Characterization of epoxy syntactic foams by dynamic mechanical analysis

Epoxy syntactic foams that are capable of withstanding use-temperatures in the range of 106 to 175°C were fabricated with DGEBA or novolac based epoxy resins and appropriate amine hardener materials. These foams were characterized for dynamic mechanical properties in single cantilever mode. The storage modulus, loss modulus and tan δ values were recorded over a wide temperature range. A typical density value of around 0.45 g/cm³ of the syntactic foams made respectively from a cycloaliphatic amine hardener, aromatic amine hardener-I, aromatic amine hardener-II recorded storage modulus (E′) values of 1354 MPa, 1500 MPa and 1530 MPa respectively and tan δ values of 0.0139, 0.0090, 0.01039 respectively at 30°C. The storage modulus values gradually decreased with increasing temperature while the loss modulus values showed corresponding gradual increase in the same temperature range. There is a steep variation in these values when the material softens in the vicinity of the glass transition temperature (T _g) indicating the upper temperature limits to which they can be put in use. The reduction in the storage modulus values with increasing temperature and the glass transition temperature values are characteristic of the resin/hardener systems as well as the curing/post curing cycles employed.     

Characterization of side-chain liquid crystal polymers using dynamic mechanical thermal analysis and dielectric thermal analysis

Ten members of a homologous series of side-chain liquid crystal polymers, the poly[[-(4-methoxybiphenylyl-4-oxy)--alkyl]methacrylate]s, have been characterized using dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA). For the undecyl and dodecyl homologues both techniques revealed a smectic-smectic transition not detected in previous studies either by differential scanning calorimetry or by optical microscopy. It is proposed that this corresponds to a monolayer-bilayer smectic A transition. A weak transition at ca. -30 °C is detected using DMTA for polymers with spacer lengths 4–8 and by analogy with poly(methyl methacrylate) may indicate the absorption of small amounts of water. DMTA also proved to be particularly effective in deconvoluting transitions and for the propyl homologue established the existence of a smectic phase suggested by optical microscopy.     

Study of carbon fibre surface treatments by dynamic mechanical analysis

Dynamic mechanical and thermal analysis (DMTA) has been used to study the effects of surface treatment of carbon fibres on the viscoelastic properties of composites containing them. The fibres were treated by dip-coating, electro-polymerization, and plasma polymerization, and the behaviour of these fibres is compared with that of fibres treated by ordinary commercial oxidation and sizing procedures. Analysis of the experimental results is made both in terms of conventional approaches to viscoelastic behaviour and of the power-law analysis of the glass transition in an attempt to obtain suitable parameters for the evaluation of the effects of surface treatment.     

Characterization of retrieved total ankle replacement liners

This paper describes the failure analysis of two Total Ankle Replacement (TAR) devices where one device failed mechanically and the other device failed due to excessive wear and loosening. Optical and confocal imaging procedures were used to identify various failure modes. Fourier transform infrared spectroscopy was used to determine the oxidation index and crystallinity of the liners and compared them with values obtained for a shelf-aged liner which is used as a control. Regression equations were developed based on literature data to correlate oxidation index with strength of the material. 3D models of each liner were constructed to understand the damage modes at surface and sub-surface levels. Shear banding and embrittlement were observed for one of the failed liners. Both abrasive and adhesive wear were observed in the liners but they are not the dominant wear mechanisms unlike in other total joint replacement devices. Based on obtained results, the STAR™ (Scandinavian Total Ankle Replacement) device failed under higher shear and compression stresses at the bearing component resulting in fatigue-induced fracture due to higher torsion generated at the ankle joint. The Agility™ (DePuy) device showed lack of proper bony ingrowth resulting in clinical failure.     

The evaluation of two-dimensional carbon-carbon composite material by dynamic mechanical analysis

Carbon composite materials, consisting of carbon cloth densified with a carbon matrix, have been examined by dynamic mechanical analysis (DMA). Flat panel and conic section structures were investigated over the temperature range ambient to 500°C. Reproducibility of the calculated tensile storage modulus values has been shown to be within 5% at any one temperature over the entire temperature range. This technique, which has been demonstrated to be non-destructive of the sample analyzed, defines differences in mechanical properties of the composite material formed into a conic section by comparison with those of the same material formed into a flat panel. Minor heterogeneity has also been shown within a single conic section as well as differences between pitch and CVD matrix samples. A sample orientation effect was found with the conic section samples. Details of the experimental technique and assumptions made during calculation of the mechanical properties are discussed.     

Characterisation of thermal relaxations of polyaniline fibers by dynamic mechanical thermal analysis

Molecular motions and thermal transitions in polyaniline fibers (∅ = 50 μm), cast from emeraldine base powder dissolved in N,N′-dimethylpropylene urea (DMPU), have been investigated by dynamic mechanical thermal analysis (DMTA). For this purpose, a special picopendulum has been used, and a double sweep DMTA study has been performed. From these preliminary experiments, different relaxations observed have been discussed and compared to what is found in the literature.     

Characterization of polyethylene/EPDM/silicon dioxide multicomponent composites by solid-state dynamic mechanical spectroscopy

Various composites of polyethylene, ethylene propylene diene rubber (EPDM), and filler are milled and analysed by solid-state dynamic mechanical spectroscopy. The filler used is silicon powder with an oxidized surface. This filler is a model for materials with siliceous surfaces. The torsion pendulum measurements show that the multicomponent composites exhibited complex viscoelastic behaviour. For composites of polyethylene and silicon dioxide, there is evidence of particle-particle interactions. In composites which include polyethylene, rubber and filler, interactions of the polyethylene and especially of the rubber with the filler surface are significant. Treatment of the filler surface with gamma-aminopropyltriethoxysilane (-APS) or gamma-methacryloxypropyltrimethoxysilane (-MPS) has a significant influence on the resultant composite dynamic mechanical spectrum. Maleic anhydride grafting of the EPDM rubber also changes the character of the composites. These composites appear to exhibit complex morphologies, which may be controlled to a certain extent by filler surface treatment and grafting to the rubber. There is evidence for a chemical reaction between the maleic anhydride modification of the EPDM and -APS during processing on the roll mill. Prediction of the composite properties using the extended van der Poel model is qualitatively useful.     

Aspects of dynamic mechanical analysis in polymeric composites

Patterns of behaviour of dynamic mechanical properties in the glass-transition region have been considered and it is shown that the tan δ peak always occurs at a higher temperature than the E″ peak. The temperature interval between the peaks varies significantly in unidirectional carbon-fibre/epoxy laminates, depending on the fibre orientation with respect to the applied load. The E″ peak is shown to be a more consistent indicator of the behaviour of the composites.

Fibre incorporation reduces viscoelastic damping beyond that possible by matrix volume reduction alone. This was observed in various fibre reinforced polymers and is explained in terms of fibre/matrix interactions.     

Investigation of the mechanical performance of young glass-ionomer cement using dynamic mechanical analysis

Glass-ionomer (or more correctly, glass polyalkenoate) cements have wide applications in dentistry. This paper reports an investigation using dynamic mechanical analysis (DMA) on the setting of typical conventional glass-ionomer cements of varying age. Rectangular section cement samples were stored for four weeks in distilled water at 37 °C before being tested. The experimental procedure involved the clamping of the sample in tensile mode and heating through a 37–95 °C temperature range in water. A general behavioral trend was followed where all the samples showed increased flexibility with rise in temperature until a threshold temperature was reached, whereupon sudden tensile stiffening was observed. The temperature at which the stiffening took place was dependent on the age of the cement, and was interpreted in terms of the secondary cement forming reactions of silica and phosphate. The younger samples stiffened at significantly lower temperatures than the older ones. The activated nature of glass-ionomer setting chemistry meant that younger cements could be prematurely aged through heating. Differential scanning calorimetry was used to study the effect of heating on the distribution of loosely bound water in the cements that had, and had not been exposed to a DMA cycle. Most notably, it was seen that the DMA process did not affect the water in the matrix. This leant further credence to the hypothesis that the stiffening observed during the DMA heating process was caused by accelerated network formation.     

Influence of dibutyl phthalate on the mechanical,thermal, and relaxation behaviour of poly (methyl methacrylate) for denture-base soft liners

Methyl methacrylate and six solutions of methyl methacrylate/dibutyl phthalate (nominally 5 to 30% v/v) were polymerized into thin sheets using gamma radiation. Dynamic mechanical spectra of the storage modulus, loss modulus and loss tangent, as well as changes in length, were investigated as a function of temperature. From these measurements, the depression of the storage modulus and glass-transition temperature were obtained. Subsequently, differential scanning calorimetry (DSC) and cross-polarization-magic-angle-spinning NMR were used to obtain additional glass-transition and relaxation-time measurements. Based upon these experiments, a specific form of the rule of mixtures described the depression of the glass-transition temperature. From storage-modulus measurements, antiplasticization was evidenced at very low temperatures and at compositions greater than 25% v/v. Solid-state NMR confirmed that plasticization causes an increase in polymer main-chain motion via the physical loosening of secondary bonds between polymer chains.     

Sensitivity analysis for dynamic mechanical systems with finite rotations

This paper presents a sensitivity analysis for dynamic systems with large rotations using a semi‐analytical direct differentiation technique. The choice of a suitable time integration strategy for the rotation group appears to be critical for the development of an efficient sensitivity analysis. Three versions of the generalized‐α time integration scheme are considered: a residual form, a linear form, and a geometric form. Their consistency is discussed, and we show that the residual form, which is the most direct extension of the generalized‐α algorithm defined in structural dynamics, should not be used for problems with large rotations. The sensitivity analysis is performed and close connections are highlighted between the structure of the sensitivity equations and of the linearized dynamic equations. Hence, algorithms developed for the original problem can be directly reused for the sensitivities. Finally, a numerical example is analysed in detail. Copyright © 2007 John Wiley & Sons, Ltd.     

对苯二异氰酸酯型TPU的动态力学分析

考察了异氰酸酯、多元醇和扩链剂种类对对苯二异氰酸酯(PPDI)型热塑性聚氨酯弹性体(TPU)机械性能和动态力学性能的影响.结果表明,PPDI型TPU的耐热和内生热性能均优于MDI体系,软段分子结构的不同会影响TPU的热稳定性,HQEE可提高材料的耐热性能.     

Characterization of Ti-HA composite fabricated by mechanical alloying

Titanium (Ti) and its alloys possess suitable mechanical characteristics for utilization in orthopedic implants. However, their poor integrity with native tissues is a major challenge in their clinical application. Composite structures of Ti and hydroxyapatite (HA) can be used to promote the bone ingrowth and integration of the implant with the surrounding tissue. Here, we report the fabrication of Ti-HA nanocomposite powders using a high energy planetary ball mill. We investigate the effects of fabrication parameters including HA content (10–30% w/w), milling time (20 and 50 h), and HA particle size (50 nm and 15 μm) on the characteristics of the fabricated composites. In particular, we determine the samples hardness, sintering density, surface roughness and topography for different conditions. The results show that the addition of HA to Ti decreases the sintering density and enhances the surface hardness. Also, we observe a direct relationship between HA concentration in the Ti matrix and the surface roughness.     

Improved dynamic analysis of structures with mechanical uncertainties under deterministic input

This paper addresses the dynamic analysis of linear systems with uncertain parameters subjected to deterministic excitation. The conventional methods dealing with stochastic structures are based on series expansion of stochastic quantities with respect to uncertain parameters, by means of either Taylor expansion, perturbation technique or Neumann expansion and evaluate the first- and second-order moments of the response by solving deterministic equations. Unfortunately, these methods lead to significant error when the coefficients of variation of uncertainties are relatively large. Herein, an improved first-order perturbation approach is proposed, which considers the stochastic quantities as the sum of their mean and deviation. Comparisons with conventional second-order perturbation approach and Monte Carlo simulations illustrate the efficiency of the proposed method. Applications are discussed in order to investigate the influence of mass, damping and stiffness uncertainty on the dynamic response of the system.     

Glass transitions of hygrothermal aged pultruded glass fibre reinforced polymer rebar by dynamic mechanical thermal analysis

The changes that can occur in glass fibre reinforced polymer (GFRP) composites with ageing can affect its application, performance and lifetime. Hygrothermal ageing (i.e. accelerated ageing by moisture absorption and temperature change) is a very useful technique to evaluate durability as well as development of GFRP composites in a reasonable timeframe. Dynamic mechanical thermal analysis (DMTA) is essentially able to detect all changes in the state of molecular motion in polymer composites as temperature is scanned. In this work, pultruded GFRP rebars were accelerated aged in an alkaline aqueous environment at 60 °C for 1, 2, 3, 4 and 6 months to evaluate the changes in glass transition of viscoelastic GFRP rebars by DMTA. Five different glass transitions in an average temperate range from 110 to 165 °C were observed at storage modulus, loss modulus and damping factor traces of DMTA. It was also found that glass transition temperature (T_g) of the aged samples changed up to maximum 6 °C compared with that of controlled sample. This change in T_g with ageing time was believed to be due to moisture absorption by rebars.     

Dynamic mechanical analysis and water sorption of some experimental elastomeric soft lining materials

This research was undertaken to develop a better understanding of the relationships among the compositions, structures and properties of denture soft liners. Five butadiene-styrene-acrylic elastomers were prepared. They were prepared using 50% of powdered prepolymerized butadiene-styrene polymer combined with 50% of a methacrylate monomer (HMA or EHMA) plus varying amounts of initiator and crosslinker. The mixtures were gelled and processed conventionally. Specimens were then committed to dynamic mechanical analysis and water sorption. Dynamic mechanical analysis was performed over the temperature range 5–95°C at the rate of 2.5°C/min using a Perkin Elmer DMA-7 with 3 mm flat tip probe at 1 Hz. Wet and dry values for storage modulus (E') and damping factor (tan ) were determined at 37°C. Water sorption of these butadiene styrene elastomer-acrylic systems from solutions of varying concentrations was measured in order to establish the role of osmotic pressure. Diffusion coefficient (D _d) was determined from the desorption values. The relatively lower values of D _d observed in most highly concentrated solutions particularly 1 m sodium chloride and glucose may be interpreted as related to reduced water sorption from these solutions. Increasing crosslinking increased the modulus and decreased water sorption. Using hydrophobic EHMA instead of HMA reduced water uptake, reduced dry modulus and reduced the decrease in modulus caused by water sorption. Dynamic moduli and water sorption generally exceeded those of the commercial materials studied. For all experimental materials, water uptake from saline and glucose solutions confirmed that the diffusion process is osmotically driven.