Response surface predictions of the viscoelastic properties of vapor‐grown carbon nanofiber/vinyl ester nanocomposites

A full factorial design of experiments and response surface methodology were used to investigate the effects of formulation, processing, and operating temperature on the viscoelastic properties of vapor‐grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites. Factors included VGCNF type (pristine, oxidized), use of a dispersing agent (DA) (no, yes), mixing method (ultrasonication, high‐shear mixing, and a combination of both), VGCNF weight fraction (0.00, 0.25, 0.50, 0.75, and 1.00 parts per hundred parts resin (phr)), and temperature (30, 60, 90, and 120°C). Response surface models (RSMs) for predicting storage and loss moduli were developed, which explicitly account for the effect of complex interactions between nanocomposite design factors and operating temperature on resultant composite properties; such influences would be impossible to assess using traditional single‐factor experiments. Nanocomposite storage moduli were maximized over the entire temperature range (～20% increase over neat VE) by using high‐shear mixing and oxidized VGCNFs with DA or equivalently by employing pristine VGCNFs without DA at ～0.40 phr of VGCNFs. Ultrasonication yielded the highest loss modulus at ～0.25 phr of VGCNFs. The RSMs developed in this investigation may be used to design VGCNF‐enhanced VE matrices with optimal storage and loss moduli for automotive structural applications. Moreover, a similar approach may be used to tailor the mechanical, thermal, and electrical properties of nanomaterials over a range of anticipated operating environments. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Characterization,prediction, and optimization of flexural properties of vapor‐grown carbon nanofiber/vinyl ester nanocomposites by response surface modeling

A design of experiments and response surface modeling were performed to investigate the effects of formulation and processing factors on the flexural moduli and strengths of vapor‐grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites. VGCNF type (pristine, surface‐oxidized), use of a dispersing agent (no, yes), mixing method (ultrasonication, high‐shear mixing, and a combination of both), and VGCNF weight fraction (0.00, 0.25, 0.50, 0.75, and 1.00 parts per hundred parts resin (phr)) were selected as independent factors. Response surface models were developed to predict flexural moduli and strengths as a continuous function of VGCNF weight fraction. The use of surface‐oxidized nanofibers, a dispersing agent, and high‐shear mixing at 0.48 phr of VGCNF led to an average increase of 19% in the predicted flexural modulus over that of the neat VE. High‐shear mixing with 0.60 phr of VGCNF resulted in a remarkable 49% increase in nanocomposite flexural strength relative to that of the neat VE. This article underscores the advantages of statistical design of experiments and response surface modeling in characterizing and optimizing polymer nanocomposites for automotive structural applications. Moreover, response surface models may be used to tailor the mechanical properties of nanocomposites over a range of anticipated operating environments. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2087–2099, 2013     

Preparation and properties of silanized vapor‐grown carbon nanofibers/epoxy shape memory nanocomposites

Silanized vapor‐grown carbon nanofiber/epoxy (silanized‐VGCNF/EP) shape memory polymer (SMP) nanocomposites are successfully fabricated by using a composite molding technology. The surface functionalization of VGCNF is performed using an acid treatment followed by a reaction with silane. The oxidation as well as silanization of VGCNF and silanized‐VGCNF/EP nanocomposites are systematically and explicitly characterized using various analytical methods. The influence of the silane‐functionalized VGCNF on the properties of VGCNF/EP nanocomposites is investigated using field emission scanning electronic microscopy (FE‐SEM) and a dynamic mechanical analysis (DMA). The shape memory properties of the silanized‐VGCNF/EP nanocomposites are evaluated by a fold‐deploy shape memory test. The results reveal that the silanized‐VGCNF is preferably dispersed in the epoxy resin matrix. Furthermore, the glass transition temperature of silanized‐VGCNF/EP nanocomposites is enhanced, and the shape memory properties of the silanized‐VGCNF/EP nanocomposites are significantly improved. POLYM. COMPOS., 35:412–417, 2014. © 2013 Society of Plastics Engineers     

Processing-microstructure-property relationship in conductive polymer nanocomposites

The processing-microstructure-property relationship in conductive polymer nanocomposites was investigated. Nanocomposites of vapor grown carbon nanofiber (VGCNF)/high density polyethylene (HDPE) with different levels of nanofiber dispersion were formulated by changing the nanocomposites’ compounding temperature. Direct (SEM and optical microscopy) and indirect methods (linear viscoelastic properties) were used to characterize the dispersion of nanofiller. VGCNF aspect ratio before and after mixing was measured. Increasing processing temperature was found to increase the nanofiller agglomeration and reduce the breakage of nanofiller because of the decrease in the mixing shear stress and energy. The electrical and electromagnetic interference (EMI) shielding properties of the VGCNF/HDPE nanocomposites decreased with increase in processing temperature from 180 °C to 220 °C because the increase in the agglomeration of VGCNF was more significant than the preservation of the VGCNF aspect ratio. This finding does not mean that the increase in processing temperature will always lead to decrease in the electrical conductivity and EMI shielding properties for all polymer composites. For some composites, it is possible to preserve the filler aspect ratio enough so that the increase in agglomeration is less of a factor.     

Molecular dynamics simulations of oxidized vapor-grown carbon nanofiber surface interactions with vinyl ester resin monomers

Surface oxidation effects on the liquid vinyl ester (VE) monomer distributions near two oxidized vapor-grown carbon nanofiber (VGCNF) surfaces were studied using molecular dynamics simulations. Two overlapping graphene sheets containing oxygenated functional groups represented the oxidized VGCNF surfaces. Two liquid VE bisphenol-A dimethacrylates (designated VE1 and VE2, respectively) and styrene constituted the resin. Temporally and spatially averaged relative monomer concentrations, calculated in a direction away from the oxidized graphene surfaces, showed increased styrene and VE1 concentrations. Monomer molar ratios found within a 10 Å thick region adjacent to the oxidized graphene sheets were substantially different from those in the bulk resin. Curing should result in the formation of a very thin interphase region of different composition. The crosslink structure of such an interphase will be distinct from that of an unoxidized VGCNF surface. The enhanced VE1 concentration near this oxidized surface should give a higher crosslink density, leading to a stiffer interphase than that adjacent to unoxidized VGCNF surfaces. VGCNF–matrix adhesion may also be modified by the different interphase monomer molar ratios. These studies may facilitate multiscale material design by providing insight into carbon nanofiber–matrix interactions leading to improved macroscale composite properties.     

Separating stress and time dependent effects in the temperature dependent creep of polyethylene nanocomposites

The nonlinear time dependent creep of linear‐low density polyethylene (LLDPE) reinforced with montmorillonite layered silicate was investigated. A previous study related the time/stress dependence of creep compliance of the material at room temperature using the Burger and Kohlrausch‐Williams‐Watts models. Using both the creep and recovery compliance curves, we employ the Schapery formulation to study the relationship between deformation, time, stress, and temperature of LLDPE nanocomposites. Smooth mastercurves are constructed using time–temperature–stress superposition principles. The stress and temperature‐related creep constants and shift factors were determined for the material using the Schapery nonlinear viscoelastic equation. The prediction results confirm the enhanced creep resistance of nanofillers even at extended time scales and low temperatures. POLYM. ENG. SCI., 50:1646–1657, 2010. © 2010 Society of Plastics Engineers     

Fabrication and characterization of vapor grown carbon nanofiber/epoxy magnetic nanocomposites

Co₃O₄ nanoparticle‐decorated vapor‐grown carbon nanofiber (VGCNF) hybrid materials were successfully synthesized and served as nanofillers for preparing magnetic epoxy (EP) nanocomposites. The Co₃O₄‐decorated VGCNF (Co₃O₄‐VGCNF) and Co₃O₄‐VGCNF/EP nanocomposites were systematically and explicitly investigated by combined analytical techniques. The composition and phase structure of Co₃O₄‐VGCNF hybrid materials were characterized by Fourier transform infrared spectroscopy and X‐ray diffraction analyses. The morphology of Co₃O₄ was investigated using field‐emission scanning electronic microscopy (FE‐SEM). Results revealed the presence of Co₃O₄ nanoparticles firmly immobilized on VGCNF sidewalls. The tensile mechanical, thermomechanical, and magnetic properties of Co₃O₄‐VGCNF/EP nanocomposites were also investigated in detail. Results indicated that the tensile strength of Co₃O₄‐VGCNF/EP nanocomposites (filler = 0.5 wt%) improved by 44.6% compared with that of raw VGCNF/EP nanocomposites (filler = 0.5 wt%). Magnetization measurements revealed that Co₃O₄‐VGCNF/EP nanocomposites exhibited ferromagnetic behavior, and the saturation magnetization and coercivity of the nanocomposites with 2 wt% of Co₃O₄‐VGCNF were 0.055 emu g⁻¹ and 0.75 kOe, respectively. POLYM. COMPOS., 37:1728–1734, 2016. © 2014 Society of Plastics Engineers     

Microwave processing of SiC nanoparticles infused polymer composites: Comparison of thermal and mechanical properties

The goal of this study is to compare thermal and mechanical properties of an epoxy resin system reinforced with SiC nanoparticles using both conventional thermal curing and microwave irradiation techniques. The microwave curing technique has shown potential benefits in processing polymeric nanocomposites by reducing the curing time without compromising the thermo‐mechanical performances of the materials. It was observed from this investigation that, the curing time was drastically reduced to ～30 min for microwave curing instead of 12 h room temperature curing with additional 6 h post curing at 75°C. Ductile behavior was more pronounced for microwave curing technique while thermal curing showed brittle like behavior as revealed from flexural test. The maximum strain to failure was increased by 25–40% for microwave‐cured nanocomposites over the room temperature cured nanocomposites for the same loading of nanofillers. The glass transition temperature (T_g) also increased by ～14°C while curing under microwave irradiation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41708.     

Mechanical,thermomechanical, and creep performance of CNT embedded epoxy at elevated temperatures: An emphasis on the role of carboxyl functionalization

In contrast to polymeric composites, the role of interface/interphase has been widely acknowledged to govern their overall properties and performance. Environmental temperature has substantial effects on the interfacial durability of polymer nanocomposites. In this regard, present investigation has been carried out to study the mechanical performance of pristine (UCNT) and carboxylic functionalized CNT (FCNT) embedded epoxy nanocomposites under different elevated temperatures. Higher flexural strength and modulus of FCNT‐EP nanocomposite were recorded over UCNT‐EP and neat epoxy at room temperature environment. Flexural testing at elevated temperatures revealed a higher rate of strength degradation in polymer nanocomposites over neat epoxy. Postfailure analysis of specimens has been conducted to understand the alteration in failure micro‐mechanisms upon UCNTs and FCNTs addition in epoxy. Variation in viscoelastic properties with temperature has been studied from dynamic mechanical thermal analysis and significant reduction in glass transition temperature (T_g) is observed for nanocomposites. In the studied temperature and stress combinations, FCNT‐EP nanocomposites exhibited better creep resistance over UCNT‐EP and neat epoxy. Room temperature strengthening, elevated temperature strength degradations, improved creep resistance and reduction in T_g in nanocomposites over neat polymer have been discussed in terms of dynamic nature and gradient structure of CNT/epoxy interphase. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44851.     

The effect of silica nanoparticles on the thermomechanical properties of polystyrene

A series of polystyrene (PS)/SiO₂ nanocomposites were prepared. Silica nanoparticles with an average diameter of 16 nm were used, and treated with dimethyldichlorosilane, while their weight fraction varied from 4 up to 10%. The viscoelastic‐thermomechanical properties of the nanocomposites and their interrelation with the material's structure were studied with various experimental techniques. Scanning electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, and tensile testing at three different temperatures were applied. The stress–strain curves at 85°C, where the material's viscoplastic response is manifested, were simulated through a plasticity model, developed in previous works. The 4% weight fraction was found to be the optimum one for the enhancement of the thermomechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of oxirane groups on curing behavior and thermal stability of vinyl ester resins

The effects of oxirane groups in vinyl ester (VE) resin and reactive diluent on curing characteristics and thermal behavior of cured resins are described. Stoichiometric (0.5:1, sample A) as well as nonstoichiometric (0.5:0.85, sample B) ratios of the diglycidyl ether of bisphenol-A (DGEBA) and methacrylic acid (MA) were used for the synthesis of VE resins. Resin sample B had more residual epoxy groups because of the stoichiometric imbalance of the reactants. VE resins thus obtained were diluted with methyl methacrylate (MMA; 1:1, w/w), and controlled quantities of epoxy groups were introduced by partial replacement of MMA with glycidyl methacrylate (GMA), keeping the overall ratio of resin and reactive diluent constant. Increase of GMA content in resin A or B resulted in a decrease in gel time, indicating that the curing reaction is facilitated by the presence of epoxy groups. An increase in initiator content also reduced the gel time. In the differential scanning calorimetry (DSC) scans, a sharp curing exotherm was observed in the temperature range 107 ± 3–150 ± 1 °C. The onset temperature (T_onset) and peak exotherm temperature (T_exo) decreased with increase in GMA content. Heat of curing (ΔH) also increased with increase in GMA content. A broad exotherm was observed after the initial sharp exotherm that was attributed to the etherification reaction. Cured VE resins were stable up to 250–260 °C, and started losing weight above this temperature. Rapid decomposition was observed in the temperature range 400–500 °C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 416–423, 2001     

Polyimide/substituted polyaniline–copolymer–nanoclay composite thin films with high damping abilities

Polyimide (PI)/poly(N‐ethyl aniline‐co‐aniline‐2‐sulfonic acid)–clay (SPNEAC) nanocomposite films containing water‐soluble SPNEAC were successfully synthesized. Atomic force microscopy studies showed a homogeneous distribution of coated clay particles in the PI matrix. The particle sizes varied between about 50 nm and about 220 nm in height and 6–7 μm in length in the nanocomposite containing 5 wt % SPNEAC. Average surface roughnesses of 0.253 and 34.9 nm were obtained for neat PI and the 5 wt % SPNEAC–PI nanocomposite, respectively. Dynamic mechanical spectrometry was used to study the viscoelastic transitions and their temperatures. The dynamic mechanical spectrometry results show a decreasing glass‐transition temperature of the nanocomposites with increasing SPNEAC weight fraction. The area under the α‐transition peak, which is associated with damping and impact energy, increased with increasing SPNEAC weight fraction. The impact energy of the nanocomposites was estimated with a viscoelastic model. It increased with increasing SPNEAC weight fraction, and a maximum value of 84.9 mJ was obtained. The viscoelastic model was based on the area under the α‐transition peak, rubbery plateau modulus, and sample volume. A 5 wt % addition of SPNEAC improved the impact energy of neat PI films by 300%. Scanning electron micrographs of the nanocomposite films showed a less compact cross‐sectional morphology. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Low‐Dielectric Constant and Low‐Temperature Curable Polyimide/POSS Nanocomposites

With the rapid development of ultra large scale integrated circuits, low stress, low thermal expansion, low dielectric constant, and low temperature curable (<250 °C) polyimides (PIs) with excellent mechanical, thermal properties are required. Unfortunately, high curing temperatures above 300 °C and limited dielectric property still remain to be solved. Herein, a new type of aminopropyl isobutyl polysilsesquioxane (POSS) with single vertex activity is introduced by in situ polymerization resulting in the PI‐POSS nanocomposites which exhibit a low dielectric constant (κ ≤ 2.6). Furthermore, low‐temperature curing at 200 °C (99.4% imidization) under the catalysis of quinoline is also achieved. The as‐prepared PI‐POSS nanocomposites also show excellent mechanical properties of which the tensile strength can reach up to 148 MPa and the elongation at break achieves 98%. Moreover, the temperature of weight loss 5% is as high as 550 °C and the glass transition temperature can also reach 349 °C. The as‐prepared PI‐POSS nanocomposites prove excellent electrical performance and mechanical properties, showing a huge market prospect of 5G chip packaging and millimeter wave antenna in the future.     

Molecular dynamics simulations of vinyl ester resin monomer interactions with a pristine vapor-grown carbon nanofiber and their implications for composite interphase formation

A molecular dynamics simulation study was performed to investigate the role of liquid vinyl ester (VE) resin monomer interactions with the surface of pristine vapor-grown carbon nanofibers (VGCNFs). These interactions may influence the formation of an interphase region during resin curing. A liquid resin having a mole ratio of styrene to bisphenol-A-diglycidyl dimethacrylate VE monomers consistent with a commercially available 33 wt.% styrene VE resin was placed in contact with both sides of two pristine graphene sheets overlapped like shingles to represent the outer surface of a pristine VGCNF. The relative monomer concentrations were calculated in a direction away from the graphene sheets. At equilibrium, the styrene/VE monomer ratio was higher in a 5 Å thick region adjacent to the nanofiber surface than in the remaining liquid volume. The elevated concentration of styrene near the nanofiber surface suggests that a styrene-rich interphase region, with a lower crosslink density than the bulk matrix, could be formed upon curing. Furthermore, styrene accumulation in the immediate vicinity of the nanofiber surface might, after curing, improve the nanofiber–matrix interfacial adhesion compared to the case where the monomers were uniformly distributed throughout the matrix.     

Morphology,rheology, and mechanical properties of dynamically cured EPDM/PP blend: Effect of curing agent dose variation

The structure development, rheological behavior, viscoelastic, and mechanical properties of dynamically cured blend based on the ethylene–propylene–diene terpolymer (EPDM) and polypropylene (PP) with a ratio of 60/40 by weight were studied. The variation of two‐phase morphology was observed and compared as the level of curing agent was increased. Meanwhile, as the level of curing agent increased, viscosity as a function of shear stress always increased at a shear stress range of 2.2 × 10⁴ to 3.4 × 10⁵ Pa at the temperature of 200°C, yet viscosity of the blend approached each other at high shear stress. Dynamic mechanical spectra at different temperatures show that dynamic modulus (E′) of the blend exhibits two drastic transitions corresponding to glass transition temperature (T_g) of EPDM and T_g of PP, respectively. In the blends T_gs of EPDM increase and T_gs of PP almost remain unchangeable with an increase in curing agent level. Tensile strength increased, yet elongation at break decreased as the level of curing agent is increased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 357–362, 2004     

Influence of post-curing temperature on the structure,properties, and adhesion of vinyl ester adhesive

Vinyl ester (VE) resins are widely used as thermoset adhesives in structural joints and composites, but complete curing under environmental conditions is not produced. The existing literature dealing with the effect of post-curing on the structure, viscoelastic, mechanical, and adhesion properties of VE resin is scarce. Therefore, in this study, VE resin was subjected to different post-curing temperatures (50–140 °C) for one hour, and the changes in structure and properties were assessed. The degree of cross-linking of the VE resin depended on the post-curing temperature and cure started to be completed above 100 °C, a temperature close to the glass transition temperature (115 °C) of the completely cross-linked polymer. Furthermore, gel formation in VE resin was evidenced for post-curing temperature below 100 °C. In order to fully cross-link the VE resin, post-curing at 140 °C for one hour was necessary, and it was evidenced by an increase in the glass transition temperature and in the mechanical properties; an increase in adhesion to cold rolled steel was obtained although the shear strength was lower than in the joint produced with the non-post-cured VE resin.     

Methacrylate/acrylate terminated derivatives of diglycidyl hexahydrophthalate: Synthesis,structural, and thermal characterization

Mono‐ or di(meth)acrylate‐terminated derivatives of diglycidyl hexahydrophthalate (ER) were prepared by reacting 1 : 1 or 1 : 2M ratio of ER and methacrylic acid or acrylic acid. These vinyl ester (VE) resins were characterized by determining epoxy equivalent weight, acid number, and molecular weight by gel permeation chromatography. Structural characterization was done by FTIR and ¹H NMR spectroscopy. In the ¹H NMR spectra of acrylate‐terminated VE resins, three proton resonance signals were observed in the region 5.8–6.4 ppm due to vinyl group while in methacrylate‐terminated VE resins only two proton resonance signals due to vinylidene protons were observed at 5.6–6.1 ppm. The Brookfield viscosity (room temperature (25 ± 2)°C) of these resins diluted with varying amounts of MMA was determined at 20 rpm. Curing behavior was monitored by determination of gel time and differential scanning calorimetry. An exothermic transition was observed in the DSC scans in the temperature range of (81–150)°C. Isothermal curing of MMA‐diluted VE resins containing AIBN as an initiator was done at 60°C for 2 h in N₂ atmosphere, and then heating for another 2 h in static air atmosphere. Thermal stability of isothermally cured resins in N₂ atmosphere was evaluated by thermogravimetric analysis. All cured resins decomposed above 310°C in single step. Thermal stability of the cured resins having acrylate end caps was marginally higher than the resins having methacrylate end groups. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

A method for determination of time‐ and temperature‐dependences of stress threshold of linear–nonlinear viscoelastic transition: Energy‐Based Approach

A methodology for determination of time‐ and temperature‐dependences of stress threshold of linear–nonlinear viscoelastic transition is proposed and validated by example of uniaxial creep of epoxy resin. Energy approach is applied for characterization of the region of linear viscoelasticity (LVE) and the threshold of LVE is given in the stress–strain representation as the master curve independent of time and temperature. Time‐ and temperature‐dependences of the stress threshold are calculated by extending LVE theory and time–temperature superposition principles (TTSP) to the energy relations. Reasonable agreement between experimental data and calculations is obtained. It is shown that number of tests required for characterization of LVE region in a wide range of test time and temperatures can be considerably reduced by applying the proposed methodology. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of the comonomer content on the solid‐state mechanical and viscoelastic properties of poly(propylene‐co‐1‐butene) films

In this study, we quantified the thermal and solid‐state mechanical and viscoelastic properties of isotactic polypropylene (i‐PP) homopolymer and poly(propylene‐1‐butene) copolymer films having a 1‐butene ratio of 8, 12, and 14 wt %, depending on the comonomer content. The uniaxial tensile creep and stress‐relaxation behaviors of the samples were studied in a dynamic mechanical analyzer at different temperatures. The creep behaviors of the samples were modeled with the four‐element Burger equation, and the long‐term creep strains were predicted with the time–temperature superposition method. The short‐term mechanical properties of the samples were also determined with tensile and impact testing at room temperature. We found that the Young's modulus and ultimate strength values of the samples decreased with increasing amount of 1‐butene in the copolymer structure. On the other hand, the strain at break and impact strength values of the samples improved with increasing amount of 1‐butene. Creep analysis showed that i‐PP exhibited a relatively lower creep strain than the poly(propylene‐co‐1‐butene)s at 30 °C. However, interestingly, we discovered that the temperature increase resulted in different effects on the creep behaviors. We also found that short‐chain branching improved the creep resistance of polypropylene at relatively high temperatures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46350.     

Application of time–stress superposition to viscoelastic behavior of polyamide 6,6 fiber and its “true” elastic modulus

The viscoelastic behavior of semi‐crystalline polyamide 6,6 fiber is exploited in viscoelastically prestressed polymeric matrix composites. To understand better the underlying prestress mechanisms, strain–time performance of the fiber material is investigated in this work, under high creep stress values (330–665 MPa). A latch‐based Weibull model enables prediction of the “true” elastic modulus through instantaneous deformation from the creep‐recovery data, giving 4.6 ± 0.4 GPa. The fiber shows approximate linear viscoelastic characteristics, so that the time–stress superposition principle (TSSP) can be implemented, with a linear relationship between the stress shift factor and applied stress. The resulting master creep curve enables creep behavior at 330 MPa to be predicted over a large timescale, thus creep at 590 MPa for 24 h would be equivalent to a 330 MPa creep stress for ～5200 years. Similarly, the TSSP is applied to the resulting recovery data, to obtain a master recovery curve. This is equivalent to load removal in the master creep curve, in which the yarns would have been subjected to 330 MPa creep stress for ～4.56 × 10⁷ h. Since our work involves high stress values, the findings may be of interest to those involved with long‐term load‐bearing applications using polyamide materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44971.