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.

Tribological Behavior of Polymers Simulated by Molecular Dynamics

2004 ◽  
Vol 19 (3) ◽  
pp. 851-856 ◽  
Author(s):  
Witold Brostow ◽  
J. Adam Hinze ◽  
Ricardo Simões
Keyword(s):  
Molecular Dynamics ◽  
Liquid Crystalline ◽  
Tribological Behavior ◽  
Polymeric Materials ◽  
Scratch Resistance ◽  
Polymer Surfaces ◽  
Second Phase ◽  
Scratch Testing ◽  
Two Phase ◽  
First Results

Using molecular dynamics to simulate behavior of polymer surfaces during scratch testing, we report the first results of computer simulations of scratch behavior of noncrystals. A previously described procedure for creating realistic polymeric materials on the computer [W. Brostow, A.M. Cunha, and R. Simoes, Mater. Res. Innovat. 7, 19 (2003)] and used until now to simulate mechanical behavior of metals [S. Blonski, W. Brostow, and J. Kubat, Phys. Rev. B 49, 6494 (1994)] and one- and two-phase polymers [W. Brostow, A.M. Cunha, J. Quintanilla, and R. Simoes, Macromol. Theory Simul. 11, 308 (2002); W. Brostow, A.M. Cunha, and R. Simoes, Proc. Ann. Tech. Conf. Soc. Plastics Engrs. 60, 3105 (2002)] was applied. While experiments provide only the macroscopic penetration depth and the recovery (healing) depth, the simulations give the behavior of each macromolecular chain segment at each moment in time. We report results for one-phase polymers and also for systems with varying concentrations of a liquid crystalline (LC) second-phase that acts as a reinforcement. We relate the local structure to scratch resistance and recovery. The orientation of the chemical bonds is a major factor. The presence of a LC phase improves the tribological properties; however, the effect is not as significant as might have been expected.

Morphological features and mechanical behavior of one- and two-phase polymeric materials simulated by molecular dynamics

Polymer ◽  
2004 ◽  
Vol 45 (22) ◽  
pp. 7767-7777 ◽  
Author(s):  
Ricardo Simões ◽  
António M. Cunha ◽  
Witold Brostow
Keyword(s):  
Molecular Dynamics ◽  
Mechanical Behavior ◽  
Polymeric Materials ◽  
Morphological Features ◽  
Two Phase

On the Formation of Martensite in In0.77TL0.23.

1990 ◽  
Vol 205 ◽  
Author(s):  
M. Wuttig ◽  
X. Zhou ◽  
S. Nahm ◽  
J. Li
Keyword(s):  
Transformation Temperature ◽  
Mechanical Response ◽  
High Temperature Phase ◽  
Second Phase ◽  
Temperature Phase ◽  
Product Phase ◽  
X Ray Diffraction ◽  
Two Phase ◽  
X Ray ◽  
Precursor Structure

AbstractIt has been proposed that martensite is formed by heterogeneous nucleation and growth or evolves from a precursor. In order to examine these theories, high resolution X-ray diffraction experiments have been performed on In0.77Tl0.23. It is known that the transformation of the alloy is close to second order and tweed has been observed which could be a possible precursor structure. Our experimental results do show precursors but of a different nature: satellites around the 220 Bragg peak have been detected up to 15 degrees above the transformation temperature. They develop reversibly at the angular positions of the product phase. The results are not compatible with the “crest-riding-peridon” model but rather show an equilibrium two phase mixture above the transformation temperature in which the second phase is structurally equal to the product phase. We have also investigated the mechanical response of the high temperature phase and found that both shear ‘elastic constants’ soften. This result can be understood in terms of twin boundary or stacking fault motion.

Detection of Hyperfine Precipitates in Nickel-Base Alloys

1968 ◽  
Vol 26 ◽  
pp. 438-439
Author(s):  
P. Beardmore
Keyword(s):  
Fine Particles ◽  
Dark Field ◽  
Deformation Mechanisms ◽  
Second Phase ◽  
Two Phase ◽  
Realistic Interpretation ◽  
Metal Foils ◽  
Fluorescent Screen ◽  
Dark Field Microscopy ◽  
Nickel Base

One of the primary objectives of the use of the electron microscope in the examination of metal foils is to ascertain the exact details of the microstructure in order that a realistic interpretation of the deformation mechanisms can be made. However, problems can arise in two phase structures in which the second phase is present as particles of widely differing size. In such cases it is possible to overlook the extremely fine particles because of the predominance of the larger particles on the fluorescent screen. Thus, fine details of the microstructure can remain undetected. This is particularly true in alloys in which both the precipitate and matrix have a common crystal structure and differ only in state of order. In such a structure, the detection and clarity of the precipitates is enhanced by dark field microscopy.

scholarly journals Optimal assignment and scheduling of workers and tasks on an assembly line

2009 ◽  
Vol 28 (1) ◽  
pp. 64-84
Author(s):  
Lieschen Venter ◽  
Stephan Visagie
Keyword(s):  
Assembly Line ◽  
Labour Cost ◽  
Second Phase ◽  
Total Production ◽  
Temporary Workers ◽  
Optimal Assignment ◽  
Two Phase ◽  
Optimal Sequence ◽  
The Cost

In this paper the assignment of cross-trained and temporary workers to tasks on an assembly line is investigated. Cross-trained workers are skilled to perform more than one task on the assembly line in the production process. Temporary workers are viewed as either trained or untrained and may be hired or laid off as required. The solution procedure may be divided into three parts. During the first part a model is formulated to determine an optimal assignment of the workers to the production tasks. During the second part the model is extended to determine the effect of the assignment of both trained and untrained temporary workers to the tasks on the assembly line. During the final part of the model an optimal sequence of tasks in the assembly line is determined that minimises the resulting execution times of these tasks. During the first part the objective is to maximise the total production utility. This is achieved by implementing a two-phase model. The first phase maximises the utility of pro-duction by minimising labour shortage in the assembly line. During the second phase the improvement of the workers’ levels of skill is maximised while the effect of the learning and forgetting of skills is taken into consideration. A learn-forget-curve model (LFCM) is implemented to model the effect of this human characteristic on the master model. This approach ensures that the advantageous cross-trained nature of the workers is maintained and optimized, without a large deviation from the solution determined by the first phase. The objective of the second part is to minimise the labour cost of production by determin-ing the best type of workers for a certain task as well as the manner in which they should be hired or laid off. A worker is classified as either permanently or temporarily employed. Tem-porarily employed workers are further classified as either untrained or cross-trained workers. The assignment of workers to tasks on the assembly line is achieved by means of a Master Production Scheduling (MPS) model. The MPS has as its objective the minimisation of the total labour cost of performing all the tasks. The labour cost is defined as the sum of the temporary workers’ daily wages, the overtime cost of permanent workers, the overtime cost of temporary workers and the cost of employing and laying off temporary workers. Finally, during the third part an optimal sequence of tasks is determined in the production process in order to minimise the total production time. This is achieved by means of a two-phase dynamic assembly line balancing model, which is adjusted to incorporate the critical path method. During the first phase, an optimal task sequence is determined, while during the second phase, an optimal assignment of tasks to workstations and the timing thereof, is determined. The practical applicability of the model is demonstrated by means of a real life case study. The production of various styles of shoes in a leatherworks factory is considered. The production of each style requires a different set of tasks and each task requires a different level of skill. The factory under consideration employs both cross-trained and temporary workers and data sets were obtained empirically by observation, interviews and questionnaires. Upon execution of the first phase of the assignment model, an optimal utility is found and the second phase is able to maximise the increase of the workers’ skill level without deviation from this optimum. Upon execution of the employment model, it is found that labour costs are minimized by increasing the use of temporary workers and by assigning the maximum allowable number of overtime hours to them. Upon application of the scheduling model, an improved time is obtained compared to the standard execution time of each style. The results obtained from the case study indicate that the application of the model presented in this paper shows a substantial improvement in production, while reducing the cost of labour as well as improving the overall level of workers’ skills. A multi-objective model is thus developed which successfully maximises production utility, maximises skill development of workers, minimises labour costs and the occurrence of idle workers as well as minimises total execution time. 

Recent Advances on the Deformation Behavior of Two-Phase α+β Titanium Alloys

2019 ◽  
Vol 950 ◽  
pp. 55-59 ◽  
Author(s):  
Sreeramamurthy Ankem ◽  
William J. Joost ◽  
Samuel C. Schwarm
Keyword(s):  
Deformation Behavior ◽  
Single Phase ◽  
Elastic Interaction ◽  
Deformation Mechanisms ◽  
Second Phase ◽  
General Will ◽  
Two Phase ◽  
Ti Alloys ◽  
The Difference ◽  
The Individual

Two-phase materials, such as α+β Titanium (Ti) alloys, are technologically important. A number of factors can affect deformation behavior, including the interaction stresses between phases, the crystallographic relationships between phases, and the morphology. As a result, the deformation mechanisms of two-phase alloys may be different from the individual single-phase materials. For example, twinning may not occur in a single phase material if the grain size is very small but twinning can occur in a very fine grained alloy if the second phase contributes to the interfacial stresses due to elastic interactions. Interaction stresses can result from the difference in the elastic properties of the two phases. In particular, these elastic interaction stresses can be quantified by the finite element method (FEM). In this paper recent developments regarding two-phase deformation mechanisms will be reviewed and the ramifications on mechanical behavior in regard to two-phase Ti alloys in particular and on two-phase metallic materials in general will be outlined.

scholarly journals An Improved PBMM Algorithm by Reduce Cloud Data Traffic and Transfer Costs in Cloud of Things

2019 ◽  
Vol 9 (1) ◽  
pp. 2688-2699
Keyword(s):  
State Of The Art ◽  
Third Party ◽  
Second Phase ◽  
Data Traffic ◽  
Two Phase ◽  
Link Capacity ◽  
Cloud Data ◽  
And Performance ◽  
The Cost ◽  
Priority Levels

Cloud computing has been widely studied over the recent years. Researchers have developed different algorithms for improving the performance and minimizing the cost. This paper proposes a new algorithm to improve and enhance the PBMM algorithm (Priority Based on Min-Min Algorithm). The proposed algorithm works with the aid of one of the Cloud of Things (CoT) services; this service is Sensing and Actuation as a Service (SAaaS). The proposed Algorithm works on third-party broker. However, it has two-phase: the first phase is Sensing: in this phase, the sensor observes the throughput for all tasks and compares it with the link capacity. The Second phase is Actuation: depending on the comparison in the first phase, the priority of all the takes will change depending on the link capacity, all tasks will have the same priority if the throughput is low (Green throughput). All tasks will have two priority levels (high, low) if the throughput medium (Yellow throughput), and finally, if the throughput is high (red throughput) all tasks will have a default priority which assigned to them when they are created. However, the efficiency and performance of the IPBMM algorithm depend on the capacity of the link. If capacity is high (traffic in the network is high), the performance is very good and the costly, but if the capacity is medium (traffic in the network is medium), the performance is good as well as the cost. While if the capacity is low (traffic in the network is low), the performance is good and the cost is free. Therefore, the outcomes of the proposed algorithm experiment given 30% better results than the PBMM algorithm and other state-of-the-art algorithms

scholarly journals A multi-objective fuzzy mathematical approach for sustainable reverse supply chain configuration

2017 ◽  
Vol 11 ◽  
Author(s):  
Jyoti D. Darbari ◽  
Vernika Agarwal ◽  
Venkata S.S. Yadavalli ◽  
Diego Galar ◽  
Prakash C. Jha
Keyword(s):  
Social Performance ◽  
Fuzzy Model ◽  
Three Dimensions ◽  
Fuzzy Decision Making ◽  
Second Phase ◽  
Reverse Supply Chain ◽  
Two Phase ◽  
Multi Objective ◽  
Cost Differential ◽  
The Cost

Background: Designing and implementation of reverse logistics (RL) network which meets the sustainability targets have been a matter of emerging concern for the electronics companies in India.Objectives: The present study developed a two-phase model for configuration of sustainable RL network design for an Indian manufacturing company to manage its end-of-life and endof-use electronic products. The notable feature of the model was the evaluation of facilities under financial, environmental and social considerations and integration of the facility selection decisions with the network design.Method: In the first phase, an integrated Analytical Hierarchical Process Complex Proportional Assessment methodology was used for the evaluation of the alternative locations in terms of their degree of utility, which in turn was based on the three dimensions of sustainability. In the second phase, the RL network was configured as a bi-objective programming problem, and fuzzy optimisation approach was utilised for obtaining a properly efficient solution to the problem.Results: The compromised solution attained by the proposed fuzzy model demonstrated that the cost differential for choosing recovery facilities with better environmental and social performance was not significant; therefore, Indian manufacturers must not compromise on the sustainability aspects for facility location decisions.Conclusion: The results reaffirmed that the bi-objective fuzzy decision-making model can serve as a decision tool for the Indian manufacturers in designing a sustainable RL network. The multi-objective optimisation model captured a reasonable trade-off between the fuzzy goals of minimising the cost of the RL network and maximising the sustainable performance of the facilities chosen.

scholarly journals A Molecular Dynamics Simulations Study of the Influence of Prestrain on the Pop-In Behavior and Indentation Size Effect in Cu Single Crystals

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5220
Author(s):  
Rongguang Xu ◽  
Hengxu Song ◽  
Yongsheng Leng ◽  
Stefanos Papanikolaou
Keyword(s):  
Molecular Dynamics ◽  
Residual Stresses ◽  
Size Effect ◽  
Molecular Dynamics Simulations ◽  
Single Crystals ◽  
Mechanical Response ◽  
Indentation Size Effect ◽  
Deformation Mechanisms ◽  
Indentation Size ◽  
Dynamics Simulations

The pop-in effect in nanoindentation of metals represents a major collective dislocation phenomenon that displays sensitivity in the local surface microstructure and residual stresses. To understand the deformation mechanisms behind pop-ins in metals, large scale molecular dynamics simulations are performed to investigate the pop-in behavior and indentation size effect in undeformed and deformed Cu single crystals. Tensile loading, unloading, and reloading simulations are performed to create a series of samples subjected to a broad range of tensile strains with/without pre-existing dislocations. The subsequent nanoindentation simulations are conducted to investigate the coupled effects of prestrain and the presence of resulting dislocations and surface morphology, as well as indenter size effects on the mechanical response in indentation processes. Our work provides detailed insights into the deformation mechanisms and microstructure-property relationships of nanoindentation in the presence of residual stresses and strains.

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