Mechanical Analysis Techniques Research Articles

The viscoelastic properties of cork

The viscoelastic properties of cork (from Quercus suber) have been investigated in the temperature range −40 to 120°C using the technique of Dynamic Mechanical Analysis (DMA). The results were compared with dielectric data previously reported. A relaxation was detected with a maximum in tan δ at ca 20°C (f = 1 Hz) and with a mean activation energy of 140 kJ · mol−1. A decrease in the intensity of the relaxation and an increase of the storage modulus is observed when cork is previously subjected to an annealing process above 60°C. This result is in agreement with previously reported dielectric data. Thermogravimetric experiments seem to confirm that such effect could be caused by the desorption of water molecules. Specimens oriented along the prismatic direction presented higher storage modulus than the ones oriented along the transverse prismatic direction. The rheological properties of cork also showed a dependence upon the mechanical mode used during measurements: for example, the stiffness is the highest for the tensile mode and the lowest for the compression mode.

Catalyst for solid polymer electrolyte fuel cells

Nuclear magnetic resonance spectroscopy (n.m.r.), dynamic mechanical thermal analysis (d.m.t.a.) and AC impedance techniques have been used in combination to probe the effect of electrolyte composition in an archetypal solid polymer electrolyte (SPE). A series of solid polymer electrolytes (SPEs) based on a urethane-crosslinked trifunctional poly(ethylene glycol) polymer host containing dissolved ionic species (LiClO4 and LiCF3SO3) have been studied. D.m.t.a. has established that increasing LiClO4 concentration causes a decrease in the polymer segmental mobility, owing to the formation of transient crosslinks via cation–polymer interaction. Investigation of the distribution of mechanical/structural relaxation times for the LiClO4/polymer complex with d.m.t.a. reveals that increasing LiClO4 concentration causes a slight broadening of the distribution, indicating a more heterogeneous environment. Results of n.m.r. 7Li T1 and T2 relaxation experiments support the idea that higher salt concentrations encourage ionic aggregation. This is of critical importance in determining the conductivity of the material since it affects the number of charge carriers available. Introduction of the plasticiser tetraglyme into the LiClO4-based SPEs suppresses the glass transition temperature of the SPE, and causes a significant broadening of the relaxation time distribution (as measured by d.m.t.a.).

Dynamic stress/strain response of the interphase in polymer matrix composites

AbstractThe interphases of various sized E‐glass‐fiber/epoxy‐amine systems were tested at displacement rates in the range of 230 to 2450 fxm/sec using a new experimental technique (dynamic micro‐debonding technique). The fiber systems include unsized, epoxy‐amine compatible sized, and epoxy‐amine incompatible sized glass fibers. A data reduction scheme was developed to relate the force vs. displacement response obtained from the dynamic micro‐debonding technique to interphase shear stress/strain response. The stress/strain curves and interphase shear modulus values were obtained from these composite systems under average shear strain rates (ASSR) in the range of 215–3278 (1/s). The results showed that the magnitude of the interphase shear modulus was sizing and strain rate dependent. In all cases, the shear modulus was found to be more compliant than the bulk matrix. The two sized fiber systems exhibited the highest strain rate sensitivity, with modulus increasing about threefold over the range studied. In addition, the rate dependent behavior of the model interphase materials were determined using the dynamic mechanical analysis (DMA) technique. The model interphase materials closely resemble the interphase that forms on unsized and compatible sized fibers. Master curves relating the flexural storage modulus to strain rate were constructed based on the time‐temperature superposition principle from DMA frequency sweep measurements. The DMA measured results are consistent with the dynamic micro‐debonding test results, providing confidence in the test method as a reliable technique for characterizing the high strain rate properties of the interphase in composites.

Study of carbon black distribution in BR/NBR blends based on damping properties: Influences of carbon black particle size, filler, and rubber polarity

AbstractEffects of filler and rubber polarity on the distribution of filler in butadiene/nitrile rubber (BR/NBR) blends were investigated, using the dynamic mechanical thermal analysis technique. As 30‐phr filler is added, the reduction in heights of damping peaks (tan δmax), attributed to the dilution effect, was observed. It was also found that the BR phase in the blends, compared to the NBR phase, is more preferential for small‐ and large‐particle size carbon blacks to reside, probably because of the lower viscosity and lower polarity of the BR phase. The addition of silica instead of carbon black leads to an increase in filler migration to the NBR in the 20/80 BR/NBR blend, which is attributed to the strong silica–NBR interaction. In addition, an increase in NBR polarity promotes carbon black migration to the BR phase. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3198–3203, 2001

Erasure below glass‐transition temperature of effect of isothermal physical aging in fully cured epoxy/amine thermosetting system

AbstractThe erasure below the glass‐transition temperature (Tg) of the effect of isothermal physical aging (at aging temperature Ta) in a fully cured epoxy/amine thermosetting system is investigated using the torsional braid analysis (TBA) dynamic mechanical analysis technique and the differential scanning calorimetry (DSC) technique. From the TBA temperature scans, the intensity of the localized perturbation of the moduli in the vicinity of the Ta (90°C), due to isothermal physical aging, is decreased by heating to below the Tg (Tg∞ = 177°C), indicating that the physical aging effect can be eliminated by heating to below the Tg. The isothermal aging effect in the vicinity of the Ta is almost completely eliminated by heating to 50°C above the Ta (i.e., 140°C); however, a competing aging effect occurs above Ta at higher temperatures during the heating. Erasure below Tg of the isothermal physical aging effect is inferred from DSC experiments from the diminished relaxation enthalpy in the vicinity of the Tg, which is measured from the difference in areas between the aged (Ta = 150°C) and deaged thermograms. A comparison of the TBA and DSC results is made. Implications on the heterogeneous nature of the amorphous glassy state of polymers are discussed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 396–404, 2001

A study of the morphology of polyurethane–polystyrene interpenetrating polymer networks by means of small angle X‐ray scattering, modulated‐temperature differential scanning calorimetry, and dynamic mechanical thermal analysis techniques

The morphology of polyurethane–polystyrene (PU-PS) (60 : 40 by weight) interpenetrating polymer networks (IPNs), in which internetwork grafting via 2-hydroxyethyl methacrylate resides (HEMA) (1, 2.5, and 10 wt %, respectively) in the polystyrene networks has been studied by means of small angle X-ray scattering (SAXS), modulated-temperature scanning calorimetry (M-TDSC), and dynamical mechanical thermal analysis (DMTA) techniques. With increasing internetwork grafting, the average size of domains became smaller (SAXS data) and the degree of component mixing increased (M-TDSC and DMTA results). For the PU-PS (60 : 40 by weight) IPN with 10% HEMA, the DMTA tan δ-temperature plot showed a single peak. This DMTA result implied that the morphology of this PU-PS IPN is homogeneous. However, the M-TDSC data showed that three PU-PS (60 : 40) IPNs samples (with 1, 2.5, and 10 wt % HEMA, respectively) were phase separated. For the three IPN samples, the correlation length of the segregated phases, obtained from SAXS data based on the Debye–Bueche method, did not show distinct differences. With increasing internetwork grafting, the scattered intensity decreased. This study concluded that for these IPNs, SAXS is sensitive to the size of domains and component mixing, but no quantitative analysis was given for the component mixing. M-TDSC is suitable to be used to quantify the degree of component mixing or the weight fraction of interphases, and DMTA is sensitive to damping behavior and to phase continuity. However, DMTA cannot provide quantitative information about the degree of component mixing or the weight (or volume) fraction of the interphases. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1958–1964, 2001

A study of the morphology of polyurethane-polystyrene interpenetrating polymer networks by means of small angle X-ray scattering, modulated-temperature differential scanning calorimetry, and dynamic mechanical thermal analysis techniques

The morphology of polyurethane–polystyrene (PU-PS) (60 : 40 by weight) interpenetrating polymer networks (IPNs), in which internetwork grafting via 2-hydroxyethyl methacrylate resides (HEMA) (1, 2.5, and 10 wt %, respectively) in the polystyrene networks has been studied by means of small angle X-ray scattering (SAXS), modulated-temperature scanning calorimetry (M-TDSC), and dynamical mechanical thermal analysis (DMTA) techniques. With increasing internetwork grafting, the average size of domains became smaller (SAXS data) and the degree of component mixing increased (M-TDSC and DMTA results). For the PU-PS (60 : 40 by weight) IPN with 10% HEMA, the DMTA tan δ-temperature plot showed a single peak. This DMTA result implied that the morphology of this PU-PS IPN is homogeneous. However, the M-TDSC data showed that three PU-PS (60 : 40) IPNs samples (with 1, 2.5, and 10 wt % HEMA, respectively) were phase separated. For the three IPN samples, the correlation length of the segregated phases, obtained from SAXS data based on the Debye–Bueche method, did not show distinct differences. With increasing internetwork grafting, the scattered intensity decreased. This study concluded that for these IPNs, SAXS is sensitive to the size of domains and component mixing, but no quantitative analysis was given for the component mixing. M-TDSC is suitable to be used to quantify the degree of component mixing or the weight fraction of interphases, and DMTA is sensitive to damping behavior and to phase continuity. However, DMTA cannot provide quantitative information about the degree of component mixing or the weight (or volume) fraction of the interphases. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1958–1964, 2001

Investigation of properties of fiber/matrix interphase formed due to the glass fiber sizings

Sizings on glass fibers consist of a silane-based network that is chemically bound to the fiber and other compounds that are adsorbed onto the glass surface. Formation of interphase involves dissolution of adsorbed species and inter-diffusion of these compounds and resin monomers into the interphase region and chemical reaction of available functional groups. All these phenomena occur at the presence of the silane-based network. In this study, the effects of the silane-based network on the properties of the interphase region are investigated for an epoxy/amine resin system and compatible sized glass fibers. The composition of the sizing material bound to glass was determined using nuclear magnetic resonance (NMR) spectroscopy. Based on this information, model interphase materials were synthesized that were a blend of an epoxy/amine matrix and inclusions. The inclusions consist of an interpenetrating network of silane-based polymer and epoxy/amine thermoset that represents the interphase material formed during processing. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) techniques were used to characterize the glass transition temperature and flexural modulus of the model materials. The properties of the model interphase material were obtained using the DMA results and established micromechanics models. The results show that the glass transition temperature of the model interphase is about −5°C, and its flexural storage modulus at room temperature is about 50% of that of the bulk matrix. This work has also shown that a reduction in the cross-link density of the bound network might significantly reduce the modulus within the interphase region by a factor of 5 to 8.

THERMAL BEHAVIOUR OF SILVER-FILLED EPOXY ADHESIVES Technological implications in microelectronics

One-component silver-filled epoxy adhesives electrically conductive with low extractable ionic content have been used in microelectronics for attach applications. For the specific application described here there was evidence showing that adhesive polymerisation was not complete with negative consequences for the electronic devices. The present study aimed at understanding the causes of such disadvantages and setting up the best conditions to make the epoxy adhesive perfectly suitable for the required applications. The work was carried out mainly by means of differential scanning calorimetry (DSC) and with the help the dynamic mechanical thermal analysis (DMTA) technique. The study succeeded in determining that the technological problems were due to incomplete polymerisation that caused solvent and monomer retention. These residues produced a leakage of the insulating properties of some capacitors present in the devices jeopardising the sensor working. Moreover, the study also showed that it was possible to avoid these difficulties adjusting the polymerisation temperature to 130°C and respecting curing time of 3 h: with these new curing conditions excellent results were achieved.

Thermal characterization of an epoxy-based underfill material for flip chip packaging

Epoxy-based underfill encapsulant materials are used in advanced microelectronic packaging to reduce thermal stresses on the solder joints and interconnections in integrated circuits. Therefore, their thermal properties directly affect package performance and reliability. In this study, the thermal properties of an epoxy-based underfill material developed for Intel’s flip chip packaging were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), thermomechanical analysis (TMA), dynamic mechanical thermal analysis (DMTA) and DMA techniques. Experimental results showed that this epoxy can be cured rapidly with low cure weight loss. Near room temperature, the cured epoxy has a low coefficient of thermal expansion (CTE) and a moderate storage modulus, resulting in a low stress index. The glass transition temperature and thermomechanical properties as a function of epoxy curing conditions will be discussed.

Dynamic mechanical properties of plasma sprayed Ni-based alloys

This paper describes the use of dynamic mechanical analyzer techniques to measure the temperature dependence of the dynamic mechanical properties of Nickel-based bond coats: NiAl, NiCrAlY, and NiCoCrAlY in the temperature range 30–950°C. The experimental measurements revealed that the brittle-to-ductile transition process for α-Ni is governed by the diffusion of nickel atom with an activation energy of Q=207.7 kJ/mol. NiCrAlY bond coat displayed the lowest modulus at all temperature investigated. The drop in modulus at about 600°C was attributed to the resolution of γ′ to γ with activation energy of Q=241.7 kJ/mol. The NiCoCrAlY bond coat displayed an excellent storage modulus at all temperatures. The addition of cobalt has improved the γ′ to γ resolution temperature. The process’s kinetic activation energy was measured to be Q=279.9 kJ/mol.

Molecular motions in a polycarbonate composite as studied by thermally stimulated recovery and dynamic mechanical analysis

AbstractThe viscoelastic properties of a short carbon‐fibre reinforced polycarbonate are studied in the glassy state and in the glass transition region by means of Thermally Stimulated Recovery (TSR) and Dynamic Mechanical Analysis (DMA) techniques in the flexural mode. The temperature calibration of the apparatus is discussed. Each thermal sampling experiment is analysed according to a simple Voigt‐Kelvin model in which the temperature dependence of the retardation time follows the Arrhenius equation with two adjustable thermokinetic parameters. Non‐linear fittings of the experimental data are performed with the corresponding constitutive equation. Both the activation energy and the pre‐exponential factor follow the usual trends with temperature and present the well‐known compensation phenomena. A divergence between the TSR results of the two materials is found above ± 145°C and may be a result of the effect of the interface. The observed movements in the glassy state which are still found to have a cooperative character are analysed according to the Adam‐Gibbs theory. Dynamic‐mechanical relaxation properties of the composite are reported and analysed in terms of Takayanagi's block model.

Photorefractive dynamic holographic polariscope

In the present communication we show a real time holographic polariscope. The system is based on the dynamic anisotropic diffraction properties that happen in cubic photorefractive crystals of the sillenite family. This result represents a promising technique for possible mechanical strain and stress analysis for scientific and technical applications.

Anhydride and diamine epoxy–Kevlar composites: thermal and dynamic‐mechanical properties

Differential scanning calorimetry (DSC) and dynamic–mechanical thermal analysis techniques have been used to characterize different Kevlar–epoxy composites. Tetrafunctional aliphatic amine and anhydride–diglycidyl epoxy have been used as matrix, and different quantities of continuous Kevlar fibers as reinforcement. Kevlar fibers had different effects on curing kinetics and final thermal properties depending on epoxy matrix type. As Kevlar content increased DSC heat flow curves shifted to much lower temperatures in the anhydride matrix case, while there was very little difference in the diamine–epoxy one. A significant decrease in the glass transition temperature (Tg) was observed as Kevlar content increased when anhydride matrix was used, while little change was observed in the reinforced diamine systems. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal scans. The main dynamic–mechanical relaxation and its evolution versus frequency with fiber addition was studied. An important shift to high frequencies was observed in the anhydride system. Copyright © 1999 John Wiley & Sons, Ltd.

Anhydride and diamine epoxy-Kevlar composites: thermal and dynamic-mechanical properties

Differential scanning calorimetry (DSC) and dynamic–mechanical thermal analysis techniques have been used to characterize different Kevlar–epoxy composites. Tetrafunctional aliphatic amine and anhydride–diglycidyl epoxy have been used as matrix, and different quantities of continuous Kevlar fibers as reinforcement. Kevlar fibers had different effects on curing kinetics and final thermal properties depending on epoxy matrix type. As Kevlar content increased DSC heat flow curves shifted to much lower temperatures in the anhydride matrix case, while there was very little difference in the diamine–epoxy one. A significant decrease in the glass transition temperature (Tg) was observed as Kevlar content increased when anhydride matrix was used, while little change was observed in the reinforced diamine systems. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal scans. The main dynamic–mechanical relaxation and its evolution versus frequency with fiber addition was studied. An important shift to high frequencies was observed in the anhydride system. Copyright © 1999 John Wiley & Sons, Ltd.

Composition effects in polyetherurethane-based solid polymer electrolytes

Nuclear magnetic resonance spectroscopy (n.m.r.), dynamic mechanical thermal analysis (d.m.t.a.) and AC impedance techniques have been used in combination to probe the effect of electrolyte composition in an archetypal solid polymer electrolyte (SPE). A series of solid polymer electrolytes (SPEs) based on a urethane-crosslinked trifunctional poly(ethylene glycol) polymer host containing dissolved ionic species (LiClO 4 and LiCF 3SO 3) have been studied. D.m.t.a. has established that increasing LiClO 4 concentration causes a decrease in the polymer segmental mobility, owing to the formation of transient crosslinks via cation–polymer interaction. Investigation of the distribution of mechanical/structural relaxation times for the LiClO 4/polymer complex with d.m.t.a. reveals that increasing LiClO 4 concentration causes a slight broadening of the distribution, indicating a more heterogeneous environment. Results of n.m.r. 7Li T 1 and T 2 relaxation experiments support the idea that higher salt concentrations encourage ionic aggregation. This is of critical importance in determining the conductivity of the material since it affects the number of charge carriers available. Introduction of the plasticiser tetraglyme into the LiClO 4-based SPEs suppresses the glass transition temperature of the SPE, and causes a significant broadening of the relaxation time distribution (as measured by d.m.t.a.).

Phase behaviour of ternary blends of poly(ethylene naphthalate), poly(ether imide) and poly(ether ether ketone)

The phase behaviour of melt mixed binary and ternary blends of PEN, PEI and PEEK were investigated using differential scanning calorimetry (d.s.c.) and dynamic mechanical thermal analysis (DMTA) techniques. Both PEN/PEI and PEN/PEEK binary blends exhibit single glass transition temperatures ( T gs) in full composition range and PEN and PEEK were found to be immiscible particularly at mid-concentration range. When PEI is added to the immiscible PEN/PEEK system, first the blends form two separate PEN-rich and PEEK-rich phases below about 40% PEI concentration, and above this concentration, these three homopolymers form a miscible phase in the amorphous state exhibiting a single T g. Based on the d.s.c. and DMTA results, an approximate ternary phase diagram is drawn. Three component Fox equations were found to describe the T gs of the ternary blends in the miscible regions quite well.

Effect of Hybridization on the Creep and Stress Relaxation Characteristics of Pultruded Composites

Pultrusion manufacturing process is a well established technique for the cost-effective production of high-modulus and lightweight composite materials having constant cross-sectional profiles. The pultruded composites are widely used as structural members viz., beams, trusses and stiffeners, owing to the presence of high proportion of axial fibers necessary to sustain large tractive forces. These structural members are subjected to a combination of static and dynamic loading conditions at wide temperature ranges and over longer periods. Since polymeric composites exhibit viscoelastic behavior, the effectiveness of these materials as structural members must be thoroughly evaluated to ensure long-term stability. In previous research, the dynamic performance characteristics of pultruded glass-graphite/epoxy hybrids were evaluated at room temperature. The effects of temperature, frequency, post-curing, along with the type and placement of fibers on the dynamic flexural properties of glass/epoxy and hybrid glass-graphite/epoxy were also investigated. This paper focuses on the evaluation of creep and stress relaxation performance characteristics of pultruded glass-graphite/epoxy hybrid composites. Dynamic mechanical analysis technique was adopted for the accelerated creep and stress relaxation testing. Time-temperature superposition principle, which greatly reduced the experimental time, was effectively utilized for predicting the creep and stress relaxation properties of the hybrid composites. Results indicate that the type and amount of fibers as well as their lay-up sequence plays a significant role in determining the flow and load bearing characteristics.

Synthesis and Characterization of Styrene-Butadiene Block Copolymer/Silicate Hybrid Materials via the Sol-Gel Process I. Four-Arm Star Styrene-Butadiene Block Copolymer/Silica Hybrids

Novel hybrid materials incorporating four-arm star styrene-butadiene block copolymer (SB-4A) with tetraethoxysilane (TEOS) have been successfully prepared by a sol-gel process. The properties, microstructure, and dynamics of the hybrid materials were investigated in detail by means of dynamic mechanical analysis (DMA), thermogravimetry (TG), and NMR techniques. The results indicate that the properties of the hybrids strongly depend on the TOES content and the silica networks prefer to form in the polystyrene (PS) domains. There exists an optimum range of TEOS content, in this work 30–50% by weight, within which the properties of the hybrids obtained were well improved: storage modulus increases, thermal stability raises, and the high-temperature Tg shifts to higher temperature. 29Si NMR spectrum shows that in the hybrids with well improved properties silica networks formed with Q4 in the greatest abundance.

Cure characterization of rubber modified epoxy novolacs

A new type of toughened epoxy polymer based on epoxy cresol novolac resin (ECN) and carboxy terminated polybutadiene (CTPB) liquid functional rubber has been studied. ECN has been synthesized in the laboratory and CTPB used was also of indigenised origin. Rubber modified epoxies were characterized with the help of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM) techniques.