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The current work investigates the auxetic tensile deformation behavior of the inversehoneycomb structure with 5 × 5 cells made of biodegradable poly(butylene adipate-coterephthalate) (PBAT). Fused deposition modeling, an additive manufacturing method, produced such specimens. Residual stress (RS) and warpage, more or less, always exist in such specimens due to layer-by-layer fabrication, i.e., repeated heating and cooling. The RS influences the auxetic deformation behavior, but its measurement is challenging due to the very fine structure. Instead, the finite-element(FE)-based process simulation realized by an ABAQUS plug-in numerically predicts the RS and warpage. The predicted warpage shows a negligible slight deviation compared to the design topology. This process simulation also delivers the temperature evolution of a small volume material, revealing the local cyclic heating and cooling. The achieved RS serves as the initial condition for the FE model used to investigate the auxetic tensile behavior. With the outcomes from FE calculation without considering RS at hand, the effect of the RS on the deformation behavior is discussed for the global force-displacement curve, the structural Poisson’s ratio evolution, the deformed structural status, the stress distribution, and evolution, where the first three and the warpage are also compared with experimental results. Furthermore, the FE simulation can easily provide the global stress-strain flow curve with the total stress calculated from the elemental ones.

The behavior of Auxetic structures is highly dependent on the geometric parameters of the unit cell. To achieve the desired behavior, it is necessary to perform a parametric study on the unit cell. A conventional parametric study (which includes modeling and analysis with different parameters) is very time consuming and error prone. The Auxetica plugin was produced to solve this problem. Auxetica is an Abaqus plugin developed to estimate Auxetic structures' performance. In this paper, the features and instructions of this plugin are presented. This tool can automatically generate and analyze re-entrant, chiral, (Tri-chiral, Tetra-chiral, Hexa-chiral) and anti-chiral (Tri-anti-chiral and Tetra-anti-chiral) in planar and cylindrical geometries. The plugin tasks can be categorized as follows: the first task is to generate a model based on parametric input. The second task is an automatic analysis and extraction of the target output. The third task is to generate models that are ready for 3D printing and testing. To validate the plugin, an experimental setup is prepared and samples which are made by 3D printing are tested. The simulation result is validated with experimental data before any parametric study would be carried out. Moreover, to understand the plugin functionality better, a parametric study has been done. This plugin helps to perform the parametric study by the user in the shortest time and with the most accuracy with the desired inputs.

Auxetic materials are a family of rationally designed artificial structures that have unique effective properties gained from the distribution of the internal architecture rather than of the chemical composition. This article used the modified solid isotropic material with penalization method for topology optimization of 2D re-entrant auxetic structures with different Poisson’s ratios and volume fractions. The obtained structures were verified by the finite-element method (FEM) using the commercial FEM software and also validated by the experimental approach. A good agreement was achieved between the experimental and numerical results. Then, the cell geometry effect on Poisson’s ratio under large tension was investigated. Our study revealed that the location and stiffness of rotation joints are two new parameters affecting Poisson’s ratio value. Poisson’s ratio will decrease by decreasing the stiffness of rotation joints and positioning the rotation joints closer to the middle of the structure. So, from the investigation of the optimizer performance, it was achieved that re-entrant auxetic structures with different Poisson’s ratios could be easily designed by changing just the location of rotation joints. This will be applicable in many applications like sensor field.

The effect of hydrogen on the microdamage evolution of 1200M advanced high-strength steel was evaluated by the combination of experimental and numerical approaches. In the experimental section, the tensile test was performed under different testing conditions, i.e., vacuum, in-situ hydrogen plasma charging (IHPC), ex-situ electrochemical hydrogen charging (EEHC), and ex-situ + in-situ hydrogen charging (EIHC) conditions. The post-mortem analysis was conducted on the fracture surface of specimens to illuminate the impact of hydrogen on the microstructure and mechanical properties. The results showed that under all of hydrogen charging conditions, the yield stress and ultimate tensile strength were slightly sensitive to hydrogen, while tensile elongation was profoundly affected. While only ductile dimple features were observed on the fracture surfaces in vacuum condition, the results indicated a simultaneous action of the hydrogen-enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of hydrogen under the IHPC and EEHC conditions. At the EIHC condition, the HEDE model was the dominant failure mechanism, which was manifested by the HE-induced large crack. In the numerical approach, a finite-element analysis was developed to include the Gorson–Tvergaard–Needleman (GTN) damage model in Abaqus™ software. To numerically describe the damage mechanism, the GTN damage model was utilized in the 3D finite-element model. After calibration of damage parameters, the predicted damage mechanisms for two testing conditions, i.e., vacuum and EIHC, were compared with experimental results.

Implant failure is due to stress shielding and interface micromotion. The application of porous structures in the femoral implant has a great effect on reducing stress shielding and improving the stability of the bone-implant interface. The performance of femoral stems with triply periodic minimal surface (TPMS) structures, IWP, and Gyroid structures was evaluated using finite element analysis. We studied the stress shielding phenomenon of the porous femoral stem based on the ability of stress transfer to the femur. The micromotion at the bone-implant interface was explored for different porous femoral stems. The effect of gradient structure design was investigated in the axial direction of the stem. These gradient designs involved a stem with an increasing volume fraction in the axial direction (IAGS) and a decreasing volume fraction along the stem (DAGS). The results showed that the axial stiffness of the stem has a direct effect on stress shielding and an inverse relation to bone-implant micromotion. The finite element analysis results inferred that bone resorption is higher in the stems with IWP structure than in Gyroid at the same volume fraction. Axially graded stems transfer higher stress to the femur than homogenous porous stems. DAGS design of IWP and Gyroid and IAGS Gyroid increased the stress on the proximal-medial of the femur. Homogeneous porous stems with high porosity (80% porosity for IWP and 70% porosity for Gyroid) and DAGS design exhibited low stress shielding and controlled bone-implant interface micromotion within an acceptable range for bone ingrowth.

Metal additive manufacturing (AM) has led to an evolution in the design and fabrication of hard tissue substitutes, enabling personalized implants to address each patient's specific needs. In addition, internal pore architectures integrated within additively manufactured scaffolds, have provided an opportunity to further develop and engineer functional implants for better tissue integration, and long-term durability. In this review, the latest advances in different aspects of the design and manufacturing of additively manufactured metallic biomaterials are highlighted. After introducing metal AM processes, biocompatible metals adapted for integration with AM machines are presented. Then, we elaborate on the tools and approaches undertaken for the design of porous scaffold with engineered internal architecture including, topology optimization techniques, as well as unit cell patterns based on lattice networks, and triply periodic minimal surface. Here, the new possibilities brought by the functionally gradient porous structures to meet the conflicting scaffold design requirements are thoroughly discussed. Subsequently, the design constraints and physical characteristics of the additively manufactured constructs are reviewed in terms of input parameters such as design features and AM processing parameters. We assess the proposed applications of additively manufactured implants for regeneration of different tissue types and the efforts made towards their clinical translation. Finally, we conclude the review with the emerging directions and perspectives for further development of AM in the medical industry.

Fall drop impact test for closed-cell aluminum foams were conducted experimentally and numerically. Deformation mechanisms at the cell level were discussed. The deformation mechanisms of cells were investigated and a novel FE model was proposed. Our model is combination of cellular part in the middle and solid part with the mechanical property of the same foam to adopt boundary condition correctly in order to reduce run time.

Foam filled tubes (FFT) are novel structures with high energy absorption, enhanced strength to weight ratio, and tailoring capability. In the present paper, we have analyzed quasi-static uniaxial compression and low-velocity impact behavior of FFT with closed-cell metallic foam cores and functionally graded densities both experimentally and numerically. Alporas foams were manufactured using liquid state method with TiH2 blowing agent. We prepared Specimens with graded composition and densities by stacking of several layers of pure aluminum and A356 alloy Alporas foams with cubic geometry. We conducted several standard uniaxial compression experiments to determine the non-linear mechanical properties and hardening. Square aluminum tubes are manipulated to enhance the performance and tailoring specification of the structure. We generated microstructural models using a hybrid 3D Voronoi diagram and CT-scan images to predict mechanical behavior numerically. Computed tomography is used to determine the inner cells morphological characterization. Also, the modified Kelvin cell with a beam element in edge regions is manipulated to enhance accuracy. Comparing the quasi-static experiment and FEA results show good accordance, and hence, we achieved the calibrated model. Finally, we used the numerical model in FFT tailoring and mechanical properties design.

Erosion of components working in particulate environment is a serious problem that causes premature failure. In this study, we want to identify different areas caused by particle impact erosion and also express a permanent impression using experimental method. Our study was performed on the real turbine blade worked in the industry. This paper investigated the effect of particle velocity and particle diameter on erosion rate of a smooth surface using FE method. Criterion of erosion rate calculation is sum of the all elements with strain of more than 0.2%. Particle velocity and particle diameter were considered in the range of 100–500 m/s and 1–5 mm, respectively.

In the recent decade, dual-phase steel has been used extensively in the industry due to its high strength and formability. In this paper, deformation pattern and mechanical behavior of DP steel are predicted using the 2D and 3D representative volume element (RVE) and finite elements method. Also, the obtained results were compared with the experimental SEM images. The experiments are performed in three stages to obtain the stress–strain curve and failure pattern in the specimens with the different state of stress distribution at the test sections. In the 3D state of stress, the state of applied stress to the RVE is obtained from macro-modeling of the test specimens and this model was analyzed using the finite element method. Furthermore, the effects of volume fraction and mesh size in 3D simulation on the stress–strain behavior are investigated. Metallography and SEM images are also used to access the failure mechanism at the microscale. It is shown that the martensite particles remain almost in their original form and their deformations are very small for the specimens with the thickness-to-width ratio of 0.8 (3D state of stress). This phenomenon is completely different from those obtained for smaller thickness-to-width ratio that the martensite particles were pulled and its length was increased. On the other hand, SEM images show that voids are located in the phase boundaries. According to the experimental and numerical results, although the main factor in the formation and growth of 2D voids is shear stress, in the 3D state of stress, the voids grow in spherical form due to the existence of large hydrostatic stresses.

Aluminum foam sandwich (AFS) structures are suitable for impact protection in lightweight structural components due to their specific energy absorption capability under compression. However, tailoring the deformation patterns of the foam cells is a difficult task due to the randomness of their internal architecture. The objective of this study is to analyze the effect of embedding aluminum pins into an AFS panel (Z-pinning) to better control its deformation pattern and improve its energy absorption capability. This study considers a closed-cell AFS panel and analyzes the effect of multi-pin layout parallel to the direction of the uniaxial compressive loading . The results of the experimental tests on the reference (without Z-pinning) AFS are utilized to develop numerical models for the reference and Z-pinned AFS structures. Physical experiments and numerical simulations are carried out to demonstrate the advantages of Z-pinning with aluminum pins. The results exhibit a significant increase in elastic modulus , plateau stress and energy absorption capability of the Z-pinned samples. Also, the effect of the pin size and Z-pinning layout on the mechanical performance of the Z-pinned AFS is also investigated using numerical simulations.

This paper studies the effect of different factors on high cycle fatigue failure of additive manufactured lattice structure by means of numerical simulation and compare the results with experimental data in the literature. Finite element method in conjunction with failure event-based algorithm is used to simulate high cycle fatigue. The proposed algorithm is efficient and accurate for our purpose. It is shown that relative density, the fatigue strength of the bulk material and cell geometry determined the coefficient of power law function while the solid distribution and bulk material fatigue properties affect the exponent. A power law expression is proposed to predict the fatigue strength of the cellular material. The effect of different parameters on constants of the equation is discussed in detail. The results of this study render the need for performing a vast amount of experiment to determine fatigue of properties of cellular materials.

Laser additive manufacturing has led to a paradigm shift in the design of next-generation customized porous implants aiming to integrate better with the surrounding bone. However, conflicting design criteria have limited the development of fully functional porous implants; increasing porosity improves body fluid/cell-laden prepolymer permeability at the expense of compromising mechanical stability. Here, functionally gradient porosity implants and scaffolds designed based on interconnected triply periodic minimal surfaces (TPMS) are demonstrated. High local porosity is defined at the implant/tissue interface aiming to improve the biological response. Gradually decreasing porosity from the surface to the center of the porous constructs provides mechanical strength in selective laser melted Ti-6Al-4V implants. The effect of unit cell size is studied to discover the printability limit where the specific surface area is maximized. Furthermore, mechanical studies on the unit cell topology effects suggest that the bending-dominated architectures can provide significantly enhanced strength and deformability, compared to stretching-dominated architectures. A finite element (FE) model developed also showed great predictability (within ∼13%) of the mechanical responses of implants to physical activities. Finally, in vitro biocompatibility studies were conducted for two-dimensional (2D) and three-dimensional (3D) cases. The results of the 2D in conjunction with surface roughness show favored physical cell attachment on the implant surface. Also, the results of the 3D biocompatibility study for the scaffolds incorporated with a cell-laden gelatin methacryloyl (GelMA) hydrogel show excellent viability. The design procedure proposed here provides new insights into the development of porous hip implants with simultaneous high mechanical and biological responses.

Strain sensing in applications such as soft robotic, human motion detection, health and sports monitoring, mass measurement, human-machine interfaces has attracted increasing attention. In the present paper, a piezoresistive composite strain sensor based on chopped carbon fiber (CCF) as a conductive element and silicone rubber as a stretchable polymeric matrix was introduced. The results of the electromechanical evaluation under cyclic loading suggest high sensitivity (maximum gauge factor of 50) within the strain amplitudes of up to 25 %. The nonlinear electromechanical behavior of the CCF/silicone strain sensors revealed a positive-to-negative piezoresistivity due to the deformation mechanisms including axial deformation, Poisson’s effect, and viscoelastic characteristics. The sensors were employed to monitor human joint motion detection at the wrist, knee, as well as the elbow. The results showed high reversibility and strong sensing performance in action. The results showed that the fabricated sensors could be integrated with human textiles to record the motion data as the signals were observed to be well stable and highly sensitive to both small and large deformations induced by human motion.

In this study, some new 2D auxetic metamaterials were investigated and called octagonal auxetic metamaterials. The structures were examined by numerical and experimental approaches and 3D printing additive manufacturing technique was employed to fabricate the structures from thermoplastic polyurethane elastomer (TPU) which is considered as a hyperelastic material. Auxetic behavior was caused by adding small triangles and squares to the vertices of the octagonal structure and applying high compressive strain. Although the octagonal structure showed negative Poisson's ratio at high compressive strain, the results suggested that adding triangles to the vertices of the octagonal structure as well as increasing the triangle edge length led to higher negative Poisson's ratio. In contrast, with small squares adding to the vertices of the octagonal structure, Poisson's ratio became slightly more negative. In addition, by increasing the square edge length, Poisson's ratio measured near zero or even positive values. Moreover, a parametric study was carried out by Python 3.6.5 programming language to find the best triangle and square edge length which caused the most auxeticity.

s Co-continuous multimaterial composites are novel types of multifunctional structures. This study focuses on numerical and experimental investigation of the mechanical behavior of 3D periodic single-material cellular D-structure and the corresponding co-continuous composite. Different volume fractions of desired geometry were fabricated by multimaterial fused deposition modeling (FDM) technology and compressive mechanical properties of the samples were obtained by mechanical tests. It was observed that embedding a hyperelastic material to the cellular structure dramatically hindered the shearing bands in localized regions to develop, thereby made it feasible for composite material to undergo larger deformations without failure. Furthermore, it was demonstrated that the soft phase in multimaterial composite induces a homogeneous deformation to cellular structure, which enhances the load-bearing capacity and flexibility of the whole composite. In this paper, it was shown that the co-continuous multimaterial composite provides a well-balanced approach between desired flexibility and load-bearing which is referred to as compliancy. A strain recovery between 82 and 93% was also measured when unloading for multimaterial composite. These integrated properties could be valuable to various engineering applications such as synthetic limbs, soft robotics, and wearable structures as shoes and splints.

Dual phase (DP) steels, which have an intricate microstructure, consist of ferrite and martensite phases and because of interaction between the ferrite and martensite phases, those have complex behaviors. In this study, the flow curves of two heat-treated DP steels, DP800 and DP980, were compared with those of the 2D and 3D micromechanical models based on actual microstructure under symmetric and periodic boundary conditions. The effects of martensite phase distributions on the flow curves of 2D and 3D micromechanical models were investigated. Moreover, two different microstructures of DP980 with two different distributions of martensite phases were compared together to investigate the effect of martensite phase distribution in 2D and 3D micromechanical models on the stress-strain curve of DP980. Also, an in-situ tensile setup test was employed in order to investigate the initiation of localized strain patterns in the ferrite phase. The stress-strain curve, localization patterns and initiation of slip bands obtained from 2D and 3D micromechanical models were compared with the experimental results. The numerical results revealed that the stress-strain curves obtained from 3D models in comparison with 2D models are in closer agreement with experimental data.

Taking inspiration from nature, triply periodic minimal surfaces (TPMS) are tailored as a promising tool for designing internal pore architecture of porous biomaterials. In the next generation of scaffolds, meeting the conflicting biological and mechanical requirements is achieved by locally modulating biomechanical properties through a graded pore architecture design. To this, structure-property relationships have to be known for uniform scaffolds. In this study, numerical procedures were performed for a library of 240 TPMS-based unit cells (comprised of 10 volume fractions of 24 selected architectures) to explore the role of pore characteristics in determining normalized values stiffness, strength, and permeability. The associated design maps were developed based on which highly porous architectures with extreme properties were selected for experimental evaluations. Calcium sulfate scaffolds were designed based on the critical designs and 3D-printed (using a powder-based technique) in different cell sizes and size effects were addressed. The scaffolds were subjected to mechanical compression tests and the results were correlated with the computational data. Coupled experimental and numerical results suggest a great potential for TPMS-based architectures to be served in design and manufacturing of graded porosity/architecture scaffolds. Keywords: Scaffold, Triply periodic minimal surfaces, Mechanical properties, Deformation mechanism, Permeability, Additive manufacturing

Modulating deformation mechanism through manipulating morphological parameters of scaffold internal pore architecture provides potential to tailor the overall mechanical properties under physiological loadings. Whereas cells sense local strains, cell differentiation is also impressed by the elastic deformations. In this paper, structure-property relations were developed for Ti6–Al–4V scaffolds designed based on triply periodic minimal surfaces. 10 mm cubic scaffolds composed of 5×5×5 unit cells formed of F-RD (bending dominated) and I-WP (stretching dominated) architectures were additively manufactured at different volume fractions and subjected to compressive tests. The first stages of deformation for stretching dominated structure, was accompanied by bilateral layer-by-layer failure of unit cells owing to the buckling of micro-struts, while for bending dominated structure, namely F-RD, global shearing bands appeared since the shearing failure of struts in the internal architecture. Promoted mechanical properties were found for stretching dominated structure since the global orientation of struts were parallel to loading direction while inclination of struts diminished specific properties for bending dominated structure. Moreover, elastic–plastic deformation was computationally studied by applying Johnson-Cook damage model to the voxel-based models in FE analysis. Scaling analysis was performed for mechanical properties with respect to the relative density thereby failure mechanism was correlated to the constants of power law describing mechanical properties.

Micromechanical analyses of various materials under high cycle fatigue (HCF) loading have been investigated previously. Experimental findings have shown that failure due to HCF occurred with different pattern comparing to the other loading conditions. The current work tries to carry out both experiments and simulations at micro scale. In this research, scanning electron microscopy (SEM) and metallography images of the specimens are taken to investigate the failure and deformation patterns in dual phase (DP) steel under high cycle fatigue loading. Failure mechanisms of DP steels are also predicted using a real representative volume element (RVE) and microstructural finite element (FE) modeling. The linear damage accumulation rule (Miner's damage rule) is used to determine the material degradation due to fatigue loading. The cyclic loading is implemented in the FE model of the microstructure by developing ANSYS parametric design language (APDL) code to obtain the damage, failure pattern and fatigue life of the RVE. It is also shown that the finite element modeling of the real RVE considering both plasticity and fatigue damage leads to acceptable compatibility between the obtained cracking patterns from SEM images (experiments) and finite element predictions.

Coronary stents are medical/mechanical micro devices which are used to open the arteries occluded by the build-up over time of fat, cholesterol, or other substances. A wide range of studies should be conducted on coronary stents since they play an important role in the health of patients who suffer from heart diseases. However, due to micro scale of these tools, and also their gripping and loading complexity during a test, it is very difficult to conduct experimental studies to understand their behavior. Moreover, because of their micro dimensions and subsequently, existence of only a few grains along their thickness, J2 flow theory is not appropriate to be implemented in order to define the mechanical behavior of such devices. Therefore, in this paper, 3D crystal plasticity finite element method (3D-CP-FEM) is used to understand the behavior of these devices. To achieve this goal and to find the hardening constants of strut, some simulations were designed and compared with an experimental study. Also, the effect of grain size in terms of w/d and l/d was investigated on the failure strain of struts under uniaxial tensile test. “w” and “l” are the width and length of the strut, respectively, and “d” is the average grain size. The results showed that failure strain increases within creasing w/d and decreasing l/d. Parameter waviness was used to measure the qualification of stent struts in bending and unbending simulations. Results revealed that the edges of strut are the critical areas and have more potential to failure. Additionally, it was found that with the increase in the w/d ratio, waviness decreases and the struts become homogeneous in behavior.

Since the advent of additive manufacturing techniques, triply periodic minimal surfaces have emerged as a novel tool for designing porous scaffolds. Whereas scaffolds are expected to provide multifunctional performance, spatially changing pore patterns have been a promising approach to integrate mechanical characteristics of different architectures into a unique scaffold. Smooth morphological variations are also frequently seen in nature particularly in bone and cartilage structures and can be inspiring for designing of artificial tissues. In this study, we carried out experimental and numerical procedures to uncover the mechanical properties and deformation mechanisms of linearly graded porosity scaffolds for two different mathematically defined pore structures. Among TPMS-based scaffolds, P and D surfaces were subjected to gradient modeling to explore the mechanical responses for stretching and bending dominated deformations, respectively. Moreover, the results were compared to their corresponding uniform porosity structures. Mechanical properties were found to be by far greater for the stretching dominated structure (P-Surface). For bending dominated architecture (D-Surface), although there was no global fracture for uniform structures, graded structure showed a brittle fracture at 0.08 strain. A layer by layer deformation mechanism for stretching dominated structure was observed. For bending dominated scaffolds, deformation was accompanied by development of 45° shearing bands. Finite element simulations were also performed and the results showed a good agreement with the experimental observations.

In this paper, the effects of cell geometry and relative density on the high-cycle fatigue behavior of Titanium scaffolds produced by selective laser melting and electron beam melting techniques were numerically investigated by finite element analysis. The regular titanium lattice samples with three different unit cell geometries, namely, diamond, rhombic dodecahedron and truncated cuboctahedron, and the relative density range of 0.1–0.3 were analyzed under uniaxial cyclic compressive loading. A failure event based algorithm was employed to simulate fatigue failure in the cellular material. Stress-life approach was used to model fatigue failure of both bulk (struts) and cellular material. The predicted fatigue life and the damage pattern of all three structures were found to be in good agreement with the experimental fatigue investigations published in the literature. The results also showed that the relationship between fatigue strength and cycles to failure obeyed the power law. The coefficient of power function was shown to depend on relative density, geometry and fatigue properties of the bulk material while the exponent was only dependent on the fatigue behavior of the bulk material. The results also indicated the failure surface at an angle of 45° to the loading direction.

In this paper, the modified SIMP topology optimization (TO) method was used, to introduce diverse auxetic unit cells with different volume fractions, composing of the symmetric, chiral and re-entrant unit cells. The output results suggested that the geometry of the 2D auxetic structures were extremely dependent on the values of SIMP method parameters, including initial designs and volume fractions. The brilliant modes of deformation in the auxetic structures, whose unit cells are symmetric, are based on either buckling or bending. To validate the TO results, four structures containing symmetric unit cells were chosen, called structure 1, 2, 3 and 4. The auxetic structures were produced by using 3D printing, with TPU as a hyperelastic material as well. Under Compression, the dominating mode of deformation in structures 1 and 2 is based on bending, caused by the movement of the oblique struts between the unit cells. There is also a linear relationship between the vertical and horizontal displacements in structure 1, the structure with 50 % volume fraction and -0.55 Poisson’s ratio value. However, the deformation mechanisms in structures 3 and 4 are based on buckling, called shearing deformation, which is the result of the buckling of the vertical struts between the unit cells.

In this study, a micromechanical finite element model is proposed based on experimental data and the rule of the mixture (RoM) in order to predict the tensile behavior of mechanical properties of heat-treated dual-phase medical-grade titanium (Ti–6Al–4V). Tensile tests, micro-hardness measurements, and RoM were used to obtain flow curves for the α and β phases. Scanning electron microscopy (SEM) imaging was used to determine phase fractions and to create representative volume elements (RVEs). Furthermore, the Gurson-Tvergaard-Needleman (GTN) damage model was calibrated using the Taguchi design of experiment (DOE) method in order to predict damage in the microstructure and the results were compared to fracture surface obtained using fractography in order to investigate failure mechanisms. The final micromechanical model could accurately predict stress-strain curves and showed that void formation and coalescence is the primary mechanism of failure. Finally, analyses of the surfaces showed that a fully ductile fracture occurs at the failure point, which agrees with the results of the damage model. The results suggest that the proposed model can predict the failure of heat-treated Ti–6Al–4V bio-alloys.

In this study, the mechanical behavior of two cold rolled commercial dual phase steels (DP) were analyzed on micro and macro scales. First, the anisotropic behavior of these steels were investigated by standard tensile tests in three directions. The results showed that the anisotropy behavior of the fracture strain of DP980 is more pronounced than of DP600. Then, in order to assess the influence on the stress state on the mechanical behavior, four specimens with different stress states were analyzed by ARAMIS approach which is based on digital image correlation (DIC). The ARAMIS results were compared with 3D numerical simulations using the Abaqus/Explicit solver. In this part, the effect of stress state on flow curve and strain distribution in the specimens (i.e. tensile, notched-tensile, shear and bulge specimens) were investigated. To predict the fracture behavior of DP600 and DP980 steels under various loading conditions, the Modified Mohr-Coulomb (MMC) damage model was utilized. A VUMAT subroutine was developed to include a MMC damage model in the 3D models, and good agreement between the numerical and experimental results was observed. Finally, the microstructure failure mechanisms at three different stages (i.e. strain localization, micro-crack initiation and micro-crack coalescence) during uniaxial tensile loading were investigated inside the microstructure of DP600 and DP980 steels using an interrupted in-situ setup. In the results three different damage localizations were observed in both materials, and strain localization in the center of large ferrite phases and at the boundary of ferrite and martensite phases were dominant in DP600 and DP980, respectively. Two different micro-crack initiation mechanisms were observed that were similar in both materials.

An auxetic structure as a substrate material in sensor applications improves sensitivity performance due to lateral expansion under tensile loading. The presented stretchable, highly sensitive at-low-strain piezoresistive sensor was manufactured by mixing the silicone rubber and chopped carbon fibers in an auxetic re-entrant structure form. Auxetic re-entrant die was printed by using a 3D printing technique. The main feature of this sensor is the high sensitivity for strains lower than 6%, in which previous sensors could not recognize this range of strain well. In order to justify the excellent performance of the sensor, the deformation modes of the auxetic re-entrant structures were investigated and also connected to piezoresistive sensitivity. The shifting strain is defined as strain value, where the Poisson’s ratio of structure shifts from negative to positive Poisson’s ratio. Our study revealed that auxetic sensors have excellent sensitivity performance until the shifting strain due to having negative Poisson’s ratio, and after that, their sensitivity performance is going to be weak due to having positive Poisson’s ratio. In the present work, silicone rubber as the substrate material was used. This is a very soft material and made it possible to have low shifting strain resulting in perfect sensitivity performance for low-strain applications. The presented sensor has applications in many fields which are in low-strain conditions such as measuring the Vocal Cord Dysfunction (VCD), wrist pulse, or even earth vibration.

In this study, 2D triangular anti-trichiral structures and auxetic stents, under compression, were introduced. The cores of the anti-trichiral structures were the equilateral triangles. The deformation mechanisms in 2D structures were based on the rotation of the triangles and bending of the ligaments. A parametric study was carried out to investigate the dependence of the Poisson's ratio to the triangle edge lengths. The most auxeticity, with the values of υ y z = −0.55 and υ z y = −1.6, was obtained in the structure in which the triangle edge lengths were considered 13 mm. Next, the auxetic stents with the aims of uniform shrinkage behaviors as well as high energy absorption were introduced. For this purpose, the equilateral triangles were distributed on the cylindrical surfaces along with the peripheral and longitudinal directions. Under compression, the stent with 15mm triangle edge lengths possessed uniform shrinkage behavior, and the values of Poisson's ratio were measured υ z x = −2.2 and υ z y = −2.19. Finally, the comparisons between triangular and conventional anti-trichiral stents were performed. It was observed that the lateral displacements, as well as energy absorption of the triangular stents were twice and three times as high as the conventional anti-trichiral stents respectively.

A plate of dual phase steel was produced from low carbon steel with intercritical annealing treatment. Its optically determined surface microstructure was utilized to construct three different microstructural models. To describe the ductile damage in the ferritic matrix, the Gurson-Tvergaard-Needleman model was used with the failure in the martensite phase being ignored. The numerical results obtained for the mechanism of void initiation and coalescence were compared with the experimental observations. The numerical results obtained from the randomly extruded 3D model showed a significantly better agreement with the experimental ones than those obtained from the 2D model or the uniformly extruded 3D model.

Since the advent of additive manufacturing techniques, regular porous biomaterials have emerged as promising candidates for tissue engineering scaffolds owing to their controllable pore architecture and feasibility in producing scaffolds from a variety of biomaterials. The architecture of scaffolds could be designed to achieve similar mechanical properties as in the host bone tissue, thereby avoiding issues such as stress shielding in bone replacement procedure. In this paper, the deformation and failure mechanisms of porous titanium (Ti6Al4V) biomaterials manufactured by selective laser melting from two different types of repeating unit cells, namely cubic and diamond lattice structures, with four different porosities are studied. The mechanical behavior of the above-mentioned porous biomaterials was studied using finite element models. The computational results were compared with the experimental findings from a previous study of ours. The Johnson–Cook plasticity and damage model was implemented in the finite element models to simulate the failure of the additively manufactured scaffolds under compression. The computationally predicted stress–strain curves were compared with the experimental ones. The computational models incorporating the Johnson–Cook damage model could predict the plateau stress and maximum stress at the first peak with less than 18% error. Moreover, the computationally predicted deformation modes were in good agreement with the results of scaling law analysis. A layer-by-layer failure mechanism was found for the stretch-dominated structures, i.e. structures made from the cubic unit cell, while the failure of the bending-dominated structures, i.e. structures made from the diamond unit cells, was accompanied by the shearing bands of 45°.

In this study, experimental procedure and numerical methods were utilized to evaluate the effect of regular and irregular pore distribution as well as loading direction on compressive properties and deformation mechanism of hollow sphere aluminum foams. In order to study scaling laws, different volume fractions of the regular samples were produced and loaded in horizontal and vertical directions to address the loading conditions effects. For this purpose, expanded polystyrene (EPS) grains were expanded to a designed diameter size and positioned in different configurations. Compression test results showed higher elastic properties for irregular sample due to the thicker cell walls while energy absorption capability at high strains was found to be reduced due to the non-uniform deformation in comparison with regular foams. In regular samples, a nonlinear behavior in the elastic regime was observed since the imperfections during casting procedure. Furthermore, similar deformation mechanisms were found for the set of samples with similar pore configurations indicating the feasibility of controlling deformation mechanism by manipulating morphological characteristics. Finite element results well predicted deformation mechanism of structures and plastic properties of regular hollow sphere samples especially for plateau stress with less than 12% relative error. Keywords: Hollow sphere, Space holder technique, Centrifugal casting, Regular and irregular pore distribution, Compressive properties, Failure mechanism, Finite element method

The phenomenon of strain localization is considered the most effective cause of failure in dual phase steels. In the present study, we have performed in-situ tensile tests to investigate the strain localization in ferrite phase. In order to quantify the level of microscopic deformation, an image processing code was used and the the strain map was subsequently superimposed onto the scanning electron microscopy (SEM) image obtained from the in-situ test. The SEM image that was captured during the in-situ tensile test was further used in a finite element dislocation density model, based on which the similarities and differences between the experimental and simulation results were discussed. The amount of localized deformation in the ferrite phase was found to be much higher in the regions between martensite islands. A parametric study was then performed to gain deeper insights on the effect of martensite grain size on the strain localization of the neighboring ferrite. Furthermore, using the experimental results, the localization of strain inside the high deformational fields before the final failure was discussed.

Stress–strain response of multiphase materials similar to dual phase (DP) steel depends on the elastic–plastic and damage behavior of all ingredient phases. DP steels typically contains of ferrite and martensite phases, but the grain boundaries of martensite phase may act as important location with possible occurrence of damage or debonding under static loading. The focus of this paper is consideration of ferrite and martensite interface debonding in addition to the elastic–plastic behavior of ferrite and martensite to predict the stress–strain behavior of DP steel using a finite element (FE) micromechanical approach. For this purpose the micromechanics representative geometry is selected from scanning electron microscopy (SEM) images and the finite element mesh is generated based on the real shape of grains. Interface elements based on the cohesive zone modeling are also used for consideration of damage or debonding on the ferrite and martensite interfaces. Therefore, the developed micro mechanic finite element model is based on the real microstructure, uses cohesive elements between martensite islands and ferrite matrix and also considers the elastic–plastic behavior of ferrite and martensite phases. Handling of such simulation procedure with two source of material nonlinearity (plasticity and cohesive zone damage) is not an easy task. It is shown that the obtained stress–strain behaviors are in well agreement with the experimental results.

In many industrial applications, we deal with the impact of micron-scale particles onto a target surface. So, a large number of studies have been conducted to perceive damage mechanism and identify effective parameters of this phenomenon at micron scale. In all of these studies, target surface has been considered as ideally smooth. However, it is very obvious, the ideally smooth surface is not imaginable at this micron level and a few works have been performed on rough surface. In this paper, single impact of micron-scale particle onto a small area of rough surface was simulated using ABAQUS/Explicit Version 6-11. In our experimental study, damage mechanism of rough surface due to multiple particle impact on a large area of a real turbine blade surface was studied and the created zones were characterized. Also, permanent impression was expressed for the damage mechanism. The experimental results were implicated from the simulated model in order to validate the present numerical study. Effects of the particle parameters including particle shape, impact location, and impact angle on erosion rate were separately investigated. For each of them, a simple power relation in terms of erosion rate was reported using finite element model calculation.

The effect of hydrogen on the mechanical properties of X70 pipeline steel was investigated by a combination of macro- and microscale approaches. Various tensile tests under vacuum, in-situ H-plasma charging (IHPC), and ex-situ electrochemical H-charging (EEHC) conditions were conducted to elucidate the hydrogen effect in the macroscale approach. All tensile tests were performed inside an environmental scanning electron microscopy (ESEM) chamber. The IHPC, as a novel hydrogen charging technique, was compared with conventional EEHC while uncharged tensile specimens were used as a reference. The results demonstrated that the variations in the IHPC condition were negligible compared to the vacuum condition, whereas the differences in the ex-situ condition were more prominent. Furthermore, susceptibility to hydrogen in the vacuum-ex situ regime was manifested in the reduction of yield strength and ultimate tensile strength. These findings were confirmed by the fractographic analysis, where some of the effects of hydrogen (e.g. the formation of secondary cracks by detrimental inclusions (MnS and Al2O3) and the transition of fracture features from ductile dimples to cleavage patterns) were well illustrated. On the other hand, micro-cantilever bending tests were performed in the air to avoid hydrogen effects and applied inside a miniaturized electrochemical cell to promote hydrogen uptake. The bending results and post-mortem analysis of the tested cantilevers indicated that the hydrogen-reduced flow stress and hydrogen-induced cracking occurred for the H-charged bent cantilever, while only increased plastic behavior occurred for the cantilever bent in the air.

In many industrial conditions, we deal with impact of particles on a surface that can cause premature failure. A series of studies have been conducted to investigate the effect of parameters on this phenomenon on smooth surfaces at micron-scale. But there is no ideally smooth surface at this micron level. Our study investigated the effect of particle parameters on erosion rate on rough surfaces and obtained their diagram in terms of erosion rate. The modeled particle velocity was in a range between 25 and 150 m/s, and particle diameter is in a range between 216 and 1080 μm. In our numerical study, an erosion model that is based on the impact of a single particle on a small area of surface was described. Then, in our experimental study, different zones that are created due to multiple particle impact on large area of surface were identified.

Failure in dual phase (DP) steels is a phenomenon that has been extensively investigated in the last decade through experimental tests and simulation methods. Experimental procedures have shown that failure has a ductile pattern and that shear failure is dominant in these materials. In this research, both experimental and numerical methods were employed to investigate shear failure in dual phase steels. Scanning electron microscopy (SEM) images of the specimens depicted the voids and shear driven voids growth in regions of localized plastic strain in the ferrite matrix. In the simulation section, mechanisms of shear failure in DP steels were simulated by a micro-structural ductile damage model. Solution and convergence of a finite element (FE) problem with irregular geometry, plasticity and ductile progressive damage was a challenging task. The criteria for shear localization were implemented in a FE model of a DP steel microstructure by ANSYS parametric design language (APDL) code to investigate pattern of shear failure. On the other hand, global stress strain behavior was investigated and compared with experimental results. It was concluded that localization criteria could reliably predict shear failure of DP steels.

Rapid prototyping (RP) has been a promising technique for producing tissue engineering scaffolds which mimic the behavior of host tissue as properly as possible. Biodegradability, agreeable feasibility of cell growth, and migration parallel to mechanical properties, such as strength and energy absorption, have to be considered in design procedure. In order to study the effect of internal architecture on the plastic deformation and failure pattern, the architecture of triply periodic minimal surfaces which have been observed in nature were used. P and D surfaces at 30% and 60% of volume fractions were modeled with 3∗3∗ 3 unit cells and imported to Objet EDEN 260 3-D printer. Models were printed by VeroBlue FullCure 840 photopolymer resin. Mechanical compression test was performed to investigate the compressive behavior of scaffolds. Deformation procedure and stress-strain curves were simulated by FEA and exhibited good agreement with the experimental observation. Current approaches for predicting dominant deformation mode under compression containing Maxwell's criteria and scaling laws were also investigated to achieve an understanding of the relationships between deformation pattern and mechanical properties of porous structures. It was observed that effect of stress concentration in TPMS-based scaffolds resultant by heterogeneous mass distribution, particularly at lower volume fractions, led to a different behavior from that of typical cellular materials. As a result, although more parameters are considered for determining dominant deformation in scaling laws, two mentioned approaches could not exclusively be used to compare the mechanical response of cellular materials at the same volume fraction.