Thermodynamics and statistical mechanics of multilayer adsorption

The multilayer adsorption models of Brunauer-Emmett-Teller and Guggenheim-Anderson-de Boer are reconsidered. The relationship between the fitting parameters and the physical parameters of the equation is discussed. The preexponential factors of the parameters are shown to be in general far different from unity, contrary to a widespread use. A thermodynamical derivation illuminates the hypothesis on which the multilayer sorption equation is dependent and frees it from too restrictive hypothesis usually taken as necessary for its validity. Equations are derived for the number fraction of sorption sites occupied by different numbers of molecules. The Guggenheim-Anderson-de Boer equation is shown to imply incomplete occupation (jamming) of the first sorption layer at saturation.     

Determination of the long-term hydrostatic strength of multilayer pipes

In this paper, a new methodology for prediction of the long-term (creep rupture) behavior of multilayer pipes under internal hydrostatic pressure is presented. For this purpose, a procedure using the three dimensional theory of thick-walled multilayer pipes together with a combined quadratic/linear regression analysis is used. The theory of thick walled tubes is used to assess the role of each layer in carrying the internal pressure and also the onset of the creep rupture in the composite pipe. For long-term extrapolation, a combined quadratic and linear regression analysis was used and the contribution of each component to the long-term strength of the composite pipe was quantitatively assessed. Using this procedure, the layer at which the creep rupture under internal pressure first initiates would be identified and the additional capacity of the remaining layer would be quantitatively assessed. This procedure is already incorporated in the pipe software called ADAP dealing with the automated design and analysis of pipelines. An example showing this procedure using ADAP is presented. The proposed methodology overcomes the limitations in the existing testing and extrapolation standards and, thus, can be used as a new extrapolative procedure for prediction of the service life of multilayer plastic pipes and pipe fittings. As particular applications, the procedure can be used for the estimation of the long-term behavior of multilayer pipes with metallic inter-layers and also single layer as well as structured pipes.     

Multiaxial fatigue/static test machine for large fibre-wound plastic pipes

The first part of this paper is concerned with the design, development and control of a machine built to test 70 and 50 mm diameter fibre-wound plastic pipes in various combinations of stress and with the capacity for varying the test environment. Provision was made to both grip and seal the specimen up to the ultimate burst strength of the pipe even though the pipe had failed functionally through seepage.The second part of this paper gives details, graphs and some data from the final proving and initial test programmes on glass wound polyester resin pipes.These tests were the first in a programme which was used to characterise the failure behaviour of fibre-reinforced pipes and also to investigate the importance of loading path on the ultimate failure behaviour.     

Fracture mechanics analysis of arc shaped specimens for pipe grade polymers

Instrumented three-point bend impact fracture tests are widely used to evaluate pipe grade polymers. Often specimens cut from small-diameter pipe are used, and these are necessarily arc-shaped. Because the orientation and thermal history may differ between extruded pipe and compression moulded plaque material, this additional difference in geometry must be properly accounted for, or it may mask any effects on material properties. This paper modifies a previously published solution for the geometry-dependent energy correction factor for arc-shaped specimens, and extends it to a wider range of standard pipe geometries. When the results are properly corrected, the effects of processing on a commercial PE100 appear to be minor.     

Evaluation of hybrid laser-cut and cast miniature fracture specimens

This paper presents a new hybrid laser-cutting method for producing fracture test specimens from thermosetting materials. The hybrid approach combines casting of a sheet of material with subsequent laser-cutting of the test specimens. The new approach was compared to the traditional casting method using a fracture toughness test. For this study, a compact version of the tapered double cantilever beam (cTDCB) was used as a specimen geometry for both manufacturing methods. The cTDCB specimen is crack length independent, and crack length investigations were performed to ensure the crack length independence of the cTDCB specimens. The specimens that were made by the hybrid laser-cut method were found to be comparable to the specimens obtained by the traditional casting method. Moreover, the laser-cut method provides a fast and accurate method to make a significant number of samples in a reasonable time. These tests show that the hybrid laser-cut method could be a good alternative to the traditional casting method.     

On the experimental measurement of fracture toughness in SENT rubber specimens

This work provides a direct comparison of several experimental approaches used in the literature to measure fracture toughness of rubber of rubber using single edge notched in tension (SENT) specimens, with the final aim to provide guidelines for an optimal testing procedure. Digital image correlation measurements were used to get new insights into the fracture process. SENT is experimentally advantageous because of the simple preparation from laboratory plates and the small amount of material required. The most common experimental approaches to measure fracture toughness of rubber rely on the energy release rate, measured by the tearing energy or the J-integral parameters. This work points out the importance of experimental conditions and test procedures: long specimens and short notches are preferred, identification of fracture initiation from the front view is necessary, strain energy density should not be evaluated from un-notched specimens at the critical stretch level, rather alternative strategies are shown in this work.     

Impact tensile fracture testing of a brittle polymer

The fracture behavior of a brittle polymer, methylmethacrylate–butadiene–styrene resin, under impact tensile loading was studied using single-edge-cracked specimens. The dynamic load and displacement were measured with a Piezo sensor and a high-speed extensometer, respectively. The load and displacement diagram, i.e., the external work, U_ex, applied to the specimen was used to determine the elastic energy, E_e, and non-elastic energy, E_n, due to viscoelastic and plastic deformation, and the fracture energy, E_f, for creating new fracture surface, A_s. The energy-release rates were then estimated using G_t=U_ex/A_s and G_f=E_f/A_s. The values of G_t and G_f were correlated with the fracture loads and the mean crack velocities determined from the load and time relationships.     

Intercalated clay nanocomposites: Morphology,mechanics, and fracture behavior

Intercalated nanocomposites of modified montmorillonite clays in a glassy epoxy were prepared by crosslinking with commercially available aliphatic diamine curing agents. These materials are shown to have improved Young's modulus but corresponding reductions in ultimate strength and strain to failure. The results were consistent with most particulate‐filled systems. The macroscopic compressive behavior was unchanged, although the failure mechanisms in compression varied from the unmodified samples. The fracture toughness of these materials was investigated and improvements in toughness values of 100% over unmodified resin were demonstrated. The fracture‐surface topology was examined using scanning electron and tapping‐mode atomic force microscopies and shown to be related to the clay morphology of the system. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1137–1146, 2001     

Long-term behavior of GFRP pipes: Optimizing the distribution of failure points during testing

The certification of glass-fiber reinforced plastic (GFRP) piping systems is regulated by normative standards in which test series of 10,000 h are needed to predict the residual property of the expected life (normally, 50 years). In this paper, optimization of statistical distribution of the test is proposed. This system involves using orthogonal design and test schemes lasting under 10,000 h. Experimental results for long-term ring-bending strain (S_b) of GFRP pipes from the standard test procedure indicated that this system is practical and effective. The estimation error when using the proposed method was consistently less than 8% if compared to the standard method.     

Interlaminar fracture toughness of unidirectional DCB specimens: A novel theoretical approach

A novel theoretical approach is presented to calculate the mode I interlaminar fracture toughness (G_Ic) of double cantilever beam (DCB) specimens with low ratio of initial crack length-to-thickness (a₀/2h). This method is based on a sixth-order beam theory, namely Reddy-Bickford beam (RB), on Winkler elastic foundation (WEF) to account for both transverse shear deformation of the beam and local effects at the delamination front (root rotation). RB with only two generalized displacements w and ?; and three boundary conditions at ends and loading points of a shear deformable beam gives more accurate results than the fourth-order Timoshenko beam theory. The accuracy of the proposed method in prediction of initiation G_Ic values is evaluated together with other available models considering the experimental fracture toughness for moderately thick unidirectional E-glass/epoxy DCB specimens with small initial delamination lengths.     

The application of fracture mechanics to the impact behaviour of rubber-toughened polyamides

Rubber-modification of polyamide is a widely-applied method of improving material resistance under high strain rate loading. The processing conditions used for preparing such two-phase blends strongly influence their structure and thus their subsequent impact properties. In the present work the relationships between production parameters, phase structure and impact resistance have been studied, and the rǒle of the rubber phase in promoting energy absorption investigated. It has been found that improved impact resistance, defined as a combination of high resistance to crack initiation and to crack propagation, is achieved by decreasing the polyamide phase viscosity while increasing the extrusion and injection temperatures, the mixing shear rate and the rubber phase volume fraction; an EPR modifier offers superior performance to a polybutadiene modifier; the dominant mechanisms of energy-absorption are shearing and void formation, there being no clear evidence of crazing; the J-integral technique of plastic fracture mechanics can be applied to Charpy impact testing; TEM allied with image analysis techniques provides quantitative morphological information on polymer blends.     

Translaminar fracture toughness testing of composites: A review

A comprehensive review of techniques for the experimental characterisation of the fracture toughness associated with the translaminar (fibre-breaking) failure modes of continuously reinforced laminated composites is presented. The collection of work relating to tensile failure reveals a varied approach in terms of specimen configuration, size and data reduction, despite the existence of an ASTM standard. Best practices are identified and suggestions for extending the scope of the current standard are made. Works on compressive failure are found to be less comprehensive. Measurement of the toughness associated with initiation of the failure mode in isolation has been achieved, but this review finds that significant research steps need to be taken before a resistance curve can be fully characterised.     

Polymeric multilayer capsules for drug delivery

The advent of Layer-by-Layer (LbL) assembly to fabricate polymeric as well as hybrid multilayer thin films has opened exciting avenues for the design of multifunctional drug carriers with extreme control over their physico-chemical properties. These polymeric multilayer capsules (PMLC) are typically fabricated by sequential adsorption of polymers onto a spherical substrate with dimensions varying from 10 nm to several microns and larger. In this critical review, we give an overview of the recent advances in the field of PMLC with respect to drug delivery and point out how sophisticated capsule engineering can lead to well-defined drug carriers with unique properties (139 references).     

Structural studies of fracture patterns in adhesive joints after pullout testing

The adhesive strength of compounds based on epoxy resin ED-20 with the TEAT and PEPA hardeners is determined by pullout testing before and after administering shungite (20 wt %) as filler in their composition. The results of structural studies of the samples after the tests, which allowed determining the fracture type (adhesive or cohesive) and the number of samples that corresponds to each fracture type, are shown.     

Dynamic fracture testing of polymethyl-methacrylate (PMMA) single-edge notched beam

Dynamic fracture in single-edge notched polymethyl-methacrylate (PMMA) beams have been investigated by three-point-bending impact testing with a drop-weight machine. A high-speed camera combined with the digital image correlation (DIC) method is used to capture the impact-induced crack initiation and propagation, as well as the beam deformation fields and the open mode strain at the original notch tip. The crack propagation length is recorded and the instantaneous crack velocity is calculated. Furthermore, the dynamic fracture toughness K_Id is quantified from the loading-displacement relations at different impact velocities. The effects of the impact velocity and impact energy on dynamic fracture toughness, fracture initiation strain, as well as the corresponding influences on the fracture propagation velocity, are discussed.     

Molecular fracture in natural rubber during tensile testing at low temperatures

Sulfur-cured natural rubber and other elastomers subjected to tensile tests at low temperatures and low strain rates are found to swell and “foam” after testing when brought to room temperature. The conditions under which this phenomenon can occur are established and related to load-extension curves. Free radicals formed during tensile testing are studied by electron spin resonance (ESR) techniques. It is found that the free radicals observed at the low temperatures are stable below the glass transition temperature of the material, and it is suggested that these radicals arise from mainchain fracture occurring during yielding of the material. The subsequent swelling at higher temperatures is found to be due to the expansion of environmental gases absorbed during tensile testing and to the release of hydrogen in certain cases from the materials tested. It is also suggested that yielding of the material which gives rise to these characteristics occurs by crazing of the material; the voids in the craze bands absorbing the environmental gases which subsequently cause the foaming at higher temperatures.     

Chemorheology investigation of a glassy epoxy thermoset on tensile plastic flow and fracture morphology

Reproducible and uncharacteristic tensile stress–strain behavior of cured glassy epoxy‐amine networks produces distinctive fracture surfaces. Test specimens exhibiting plastic flow result in mirror‐like fracture surfaces, whereas samples that fail during yield or strain softening regions possess nominal mirror‐mist‐hackle topography. Atomic force microscopy and scanning electron microscopy reveal branched nodule morphologies in the 50‐nm size scale that may be responsible for the unusual tensile properties. Current hypothesis is that plastic flow of the glassy thermoset occurs through the existence and deformation of these nodular nanostructures. The thermal cure profile of the epoxy‐amine thermoset affects the size and formation of the nodular nanostructure. Eliminating vitrification during thermoset polymerization forms a more continuous phase, reduction in size of the nodules, and eliminates the capacity of the material to yield in plastic flow. This maximizes nanostructure connectivity of the glassy epoxy‐amine thermoset and reduces strain to failure significantly. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1333–1344.     

Theory for non-equilibrium statistical mechanics

This paper reviews a new theory for non-equilibrium statistical mechanics. This gives the non-equilibrium analogue of the Boltzmann probability distribution, and the generalization of entropy to dynamic states. It is shown that this so-called second entropy is maximized in the steady state, in contrast to the rate of production of the conventional entropy, which is not an extremum. The relationships of the new theory to Onsager's regression hypothesis, Prigogine's minimal entropy production theorem, the Langevin equation, the formula of Green and Kubo, the Kawasaki distribution, and the non-equilibrium fluctuation and work theorems, are discussed. The theory is worked through in full detail for the case of steady heat flow down an imposed temperature gradient. A Monte Carlo algorithm based upon the steady state probability density is summarized, and results for the thermal conductivity of a Lennard-Jones fluid are shown to be in agreement with known values. Also discussed is the generalization to non-equilibrium mechanical work, and to non-equilibrium quantum statistical mechanics. As examples of the new theory two general applications are briefly explored: a non-equilibrium version of the second law of thermodynamics, and the origin and evolution of life.     

A DANREF certified reference plastic for measurement of overall migration into the food simulant olive oil by single sided testing

A reference material for the determination of overall migration from a plastic coextrudate into the fatty food simulant olive oil was produced and certified in an interlaboratory study. The analyses were carried out according to the ENV 1186 standard from the European Committee for Standardization (CEN) [1, 2, 3] with exposure of the coextrudate to olive oil for 10 days at 40?°C. After an initial preliminary interlaboratory study eight laboratories participated in the certification round, and two different methods were used to obtain single sided exposure of the plastic to the oil. The certified value was determined as the mean of laboratory mean values. No outliers were found. A reference value of 8.6 mg/dm²± 1.4 mg/dm² (± half width of the 95% confidence interval) was obtained which is within the range relevant for the regulatory limit (10 mg/ dm²), making this reference material suitable for laboratories measuring according to the EU overall migration limit [4]. The material has been found stable over 45 months.