Human Bone: Functionally Graded Material Structures with Complex Geometry and Loading By: Albert Marin and Dr. Arturo A. Fuentes Department of Mechanical

Human Bone: Functionally Human Bone: Functionally Graded Material Structures Graded Material Structures

with Complex Geometry and with Complex Geometry and LoadingLoading

By:By:

Albert Marin and Dr. Arturo A. FuentesAlbert Marin and Dr. Arturo A. Fuentes

Department of Mechanical Engineering Department of Mechanical Engineering

The University of Texas-Pan AmericanThe University of Texas-Pan American

Figure source: <http://www.biovere.com/cart/images/Real_bone_femur_left_s.jpg>.

What is a Functionally Graded What is a Functionally Graded Material?Material?

A Functionally Graded Material (FGM) is:A Functionally Graded Material (FGM) is: A material which both its composition and A material which both its composition and

structure gradually change over volume therefore structure gradually change over volume therefore changing the properties of the material in order to changing the properties of the material in order to perform a certain function(s). Thus, material perform a certain function(s). Thus, material properties depend on the spatial position in the properties depend on the spatial position in the structure. The properties that may be structure. The properties that may be designed/controlled for desired functionality designed/controlled for desired functionality include chemical, mechanical, thermal, and include chemical, mechanical, thermal, and electrical properties.electrical properties.

Note: Typical Solids Mechanics equations assume the use homogeneous materials have uniformed properties. Significant research is being done by Industry, Universities, National Labs, and Federal Agencies to take more FGMs to the marketplace.

Source: Miyamoto, Y., W. A. Kaysser, B. H. Rabin, A. Kawasaki, and R. G. Ford. Source: Miyamoto, Y., W. A. Kaysser, B. H. Rabin, A. Kawasaki, and R. G. Ford. Functionally Graded Materials: Design, Processing and Functionally Graded Materials: Design, Processing and ApplicationsApplications. Dordrecht/Boston/London: Kluwer Academic.. Dordrecht/Boston/London: Kluwer Academic.

Types of Graded StructuresTypes of Graded Structures Stepwise Graded StructuresStepwise Graded Structures

An example is a spark plug which An example is a spark plug which gradient is formed by changing its gradient is formed by changing its composition from a refractory ceramic to composition from a refractory ceramic to a metala metal

Continuous Graded StructuresContinuous Graded Structures An example is the human bone which An example is the human bone which

gradient is formed by its change in gradient is formed by its change in porosity and compositionporosity and composition

Change in porosity happens across the Change in porosity happens across the bone because of miniature blood vessels bone because of miniature blood vessels inside the boneinside the bone

Note: Desired properties gradients may designed by Note: Desired properties gradients may designed by controlling crystal structure and crystal controlling crystal structure and crystal orientation, particulate diameter, bonding state, orientation, particulate diameter, bonding state, etc.etc.


Advantages and Challenges of Advantages and Challenges of FGM’sFGM’s

Advantages of FGMsAdvantages of FGMs Provide multifunctionality Provide ability to control deformation,

dynamic response, wear, corrosion, etc. and ability to design for different complex environments

Provide ability to remove stress concentrations

Provide opportunities to take the benefits (pros) of different material systems [e.g. ceramics and metals such as resistance to oxidation (rust), toughness, machinability, and bonding capability]

Challenges of FGMsChallenges of FGMs Mass production Quality control Cost

Example of a FGM The human bone is a an example

of a FGM. It is a mix of collagen (ductile protein polymer) and hydroxyapatite (brittle calcium phospate ceramic). The yellow marrow consists of fat which contributes to the weight and the red marrow is where the formation of red blood cells occur. A gradual increase in the pore distribution from the interior to the surface can pass on properties such as shock resistance, thermal insulation, catalytic efficiency, and the relaxation of the thermal stress. The distribution of the porosity affect the tensile strength and the Young’s modulus Figure source: Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. By Donald L. Bartel, Dwight T. Davy, and Tony

M. Keaveny. Upper Saddle River, New Jersey: Pearson Education, Inc, 2006.

Applications of FGMs Current applications of Current applications of

FGMs include:FGMs include: Structural walls that Structural walls that

combine two or more combine two or more functions including functions including thermal and sound thermal and sound insulationinsulation

Enhanced sports Enhanced sports equipment such as golf equipment such as golf clubs, tennis rackets, and clubs, tennis rackets, and skis with added graded skis with added graded combinations of flexibility, combinations of flexibility, elasticity, or rigidityelasticity, or rigidity

Enhanced body coatings Enhanced body coatings for cars including graded for cars including graded coatings with particles coatings with particles such as dioxide/micasuch as dioxide/mica


More Applications of FGM’sMore Applications of FGM’s


Human Bone: Functionally Human Bone: Functionally Graded Material StructureGraded Material Structure

The human bone has high strength at the surface as The human bone has high strength at the surface as it gradually lowers toward the inside by altering the it gradually lowers toward the inside by altering the porosityporosity

From an engineering perspective, the human bone is From an engineering perspective, the human bone is a remarkable material having unique material a remarkable material having unique material properties that has the ability to repair itself and to properties that has the ability to repair itself and to adapt to its mechanical environmentadapt to its mechanical environment

Multifunctionality of Bones Natural

Hematopoiesis Formation of red blood cells which occur in the spongy

and porous ends of long bones such as the femur Mineral Storage

99% of calcium is stored in bones

Mechanical Protection of vital organs

Such as the brain, heart, spinal cord, lungs Developed to absorb large amounts of energy yet remain

lightweight

Support and Motion Bones provide a frame that is able to withstand huge

amounts of forces during motion for mobilitySource: Bartel, Donald L., Dwight T. Davy, and Tony M. Keaveny. Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. Upper Saddle River, New Jersey: Pearson Education, Inc., 2006. 7-9.

Support and Motion

Bones are links like those of a truss which enable the body to transmit large forces from link to link

Figure source: Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. By Donald L. Bartel, Dwight T. Davy, and Tony M. Keaveny. Upper Saddle River, New Jersey: Pearson Education, Inc, 2006.


Complex Geometry of BonesComplex Geometry of Bones

Source: Bartel, Donald L., Dwight T. Davy, and Tony M. Keaveny. Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. Upper Saddle River, New Jersey: Pearson Education, Inc., 2006. 1-213.


Bones usually have a complex optimized geometry. In fact, bones exhibit a piezoelectric effect used both for detecting an external stress and to remodel bone structures so that no peak stress is developed at any point

Complex Loading of Human BoneComplex Loading of Human Bone The skeletal system is like a machine

that allow us to perform all types of activities including physical work and playing sports

Many bones undergo combined loading (axial, torsion, and bending loading)

The skeletal system, as a machine, gets damaged. Under certain loadings, bones break and joints wear out. Our advantage is that our skeletal system is usually able to repair itself

Source: Bartel, Donald L., Dwight T. Davy, and Tony M. Keaveny. Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. Upper Saddle River, New Jersey: Pearson Education, Inc., 2006. 18-21.

Final RemarksFinal Remarks

By exploiting the possibilities in the By exploiting the possibilities in the FGM concept, it is anticipated that FGM concept, it is anticipated that scientists and engineers will optimize scientists and engineers will optimize the properties of material systems the properties of material systems and new and novel and new and novel multifunctionalities will be createdmultifunctionalities will be created

Questions?Questions?

Documents

Human Bone: Functionally Graded Material Structures with Complex Geometry and Loading By: Albert Marin and Dr. Arturo A. Fuentes Department of Mechanical