@article {604349,
	title = {Kirigami skins make a simple soft actuator crawl},
	journal = {Science Robotics},
	volume = {3},
	number = {15},
	year = {2018},
	note = {\&nbsp;Featured\&nbsp;on Science Robotics Cover, Harvard SEAS News, Scientific American,\&nbsp;Wired, The Verge, IEEE Spectrum, Digital Trends, NewsWeek, LA Times, DailyMail, BBC Click},
	month = {Feb 2018},
	pages = {eaar7555},
	abstract = {Bioinspired soft machines made of highly deformable materials are enabling a variety of innovative applications, yet their locomotion typically requires several actuators that are independently activated. We harnessed kirigami principles to significantly enhance the crawling capability of a soft actuator. We designed highly stretchable kirigami surfaces in which mechanical instabilities induce a transformation from flat sheets to 3D-textured surfaces akin to the scaled skin of snakes. First, we showed that this transformation was accompanied by a dramatic change in the frictional properties of the surfaces. Then, we demonstrated that, when wrapped around an extending soft actuator, the buckling-induced directional frictional properties of these surfaces enabled the system to efficiently crawl.},
	url = {https://dx.doi.org/10.1126/scirobotics.aar7555},
	author = {A. Rafsanjani and Y. Zhang and Liu, B. and S. M. Rubinstein and Bertoldi, K.}
}
@article {570316,
	title = {Durable Bistable Auxetics Made of Rigid Solids},
	journal = {Journal of Materials Research, Focus Issue: Architected Materials},
	volume = {33},
	number = {3},
	year = {2018},
	note = {[available on arXiv]Featured in MRS Bulletin},
	pages = {300-308},
	abstract = {Bistable Auxetic Metamaterials (BAMs) are a class of monolithic perforated periodic structures with negative Poisson{\textquoteright}s ratio. Under tension, a BAM can expand and reach a second state of equilibrium through a globally large shape transformation that is ensured by the flexibility of its elastomeric base material. However, if made from a rigid polymer, or metal, BAM ceases to function due to the inevitable rupture of its ligaments. The goal of this work is to extend the unique functionality of the original kirigami architecture of BAM to a rigid solid base material. We use experiments and numerical simulations to assess performance, bistability and durability of rigid BAMs at 10,000 cycles. Geometric maps are presented to elucidate the role of the main descriptors of BAM architecture. The proposed design enables the realization of BAM from a large palette of materials, including elastic-perfectly plastic materials and potentially brittle materials.},
	url = {https://doi.org/10.1557/jmr.2017.417},
	author = {X. Shang and Liu, L. and A. Rafsanjani and D. Pasini}
}
@article {559821,
	title = {On the design of porous structures with enhanced fatigue life},
	journal = {Extreme Mechanics Letters},
	volume = {16},
	year = {2017},
	pages = {13-17},
	abstract = {Many components of gas turbines, including the combustion liners, ducts, casings and sealing structures, comprise metallic sheets perforated with arrays of circular cooling holes. These parts are highly prone to fatigue failure due to the stresses induced by temperature variations during operation. Here, we demonstrate both experimentally and numerically that the fatigue life of these porous components can be greatly enhanced by carefully designing the pores{\textquoteright} shape. In particular, we show that while the fatigue life of a metallic sheet with a square array of conventional circular cooling holes is \&lt;100k cycles, by replacing the pores with novel orthogonal S-shaped holes the life of the structure increases up to more than one million cycles. This is because the S-shaped pores introduce a soft mode of deformation based on rotation of the domains between neighboring holes that significantly affect the stress distribution and crack propagation in the structure.},
	url = {https://doi.org/10.1016/j.eml.2017.08.002},
	author = {F. Javid and Liu, J. and A. Rafsanjani and M. Schaenzer and M. Q. Pham and D. Backman and S. Yandt and M. C. Innes and C. Booth-Morrison and M. Gerendas and T. Scarinci and A. Shanian and Bertoldi, K.}
}
@article {500046,
	title = {Buckling-Induced Kirigami},
	journal = {Physical Review Letters},
	volume = {118},
	year = {2017},
	note = {[avialable on arXiv]On the PRL Cover,\&nbsp;Harvard News, SNF Science Now, MRS Bulletin, InsideScience, SNSF Horizons},
	pages = {084301},
	abstract = {We investigate the mechanical response of thin sheets perforated with a square array of mutually orthogonal cuts, which leaves a network of squares connected by small ligaments. Our combined analytical, experimental and numerical results indicate that under uniaxial tension the ligaments buckle out-of-plane, inducing the formation of 3D patterns whose morphology is controlled by the load direction. We also find that by largely stretching the buckled perforated sheets, plastic strains develop in the ligaments. This gives rise to the formation of kirigami sheets comprising periodic distribution of cuts and permanent folds. As such, the proposed buckling-induced pop-up strategy points to a simple route for manufacturing complex morphable structures out of flat perforated sheets.},
	url = {https://doi.org/10.1103/PhysRevLett.118.084301},
	author = {A. Rafsanjani and Bertoldi, K.}
}
@article {457346,
	title = {Bistable Auxetic Mechanical Metamaterials Inspired by Ancient Geometric Motifs},
	journal = {Extreme Mechanics Letters},
	volume = {9},
	year = {2016},
	note = {[available on arXiv]Watch a video about this work\&nbsp;on Vimeo!A US Patent (US2017/0362414A1) is filed for Bistable Auxetics and we are actively seeking commercialization opportunities.Featured in PhysicsWorld Magazine,\&nbsp;APS News,\&nbsp;BBC News,\&nbsp;Ahmad{\textquoteright}s interview with BBC Newshour,\&nbsp;BBC Newsroom report, NewScientist, PhysicsWorld, Creators, Science, McGill Tribune,\&nbsp;Smithsonian Magazine, PNAS},
	pages = {291-296},
	abstract = {Auxetic materials become thicker rather than thinner when stretched, exhibiting an unusual negative Poisson{\textquoteright}s ratio well suited for designing shape transforming metamaterials. Current auxetic designs, however, are often monostable and cannot maintain the transformed shape upon load removal. Here, inspired by ancient geometric motifs arranged in square and triangular grids, we introduce a class of switchable architected materials exhibiting simultaneous auxeticity and structural bistability. The material concept is experimentally realized by perforating various cut motifs into a sheet of rubber, thus creating a network of rotating units connected with compliant hinges. The metamaterial performance is assessed through mechanical testing and accurately predicted by a coherent set of finite element simulations. A discussion on a rich set of mechanical phenomena follows to shed light on the main design principles governing bistable auxetics.},
	url = {http://dx.doi.org/10.1016/j.eml.2016.09.001},
	author = {A. Rafsanjani and D. Pasini}
}
@article {457366,
	title = {Hierarchies of Plant Stiffness},
	journal = {Plant Science},
	volume = {250},
	year = {2016},
	pages = {79-96},
	abstract = {Plants must meet mechanical as well as physiological and reproductive requirements for survival. Management of internal and external stresses is achieved through their unique hierarchical architecture. Stiffness is determined by a combination of morphological (geometrical) and compositional variables that vary across multiple length scales ranging from the whole plant to organ, tissue, cell and cell wall levels. These parameters include, among others, organ diameter, tissue organization, cell size, density and turgor pressure, and the thickness and composition of cell walls. These structural parameters and their consequences on plant stiffness are reviewed in the context of work on stems of the genetic reference plant\&nbsp;Arabidopsis thaliana\&nbsp;(Arabidopsis), and the suitability of Arabidopsis as a model system for consistent investigation of factors controlling plant stiffness is put forward. Moving beyond Arabidopsis, the presence of morphological parameters causing stiffness gradients across length-scales leads to beneficial emergent properties such as increased load-bearing capacity and reversible actuation. Tailoring of plant stiffness for old and new purposes in agriculture and forestry can be achieved through bioengineering based on the knowledge of the morphological and compositional parameters of plant stiffness in combination with gene identification through the use of genetics.},
	url = {http://dx.doi.org/10.1016/j.plantsci.2016.06.002},
	author = {V. Brul{\'e} and A. Rafsanjani and D. Pasini and T. L. Western}
}
@article {457361,
	title = {Hydro-Responsive Curling of the Resurrection Plant Selaginella lepidophylla},
	journal = {Scientific Reports},
	volume = {5},
	year = {2015},
	note = {[available on arXiv]},
	pages = {8064},
	abstract = {
	
		
			The spirally arranged stems of the spikemoss\&nbsp;Selaginella lepidophylla, an ancient resurrection plant, compactly curl into a nest-ball shape upon dehydration. Due to its spiral phyllotaxy, older outer stems on the plant interlace and envelope the younger inner stems forming the plant centre. Stem curling is a morphological mechanism that limits photoinhibitory and thermal damages the plant might experience in arid environments. Here, we investigate the distinct conformational changes of outer and inner stems of\&nbsp;S. lepidophylla\&nbsp;triggered by dehydration. Outer stems bend into circular rings in a relatively short period of desiccation, whereas inner stems curl slowly into spirals due to hydro-actuated strain gradient along their length. This arrangement eases both the tight packing of the plant during desiccation and its fast opening upon rehydration. The insights gained from this work shed light on the hydro-responsive movements in plants and might contribute to the development of deployable structures with remarkable shape transformations in response to environmental stimuli.
		
	

},
	url = {http://dx.doi.org/10.1038/srep08064},
	author = {A. Rafsanjani and V. Brul{\'e} and T. L. Western and D. Pasini}
}
@article {457386,
	title = {Poromechanical modeling of moisture induced swelling anisotropy in cellular tissues of softwoods},
	journal = {RSC Advances},
	volume = {5},
	number = {5},
	year = {2015},
	pages = {3560-3566},
	abstract = {Experimental studies reveal that softwoods exhibit different swelling patterns at the cellular scale depending on the position of the tracheid cells within the growth ring. Thin-walled earlywood cells show anisotropic swelling behavior while the swelling of thick-walled bulky latewood cells is generally isotropic. A poromechanical model is developed to explore the anisotropic swelling behavior of softwoods at the cellular scale. The general description for the macroscopically observable free swelling strain of cellular tissues is derived by upscaling the constitutive equations of a double porosity medium which is found to be dependent on stiffness, Biot coefficient, Biot modulus and the geometry of the cells. The effective poroelastic constants of earlywood and latewood cells are computed from a periodic honeycomb unit cell by means of an efficient finite-element-based computational upscaling scheme. The estimated swelling coefficients compare well with experimental measurements. It is found that the anisotropy in swelling behavior of wood cells can be related to the anisotropy of elastic properties at the cell wall level and the geometry of the cells. The proposed poromechanical model provides a physically relevant description of swelling behavior which originates from the coupled interaction of water and solid phases within the porous cell walls of softwoods.},
	url = {http://dx.doi.org/10.1039/C4RA14074E},
	author = {A. Rafsanjani and D. Derome and J. Carmeliet}
}
@article {457351,
	title = {Snapping Mechanical Metamaterials under Tension},
	journal = {Advanced Materials},
	volume = {27},
	number = {39},
	year = {2015},
	note = {[available on arXiv], Watch it\&nbsp;on Vimeo!Featured in Nature Materials,\&nbsp;Advanced Materials Frontispiece\&nbsp;},
	pages = {5931{\textendash}5935},
	abstract = {A snapping mechanical metamaterial is designed, which exhibits a sequential snap-through behavior under tension. The tensile response of this mechanical metamaterial can be altered by tuning the architecture of the snapping segments to achieve a range of nonlinear mechanical responses, including monotonic, S-shaped, plateau, and non-monotonic snap-through behavior.},
	url = {http://dx.doi.org/10.1002/adma.201502809},
	author = {A. Rafsanjani and A. Akbarzadeh and D. Pasini}
}
@article {457476,
	title = {Micro-Scale Restraint Methodology for Humidity Induced Swelling Investigated by Phase Contrast X-Ray Tomography},
	journal = {Experimental Mechanics},
	volume = {54},
	number = {7},
	year = {2014},
	pages = {1215-1226},
	abstract = {A new methodology for restraining the swelling of spruce wood samples in the micrometre range is developed and presented. We show that the restraining device successfully prevents the free swelling of wood during moisture adsorption, thus modifying significantly the anisotropy of swelling and provoking the intended collapse and large deformations of the wood cells at the edges of the sample in contact with the restraining device. The device consists in a slotted cube designed to restrain swelling and is made of PMMA manufactured by laser ablation. The sample undergoing the restraining experiment is imaged with high-resolution synchrotron radiation phase contrast X-Ray Tomographic Microscopy. The deformation of the restraining device itself is only approximately 2\&nbsp;μm with respect to a 500\&nbsp;μm width in cubes containing latewood samples and half of that in the case of cubes containing earlywood.},
	url = {http://dx.doi.org/10.1007/s11340-014-9894-y},
	author = {A. Patera and K. Jefimovs and A. Rafsanjani and F. Voisard and R. Mokso and D. Derome and J. Carmeliet}
}
@article {457381,
	title = {Hygroscopic swelling and shrinkage of latewood cell wall micropillars reveal ultrastructural anisotropy},
	journal = {Journal of The Royal Society Interface},
	volume = {11},
	number = {95},
	year = {2014},
	pages = {20140126},
	abstract = {We document the hygroscopic swelling and shrinkage of the central and the thickest secondary cell wall layer of wood (named S2) in response to changes in environmental humidity using synchrotron radiation-based phase contrast X-ray tomographic nanoscopy. The S2 layer is a natural fibre-reinforced nano-composite polymer and is strongly reactive to water. Using focused ion beam, micropillars with a cross section of few micrometres are fabricated from the S2 layer of the latewood cell walls of Norway spruce softwood. The thin neighbouring cell wall layers are removed to prevent hindering or restraining of moisture-induced deformation during swelling or shrinkage. The proposed experiment intended to get further insights into the microscopic origin of the anisotropic hygro-expansion of wood. It is found that the swelling/shrinkage strains are highly anisotropic in the transverse plane of the cell wall, larger in the normal than in the direction parallel to the cell wall{\textquoteright}s thickness. This ultrastructural anisotropy may be due to the concentric lamellation of the cellulose microfibrils as the role of the cellulose microfibril angle in the transverse swelling anisotropy is negligible. The volumetric swelling of the cell wall material is found to be substantially larger than the one of wood tissues within the growth ring and wood samples made of several growth rings. The hierarchical configuration in wood optimally increases its dimensional stability in response to a humid environment with higher scales of complexity.},
	url = {http://dx.doi.org/10.1098/rsif.2014.0126},
	author = {A. Rafsanjani and M. Stiefel and K. Jefimovs and R. Mokso and D. Derome and J. Carmeliet}
}
@inbook {457401,
	title = {Swelling of Wood Tissue: Interactions at the Cellular Scale},
	booktitle = {Nonlinear Elasticity and Hysteresis: Fluid-Solid Coupling in Porous Media},
	year = {2014},
	pages = {153-170},
	publisher = {Wiley-VCH Verlag GmbH \& Co. KGaA},
	organization = {Wiley-VCH Verlag GmbH \& Co. KGaA},
	abstract = {The swelling behavior is of interest as the locus of the nice interaction of moisture and mechanical behavior. We take wood as our model material. Although, moisture behavior is known to be hysteretic in terms of relative humidity, we demonstrate that it is not hysteresis in terms of moisture content and take this as an opportunity to look for a full description of this moisture/mechanical interaction. Investigations by phase contrast synchrotron X-ray microtomography and by hygro-elastic modeling allows to see the strong effects of porosity and cellular geometry on the anisotropy of swelling. We end with a few observations on moisture-induced shape memory.},
	url = {http://dx.doi.org/10.1002/9783527665068.ch7},
	author = {D. Derome and J. Carmeliet and A. Rafsanjani and A. Patera and R. A. Guyer}
}
@article {457431,
	title = {The role of water in the behavior of wood},
	journal = {Journal of Building Physics},
	volume = {36},
	number = {4},
	year = {2013},
	pages = {398-421},
	abstract = {Wood, due to its biological origin, has the capacity to interact with water. Sorption/desorption of moisture is accompanied with swelling/shrinkage and softening/hardening of its stiffness. The correct prediction of the behavior of wood components undergoing environmental loading requires that the moisture behavior and mechanical behavior of wood are considered in a coupled manner. We propose a comprehensive framework using a fully coupled poromechanical approach, where its multiscale implementation provides the capacity to take into account, directly, the exact geometry of the wood cellular structure, using computational homogenization. A hierarchical model is used to take into account the subcellular composite-like organization of the material. Such advanced modeling requires high-resolution experimental data for the appropriate determination of inputs and for its validation. High-resolution x-ray tomography, digital image correlation, and neutron imaging are presented as valuable methods to provide the required information.},
	url = {http://dx.doi.org/10.1177/1744259112473926},
	author = {D. Derome and A. Rafsanjani and S. Hering and M. Dressler and A. Patera and C. Lanvermann and M. Sedighi-Gilani and F. K. Wittel and P. Niemz and J. Carmeliet}
}
@article {457396,
	title = {Micromechanics investigation of hygro-elastic behavior of cellular materials with multi-layered cell walls},
	journal = {Composite Structures},
	volume = {95},
	year = {2013},
	pages = {607-611},
	abstract = {In this paper, the hygro-elastic behavior of two-dimensional periodic honeycombs composed of multi-layered cell walls is investigated using a computational micromechanics approach. Detailed numerical results for the effective hygro-expansion coefficients and the elastic moduli of honeycombs are obtained. The influence of the arrangement of the cell wall layers and the geometrical parameters of the honeycombs on the effective hygro-elastic properties is examined. Limiting cases are considered, and the validity of the model is established by comparison with the analytical solutions available in the existing literature. The obtained results suggest that the layered architecture of the cell wall enhances the anisotropy in swelling behavior of honeycombs with irregular configuration which is reflected in their transverse hygro-expansion coefficients while regular honeycombs show isotropic behavior. The proposed model explains the complex thermo-hygro-mechanical behavior of natural cellular materials and provides a predictive tool for bio-mimetic material design.},
	url = {http://dx.doi.org/10.1016/j.compstruct.2012.08.017},
	author = {A. Rafsanjani and D. Derome and J. Carmeliet}
}
@article {457391,
	title = {Multiscale analysis of free swelling of Norway spruce},
	journal = {Composites Part A: Applied Science and Manufacturing},
	volume = {54},
	year = {2013},
	pages = {70-78},
	abstract = {The swelling of the hierarchical cellular structure of wood can be properly predicted when both the cellular and the growth ring scales are taken into account. In this study, a multiscale computational upscaling finite element model is utilized for the estimation of the free swelling behavior of Norway spruce softwood. The microstructural information, e.g. the geometry of the wood cells, the local density and the microfibril angle across the growth rings is the input of the lower scale cellular model. The elastic properties and the swelling coefficients within the growth ring are estimated using a periodic honeycomb unit cell model. Based on this model, the transverse anisotropy in the swelling behavior of softwood at timber or growth ring level is then predicted. Comparison of simulation results with experimental measurements obtained using digital image correlation shows very good agreement.},
	url = {http://dx.doi.org/10.1016/j.compositesa.2013.07.005},
	author = {A. Rafsanjani and C. Lanvermann and P. Niemz and J. Carmeliet and D. Derome}
}
@mastersthesis {457406,
	title = {Multiscale poroelastic model: bridging the gap from cellular to macroscopic scale},
	number = {20821},
	year = {2013},
	type = {Dr. sc. Thesis},
	abstract = {Many biological and engineering materials are essentially porous or cellular, a feature which provides them with a low density and high strength and toughness. \&nbsp;The deformation of cellular materials in response to environmental stimuli such as changes in relative humidity is of practical interest to evaluate the durability of materials in different working conditions. In this thesis, the hygro-mechanical behavior of hierarchical cellular materials is investigated using a multiscale computational framework. Attention is focused on softwoods but the proposed model is general and can be applied to other cellular materials. In wood, the interaction of the moisture and mechanical behavior is best observed in swelling. The complicated hierarchical architecture of wood introduces a strong geometric anisotropy which is reflected in the anisotropy of its mechanical and swelling behavior. A two-step computational upscaling method is utilized to devise a finite element model for the estimation of swelling behavior of softwoods. Starting from the cellular scale which represents the underlying structure of the growth ring scale, an efficient scheme is developed for the estimation of the hygro-elastic properties of periodic honeycombs as a model for the cellular structure of wood. Predicted results are found to be comparable to experimental data at both cellular scale and growth ring level. A poromechanical approach is also presented as an alternative formulation for the estimation of the effective swelling coefficients of cellular materials. The computational approach proposed in this thesis provides a predictive tool for revealing the structure-property relations of biological and engineering cellular materials and can also be used for the design of new functional cellular materials with tailorable swelling properties.\&nbsp;},
	url = {http://dx.doi.org/10.3929/ethz-a-009774976},
	author = {A. Rafsanjani}
}
@article {457371,
	title = {Swelling of cellular solids: From conventional to re-entrant honeycombs},
	journal = {Applied Physics Letters},
	volume = {102},
	year = {2013},
	pages = {211907},
	abstract = {We find that, in two-dimensional periodic cellular solids, the hygro-expansion properties of the cell wall and the geometrical configurations of the lattice determine the effective swelling behavior of the medium. In this letter, we present the associated phase diagram for the swelling anisotropy of conventional and re-entrant honeycomb morphologies. The presented results are obtained numerically from a finite element based computational upscaling scheme. We show how the pattern of anisotropy in swelling behavior of cellular materials reverses when swelling is more important across or along the cell walls.},
	url = {http://dx.doi.org/10.1063/1.4807844},
	author = {A. Rafsanjani and D. Derome and R. A. Guyer and J. Carmeliet}
}
@article {457421,
	title = {Hygromorphic behaviour of cellular material: hysteretic swelling and shrinkage of wood probed by phase contrast X-ray tomography},
	journal = {Philosophical Magazine},
	volume = {92},
	number = {28-30},
	year = {2012},
	pages = {3680-3698},
	abstract = {Wood is a hygromorphic material, meaning it responds to changes in environmental humidity by changing its geometry. Its cellular biological structure swells during wetting and shrinks during drying. The origin of the moisture-induced deformation lies at the sub-cellular scale. The cell wall can be considered a composite material with stiff cellulose fibrils acting as reinforcement embedded in a hemicellulose/lignin matrix. The bulk of the cellulose fibrils, forming 50\% of the cell wall, are oriented longitudinally, forming long-pitched helices. Both components of cell wall matrix are displaying swelling. Moisture sorption and, to a lesser degree, swelling/shrinkage are known to be hysteretic. We quantify the affine strains during the swelling and shrinkage using high resolution images obtained by phase contrast synchrotron X-ray tomography of wood samples of different porosities. The reversibility of the swelling/shrinkage is found for samples with controlled moisture sorption history. The deformation is more hysteretic for high than for low density samples. Swelling/shrinkage due to ad/desorption of water vapour displays also a non-affine component. The reversibility of the swelling/shrinkage indicates that the material has a structural capacity to show a persistent cellular geometry for a given moisture state and a structural composition that allows for moisture-induced transitional states. A collection of qualitative observations of small subsets of cells during swelling/shrinkage is further studied by simulating the observed behaviour. An anisotropic swelling coefficient of the cell wall is found to emerge and its origin is linked to the anisotropy of the cellulose fibrils arrangement in cell wall layers.},
	url = {http://dx.doi.org/10.1080/14786435.2012.715248},
	author = {D. Derome and A. Rafsanjani and A. Patera and R. A. Guyer and J. Carmeliet}
}
@article {457411,
	title = {Computational up-scaling of anisotropic swelling and mechanical behavior of hierarchical cellular materials},
	journal = {Composites Science and Technology},
	volume = {72},
	year = {2012},
	note = {[available on arXiv]},
	pages = {744{\textendash}751},
	abstract = {
	The hygro-mechanical behavior of a hierarchical cellular material, i.e. growth rings of softwood is investigated using a two-scale micro-mechanics model based on a computational homogenization technique. The lower scale considers the individual wood cells of varying geometry and dimensions. Honeycomb unit cells with periodic boundary conditions are utilized to calculate the mechanical properties and swelling coefficients of wood cells. Using the cellular scale results, the anisotropy in mechanical and swelling behavior of a growth ring in transverse directions is investigated. Predicted results are found to be comparable to experimental data. It is found that the orthotropic swelling properties of the cell wall in thin-walled earlywood cells produce anisotropic swelling behavior while, in thick latewood cells, this anisotropy vanishes. The proposed approach provides the ability to consider the complex microstructure when predicting the effective mechanical and swelling properties of softwood.

},
	url = {http://dx.doi.org/10.1016/j.compscitech.2012.02.001},
	author = {A. Rafsanjani and D. Derome and F. K. Wittel and J. Carmeliet}
}
@article {457416,
	title = {The role of geometrical disorder on swelling anisotropy of cellular solids},
	journal = {Mechanics of Materials},
	volume = {55},
	year = {2012},
	pages = {49-59},
	abstract = {The anisotropic swelling behavior of two-dimensional cellular solids is investigated using computational upscaling of periodic honeycombs and compared with direct finite element simulations of real cellular structure of wood as a complex cellular material. In both models, the anisotropy of the cell wall material has been taken into account. The real structure model is used for inverse determination of swelling coefficients of the wood cell wall by comparing the simulation results to free swelling experimental data. The obtained results reveal that the cell walls swell to a much less extent along the cell wall than in the thickness direction. A systematic study is carried out to investigate the influence of geometrical disorder on swelling properties. It is found that periodic symmetric honeycombs provide the upper bound for anisotropic swelling ratio, while disorder in arrangement of the cellular structure reduces the swelling anisotropy.},
	url = {http://dx.doi.org/10.1016/j.mechmat.2012.08.002},
	author = {A. Rafsanjani and D. Derome and J. Carmeliet}
}
@article {457436,
	title = {Two-dimensional elasticity solution for transient response of simply supported beams under moving loads},
	journal = {Acta Mechanica},
	volume = {217},
	number = {3},
	year = {2011},
	pages = {205-218},
	abstract = {A semi-analytical analysis for the transient elastodynamic response of an arbitrarily thick simply supported beam due to the action of an arbitrary moving transverse load is presented, based on the linear theory of elasticity. The solution of the problem is derived by means of the powerful state space technique in conjunction with the Laplace transformation with respect to the time coordinate. The inversion of Laplace transform has been carried out numerically using Durbin{\textquoteright}s approach based on Fourier series expansion. Special convergence enhancement techniques are invoked to completely eradicate spurious oscillations and obtain uniformly convergent solutions. Detailed numerical results for the transient vibratory responses of concrete beams of selected thickness parameters are obtained and compared for three types of harmonic moving concentrated loads: accelerated, decelerated and uniform. The effects of the load velocity, pulsation frequency and beam aspect ratio on the dynamic response are examined. Also, comparisons are made against solutions based on Euler{\textendash}Bernoulli and Timoshenko beam models. Limiting cases are considered, and the validity of the model is established by comparison with the solutions available in the existing literature as well as with the aid of a commercial finite element package.},
	url = {http://dx.doi.org/10.1007/s00707-010-0393-7},
	author = {S. M. Hasheminejad and A. Rafsanjani}
}
@article {457456,
	title = {Nonlinear dynamic modeling of surface defects in rolling element bearing systems},
	journal = {Journal of Sound and Vibration},
	volume = {319},
	number = {3},
	year = {2009},
	pages = {1150-1174},
	abstract = {In this paper an analytical model is proposed to study the nonlinear dynamic behavior of rolling element bearing systems including surface defects. Various surface defects due to local imperfections on raceways and rolling elements are introduced to the proposed model. The contact force of each rolling element described according to nonlinear Hertzian contact deformation and the effect of internal radial clearance has been taken into account. Mathematical expressions were derived for inner race, outer race and rolling element local defects. To overcome the strong nonlinearity of the governing equations of motion, a modified Newmark time integration technique was used to solve the equations of motion numerically. The results were obtained in the form of time series, frequency responses and phase trajectories. The validity of the proposed model verified by comparison of frequency components of the system response with those obtained from experiments. The classical Floquet theory has been applied to the proposed model to investigate the linear stability of the defective bearing rotor systems as the parameters of the system changes. The peak-to-peak frequency response of the system for each case is obtained and the basic routes to periodic, quasi-periodic and chaotic motions for different internal radial clearances are determined. The current study provides a powerful tool for design and health monitoring of machine systems.},
	url = {http://dx.doi.org/10.1016/j.jsv.2008.06.043},
	author = {A. Rafsanjani and S. Abbasion and A. Farshidianfar and H. Moeenfard}
}
@article {457466,
	title = {Stress analysis for a coated fiber embedded in an infinite matrix subjected to body force},
	journal = {European Journal of Mechanics-A/Solids},
	volume = {28},
	number = {4},
	year = {2009},
	pages = {777-785},
	abstract = {A micromechanics model of a functionally graded coated fiber which is embedded in an infinite matrix is presented. Various combinations of friction-less sliding and perfect bounding conditions at interfaces are considered. The fiber loading is assumed to be a distributed body force. The mechanical properties of the graded coating are assumed to vary smoothly and continuously with the change of volume concentrations of the constituting materials along the radius according to a power law distribution. Numerical results show that the hoop stress at the fiber boundary in the matrix can be reduced to becoming negligible if an optimum volume fraction is chosen for coating.},
	url = {http://dx.doi.org/10.1016/j.euromechsol.2008.11.008},
	author = {S. Abbasion and A. Rafsanjani and N. Irani and A. Farshidianfar}
}
@article {457441,
	title = {Three-dimensional vibration analysis of thick FGM plate strips under moving line loads},
	journal = {Mechanics of Advanced Materials and Structures},
	volume = {16},
	number = {6},
	year = {2009},
	pages = {417-428},
	abstract = {An exact three-dimensional analysis for steady-state dynamic response of an arbitrarily thick, isotropic, and functionally graded plate strip due to the action of a transverse distributed moving line load which is propagating parallel to the infinite simply supported edges of the plate at constant speed is presented based on the linear elasticity theory. The inhomogeneous plate is approximated by a laminate model, for which the solution is expected to gradually approach the exact one as the number of layers increases. The problem solution is derived by using Fourier transformation with respect to a moving reference frame in conjunction with the classical transfer matrix approach entailing the continuity of displacement and stress components at the interfaces of neighboring layers. The analytical results are illustrated with numerical examples in which a metal-ceramic (ZrO 2{\textendash}Al) FGM plate strip of unit width is subjected to a half-sine normal line load of constant amplitude traveling along the strip at uniform speeds. Four types of FGM plate strips are configured, and the effects of load velocity, material compositional gradient, and plate thickness on the basic dynamic field quantities are evaluated and discussed. Also, the response curves for the FGM plates are compared with those of equivalent bilaminate plates containing comparable total volume fractions of constituent materials. Limiting cases are considered and good agreements with the solutions available in the literature are obtained.},
	url = {http://dx.doi.org/10.1080/15376490902781209},
	author = {S. M. Hasheminejad and A. Rafsanjani}
}
@article {457446,
	title = {Free vibration of microscaled Timoshenko beams},
	journal = {Applied Physics Letters},
	volume = {95},
	number = {14},
	year = {2009},
	pages = {143122},
	abstract = {In this paper, a comprehensive model is presented to investigate the influence of surface elasticity and residual surface tension on the natural frequency of flexural vibrations of microbeams in the presence of rotary inertia and shear deformation effects. An explicit solution is derived for the natural oscillations of microscaled Timoshenko beams considering surface effects. The analytical results are illustrated with numerical examples in which two types of microbeams are configured based on Euler{\textendash}Bernoulli and Timoshenko beam theory considering surface elasticity and residual surface tension. The natural frequencies of vibration are calculated for selected beam length on the order of nanometer to microns and the results are compared with those corresponding to the classical beam models, emphasizing the differences occurring when the surface effects are significant. It is found that the nondimensional natural frequency of the vibration of micro and nanoscaled beams is size dependent and for limiting case in which the beam length increases, the results tends to the results obtained by classical beam models. This study might be helpful for the design of high-precision measurement devices such as chemical and biological sensors.},
	url = {http://dx.doi.org/10.1063/1.3246143},
	author = {S. Abbasion and A. Rafsanjani and R. Avazmohammadi and A. Farshidianfar}
}
@article {457461,
	title = {Investigation of the viscous and thermal effects on ductile fracture in sheet metal blanking process},
	journal = {The International Journal of Advanced Manufacturing Technology},
	volume = {45},
	number = {5-6},
	year = {2009},
	pages = {459-469},
	abstract = {In this paper, a methodology is proposed to predict the ductile damage in the sheet metal blanking process using a coupled thermomechanical finite-element method. A constitutive material model combined with the ductile fracture criteria was used. The effect of material softening due to the heat generated during plastic work in a specimen was considered in blanking simulations. To verify the validity of the proposed model, several blanking simulations are performed and the results compared with those obtained from an experimental study. The interaction of fracture initiation and temperature distribution in the sheet metal during the process was studied. The effect of velocity and the clearance on the product shape were examined. It was seen that at high punch speeds the viscous and thermal effects have significant effects on product quality.},
	url = {http://dx.doi.org/10.1007/s00170-009-1988-9},
	author = {A. Rafsanjani and S. Abbasion and N. Irani and A. Farshidianfar}
}
@article {457471,
	title = {Frequency response calculation of non-linear torsional vibration in gear systems},
	journal = {Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics},
	volume = {221},
	number = {1},
	year = {2008},
	pages = {49-60},
	abstract = {The current paper focuses on the non-linear torsional vibration of a one-stage transmission gear system. Four different methods have been applied for solution of the equation of motion; the discretization method, the perturbation method, the Ritz method, and the step-wise time integration of the equation of motion. The time and frequency results from these analyses have been compared with each other, as well as those reported in literatures. Although all of these methods are accurate and computationally effective for finding the main spectral contribution, however, only the discretization method and the step-wise time-integration model are able to identify the other frequency components.},
	url = {http://dx.doi.org/10.1243/14644193JMBD108},
	author = {A. Farshidianfar and H. Moeenfard and A. Rafsanjani}
}
@article {457451,
	title = {Rolling element bearings multi-fault classification based on the wavelet denoising and support vector machine},
	journal = {Mechanical Systems and Signal Processing},
	volume = {21},
	number = {7},
	year = {2007},
	pages = {2933-2945},
	abstract = {Due to the importance of rolling bearings as one of the most widely used industrial machinery elements, development of proper monitoring and fault diagnosis procedure to prevent malfunctioning and failure of these elements during operation is necessary. For rolling bearing fault detection, it is expected that a desired time{\textendash}frequency analysis method has good computational efficiency, and has good resolution in both, time and frequency domains. The point of interest of this investigation is the presence of an effective method for multi-fault diagnosis in such systems with optimizing signal decomposition levels by using wavelet analysis and support vector machine (SVM). The system that is under study is an electric motor which has two rolling bearings, one of them is next to the output shaft and the other one is next to the fan and for each of them there is one normal form and three false forms, which make 8 forms for study. The results that we achieved from wavelet analysis and SVM are fully in agreement with empirical result.},
	url = {http://dx.doi.org/10.1016/j.ymssp.2007.02.003},
	author = {S. Abbasion and A. Rafsanjani and N. Irani and A. Farshidianfar}
}
