The Effect of Different Behavior in Tension than in Compression on the Mechanical Response of Polymeric Materials

1973 ◽  
pp. 417-427 ◽  
Author(s):  
E. F. Rybicki ◽  
M. F. Kanninen
Keyword(s):  
Mechanical Response ◽  
Polymeric Materials

Mechanical Behavior of the Lamellar Structure in Semi-Crystalline Polymers

2012 ◽  
Vol 730-732 ◽  
pp. 1006-1011
Author(s):  
Ricardo Simões ◽  
Júlio C. Viana ◽  
Gustavo R. Dias ◽  
António M. Cunha
Keyword(s):  
Computer Simulations ◽  
Lamellar Structure ◽  
Mechanical Response ◽  
Tensile Load ◽  
Polymeric Materials ◽  
Amorphous Region ◽  
Uniaxial Tensile ◽  
Material Response ◽  
Crystalline Polymers ◽  
Lamella Thickness

We have employed molecular dynamics simulations to study the behavior of virtual polymeric materials under an applied uniaxial tensile load. Through computer simulations, one can obtain experimentally inaccessible information about phenomena taking place at the molecular and microscopic levels. Not only can the global material response be monitored and characterized along time, but the response of macromolecular chains can be followed independently if desired. The computer-generated materials were created by emulating the step-wise polymerization, resulting in self-avoiding chains in 3D with controlled degree of orientation along a certain axis. These materials represent a simplified model of the lamellar structure of semi-crystalline polymers, being comprised of an amorphous region surrounded by two crystalline lamellar regions. For the simulations, a series of materials were created, varying i) the lamella thickness, ii) the amorphous region thickness, iii) the preferential chain orientation, and iv) the degree of packing of the amorphous region. Simulation results indicate that the lamella thickness has the strongest influence on the mechanical properties of the lamella-amorphous structure, which is in agreement with experimental data. The other morphological parameters also affect the mechanical response, but to a smaller degree. This research follows previous simulation work on the crack formation and propagation phenomena, deformation mechanisms at the nanoscale, and the influence of the loading conditions on the material response. Computer simulations can improve the fundamental understanding about the phenomena responsible for the behavior of polymeric materials, and will eventually lead to the design of knowledge-based materials with improved properties.

Molecular deformation mechanisms and mechanical properties of polymers simulated by molecular dynamics

e-Polymers ◽  
2004 ◽  
Vol 4 (1) ◽  
Author(s):  
Ricardo Simões ◽  
António M. Cunha ◽  
Witold Brostow
Keyword(s):  
Molecular Dynamics ◽  
Mechanical Response ◽  
Polymeric Materials ◽  
Spatial Arrangement ◽  
Deformation Mechanisms ◽  
Second Phase ◽  
Two Phase ◽  
Chain Slippage ◽  
The Cost ◽  
Molecular Deformation

Abstract Virtual polymeric materials were created and used in computer simulations to study their behavior under uniaxial loads. Both single-phase materials of amorphous chains and two-phase polymer liquid crystals (PLCs) have been simulated using the molecular dynamics method. This analysis enables a better understanding of the molecular deformation mechanisms in these materials. It was confirmed that chain uncoiling and chain slippage occur concurrently in the materials studied following predominantly a mechanism dependent on the spatial arrangement of the chains (such as their orientation). The presence of entanglements between chains constrains the mechanical response of the material. The presence of a rigid second phase dispersed in the flexible amorphous matrix influences the mechanical behavior and properties. The role of this phase in reinforcement is dependent on its concentration and spatial distribution. However, this is achieved with the cost of increased material brittleness, as crack formation and propagation is favored. Results of our simulations are visualized in five animations.

scholarly journals Micromechanics of creep and relaxation of wood. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Holzforschung ◽  
2009 ◽  
Vol 63 (2) ◽  
Author(s):  
Parviz Navi ◽  
Stefanie Stanzl-Tschegg
Keyword(s):  
Mechanical Response ◽  
Molecular Level ◽  
Polymeric Materials ◽  
Climatic Conditions ◽  
Time Dependent ◽  
Viscoelastic Behaviour ◽  
Single Fibres ◽  
Time Dependent Behaviour ◽  
Wood Machining ◽  
Dependent Behaviour

Abstract Wood, like all polymeric materials, shows viscoelastic behaviour. The time dependent behaviour of wood depends on material anisotropy, temperature, moisture and stresses. To predict the behaviour of wood, numerous mathematical models have been developed largely relying on experimental results. In this paper, time dependent viscoelastic behaviour of wood is reviewed under constant and cyclic climatic conditions, separately. More emphasis is given on results obtained in recent years on the behaviour of thin wood tissues, single fibres, thermo-viscoelasticity of wood, influence of hemicelluloses and the modelling of the effect of transient moisture at the molecular level on the mechanical response.

scholarly journals Bioinspired Fingertip for Anthropomorphic Robotic Hands

2014 ◽  
Vol 11 (1-2) ◽  
pp. 25-38 ◽  
Author(s):  
Marco Controzzi ◽  
Marco D'Alonzo ◽  
Carlo Peccia ◽  
Calogero Maria Oddo ◽  
Maria Chiara Carrozza ◽  
...  
Keyword(s):  
Mechanical Response ◽  
Polymeric Materials ◽  
Fe Model ◽  
Robotic Hand ◽  
Compression Tests ◽  
Robotic Hands ◽  
Experimental Conditions ◽  
Grasp Stability ◽  
Significant Step ◽  
Human Finger

Background: An artificial fingertip with mechanical features and appearance similar to the human fingertip could represent a significant step forward towards the development of the next generation artificial hands. However, so far, a fingertip showing a good trade-off among mechanical features, appearance and anthropomorphism, along with its 3D computational model, is still missing.Objective: To explore and develop an artificial fingertip demonstrating a mechanical response similar to the human fingertip, in order to improve the grasp stability of robotic hands.Methods: Taking inspiration from the multi-layered structure of the human finger, novel artificial fingertips, composed of a rigid core and covered by layers of polymeric materials with different degrees of stiffness and topped by a hard nail were developed. An accurate 3D finite element (FE) model was also developed in order to simulate and evaluate the internal mechanical behavior of the prototypes under external indentations. The mechanical response of the prototypes was assessed and compared with that of the human fingertip and the FE model results, under different experimental conditions. Finally, the artificial fingertips were integrated into an anthropomorphic robotic hand and evaluated in grip tests, in order to compare the grasp stability with respect to conventional stiff (metal) fingertips.Results: The developed prototypes demonstrated a response to compression tests similar to the human finger and the FE model showed a discrete accuracy (mean error 7%). Finally, an increased ability (by 96%) in stably holding objects during precision grips with respect to conventional stiff fingers was demonstrated.Conclusion: Multi-layered biomimetic fingertips can improve grasp stability and cosmetic appearance of anthropomorphic robot hands.

Indentation Creep and Relaxation Measurements of Polymers

2004 ◽  
Vol 841 ◽  
Author(s):  
Mark R. VanLandingham ◽  
Peter L. Drzal ◽  
Christopher C. White
Keyword(s):  
Stress Relaxation ◽  
Mechanical Response ◽  
Creep Compliance ◽  
Relaxation Modulus ◽  
Polymeric Materials ◽  
Indentation Creep ◽  
Dimethyl Siloxane ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
Creep And Stress Relaxation

ABSTRACTInstrumented indentation was used to characterize the mechanical response of polymeric materials. A model based on contact between a rigid probe and a linear viscoelastic material was used to calculate values for creep compliance and stress relaxation modulus for epoxy, poly(methyl methacrylate) (PMMA), and two poly(dimethyl siloxane) (PDMS) elastomers. Results from bulk rheometry studies were used for comparison to the indentation creep and stress relaxation results. For the two glassy polymers, the use of sharp pyramidal tips produced responses that were considerably more compliant (less stiff) than rheometry values. Additional study of the deformation remaining in epoxy after creep testing revealed that a large portion of the creep displacement measured was due to post-yield flow. Indentation creep measurements of the epoxy using a rounded conical tip also produced nonlinear responses, but the creep compliance values appeared to approach linear viscoelastic values with decreasing creep force. Responses measured for the PDMS were mainly linear elastic, but the filled PDMS exhibited some time-dependence and nonlinearity in both rheometry and indentation measurements.

Influence of the Interaction Potential Parameters on the Mechanical Response of Simulated Semi-Crystalline Polymeric Materials

2006 ◽  
Vol 514-516 ◽  
pp. 810-814 ◽  
Author(s):  
Ricardo Simões ◽  
Júlio C. Viana ◽  
Gustavo R. Dias ◽  
António M. Cunha
Keyword(s):  
Interaction Potential ◽  
Lamellar Structure ◽  
Mechanical Response ◽  
Tensile Deformation ◽  
Polymeric Materials ◽  
Amorphous Region ◽  
Apparent Modulus ◽  
Secondary Bonds ◽  
Secondary Bond ◽  
Potential Parameters

The tensile deformation of a semi-crystalline lamellar structure was simulated using coarse-grain molecular dynamics. Interactions between statistical segments are described by Lennard-Jones potentials, with two types of interactions (primary and secondary bonds) defined for the amorphous and crystalline phases. The choice of the correct interaction potentials in coarsegrain simulations requires an understanding of the influence of each interaction potential parameter on the mechanical response. The present paper reports results from that study, following a design of experiments approach. It was found that the apparent modulus is mainly determined by the width of the secondary bond potential. The yield stress and the extent of deformation of the material at a fixed force level are influenced both by the width of the secondary bond potential and the depth of the potential well of the amorphous region. Thus, the tensile mechanical properties and behaviour of the specific lamellar structure under study seems to be mainly determined by the secondary interactions in the amorphous region.

scholarly journals On the Strain Rate Sensitivity of Fused Filament Fabrication (FFF) Processed PLA, ABS, PETG, PA6, and PP Thermoplastic Polymers

Polymers ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 2924
Author(s):  
Nectarios Vidakis ◽  
Markos Petousis ◽  
Emmanouil Velidakis ◽  
Marco Liebscher ◽  
Viktor Mechtcherine ◽  
...  
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Mechanical Response ◽  
Rate Sensitivity ◽  
Polymeric Materials ◽  
Applied Strain ◽  
Sensitivity Index ◽  
Strain Rates ◽  
Thermoplastic Polymers ◽  
Fused Filament Fabrication

In this study, the strain rate sensitivity of five different thermoplastic polymers processed via Fused Filament Fabrication (FFF) Additive Manufacturing (AM) is reported. Namely, Polylactic Acid (PLA), Acrylonitrile-Butadiene-Styrene (ABS), Polyethylene Terephthalate Glycol (PETG), Polyamide 6 (PA6), and Polypropylene (PP) were thoroughly investigated under static tensile loading conditions at different strain rates. Strain rates have been selected representing the most common applications of polymeric materials manufactured by Three-Dimensional (3D) Printing. Each polymer was exposed to five different strain rates in order to elucidate the dependency and sensitivity of the tensile properties, i.e., stiffness, strength, and toughness on the applied strain rate. Scanning Electron Microscopy (SEM) was employed to investigate the 3D printed samples’ fractured surfaces, as a means to derive important information regarding the fracture process, the type of fracture (brittle or ductile), as well as correlate the fractured surface characteristics with the mechanical response under certain strain rate conditions. An Expectation–Maximization (EM) analysis was carried out. Finally, a comparison is presented calculating the strain rate sensitivity index “m” and toughness of all materials at the different applied strain rates.

scholarly journals A Mechanics Based Surface Image Interpretation Method for Multifunctional Nanocomposites

Nanomaterials ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1578 ◽  
Author(s):  
Brina J. Blinzler ◽  
Ragnar Larsson ◽  
Karolina Gaska ◽  
Roland Kádár
Keyword(s):  
Thermal Properties ◽  
Functional Properties ◽  
Material Properties ◽  
Mechanical Response ◽  
Graphene Nanosheets ◽  
Polymeric Materials ◽  
Mechanical And Thermal Properties ◽  
Graphite Nanoplatelets ◽  
Modeling Framework ◽  
Surface Image

Graphene nanosheets and thicker graphite nanoplatelets are being used as reinforcement in polymeric materials to improve the material properties or induce new functional properties. By improving dispersion, de-agglomerating the particles, and ensuring the desired orientation of the nano-structures in the matrix, the microstructure can be tailored to obtain specific material properties. A novel surface image assisted modeling framework is proposed to understand functional properties of the graphene enhanced polymer. The effective thermal and mechanical responses are assessed based on computational homogenization. For the mechanical response, the 2-D nanoplatelets are modeled as internal interfaces that store energy for membrane actions. The effective thermal response is obtained similarly, where 2-D nanoplatelets are represented using regions of high conductivity. Using the homogenization simulation, macroscopic stiffness properties and thermal conductivity properties are modeled and then compared to the experimental data. The proposed surface image assisted modeling yields reasonable effective mechanical and thermal properties, where the Kapitza effect plays an important part in effective thermal properties.

scholarly journals Sustainable Additive Manufacturing: Mechanical Response of Polypropylene over Multiple Recycling Processes

2020 ◽  
Vol 13 (1) ◽  
pp. 159
Author(s):  
Nectarios Vidakis ◽  
Markos Petousis ◽  
Lazaros Tzounis ◽  
Athena Maniadi ◽  
Emmanouil Velidakis ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Mechanical Response ◽  
Polymeric Materials ◽  
Fused Filament Fabrication ◽  
Scanning Calorimetry ◽  
3D Printed ◽  
Thermomechanical Processes ◽  
Multiple Recycling ◽  
Plastic Parts ◽  
Polymer Crystallinity

The recycling of polymeric materials has received a steadily growing scientific and industrial interest due to the increase in demand and production of durable and lightweight plastic parts. Recycling of such materials is mostly based on thermomechanical processes that significantly affect the mechanical, as well as the overall physicochemical properties of polymers. The study at hand focuses on the recyclability of Fused Filament Fabrication (FFF) 3D printed Polypropylene (PP) for a certain number of recycling courses (six in total), and its effect on the mechanical properties of 3D printed parts. Namely, 3D printed specimens were fabricated from non-recycled and recycled PP material, and further experimentally tested regarding their mechanical properties in tension, flexion, impact, and microhardness. Comprehensive dynamic scanning calorimetry (DSC), thermogravimetric analysis (TGA), Raman spectroscopy, and morphological investigations by scanning electron microscopy (SEM) were performed for the different 3D printed PP samples. The overall results showed that there is an overall slight increase in the material’s mechanical properties, both in tension and in flexion mode, while the DSC characterization indicates an increase in the polymer crystallinity over the recycling course.

Advancing Nanoscale Indentation Measurements Toward Quantitative Characterization of Polymer Properties

2000 ◽  
Vol 6 (S2) ◽  
pp. 1108-1109
Author(s):  
M. VanLandingham ◽  
J. Villarrubia ◽  
G. Meyers ◽  
M. Dineen
Keyword(s):  
Mechanical Response ◽  
Polymeric Materials ◽  
Accurate Knowledge ◽  
Force Mode ◽  
Afm Cantilever ◽  
Cantilever Probes ◽  
Ultimate Objective ◽  
Absolute Measurements ◽  
And Behavior ◽  
Micrometer Scale

The ultimate objective of instrumented indentation testing is to obtain absolute measurements of material properties and behavior. To achieve this goal, accurate knowledge of the shape of the indenter tip is required. For indentation measurements involving sub-micrometer scale contacts, accurate knowledge of the tip shape can be difficult to achieve. In this presentation, a technique referred to as blind reconstruction is applied to the measurement of tip shapes of indenters used with the atomic force microscope (AFM) to indent polymeric materials.The AFM has been used recently to make nanoscale indentation measurements and is particularly useful for evaluating the mechanical response of polymeric materials. These measurements can be made using AFM cantilever probes and operating the AFM in force mode with some modifications to account for lateral tip motion. Because the AFM was not specifically designed as an indentation device, other complications can arise due to instrumental uncertainties such as piezo hysteresis, piezo creep, and photodiode nonlinearities.

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