rpm and a traverse speed of 25 mm/min had the lowest hardness. [ABSTRACT FROM AUTHOR]

In the present study, a dual composite coating consisting of an anodized layer as the inner layer and PCLF (polycaprolactone fumarate)/silicon- and magnesium-codoped fluorapatite (Si-Mg-FA) nanocomposite as the outer layer was fabricated on AZ31 Mg alloy. The thickness of the PCLF/(Si-Mg-FA) nanocomposite coating is 9.72 μm, with the Si-Mg-FA nanoparticles being well distributed in the PCLF matrix. Electrochemical measurements showed that AZ31 Mg alloy with the anodized PCLF/Si-Mg-FA coating has a low corrosion current density (5.137 × 10–6 A/cm2), providing a sufficient protection (Rp = 5888.72 Ω cm2) for Mg alloys. Immersion tests in a simulated body fluid showed that cauliflower-like/cloudy apatite forms on AZ31 Mg alloy with the anodized PCLF/Si-Mg-FA coating and governs good bioactivity. Osteosarcoma cells adhere well to the surface of the coating. Surface modification by the anodized PCLF/Si-Mg-FA coating can be a suitable method for controlling the corrosion degradation and increasing the bioactivity and cell attachment of AZ31 Mg alloy for implant applications. [ABSTRACT FROM AUTHOR]

The goal of the present study is to verify experimentally the Averaged Strain Energy Density (ASED) criterion for brittle fracture in blunt V-notches under pure compression. For this purpose, a set of experimental results recently published in the literature regarding the compressive fracture loads of the flattened V-notched semi-disk (FVSD) specimen made of PMMA are attempted to be theoretically predicted by means of the strain energy density averaged over a control volume which surrounds the notch round edge. Comparing the theoretical and experimental results reveals that the ASED criterion works suitably on brittle fracture of V-notches under pure compression. [ABSTRACT FROM AUTHOR]

On the basis of the general variational formulation of the problem of the deformation of two bodies connected by a thin layer, a system of differential equations of equilibrium of the double-cantilever beam is obtained, taking into account the shear deformations of the cantilevers, both in the interface section and in the free section, taking into account also the elastoplastic properties of the layer. In this work, we use the connection representation of the J-integral in terms of the energy product and the energy product of dissipation. For purely elastic deformation, on the basis of the analytical solution of the system, an expression is obtained for the stress state of an extremely thin layer connecting the cantilevers, which is dependent on the material properties of both the layer and the cantilevers. The obtained expression for the elastic energy flux is compared with the known ones. The energy product at the top of the layer is found, the value of which depends only on the material properties of the consoles. With the elastoplastic behavior of the layer, the energy product of dissipation was found, which turned out to be dependent on the yield stress of the adhesive. The energy product in this case is proportional to the layer thickness. For adhesives with pronounced plastic properties, taking into account the dissipative mechanism of energy release leads to fundamental differences in the J-integral in comparison with the elastic calculation. The dependences of the DCB sample compliance with subcritical growth of the plastic deformation region in the adhesive are plotted. [ABSTRACT FROM AUTHOR]

Magnesium and its alloys have great capability for degradation in the body in a natural way, so they are one of the main new candidates as biodegradable implant materials. Of course, one of the disadvantages of pure Mg is its rapid degradation in the physiological environment that prior to bone healing has a negative impact on its mechanical integrity. In the present paper, a semipowder metallurgy coupled with hot extrusion process was utilized to fabricate Mg-6Zn/xGO (0.2 and 0.4 wt %) biocomposite. According to the microstructural characterization, graphene oxide (GO) nanosheets had uniform distribution in the composite, and also partial and gradually wrapped α-Mg grains were observed inside the Mg matrix. Results showed that the hardness and compressive yield of the Mg-6Zn/xGO composite were notably higher in comparison to pure Mg. It was revealed that the mechanical properties were enhanced because of the mechanisms of crack bridging, crack deflection, and crack tip shielding. The H2 evolution throughout their immersion in simulated body fluid (SBF) was decreased remarkably because GO nanosheets were distributed uniformly in the Mg matrix. In addition, less corrosion current density and higher corrosion resistance of the extruded Mg-6Zn and Mg-6Zn/GO in comparison to pure Mg were shown by electrochemical tests. Since the rate of the degradation process was decreased, the extruded Mg-6Zn/GO biocomposite presented great cytocompatibility. The research results show that GO nanosheets are efficient reinforcement to fabricate the extruded Mg-6Zn/GO biocomposite, which leads to the improvement of mechanical, corrosion and biological properties. [ABSTRACT FROM AUTHOR]

Epoxy resins are one of the most commonly used class of materials in polymeric composite industry. One of their main weak points is their vulnerability to moist and hot environments. In this paper, the effect of hydrophilic Fe2O3 nanoparticles, hydrophobic graphene-oxide nanoplatelets (GONPs) and a hybrid of both was experimentally studied on the moisture absorption and mechanical properties degradation of the nanocomposites. Different weight percentages of nanofillers were used for fabricating the nanocomposite specimens. The neat and nanocomposite specimens were aged in hot deionized water. The gravimetric test results revealed that the Fe2O3 nanoparticles and GONPs caused 12.4 and 6.7% reductions in the ultimate moisture uptake of the nanocomposites, respectively. The addition of 1 wt % Fe2O3 nanoparticles reduced the moisture diffusion coefficient by 11.7% due to the increased polarity of epoxy, while 0.25 wt % GONPs increased it by 38.5% due to the increased free volume of epoxy. Moreover, the wet Fe2O3/epoxy nanocomposites experienced the maximum 28.8 and 52.9% higher strength and stiffness compared to the wet neat epoxy, respectively. GONP/epoxy nanocomposites showed the maximum 22.3 and 13.4% higher values of strength and stiffness compared to the wet neat epoxy. [ABSTRACT FROM AUTHOR]

In this paper, the influence of graphene-oxide nanoplatelets (GONPs) on the response of the glass laminate aluminum reinforced epoxy (GLARE) under high-velocity impact loading was investigated. Different weight percentages of nanofillers including 0.25, 0.50 and 1.00 wt % GONPs and a hybrid of 0.25 wt % GONPs and 0.25 wt % multiwalled carbon nanotubes (MWCNTs) were used for reinforcing GLAREs. Addition of 0.5 wt % GONPs reduced the residual impactor velocity by 33% and increased the energy absorption capability of GLARE by 22.9%. The SEM micrographs showed reinforced adhesion between the fibers and matrix and the optical microscope images showed improved cohesion in the matrix of the reinforced GLARE. This caused the secondary damage region in the composite layer to decrease considerably. However, GONPs imposed negative effect on the suppression of composite layer delamination and also interfacial strength between the composite and aluminum layers that provided more extensive plastic deformation of aluminum as an important energy absorption mechanism of GLAREs. Furthermore, the composite layers of the unreinforced and reinforced GLAREs were subjected to tensile test and the results showed improvements in the tensile stiffness, strength and toughness by 33.4, 45.0 and 25.6%, respectively, due to adding of 0.5 wt % GONPs to the matrix. [ABSTRACT FROM AUTHOR]

The study is aimed at experimental verification of the validity of the averaged strain energy density criterion in predicting the brittle fracture of U-notched components under combined tension/tear loading. The fracture experiments are carried out on U-notched rectangular polymethyl methacrylate samples using an improved loading fixture, capable of testing the cracked and notched samples under various combinations of tension and out-of-plane shear. The samples with three different notch tip radii are tested to evaluate the radius effect on their load-carrying capacity. Theoretical and experimental results show that the above criterion can provide satisfactory estimation of the fracture loads applied to notched specimens and is efficient enough in predicting the brittle fracture of U-notched PMMA members under combined tension/tear loading. [ABSTRACT FROM AUTHOR]

In this study, the thermal stress distribution surrounding a quasi-triangular hole within a symmetric composite laminate made of various composite materials was investigated. A composite laminate exposed to uniform heat flux was analyzed using the complex variable method as a thermo-elastic two-dimensional problem under a steady state condition. The analytical solution was achieved with the development of the Lekhnitskii's solution and using the classical laminated plate theory and a conformal mapping function. The influence of important parameters on thermal stress distribution surrounding a hole such as the hole orientation, bluntness and aspect ratio, the heat flux angle and the laminate stacking sequence and material was studied. The results were achieved for different stacking sequences of [45°/–45°]s and [0°/90°]s. The analytical solution in this study was well validated against the finite element results. [ABSTRACT FROM AUTHOR]

Fracture of the adhesive layer (AL) of finite thickness with elastoplastic properties in a layered composite is considered in this article. The expression of the J C -integral is obtained as the sum of values of the products of the layer thickness and the increments of the specific free energy and specific dissipation. Based on the variational formulation, a solution to the model problem of shear action on a thin elastoplastic layer is obtained. From the analysis of the solution obtained, it follows that in the case of a layer degenerating into a mathematical section, the main contribution to the representation of the J C -integral is made by the term responsible for the energy dissipation, and the energy product tends to zero. In this case, it is not pure dissipation that is considered, this is the product of specific dissipation and layer thickness. The expression of the J C -integral is obtained in terms of the quantities measured in a possible experiment. [ABSTRACT FROM AUTHOR]

This paper investigates whether the Weibull parameters of the new local approach model for cleavage fractures are affected by the geometric size of the specimen. Based on the fracture test data of A508-C steel, low temperature round notched bar tensile specimens of A508-C steel with two different notch sizes are numerically simulated by using finite element analysis software ABAQUS, and the stress distributions are obtained. The Weibull parameters of two notched bars are calibrated by linear regression method. The results show that the Weibull parameters of the specimens with different notch sizes are different. This suggests that the calibration parameters are dependent on the notch size. [ABSTRACT FROM AUTHOR]

The effects of friction coefficient, stress drop ratio, the ratio of residual strength to initial stress, and the dip angle of faults on the rupture velocity under hydrostatic pressure condition, as well as the stress distribution on the fault, are investigated using General Particle Dynamics code. The numerical results indicate three distinct regimes of rupture dynamics: (i) slow rupture, (ii) sub-Rayleigh rupture, and (iii) supershear rupture. This suggests that rupture-mode selection is coupled to friction coefficient, stress drop ratio, the ratio of residual strength to initial stress, and the dip angle of faults. Moreover, supershear rupture can occur under upper-crustal (< 250 MPa), lower-crustal (250 to 1000 MPa), and upper-mantle (1000 to 10000 MPa) conditions. Since rupture velocity is fastest under upper-crustal conditions, supershear rupture most easily occurs under these condition. [ABSTRACT FROM AUTHOR]

Additive manufacturing techniques are known for the unrivalled geometric freedom they offer to designers. It is one of the mainstays of "metal 3D-printing", compared to casting, which, in contrast, implies more restrictions because some shapes do not cool evenly or may need moulds or forms. Despite the possible presence of defects inside additive manufactured components, such as oxide films, pores or unmelted powder, they can be strongly reduced or controlled by process parameters optimization. That seems not true for a casting component, in which defects can vary a lot from zone to zone according to the solidification conditions. Porosity inducing process parameters in selective laser melted AlSi10Mg aluminium alloy are carefully analysed with the aim to find optimal conditions that guarantee the maximum material density and the best mechanical properties. Finally, a model is proposed that correlates the amount of pores with the alloy ultimate tensile strength. [ABSTRACT FROM AUTHOR]

A new hybrid discrete-continuum cellular automata approach is proposed to simulate the process of new phase/grain nucleation and growth. The method couples classical thermomechanics and the logics of cellular automata switching. Within the framework of the hybrid discrete-continuum cellular automata method, the space occupied by the simulated specimen is represented as a cellular automaton—a set of ordered active elements. Every element imitates an immovable region of space related to a part of material being characterized by the certain numerical parameters. The proposed approach enables calculating the magnitude of the local force moments and simulating dissipation of torsion energy leading to the formation of new defect structures. To illustrate the capacity of the proposed hybrid discrete-continuum cellular automata approach, the numerical simulations of thermally activated recrystallization of pure titanium near crack faces were conducted. The 3D cellular automaton simulated the microstructure evolution of the V-notched specimen region that imitated the crack tip vicinity at high homologous temperatures. Calculation of heat expansion with simultaneous thermal stresses accumulation and microrotation initiation was incorporated in the simulations permitting thereby to evaluate the local entropy and to monitor the evolution of crystal defects from initiation to storage. Perspectives of the proposed algorithms for simulations of the mechanical behavior of materials experiencing thermally induced twining or phase transformations are discussed. [ABSTRACT FROM AUTHOR]

The main goal of the present research is to check the suitability of the well-known brittle fracture criterion, namely the averaged strain energy density (ASED), in predicting mixed mode I/II brittle fracture of round V notches under negative mode I conditions. For this purpose, it is attempted for the first time to theoretically predict the fracture loads of numerous round-tip V-notched Brazilian disk (RV-BD) specimens made of PMMA and subjected to mixed mode I/II loading with negative mode I contributions that have been most recently reported in the open literature. It is revealed that ASED criterion is suitable for brittle fracture prediction not only under conventional mixed mode I/II loading conditions, but also under mixed mode I/II loading with negative mode I contributions. [ABSTRACT FROM AUTHOR]

I present a possible worlds semantics for a hyperintensional belief revision operator, which reduces the logical idealization of cognitive agents affecting similar operators in doxastic and epistemic logics, as well as in standard AGM belief revision theory. (Revised) belief states are not closed under classical logical consequence; revising by inconsistent information does not perforce lead to trivialization; and revision can be subject to 'framing effects': logically or necessarily equivalent contents can lead to different revisions. Such results are obtained without resorting to non-classical logics, or to non-normal or impossible worlds semantics. The framework combines, instead, a standard semantics for propositional S5 with a simple mereology of contents. [ABSTRACT FROM AUTHOR]

This paper presents an analytical approach associated with Laplace transforms and a sequential concept over time to obtain the increment of temperature in nanoscale beam with fractional order heat conduction clamped from both ends. The governing equations are written in the forms of differential equations of matrix-vector in the domain of the Laplace transforms and are then solved by the eigenvalue technique. The analytical solutions are obtained for the increment of temperature, displacement, lateral deflection, and stresses in the Laplace domain. Numerical simulations are provided for silicon-like nanoscale beam material, with graphical display of calculated results. The physical implications of distributions of physical variables considered in this article are discussed. [ABSTRACT FROM AUTHOR]

One of the most important challenges of storing fluids in thin walled pressure vessels under internal pressure is preventing crack propagation. At low temperatures, steel shows brittle crack propagation characteristic, which is highly dangerous. In this paper, a new numerical model is presented, in order to investigate the reinforcement of a cracked thin walled pressure vessel by composite patch. The extended finite element method (XFEM) technique is used to model brittle crack propagation through the thickness of a thin-walled pressure vessel utilizing the multi-scaling technique. Crack propagation in the thickness of a pressure vessel was studied utilizing the combination of XFEM approach in fracture mechanics and multi-scaling technique. Then, the critical energy, which is the maximum strain energy that the pressure vessel can absorb before the brittle crack starts to propagate, was calculated using the numerical techniques of XFEM. In order to increase the critical energy, cohesive elements and composite patches with different stacking sequence, which were extracted from previous experimental and analytical studies, were used, and the best stacking sequence was identified using the current XFEM code. Moreover, the optimization was carried out using the traditional optimization technique for reinforcing with composite patches, which was based on the optimum ratio of the increased critical energy to the thickness of the reinforcement. Results obtained show that, keeping constant the reinforcing thickness and changing the stacking angle, the maximum energy capacity is increased by 7-11%. Also, by increasing the thickness of the reinforcement, a significant growth in strain energy capacity (up to 40%) is observed. The Hashin damage criterion was used to ensure that none of the laminas' damage during the crack propagation is critical. [ABSTRACT FROM AUTHOR]

The paper presents a comprehensive investigation of fatigue cracking behaviors under various nonproportional multiaxial cycle loading paths based on the critical plane approach. The maximum normal and shear stress/strain fields are presented to analyze the crack orientation and early growth directions in polar diagrams. The experimental observed crack paths and directions were compared with maximum strain loci of each angle to determine multiaxial fatigue failure mode. The results show that crack orientation and growth paths appear in the maximum shear and normal strain plane, respectively. Likelihood cracking regions of various loading paths are predicted according the determined failure mode. Besides, nonproportionality factor is introduced to characterize the degree of multiaxiality on these loading paths. [ABSTRACT FROM AUTHOR]

In the present paper, we have constructed the equations for generalized thermoelasticity of a fiber-reinforced anisotropic hollow cylinder. The formulation is applied in the context of dualphase-lag model. An application of hollow cylinder is investigated for the outer surface is traction free and thermally isolated, while the inner surface is traction free and subjected to thermal shock. The problem is solved numerically using a finite element method. The results of displacement, temperature and radial and hoop stress are obtained and then presented graphically. Finally, the comparisons are made between the results predicted by the coupled theory, Lord and Shulman theory and dual-phase-lag model in presence and absence of reinforcement. [ABSTRACT FROM AUTHOR]

Numerous studies have shown that crack tip constraint has an important effect on the level of conservatism when crack extension is investigated in elastic-plastic fracture mechanics. Constraint effect has been explored extensively in the past but mainly for pure mode I problems. Very few researchers have dealt with the effects of crack tip constraint on mode II or mixed mode I/II fracture in metallic materials. In this paper, the evolution of mode II constraint parameter Q in terms of applied external load is determined numerically for a test specimen under pure mode II loading. The finite element method is utilized to model the specimen and to study the range of validity of mode II constraint parameter determined from a Q—T diagram. The parameter Q calculated from the finite element simulation (or from the full field solution) is compared with the values of Q determined from the Q—T diagram. For low levels of load, the results of full field solution are shown to be consistent well with the results obtained from the Q—T diagram. However, when the external load increases significantly, the results of Q—T diagram are no longer accurate and mode II constraint parameter Q should be calculated directly from finite element results. [ABSTRACT FROM AUTHOR]

This paper provides an energetic approach useful for the prediction of critical loads on U-notched components without an ideally linear elastic behaviour. The methodology has been applied to 100 fracture specimens of short glass fibre reinforced polyamide 6 (SGFR-PA6), combining four different fibre contents (5, 10, 30 and 50 wt %) and five different notch radii (0.00, 0.25, 0.50, 1.00 and 2.00 mm). The proposal combines the application of the strain energy density criterion with the use of the whole absorbed energy in the tensile test (elastic-plastic area under the stress-strain curve). With all of this, the fracture loads have been well estimated in this type of material. [ABSTRACT FROM AUTHOR]

The present paper investigates the employment of coarse meshes in evaluating the T-stress with the displacement method. Several finite element analyses have been carried out with different mesh refinements and accuracies. Mode I and mixed mode I/II loadings have been considered in finite element analyses. Under mode I loading, single and double edge notched geometries have been considered, while plate with central crack has been considerd for mixed mode loading condition. The analyses are compared with the results by the well-nown stress based approach, and showed that the displacement method permits the evaluation of the T-stress with the employment of coarse meshes. By the way, several precautions must be taken when dealing with coarse and very coarse meshes. [ABSTRACT FROM AUTHOR]

The values of mode II fracture toughness reported in the literature for several rocks are studied theoretically by using a modified criterion based on strain energy density averaged over a control volume around the crack tip. The modified criterion takes into account the effect of T-stress in addition to the singular terms of stresses/strains. The experimental results are related to mode II fracture tests performed on the semicircular bend and Brazilian disk specimens. There are good agreements between theoretical predictions using the generalized averaged strain energy density criterion and the experimental results. The theoretical results reveal that the value of mode II fracture toughness is affected by the size of control volume around the crack tip and also the magnitude and sign of T-stress. [ABSTRACT FROM AUTHOR]

The fracture of V-notches with end holes made of tungsten-copper functionally graded material under mode I has been studied in this paper. The averaged strain energy density over a well-defined control volume was employed to predict the fracture loads. A numerical approach was used to determine the outer boundary of the control volume. Mechanical properties such as elasticity modulus, Poisson's ratio, fracture toughness K , and ultimate tensile stress have been considered to obey the power law function through the specimen width. [ABSTRACT FROM AUTHOR]

Concrete, as one of the most widely used construction materials, has a brittle behavior. Adding fibers with different types and contents would affect the ductility behavior and mechanical properties of concrete. Hence, an experimental study was conducted to investigate effects of type and content of polymer fibers on mechanical properties of fiber-reinforced concrete such as flexural strength, compressive strength, indirect tensile strength, and elastic modulus. In the present research, the concrete samples were made and, then, evaluated, using three different types of polymer fibers, including twisted, barchip, and fibrillated, with the contents of 0.2, 0.4, and 0.6 volume percentages, respectively. The results showed that by adding fibers to the concrete samples, the flexural and tensile strength was increased by 19.6-81.69% and 0.84-34.29%, respectively; besides, the addition of the fibers to concrete reduced the compressive strength and elasticity modulus by 4.57-26.32% and 12.48-37.08%, respectively. The concrete containing twisted and barchip fibers, despite the different types of fibers, had similar flexural performance. [ABSTRACT FROM AUTHOR]

In this paper the minimum strain energy density criterion is modified to predict the values of mode II fracture toughness reported in the literature for several brittle and quasi-brittle materials. The experimental results are all related to mode II fracture tests performed on the semicircular bend specimen. The modified mode II fracture criterion takes into account the effect of T-stress (in addition to the singular terms of stresses/strains) when calculating the strain energy density factor at a very small critical distance from the crack tip. It is shown that the proposed criterion provides significantly better predictions for mode II fracture toughness compared with the classical minimum strain energy density criterion. [ABSTRACT FROM AUTHOR]

In this work, some recent mixed mode I/II fracture toughness results obtained from Perspex (or polymethylmethacrylate (PMMA)) with four simple cracked specimens subjected to the conventional three-point bend loading are reanalysed based on local energy concept. Although all the mentioned samples have been tested under the same and similar mode mixities, different fracture toughness envelopes were obtained for mixed mode I/II fracture of PMMA. The averaged strain energy density (SED) criterion has been applied in the past for different types of notched specimens (including U, V, O and keyhole notches). It is shown that the mixed mode tensile-in plane shear fracture toughness data obtained from the semicircular and triangular crack type specimens are successfully predicted for sharp cracked PMMA samples using the SED criterion. [ABSTRACT FROM AUTHOR]

The main goal of this research is to propose a failure criterion based on the linear elastic notch fracture mechanics (LENFM) for predicting tensile crack initiation from a blunt V-notch, encountering large plasticity at the notch vicinity. First, some most recently published experimental results on tensile failure of V-notched ductile aluminum plates are briefly described. Then, with the aim to avoid complex and time-consuming elastic-plastic analyses, the equivalent material concept (EMC) is employed together with a LENFM-based fracture criterion, namely the averaged strain energy density (ASED) criterion, for predicting the load-carrying capacity of the V-notched aluminum plates. A very good agreement is shown to exist between the experimental results and theoretical predictions of the EMC-ASED criterion. [ABSTRACT FROM AUTHOR]

The aim of the present study is to characterize the fracture behavior of the giant magnetostrictive Terfenol-D alloy, both experimentally and numerically. Three-point bending tests have been carried out on single-edge precracked specimens, and fracture loads have been measured at different loading rates, in the presence or absence of a magnetic field. In recent years, it has been shown that the strain energy density (SED), averaged in a finite control volume, can successfully predict brittle failures of cracked, U- and V-notched specimens made of several materials. By performing coupled-field finite element analyses, the effects of the magnetic field and he loading rate on Terfenol-D failures have been analyzed, and the capability of SED criterion to capture these effects has been discussed. A relationship between the SED control volume size and the loading rate has been proposed, and failures have been quite accurately predicted in terms of the averaged SED. [ABSTRACT FROM AUTHOR]

Crack initiation from blunt V-notch borders in ductile A16061-T6 plates is investigated experimentally and theoretically under mixed mode I/II loading. Experimental observations with naked eye during loading indicated large plastic deformations around the notch tip at the onset of crack initiation, demonstrating large-scale yielding failure regime for the aluminum plates. To theoretically predict the experimentally obtained value of the maximum load that each plate could sustain, i.e. the load-carrying capacity, without performing elastic-plastic failure analyses, the equivalent material concept (EMC) is combined with a well-known brittle fracture criterion, namely the averaged strain energy density (ASED) criterion. It is shown that the combined EMC-ASED criterion could successfully predict the experimental results for various V-notch angles and radii. [ABSTRACT FROM AUTHOR]

Mixed mode I/III behavior of Perspex (polymethyl methacrylate (PMMA)) is studied experimentally and theoretically in this research using a new and simple laboratory test configuration. The specimen is a circular disc containing a sharp V-notch along the diameter that is loaded by the conventional three-point bend fixture. The critical values of notch stress intensity factors ( K and K ) were obtained for the whole combinations of modes I and III simply by changing the notch inclination angle relative to the loading rollers. The value of notch fracture toughness under pure or dominantly tension loads was greater than its corresponding value under mode III or dominantly torsion loads. The experimental results were also predicted very well by employing the local strain energy density (SED) criterion. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) elastic stress distributions in the vicinity of the sharp corners of an inclined diamond hole in a plate are investigated. A detailed 3D finite element model under different loading conditions is analyzed to study the intensity of different fracture modes due to the thickness effect. The stress results are compared with those provided by a recent theory which reduces the 3D governing equations of elasticity to a differential equation system, which includes a biharmonic equation and a harmonic equation. They provide the solution of the corresponding in-plane and out-of-plane notch problem, respectively, and have to be concurrently satisfied. Comparing numerical results and theoretical stress distributions, a good agreement is found. [ABSTRACT FROM AUTHOR]

In this paper a comprehensive investigation is carried out with regard to the state of the stress and strain in the neighbourhood of notches in bodies subjected to an anti-plane state of shear stress, within the context of a strain limiting theory of elasticity. Taking advantage of a unified analytical framework, the strain-limiting theory of elasticity is used to determine the full stress and strain field close to a pointed or radiused notch with any notch opening angle. An extensive discussion is provided that highlights the main features of stress and strain distributions, and the implications of the new theory for fracture assessments. In particular, it is proved that the obtained stress and strain solution predicts finite strains at the notch tip and allows the intensity of the stress field to be written as a function of the elastic Notch Stress Intensity Factor $$K_{3}$$ , as in the case of conventional linearized elasticity theory. This makes the strain limiting elasticity an excellent vehicle for justifying theoretically a K based-approach to the fracture of brittle elastic solids, within the context of a self consistent theory, unlike the classical linearized theory that predicts singularities for the strain at crack tips. [ABSTRACT FROM AUTHOR]

Depending on boundary conditions, welding parameters and plate thickness, high residual tresses may arise near the weld toe of a welded joint. Compressive or tensile residual stresses significantly influence the fatigue strength of the joints in the high-cycle regime. If the weld toe is modelled as a sharp, zero-radius V-shaped notch, the residual stress fields can be expressed in terms of residual notch stress intensity factors (R-NSIFs) calculated in the elastic or elastic-plastic fields. The possibility to quantify the intensity of the residual singular stress field by means of the R-NSIFs allows the designer to estimate the influence of residual stresses on the fatigue life of welded joints. In this work, the influence of residual stresses on the fatigue resistance of Al-alloy butt-welded joints is estimated by using the local stain energy density approach. Values predicted by the proposed method show a good agreement with experimental data taken from literature. [ABSTRACT FROM AUTHOR]

The main goal of the present research is to analyze tensile fracture in Al 7075-T6 thin plates weakened by blunt V-notches. For this purpose, first, 27 fracture tests are carried out on rectangular plates containing a central rhombic hole with two blunt V-shaped corners horizontally located. The experimental observations indicated that a plastic region initiates from the notch tip and grows as the tensile load monotonically increases, and finally, fracture happens suddenly with a significant opening of the notch tip. By showing significant plastic deformations around the notch tip and also inclined fracture planes, the specimens after fracture confirm well the ductile rupture in V-notched Al 7075-T6 plates. As the main experimental result, the load-carrying capacity of the notched plates corresponding to the onset of crack initiation from the notch tip is recorded. To theoretically predict the experimental results, the equivalent material concept is utilized together with the well-known brittle fracture criterion, namely the averaged strain energy density criterion. Without requiring elastic-plastic finite element analysis, it is shown that the combination of the averaged strain energy density and equivalent material concept is successful in predicting the load-carrying capacity of the V-notched Al 7075-T6 plates that fail by moderate-scale yielding regime. [ABSTRACT FROM AUTHOR]

The aim of the present research is twofold. Firstly, to provide a new set of experimental results regarding tensile brittle fracture in key-hole notches and secondly, to check the suitability of the local strain energy density (SED) criterion in predicting the test results. For this purpose, 21 fracture tests were conducted at room temperature on a new version of the well-known Brazilian disk specimen containing a central dumbbell-shaped slit with two key-ends (Key-BD specimen) made of PMMA. The experimentally obtained fracture loads were theoretically predicted for different notch radii by means of the local SED averaged over a specified control volume which embraces the notch edge. It was shown that the experimental results could be well predicted by means of the SED criterion. [ABSTRACT FROM AUTHOR]

3D crack problems are area where a further intensive research is required. 3D solutions can shed more light on fracture and fatigue phenomena, provide a more accurate evaluation of strength and fatigue life or justify the application of the classical solutions of plane theories of elasticity. These, in fact, are approximate theories even when the governing equations of these theories are solved exactly. The current paper aims to provide a brief summary of the latest investigations of 3D effects associated with crack geometries and brittle fracture. In particular, we present an overview of the coupled fracture modes and 3D vertex singularities, which are currently largely ignored in experimental and theoretical studies. We also describe a recently developed experimental method for the evaluation of the stress intensity factors. This review is concerned with the situation generally described in the literature as small scale plasticity. Large plastic deformations and other non-linear effects are beyond the scope of this article. [ABSTRACT FROM AUTHOR]

While a large bulk of experimental results from cracked specimens of polycrystalline graphite under pure modes of loading, in particular under mode I loading, can be found in the literature, only a very limited number of tests have been carried out on notches. At the best of the author knowledge dealing with the specific case of V-notches under mixed mode loading (tension + torsion) no results can be found in the literature. With the aim to fill this lack, the problem of mixed mode (I + III) brittle fracture of polycrystalline graphite is investigated systematically here for the first time. The present study considers cylindrical specimens weakened by circumferential notches characterized by different acuities. A new complete set of experimental data is provided considering different geometrical configurations by varying the notch opening angle and the notch tip radius. The multiaxial static tests have been performed considering different values of the mode mixity ratio (i.e. the ratio between the nominal stress due to tension and that due to torsion loading). A criterion based on the local strain energy density previously applied by the same authors only to pure modes of loading is extended here to the case of tension and torsion loadings applied in combination. The proposed criterion allows a sound assessment of the fracture loads. [ABSTRACT FROM AUTHOR]