Deformation Of Polymers Research Articles

Persistent homology analysis of craze formation.

We apply a persistent homology analysis to investigate the behavior of nanovoids during the crazing process of glassy polymers. We carry out a coarse-grained molecular dynamics simulation of the uniaxial deformation of an amorphous polymer and analyze the results with persistent homology. Persistent homology reveals the void coalescence during craze formation, and the results suggest that the yielding process is regarded as the percolation of nanovoids created by deformation.

Rupture of polymers by chain scission

One of the distinguishing features of elastomeric materials, which consist of a network of flexible polymeric chains, is that the deformation response is dominated by changes in entropy. Accordingly, most classical theories of rubber-like elasticity consider only the entropy and neglect any changes in internal energy. On the other hand, the fracture of strongly cross-linked elastomers is essentially energy dominated, as argued in the well-known Lake–Thomas model for the toughness of elastomers. However, a single model unifying these two phenomena is still lacking. We provide a rational yet simple model for deformation and fracture of cross-linked polymers, based on two ingredients: (i) a non-Gaussian statistical mechanics model of polymer chains that accounts for the increase in energy due to the deformation of molecular bonds; (ii) a chain scission criterion based on the bond deformation energy attaining a critical value. Using this model, we can estimate the rupture stretch of elastomeric materials from fundamental quantities describing the polymer network. We use this model to relate the flaw sensitivity of elastomers to an intrinsic material length scale related to the network structure.

Deformation of semicrystalline polymers – the contribution of crystalline and amorphous phases

The plastic deformation process of semicrystalline polymers and the micromechanisms involved are discussed. The particular attention is paid to the dependence of deformation on structure and mutual influence of deformation of crystalline and amorphous components. Deformation of a semicrystalline polymer appears a complex series of continuous processes, involving mostly crystallographic deformation mechanisms operating in the crystalline phase. However, a very important role in that sequence is played by the deformation of amorphous interlamellar layers, partially reversible on unloading, which produces not only the high orientation of amorphous component but also influences deeply and supports the deformation of crystalline phase since crystalline lamellae and amorphous interlamellar layers, intimately connected through covalent bonds of chains crossing the interface, can deform only simultaneously and consistently. In particular, an influence of the topology of the amorphous phase, including the density of the molecular network of entangled chains and number of chains connecting adjacent crystalline and amorphous layers, on deformation instabilities of crystalline component in polyethylene are discussed. The induced instabilities of crystallographic slip lead to formation of lamellar kinks and frequently to an extensive fragmentation of lamellae. These transformations of crystalline structure together with restructurization of amorphous phase at high strains influence deeply the formation of the final highly oriented structure of the deformed semicrystalline polymer.

Study on Modeling of Inelastic Deformation of Semi-crystalline Polymer based on Kinetics of Molecular Chain

Study on Modeling of Inelastic Deformation of Semi-crystalline Polymer based on Kinetics of Molecular Chain

The effect of temperature, static load and electron beam irradiation on the deformation of linear polymers

A comprehensive experimental study on the effect of temperature, static load and electron beam irradiation on thermomechanical properties of polytetrafluoroethylene material was conducted. Four regions having different nature were detected on the curves of dependences of deformation (ϵ) from temperature (t). The obtained curves of ϵ from t prove the presence of phase transitions in this film. Irradiation significantly affects the dependence of ϵ(t) and ϵ(σ).

ポリプロピレン－銅メッシュ複合材料の塑性変形過程における不均一変形の評価

To improve the plastic instability of a thermoplastic polymer composite under cold forming, a copper mesh was filled into the polypropylene (PP). PP-Cu mesh composite plate specimens with the Cu mesh inclined in various directions were formed by the compression molding of the PP pellet and Cu mesh. First, the tensile behavior of Cu meshes with the angles of 0/90°, 15/75°, 30/60° and 45° to the tensile direction was examined. The maximum stress decreased gradually with increasing Cu mesh angle to the tensile direction because the Cu wires rotated in the tensile direction. The anisotropic response was also confirmed for the PP-Cu mesh composite, and the anisotropy was emphasized for composites with the higher volume fractions of the Cu mesh. The decrease in the nominal stress, which is often seen in the tensile deformation of the thermoplastic polymer, almost disappeared for the composite specimen with the Cu mesh at the angle of 45° to the tensile direction. Also, the deformation concentration in the specimen was effectively suppressed by reducing the deformation resistance in the early stage of deformation and by increasing the strain hardening after yielding.

Large strain viscoelastic dissipation during interfacial rupture in laminated glass.

In the dynamic rupture of laminated glass, it is essential to maximize energy dissipation. To investigate the mechanisms of energy dissipation, we have experimentally studied the delamination and stretching of a polymeric viscoelastic interlayer sandwiched between glass plates. We find that there is a velocity and temperature domain in which delamination fronts propagate in a steady state manner. At lower velocities, fronts are unstable, while at higher velocities, the polymer ruptures. Studying the influence of the interlayer thickness, we have shown that the macroscopic work of fracture during the delamination of the interlayer can be divided in two main components: (1) a near crack work of fracture which is related to the interfacial rupture and to the polymer deformation in the crack vicinity. (2) A bulk stretching work, which relates to the stretching of the interlayer behind the delamination front. Digital image correlation measurements showed that the characteristic length scale over which this stretching occurs is of the order of the interlayer thickness. Finally, an estimate of the bulk stretching work was provided, based on a simple uniaxial tensile test.

Recovery behavior of thermoplastic polymers in micro hot embossing process

A series of experiments were carried out to investigate polymer recovery in the micro hot embossing process. Above the glass transition temperature (Tg), polymer deformation becomes much easier and complete filling of microcavities is generally not difficult to achieve. One of the problems restricting replication efficiency of the hot embossing technique is polymer recovery. After complete filling, if without timely cooling, large recovery may happen and lead to defective embossing results. In this study, the recovery was found to be able to cause a height reduction of 21.4%, 17.8%, and 16.0% in the hot embossed micro-pyramid arrays, micro-pillar arrays, and micro-prism arrays respectively. This recovery can be avoided by means of prolonging embossing time or increasing embossing temperature. However, prolonging embossing time increases cycle time, while increasing embossing temperature is likely to induce severe warpage or damage problems. Thus, improvement of the embossing process is in urgent need. Through investigation on the recovery phenomena, which are characterized by that an apparent height and shape difference can be observed among adjacent embossed structures in the same polymer replica, it was found that interfacial bonding formed between the mold cavity wall and the polymer material is capable of preventing the recovery from happening. By applying the energy balanced approach widely used in fracture mechanics to the polymer recovery process, a theory of competition between the recovery and the adhesion was proposed, with which the experimental phenomena can be satisfactorily explained. During unloading, if the strain energy stored in the system for recovery is not enough for breaking the interfacial bonding, the recovery will be stopped; otherwise, large recovery may happen. To verify the theory, hot embossing experiments considering effects of process conditions and improved adhesion were conducted finally, further demonstrating that in the micrometer scale the adhesion has significant impacts on the recovery behavior of the polymer. Results of this research work indicate that we can take advantage of the adhesion to prevent the recovery and to achieve high-accuracy and high-efficiency micro hot embossing in the temperature range near the Tg.

Reversible Plastic Deformation of Polymer Blends as a Means to Achieve Stretchable Organic Transistors.

Intrinsically stretchable semiconductors will facilitate the realization of seamlessly integrated stretchable electronics. However, to date demonstrations of intrinsically stretchable semiconductors have been limited. In this study, a new approach to achieve intrinsically stretchable semiconductors is introduced by blending a rigid high-performance donor-acceptor polymer semiconductor poly[4(4,4dihexadecyl4Hcyclopenta [1,2b:5,4b' ] dithiopen2yl) alt [1,2,5] thiadiazolo [3,4c] pyridine] (PCDTPT) with a ductile polymer semiconductor poly(3hexylthiophene) (P3HT). Under large tensile strains of up to 75%, the polymers are shown to orient in the direction of strain, and when the strain is reduced, the polymers reversibly deform. During cyclic strain, the local packing order of the polymers is shown to be remarkably stable. The saturated field effect charge mobility is shown to be consistently above 0.04 cm2 V-1s-1 for up to 100 strain cycles with strain ranging from 10% to 75% when the film is printed onto a rigid test bed. At the 75% strain state, the charge mobility is consistently above 0.15 cm2 V-1s-1. Ultimately, the polymer blend process introduced here results in an excellent combination of device performance and stretchability providing an effective approach to achieve intrinsically stretchable semiconductors.

A hygro-thermo-mechanical coupled cyclic constitutive model for polymers with considering glass transition

Based on the experimental observations to the cyclic deformation of polyamide-6 polymer (PA6) involving a multi-field coupled issue, a new hygro-thermo-mechanical coupled cyclic viscoelastic-viscoplastic constitutive model is constructed to describe the multi-field coupled cyclic deformation of the PA6 within the framework of irreversible thermodynamics. In the proposed model, a new free energy is introduced to obtain the appropriate independent state variables; the thermodynamic driving forces of strain-like internal variables related to the viscoelasticity, viscoplasticity, chemical reaction and glass transition are deduced from the newly constructed free energy and the Clausius-Duhem's dissipative inequality. The spatial and temporal evolutions of temperature and relative humidity are deduced from the first law of thermodynamics and the mass conservation equation, respectively. The Langmuir-type (i.e., non-Fick's) diffusion equation is deduced and a new criterion of glass transition is developed. The glass transition is caused by the intrinsic heat generation of the PA6 during the cyclic deformation. Finally, the capability of the proposed model is verified by comparing the predicted results with the corresponding experimental ones of the PA6. It is seen that the temperature-, relative humidity-, rate-dependent cyclic deformation of the PA6 and the variations of relative humidity and temperature in the PA6 can be reasonably predicted by the proposed model.

Analysis of plastic deformation of semi-crystalline polymers during ECAE process using 135° die

In this paper, analysis of plastic deformation of high density polyethylene (HDPE) and polypropylene (PP) during an equal channel angular extrusion (ECAE) process is investigated. The effects of ram speed, number of passes, processing route and temperature are tested experimentally using a 135◦ die. The results show that the pressing force decreases with an increase in the number of passes and reaches a saturation state rapidly for routes A and C compared to routes BA and BC. Furthermore, it is found that the reduced curvature of the extruded samples is obtained by route C, however, the maximum warping is obtained by route A. A slight influence of temperature on the reduction of the warping is observed on the extruded samples. In order to predict the plastic strain inside the extruded samples, an elastic viscoplastic model is identified using compressive tests at different strain rates and coupled with the finite element method (FEM). A good correlation is found between the numerical modeling and experimental findings. FEM results show that the PP samples display a higher level of plastic strain compared to HDPE samples. However, almost the same degree of strain heterogeneity is obtained for both polymers. Finally, in order to reduce the warping and improve the strain homogeneity, a controlled back-pressure with small corner angle is expected to be an adequate solution.

Polymer Colloidal Sphere-Based Hybrid Solid Immersion Lens for Optical Super-resolution Imaging.

The optical microscope is a widely used real-time investigation tool, but usually suffers from low resolution due to the Abbe diffraction limit. Herein, we design and successfully synthesize ZrO2/polymer hybrid colloidal microspheres with as high as 47.5 wt % inorganic nanoparticles by suspension polymerization of 9,9'-bis[4-(2-acryloyloxyethyloxy)phenyl]fluorene (BAEPF). Owing to the homogeneous dispersion, high density, and high refractive index of inorganic nanoparticles and deformability of polymers, the obtained ZrO2/poly(BAEPF) hybrid colloidal microspheres have a high refractive index, optical transparency, and controllable curvature and thus can be directly used as a hybrid solid immersion lens (hSIL) for the optical microscope, achieving super-resolution imaging of 50 nm and even 45 nm under a standard white light or blue light optical microscope, which is far beyond the diffraction limit for visible light optical microscopes. Our hSIL design concept and strategy demonstrate efficient, fast, and solid practical potentials for optical super-resolution imaging and may also create another application possibility for polymer colloidal spheres.

Load history and sequence effects on cyclic deformation and fatigue behavior of a thermoplastic polymer

The effect of load history and sequence on the cyclic deformation and fatigue behavior of polyether ether ketone (PEEK) thermoplastic was experimentally investigated. Various uniaxial strain-controlled multi-block fatigue tests were conducted, including (1) fully-reversed (Rε = −1) two-, three- and four-block loadings with adjusted frequency to maintain a nominal temperature rise on the specimen gage surface, (2) fully-reversed two-block loading to study the frequency effect, and (3) pulsating tension (Rε = 0) two-block loading to investigate the combine effect of pre-loading and mean stress/strain on cyclic deformation and fatigue behavior. For all fatigue tests under fully-reversed (Rε = −1) multi-block loading, cyclic stability of PEEK specimens was achieved at approximately the same reversal and with similar stress amplitudes as those without pre-loading under identical test conditions. Additionally, for tests with Rε = −1, pre-loading was found to have a significant beneficial effect on PEEK fatigue resistance, irrespective of the load sequence (i.e. high-low or low-high). However, no obvious load history and sequence effect on fatigue behavior of PEEK was observed for pulsating tension (Rε = 0) block loading tests. Experimental results also revealed that increasing test frequency generally leads to higher fatigue lives.

Development of methodologies for sliding wear measurement on liners and flexible riser pipes

Flexible riser pipes are extensively used in deep-water oil and gas exploration to transport these products from the seabed to the platform. These pipes may be severely worn out on the bend stiffener region due to the reciprocating sliding movement against the liners. This relative movement is caused by water currents, bad weather conditions and platform movements. This paper presents the development of methodologies to quantify the wear rate of flexible riser pipes and of liners using a coordinate measuring machine (CMM). Samples of six-inch flexible riser pipes and of liners tested in a large-scale tribometer were used to evaluate these methodologies. The expanded measurement uncertainty of the wear parameters was assessed according to the recommendations of the “Guide to the expression of uncertainty in measurement” (GUM-JCGM 100). Moreover, the contribution of the sample elastic deformation and of the thermal effects on the measurement uncertainty was considered. Among all the factors that affect the measurement uncertainty of the wear rate of the flexible riser pipe, the variability of the thickness along the wear track contributed most to the measurement uncertainty. This variability was caused by a rough inner surface in the riser polymeric layer. When measuring the liner wear rate, the elastic deformation of the polyurethane polymer had the highest contribution. The wear rate of the six-inch riser pipe and of the corresponding liner made it possible to estimate the lifetime of these components in the field.

Deformation of cross-linked liquid crystal polymers by light – from ultraviolet to visible and infrared

ABSTRACTCollecting and amplifying the nanoscopic molecular motions into macroscopic deformation is the unique property of cross-linked liquid crystal polymers (CLCPs). These materials can directly transfer input light energy into mechanical work when combined with photochromophores, thus fascinating many scientists. This article reviews the macroscopic and microscopic deformation of photoresponsive azobenzene-containing CLCPs and analyses the influence of mesogen alignment and chemical structure on shape change behaviour. We highlight some new methods to trigger the deformation by visible and infrared light instead of ultraviolet one, such as chemical modification of azobenzene and addition of upconversion materials.

Effect of radius of gyration on polymer deformation for thermal nanoimprint lithography

Effect of radius of gyration on polymer deformation for thermal nanoimprint lithography

Deformation and failure of semicrystalline polymers under dynamic tensile and biaxial impact loading

We propose a constitutive model to aid in the engineering design of semicrystalline polymer components that may be subjected to biaxial impact loading. To this end, we investigate the thermomechanical and failure behaviour of high density polyethylene (HDPE) under dynamic loading, both experimentally and analytically. We have carried out dynamic tensile tests at 101, 102 and 103 mm/s displacement rates. Digital image correlation (DIC) and infrared thermography were used to measure full 2D true strain fields and determine specimen temperature rise during tensile testing. The results were used to calibrate the constitutive parameters. To analyse the biaxial impact response, we have carried out falling weight impact (FWI) tests at a 4 m/s impact velocity. We assessed the model prediction capabilities by comparing numerical predictions with experimental results and good agreement was observed. The proposed model, which aims to achieve a compromise between prediction accuracy and formulation simplicity, shows that initial linear elastic response coupled with a temperature-dependent power-law viscoplastic flow element and a non-linear strain-hardening element are sufficient to model biaxial stress scenarios.

Relaxation times in deformed polymer glasses: A comparison between molecular simulations and two theories

Relaxation times in polymer glasses are computed with molecular dynamics simulations of a coarse-grained polymer model during creep and constant strain rate deformation. The dynamics is governed by a competition between physical aging that increases relaxation times and applied load or strain rate which accelerates dynamics. We compare the simulation results quantitatively to two recently developed theories of polymer deformation, which treat aging and rejuvenation in an additive manner. Through stress release and strain rate reversal simulations, we then show that the quantity governing mechanical rejuvenation is the rate of irreversible work performed on the polymer.

Modelling multi-scale deformation of amorphous glassy polymers with experimentally motivated evolution of the microstructure

Novel experimental data, obtained recently using advanced multi-scale experiments, have been used to develop a micro-mechanically motivated constitutive model for amorphous glassy polymers. Taking advantage of the experiments, the model makes use of a microstructural deformation gradient to incorporate the experimentally obtained deformation of the microstructure, as well as its evolving orientation. By comparing results from the model to experimental data, it is shown that the proposed approach is able to accurately predict glassy polymer deformation over a wide range of length-scales, from the macroscopic response (mm range) down to the deformation of the microstructure (nm range). The proposed model is evaluated by comparing the numerical response to experimental results on multiple scales from an inhomogeneous cold drawing experiment of glassy polycarbonate. Besides the macroscopic force–displacement response, a qualitative comparison of the deformation field at the surface of the specimen is performed. Furthermore, the predicted evolution of the fabric orientation is compared to experimental results obtained from X-ray scattering experiments. The model shows very good agreement with the experimental data over a wide range of length scales.

Using surface modified clay nanoparticles to improve rheological behavior of Hydrolized Polyacrylamid (HPAM) solution for enhanced oil recovery with polymer flooding

In this communication, effect of Surface Modified Clay Nanoparticles (SMCN) on rheological behavior of Hydrolized Polyacrylamid (HPAM) solution and also its resistance against the increases in temperature and salinity were investigated experimentally. An increases in polymer solution viscosity result in a decrease in mobility ratio then consequently it may increase the polymer flooding efficiency. High pressures imposed on polymers during flooding processes cause a considerable shear stress on them, which lead to breakage of polymer chains. In addition, at elevated temperatures, certain chemical reactions are accelerated and subsequently this force polymer chains to compress. This kind of behavior (compactness of polymer chains) can be observed in a saline environment. Therefore, polymer viscosity and consequent flooding process efficiency is decreased. To prevent deformation of polymers and increase the internal friction of the solution, surface of certain clay nanoparticles were modified by specific tetrahedral redundants and located between polymer chains.Finally, the potential utilization of these novel clay nanoparticles in improving the performance of polymer flooding on an unconsolidated sandpacks were investigated. According to the results, we suggest 0.1% wt concentration of SMCN as the optimum concentration in which the SMCN-HPAM solution is stable. In addition, results indicate that adding SMCN improves the resistance of polymer solution against an increases in salinity and temperature, and also its shear thinning behavior. Moreover, the experimental result indicates that SMCN-HPAM increases the oil recovery about 33% more than ordinary polymer flooding processes.