Papers by Dr. Nitin Sharma
Materials Performance and Characterization, 2014
The complex nature of bone material results in a locational variation of fracture and mechanical ... more The complex nature of bone material results in a locational variation of fracture and mechanical properties. The heterogeneity associated with bone material and complex hierarchical assembly results in several toughening mechanisms, such as plasticity, micro-cracking, viscoplasticity, etc. These toughening mechanisms and presence of water in bone material makes the linear elastic fracture mechanics (LEFM) inapplicable in such materials. The present work is focused on the elastic-plastic fracture mechanics (EPFM) approach to estimate the locational variation in fracture properties of buffalo cortical bone for longitudinal, as well as transverse orientation of cracking. Samples from upper, middle, and lower locations of bone diaphysis were tested using compact tension and single-edge notch-bending testing methods for longitudinal and transverse orientation of cracking, respectively. The crack-tip opening displacement (CTOD) approach was applied to determine fracture properties, such as CTOD toughness (d c ), J integral (J c d ), and equivalent fracture toughness (K dc ) at different locations of bone diaphysis. The effect of orientation and location on mechanical properties of cortical bone, such as elastic modulus (E) and yield strength (r ys ), was also analyzed with the help of tensile testing. The equivalent fracture toughness values (K dc ) obtained in the present work were found to be three times higher than the corresponding Manuscript values reported in the previous reports where the LEFM approach was applied favoring the application of EPFM for bone materials. The mechanical
Transactions on Engineering Technologies, 2014
Bone is a complex anisotropic and heterogeneous material. The structure of bone material is consi... more Bone is a complex anisotropic and heterogeneous material. The structure of bone material is considered to be hierarchical in nature that changes from nano to macro level. Small punch testing, used in the present study, is a very useful technique to analyze the deformational behavior of materials that are difficult to obtain in a sufficient size for conventional mechanical testing. The finite element modeling (FEM) of small punch testing was carried out using ABAQUS code. The material properties of cortical bone for FE simulation were considered to be both isotropic and transversely isotropic in nature. This study shows that isotropic tensile properties of cortical bone are sufficient to predict the deformational behavior of cortical under small punch testing.
Bone material is very complex in nature due to its anisotropic and hierarchical structure. Bone i... more Bone material is very complex in nature due to its anisotropic and hierarchical structure. Bone is weaker in shear as compared to tension and compression therefore shear properties of bone material are important to find out. Many researchers have applied different techniques to find out shear properties of bone material but these techniques either require such type of bone specimens which are difficult to prepare or provides limited information about the shear properties. Iosipescu shear test method has been applied in the present work to find out locational variation in shear properties of cortical bone. This technique seems to be very effective for the case of bone material and require less effort as compared to the other techniques applied by the other researchers in the previous reports.
Complex hierarchical assembly and presence of large amount of organics and water content are resp... more Complex hierarchical assembly and presence of large amount of organics and water content are responsible for enough amount of plasticity in bone material. Plastic properties are not only important to assess the various changes and fracture risk in bone but also for the development of better bone implants and joint replacements. The present study is focused on the post-yield behavior of cortical bone. The plastic properties of goat femoral and tibiae cortical bone were assessed and compared in terms of plastic modulus (H), tangent modulus (E t), plastic work (W p) and plastic strain (ε p) using uniaxial tensile test. Both femoral and tibiae cortical bone were found to be having similar post-yield behavior and significant stiffness loss was observed in both the bones during plastic deformation. The value of plastic modulus for femoral cortical bone was found to be 1.2 times higher as compared to the corresponding value for tibiae cortical bone. This shows higher hardening rate for femoral cortical bone. It was also observed that femoral bone requires higher energy during plastic deformation until fracture as compared to tibiae cortical bone.
Materials like Bone are considered to be very complex ones due to their heterogeneous and anisotr... more Materials like Bone are considered to be very complex ones due to their heterogeneous and anisotropic nature. Bone material also has a hierarchical structure that changes from nano-scale to macro-scale. Bone contains good amount of non linearity during deformation. This nonlinearity may be due to several toughening mechanisms and presence of water in the bone material. Many researchers used linear elastic fracture mechanics approaches such as critical stress intensity factor, critical energy released rate and crack growthresistance curve etc. for examining toughness of bone. These approaches are inadequate to characterize fracture in presence of substantial nonlinearity preceding fracture. Crack tip opening displacement (CTOD) approach based on elasticplastic fracture mechanics has been applied in the present work to provide an estimate of fracture toughness of buffalo cortical bone for longitudinal as well as transverse orientation of cracking. Fractured surfaces of buffalo cortical bone are also examined with the help of scanning electron microscope for both longitudinal and transverse orientation of cracking in order to classify micro-mechanics of cracking of such bones. It is noticed that this bone is having plexiform character. In this paper average CTOD toughness (δ c ) values are measured for buffalo cortical bone in both longitudinal and transverse orientation of cracking. The equivalent K-fracture toughness and J-toughness values are also calculated employing the corresponding δ c values in the two orientations of cracking and compared with the values available in the literature. It is suggested that the CTOD (δ c ) and J-toughness are better parameters to predict the realistic fracture resistance of bone.
Conference Presentations by Dr. Nitin Sharma
Miniature specimen test technique provides a way of obtaining mechanical properties of components... more Miniature specimen test technique provides a way of obtaining mechanical properties of components or
structures while consuming an amount of material that is very small relative to that required for full-size conventional
specimen. This technique is very helpful especially in the case of bone mechanics as bone properties are heterogeneous
and anisotropic in nature and it is difficult to obtain standard size of specimen for mechanical testing. In the present study
an effort is made to simulate punch specimen setup using mechanical properties of the cortical femur bone material for
miniature specimen while considering its nature to be transversely isotropic. The samples were taken in both longitudinal
as well as transverse direction. The various load displacement curves and contour profiles obtained for different
thicknesses of the miniature specimen using finite element simulation were compared with each other. The values of load
at breakaway point were obtained for different cases of miniature specimen. It is anticipated that these values can be
further used to evaluate yield strength of the bone material in different cases.
—Bone as a natural composite material has a complex hierarchical and heterogeneous structure. It ... more —Bone as a natural composite material has a complex hierarchical and heterogeneous structure. It is quite difficult to analyze the mechanical behavior of cortical bone due to various constraints associated with the specimen preparation. These constraints may be overcome using small size specimens of cortical bone. Small punch testing, used in the present study, is a very useful technique to analyze the deformational behavior of materials that are difficult to obtain in a sufficient size for conventional mechanical testing. The finite element modeling (FEM) of small punch testing was carried out using ABAQUS code. The material properties of cortical bone for FE simulation were considered to be both isotropic and transversely isotropic in nature. This way total six independent FE models were developed and their results were compared with the corresponding experimental one. As per the study, the FE results of 1.0 mm thick specimen were observed to be closer to the corresponding experimental results. However, for 1.5 mm thick specimen the FE model results were found to be significantly deviated from the experimental results. The heterogeneous and hierarchical structure of cortical bone was considered to be the main cause of this deviation. This study shows that isotropic tensile properties of cortical bone are sufficient to predict the deformational behavior of cortical under small punch testing.
Bone is a complex biological material due to its
heterogeneous and anisotropic nature. Finite ele... more Bone is a complex biological material due to its
heterogeneous and anisotropic nature. Finite element modeling
(FEM) has been an effective tool in the field of bone mechanics
to predict the behavior of bone material under different
loading situations and the fracture locations. Bone exhibits
different yield behavior along different material orientations
due to its anisotropic nature and therefore for better
understanding of bone behavior under multi-axial loading, it is
necessary to incorporate anisotropic yielding and post yield
properties in FEM. In the present study FE simulation of
cortical bone was carried out using different yield stress ratios
in different directions based on Hill’s criterion. Bone material
was treated as a transversely isotropic material whose effective
properties are isotropic in one of its planes. The tensile
behavior of cortical bone in longitudinal and transverse
directions was analyzed using two different uniaxial tensile
models. The uniaxial tensile models were found to be in good
agreement with the experimental results and therefore biaxial
model of cortical bone was also developed and analyzed using
the same approach. The study shows that Hill’s criterion gives
good results for anisotropic yielding in bone material and can
be used to simulate multidirectional loading situations in bone
mechanics
—In this study the inhomogeneity in energy dissipation during tensile deformation of cortical bon... more —In this study the inhomogeneity in energy dissipation during tensile deformation of cortical bone was analyzed with the help of toughness and plastic work parameters. The compositional parameters were also determined for corresponding locations of bone diaphysis to observe their effect on elastic and plastic part of energy dissipation. The plastic part of energy dissipation was found to be mainly influenced by the compositional parameters of cortical bone. This study suggests that the locational variation in energy dissipation along bone diaphysis is mainly controlled by the deformation mechanisms that take place during the plastic deformation of cortical bone.
— Bone material is heterogeneous and anisotropic in nature. It also has a hierarchical structure ... more — Bone material is heterogeneous and anisotropic in nature. It also has a hierarchical structure that changes from nano-scale to macro-scale. Bone material contains good amount of non linearity during deformation. This nonlinearity may be due to several toughening mechanisms and presence of water in the bone material. Many researchers used critical stress intensity factor, critical energy released rate and crack growth-resistance curve approaches based on linear elastic fracture mechanics to examine toughness of bone. These approaches are inadequate to characterize fracture in presence of substantial nonlinearity preceding fracture. Crack tip opening displacement (CTOD) approach based on elastic-plastic fracture mechanics has been applied in the present work to provide an estimate of fracture toughness of buffalo cortical bone for longitudinal as well as transverse orientation of cracking. The elastic modulus and yield strength of buffalo bone are also evaluated for the transverse as well as longitudinal orientation of loading and compared with the values available in the literature. The average CTOD toughness (δ c) for transverse orientation was found to be 63 μm, which is 61% more than that of longitudinal orientation of cracking (39 μm). The equivalent K-fracture toughness values obtained from the δ c values in case of transverse orientation (12.68 MPa.m 1/2) was found to be 141% more than that of longitudinal orientation of cracking (5.26 MPa.m 1/2). The J-toughness values are calculated employing the corresponding δ c values in the two orientation of cracking and compared with the values of J-toughness available in the literature. It is suggested that the CTOD (δ c) and J-toughness are better parameters to predict the realistic fracture resistance of bone.
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Papers by Dr. Nitin Sharma
Conference Presentations by Dr. Nitin Sharma
structures while consuming an amount of material that is very small relative to that required for full-size conventional
specimen. This technique is very helpful especially in the case of bone mechanics as bone properties are heterogeneous
and anisotropic in nature and it is difficult to obtain standard size of specimen for mechanical testing. In the present study
an effort is made to simulate punch specimen setup using mechanical properties of the cortical femur bone material for
miniature specimen while considering its nature to be transversely isotropic. The samples were taken in both longitudinal
as well as transverse direction. The various load displacement curves and contour profiles obtained for different
thicknesses of the miniature specimen using finite element simulation were compared with each other. The values of load
at breakaway point were obtained for different cases of miniature specimen. It is anticipated that these values can be
further used to evaluate yield strength of the bone material in different cases.
heterogeneous and anisotropic nature. Finite element modeling
(FEM) has been an effective tool in the field of bone mechanics
to predict the behavior of bone material under different
loading situations and the fracture locations. Bone exhibits
different yield behavior along different material orientations
due to its anisotropic nature and therefore for better
understanding of bone behavior under multi-axial loading, it is
necessary to incorporate anisotropic yielding and post yield
properties in FEM. In the present study FE simulation of
cortical bone was carried out using different yield stress ratios
in different directions based on Hill’s criterion. Bone material
was treated as a transversely isotropic material whose effective
properties are isotropic in one of its planes. The tensile
behavior of cortical bone in longitudinal and transverse
directions was analyzed using two different uniaxial tensile
models. The uniaxial tensile models were found to be in good
agreement with the experimental results and therefore biaxial
model of cortical bone was also developed and analyzed using
the same approach. The study shows that Hill’s criterion gives
good results for anisotropic yielding in bone material and can
be used to simulate multidirectional loading situations in bone
mechanics
structures while consuming an amount of material that is very small relative to that required for full-size conventional
specimen. This technique is very helpful especially in the case of bone mechanics as bone properties are heterogeneous
and anisotropic in nature and it is difficult to obtain standard size of specimen for mechanical testing. In the present study
an effort is made to simulate punch specimen setup using mechanical properties of the cortical femur bone material for
miniature specimen while considering its nature to be transversely isotropic. The samples were taken in both longitudinal
as well as transverse direction. The various load displacement curves and contour profiles obtained for different
thicknesses of the miniature specimen using finite element simulation were compared with each other. The values of load
at breakaway point were obtained for different cases of miniature specimen. It is anticipated that these values can be
further used to evaluate yield strength of the bone material in different cases.
heterogeneous and anisotropic nature. Finite element modeling
(FEM) has been an effective tool in the field of bone mechanics
to predict the behavior of bone material under different
loading situations and the fracture locations. Bone exhibits
different yield behavior along different material orientations
due to its anisotropic nature and therefore for better
understanding of bone behavior under multi-axial loading, it is
necessary to incorporate anisotropic yielding and post yield
properties in FEM. In the present study FE simulation of
cortical bone was carried out using different yield stress ratios
in different directions based on Hill’s criterion. Bone material
was treated as a transversely isotropic material whose effective
properties are isotropic in one of its planes. The tensile
behavior of cortical bone in longitudinal and transverse
directions was analyzed using two different uniaxial tensile
models. The uniaxial tensile models were found to be in good
agreement with the experimental results and therefore biaxial
model of cortical bone was also developed and analyzed using
the same approach. The study shows that Hill’s criterion gives
good results for anisotropic yielding in bone material and can
be used to simulate multidirectional loading situations in bone
mechanics