Growth Mechanism, Local Stresses, and Young's Moduli of Micro-Deformation Zones in Glassy Polymers Films by AFM

1993 ◽  
Vol 308 ◽  
Author(s):  
A.C.-M. Yang ◽  
M.S. Kunz ◽  
T.W. Wu
Keyword(s):  
Stress Distribution ◽  
Shear Deformation ◽  
Strain Softening ◽  
Glassy Polymer ◽  
Glassy Polymers ◽  
Young’S Moduli ◽  
Atomic Force ◽  
Local Stresses ◽  
Craze Initiation ◽  
Micro Deformation

ABSTRACTBy studying the topography of crazes and shear deformation zones in polymer films with the Atomic Force Microscope (AFM), it was found that crazes and shear deformation zones grew by a micro-necking process. This discovery indicates that when a glassy polymer undergoes local deformations, the material drawn into the deformation zones continues to be deformed until a much later time than that previously understood. Details of the craze micro-necking mechanism and its important implications will be discussed. Based on the necking mechanics, it was shown that craze initiation and growth can be examined using a modified Considere construction, and the stress distribution within a micro-deformation zone was investigated by assuming the Bridgman's theory. The results of the stress analysis are in excellent agreement with the breakdown behavior of crazes observed experimentally. The Young's moduli of the crazed and sheared polymers within the tiny deformation zones were also measured using a simple new AFM technique. Evidence of strain softening was clearly observed in that both the Young's moduli of crazes and shear deformation zones were very low compared to that in the bulk.

scholarly journals Mechanics of particulate composites with glassy polymer binders in compression

2014 ◽  
Vol 372 (2015) ◽  
pp. 20130215 ◽  
Author(s):  
J. L. Jordan ◽  
J. E. Spowart ◽  
M. J. Kendall ◽  
B. Woodworth ◽  
C. R. Siviour
Keyword(s):  
Strain Softening ◽  
Volume Fraction ◽  
Glassy Polymer ◽  
Glassy Polymers ◽  
Polymer Chains ◽  
Particulate Composites ◽  
Strain Rates ◽  
Structural Components ◽  
Compressive Response ◽  
Polymer Binders

Whether used as structural components in design or matrix materials for composites, the mechanical properties of polymers are increasingly important. The compressive response of extruded polymethyl methacrylate (PMMA) rod with aligned polymer chains and Al–Ni–PMMA particulate composites are investigated across a range of strain rates and temperatures. The particulate composites were prepared using an injection-moulding technique resulting in highly anisotropic microstructures. The mechanics of these materials are discussed in the light of theories of deformation for glassy polymers. The experimental data from this study are compared with PMMA results from the literature as well as epoxy-based composites with identical particulates. The PMMA exhibited the expected strain rate and temperature dependence and brittle failure was observed at the highest strain rates and lowest temperatures. The Al–Ni–PMMA composites were found to have similar stress–strain response to the PMMA with reduced strain softening after yield. Increasing volume fraction of particulates in the composite resulted in decreased strength.

Elastic Stress Singularities: Implications for the Attachment of Tendon to Bone

2011 ◽  
Author(s):  
Yanxin Liu ◽  
Victor Birman ◽  
Chanqing Chen ◽  
Stavros Thomopoulos ◽  
Guy M. Genin
Keyword(s):  
Stress Distribution ◽  
Abrupt Change ◽  
Elastic Stress ◽  
Insertion Site ◽  
Stress Singularities ◽  
Local Stresses ◽  
Material Mismatch ◽  
Moduli Of Elasticity

The material mismatch at the attachment of tendon to bone is amongst the most severe for any tensile connection in nature. This is related to the large difference between the stiffness of tendon and bone, whose moduli of elasticity vary by two orders of magnitude. Predictably, such an abrupt change in the stiffness realized over a very narrow insertion site results in high local stresses. One of the implications of the stress distribution is a potential for stress singularities at the junction of the insertion to the bone.

Criteria of Craze Initiation in Glassy Polymers

1971 ◽  
Vol 42 (11) ◽  
pp. 4188-4196 ◽  
Author(s):  
Tsuey T. Wang ◽  
M. Matsuo ◽  
T. K. Kwei
Keyword(s):  
Glassy Polymers ◽  
Craze Initiation

scholarly journals Mechanical Properties of Electrospun, Blended Fibrinogen: PCL Nanofibers

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1843
Author(s):  
Jacquelyn M. Sharpe ◽  
Hyunsu Lee ◽  
Adam R. Hall ◽  
Keith Bonin ◽  
Martin Guthold
Keyword(s):  
Mechanical Properties ◽  
Strain Softening ◽  
Electrospun Nanofibers ◽  
High Energy ◽  
Optical Microscope ◽  
Ductile Material ◽  
Breaking Strain ◽  
Atomic Force ◽  
Microscope Technique ◽  
Afm Probe

Electrospun nanofibers manufactured from biocompatible materials are used in numerous bioengineering applications, such as tissue engineering, creating organoids or dressings, and drug delivery. In many of these applications, the morphological and mechanical properties of the single fiber affect their function. We used a combined atomic force microscope (AFM)/optical microscope technique to determine the mechanical properties of nanofibers that were electrospun from a 50:50 fibrinogen:PCL (poly-ε-caprolactone) blend. Both of these materials are widely available and biocompatible. Fibers were spun onto a striated substrate with 6 μm wide grooves, anchored with epoxy on the ridges and pulled with the AFM probe. The fibers showed significant strain softening, as the modulus decreased from an initial value of 1700 MPa (5–10% strain) to 110 MPa (>40% strain). Despite this extreme strain softening, these fibers were very extensible, with a breaking strain of 100%. The fibers exhibited high energy loss (up to 70%) and strains larger than 5% permanently deformed the fibers. These fibers displayed the stress–strain curves of a ductile material. We provide a comparison of the mechanical properties of these blended fibers with other electrospun and natural nanofibers. This work expands a growing library of mechanically characterized, electrospun materials for biomedical applications.

Stress Distribution in Be Compact Tension Specimen

2007 ◽  
Vol 561-565 ◽  
pp. 2033-2036
Author(s):  
Rui Wen Li ◽  
Ping Dong
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Stress Distribution ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Tension Specimen ◽  
X Ray ◽  
Measured Stress ◽  
Local Stresses ◽  
Fracture Behaviors

Beryllium (Be) is susceptible to introduce stress because it is a brittle metal with a high elastic modular. The compact tension (CT) specimens of beryllium were designed to determinate stress and fracture behaviors. Stress distribution near notch in CT beryllium was measured by the combination of an X-ray stress analysis and a custom-designed load device. The results show that local stresses near notch tip are much higher than those on other area. Thus, stress concentration lead the CT specimens fracture along the notch direction. Residual stresses due to machining are remained. A finite element ( FE ) calculation on the same loaded geometry was made, and the result is agreement with the measured stress distribution near notch.

Structure and Properties of Microcomposites and Macrocomposites from Block Polymers

1978 ◽  
Vol 51 (4) ◽  
pp. 775-787 ◽  
Author(s):  
S. L. Aggarwal ◽  
R. A. Livigni
Keyword(s):  
Impact Strength ◽  
Glassy Polymer ◽  
Glassy Polymers ◽  
Polymer Composition ◽  
Structure And Properties ◽  
Block Polymers ◽  
Block Polymer ◽  
Polymer Systems ◽  
Heat Distortion Temperature ◽  
The Matrix

Abstract The incorporation of a rubber phase in glassy polymers, as is well known in the case of high impact polystyrene, leads to an increase in their impact strength. Block polymers offer three principal approaches for obtaining multiphase glassy polymers in which an elastomer phase is present in the matrix of the glassy polymer. They are: (1) control of block polymer composition, (2) blending of block polymer with homopolymers, and (3) polymerization of a solution of a block polymer in the monomer corresponding to one of the blocks. The observed properties, such as impact strength, modulus, and heat distortion temperature, desired in rubber-modified glassy polymers are discussed for block polymer systems prepared using the above approaches.

Plastic Deformation Macrolocalization. Local Stresses and Fracture in Ultrafine Grain Titanium

2014 ◽  
Vol 682 ◽  
pp. 351-356 ◽  
Author(s):  
Vladimir Danilov ◽  
Galina Shlyakhova ◽  
Boris Semukhin
Keyword(s):  
Plastic Deformation ◽  
Quantitative Assessment ◽  
Test Sample ◽  
Ultrafine Grain ◽  
Material Structure ◽  
X Ray ◽  
Force Microscopy ◽  
Qualitative And Quantitative ◽  
Atomic Force ◽  
Local Stresses

The process of plastic deformation in ultrafine grain titanium is considered. Using the methods of speckle photography and X-ray diffractometry, the distributions of local strains and of local elastic distortions were examined for the test sample work. It is shown that the method of atomic-force microscopy can be used effectively for qualitative and quantitative assessment of ultrafine grain material structure.

scholarly journals DENSITOMETRY-BASED FEM SIMULATIONS OF NOVEL POROUS IMPLANTS AND CORRESPONDING STRESS DISTRIBUTION AT THE PERI-IMPLANT AREA

2020 ◽  
Vol 26 ◽  
pp. 76-80
Author(s):  
Luboš Řehounek ◽  
Aleš Jíra
Keyword(s):  
Stress Distribution ◽  
Stress Shielding ◽  
Real Patient ◽  
Fem Model ◽  
Stl File ◽  
Young’S Moduli ◽  
Minimum Principal Stress ◽  
3D Geometry ◽  
Ct Data ◽  
Reducing Stress

The presented work focuses on determining the stress distribution at the peri-implant area around dental implants. A numerical analysis simulating the conditions of chewing food has been performed on a FEM model. This model has been created using anonymized real patient CT data and a dental implant model developed at CTU. The CT data served as a 3D geometry and also as a way to construct the global matrix of stiffness of the bone material. Bone density was used as the defining parameter in determining the values of Young’s moduli of individual finite elements by the computational program (Mechanical Finder). The implant was introduced as a user-created STL file, which was imported to the computational software and situated inside the geometry of the human mandible. The results show that, as predicted, porous implants achieve higher values of minimum principal stress in the bone as opposed to homogeneous implants (13.4 MPa vs. 7.0 MPa), thus reducing stress shielding.

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