Structure and optical investigation of the effect of electron beam‐irradiation in poly‐allyl‐diglycol‐carbonate

The effect of electron beam irradiation on the structural and optical properties of Poly‐Allyl‐Diglycol‐Carbonate CR‐39 solid state nuclear track detector was investigated. Samples from CR‐39 detector were irradiated with electron beam with doses at levels between 10 and 140 kGy. The structural and optical modifications in the electron beam irradiated CR‐39 samples have been studied as a function of dose using different characterization techniques such as FTIR spectroscopy, Vickers hardness, refractive index and color difference measurements. The electron beam irradiation in the dose range 25–140 kGy led to a more compact structure of CR‐39 polymer, which resulted in an improvement in its hardness with an increase in the refractive index. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Experimental characterization and computational simulations of the low‐velocity impact behaviour of polypropylene

The objective of this work is to validate predictive models for the simulation of the mechanical response of polypropylene undergoing impact situations. The transferability of material parameters deduced from a particular loading scenario (uniaxial loading) to a different loading situation (multiaxial loading) was studied. The material was modelled with a modified viscoplastic phenomenological model based on the G'Sell–Jonas equation. To perform the numerical simulations, a user‐material subroutine (VUMAT) was implemented in the ABAQUS/explicit finite element code. Constitutive parameters for the model were determined from isostrain rate uniaxial tensile impact test data using an inverse calibration technique. In addition, falling‐weight low‐energy impact tests were performed on disc‐shaped specimens at velocities in the range 0.7 to 3.13 m s^?1. The model predictions were evaluated by comparison of the experimental and finite element response of the falling‐weight impact tests. The G'Sell–Jonas model showed much better predictability than classical elastoplasticity models. It also showed excellent agreement with experimental curves, provided stress‐whitening damage observed experimentally was accounted for in the model using an element failure criterion. © 2013 Society of Chemical Industry     

Direct tensile behavior of ultra high performance fiber reinforced concrete (UHP-FRC) at high strain rates

This experimental study investigates the direct tensile behavior of ultra-high performance fiber reinforced concrete (UHP-FRC) at strain rates ranging from 90 to 146/s. The tests are conducted using a recently developed impact testing system that uses suddenly released strain energy to generate an impact pulse. Three fiber types were considered, a twisted fiber and two other types of straight fibers. Specimen impact response was evaluated in terms of first cracking strength, post-cracking strength, energy absorption capacity and strain capacity. The test results indicate that specimens with twisted fibers generally exhibit somewhat better mechanical properties than specimens with straight fibers for the range of strain rates considered. All UHP-FRC series tested showed exceptional rate sensitivities in energy absorption capacity, generally becoming much more energy dissipative under increasing strain rates. This characteristic highlights the potential of UHP-FRC as a promising cement based material for impact- and blast-resistant applications.     

On the application of a damped model to the falling weight impact characterization of glass beads–polystyrene composites

Instrumented falling weight impact tests were carried out to characterize the mechanical behavior of a material pattern formed by polystyrene and different amounts of glass beads. This characterization was performed at high strain rate using two different impact arrangements: the first uses high impact energy at the striker, whereas the second uses a low‐impact energy. Starting from a conservative model, a nonconservative one has been proposed for the low‐energy impact configuration as a better approach to the material behavior. In this latter model, the energy losses were quantified through the restitution coefficient. Two alternative methods for its calculation are described. The results shows good agreement between the flexural modulus and break stresses calculated in either the low‐ or the high‐energy arrangement; however, the low‐energy impact method yields more confidence results. Using the proposed model, the composites' fracture onset was determined, and also in the samples with low content of glass beads, it was possible to assess the micromechanism of failure, given the estimation for the stress to produce crazing. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1271–1284, 2004     

Radiation‐processed polychloroprene‐co‐ethylene–propene diene terpolymer blends: Evaluation of blend morphology,miscibility, and physical properties

The miscibility of polychloroprene rubber (CR) and ethylene–propylene–diene terpolymer rubber (EPDM) was studied over the entire composition range. Different blend compositions of CR and EPDM were prepared by initially mixing on a two‐roll mill and subsequently irradiating to different gamma radiation doses. The blends were characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy, density measurement, hardness measurement, and solvent permeability analysis. The compatibility of the blends was studied by measuring the glass transition temperature and heat capacity change of the blends. The immiscibility of blends was reflected by the presence of two glass transition temperatures; however, partial miscible domains were observed due to inter diffusion of phases. Permeation data fitted best with the Maxwell's model and indicated that in CR‐EPDM blends, EPDM exists as continuous phase with CR as dispersed phase for lower CR weight fractions and phase inversion occurred in 40–60% CR region. It was observed that CR improved oil resistance of EPDM; however, the effect was prominent for blends of >20% CR content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Druckverhalten feuchter kugelförmiger Zeolith 4A‐Granulate

The material behavior of three particle sizes of elastic‐plastic zeolite 4A granules has been experimentally studied using compression tests. The recorded force‐displacement curves have been approximated by mechanical models from the literature. Moreover, the influence of particle size and moisture content on the material behavior has been investigated. Furthermore, the specific fracture energy distribution and the distribution of the equivalent impact velocity at fracture have been determined. At impact stressing the energetic equivalent breakage energy corresponds to the impact velocity of a particle on a rigid wall initiating breakage of the particle.     

Design and application of an instrumented falling weight impact tester

Within the past decade, instrumented impact testers have become important tools for characterizing the response of polymers to short term loads. Unlike conventional test equipment which yield only the fracture energy, the instrumented devices are capable of providing detailed force vs time plots of the impact process. An instrumented falling weight impact tester is described which is equipped with an accelerometer which permits direct observation of the weight's deceleration as it strikes and pierces the test specimen. Integration of the resulting acceleration vs time curve provides the velocity change upon impact from which the fracture energy can he calculated. The impact tester is capable of accepting a wide range of specimen shapes and sizes and is especially useful where small amounts of material are at hand. To date, it has proved its utility in characterizing thin plastic sheets as well as fiber-reinforced laminates.     

Experimental analysis on deformation and damage behavior of Al6061/SiC functionally graded plates under low-velocity impact

Due to their promising features provided by ceramic and metal constituents in a single volume, Functionally Graded Materials (FGMs) have received great attention for impact applications. Most of the available studies on the low-velocity impact behavior of FGMs have been carried out by analytical or numerical methods. This study addresses an experimental analysis on the low-velocity impact response of Al6061/SiC FGM plates. The influence of the material composition of the FGM plate (from metal-rich to ceramic-rich) on the energy absorption mechanisms as well as on the deformation and damage behavior was investigated. The ceramic-rich FGM plate exhibits a quasi-brittle response that includes a combination of elastoplastic indentation and brittle failures with increasing impact energy, while the metal-rich and linear FGM plates show elastoplastic behavior. Plastic deformation is the primary energy absorption mechanism for the metal-rich and linear FGM plates, whereas plastic deformation, brittle failures (radial cracks and conoidal crack/fracture), delamination, and pore collapse are effective on the energy absorption of the ceramic-rich FGM plate.     

The fracture properties of a fiber metal laminate based on a self‐reinforced thermoplastic composite material

The present research program has studied the fracture properties of a Fiber‐Metal Laminate (FML) system constituted by aluminum alloy and a high‐impact self‐reinforced composite material. Here, the self‐reinforced composite system consists of a polypropylene matrix reinforced with polypropylene fibers. Initial testing has shown that a though adhesion can be achieved between the aluminum layers and the composite material by incorporating a thermoplastic adhesive interlayer at the common interface. The adhesion at the metal–composite interface has been studied under a wide range of strain rate conditions using a Single Cantilever Beam test geometry, and it has been shown that the interfacial fracture toughness is loading rate sensitive. Interlaminar delamination tests of the plain composite have also been studied and it was shown that their fracture toughness is also loading rate sensitive. Additional tensile tests have shown that the tensile strength and moduli of the FMLs are linearly influenced by the volume fraction of their constituent materials as well as are successfully predicted using a simple rule of mixture. Low velocity impact tests have also shown that the FMLs based on a self‐reinforced polypropylene composite yielded specific perforation energies well above the 30 J m²/kg. It was also shown that by increasing the number of metal and composite plies in the FMLs, resulted in hybrid structures capable of absorbing higher specific low velocity impact energies. POLYM. COMPOS., 35:427–434, 2014. © 2013 Society of Plastics Engineers     

Measurement and modelling of hollow rubber spheres: surface-normal impacts

Abstract

The performance of natural rubber sports balls under impact conditions is dominated by the material's behaviour under high strain rate conditions dictated by the impact velocity and ball dimensions. To design improved products, sports ball manufacturers need to better understand the physical phenomena associated with ball impact against both rigid and deformable surfaces. This understanding will provide the foundation for performance prediction and optimisation design tools as well as more appropriate product and ultimately material testing techniques. Rebound characteristics of pressurised and pressureless tennis balls and their respective rubber cores subject to normal impacts are presented for a range of incident velocities. High-speed video analysis has been used to measure coefficient of restitution, impact duration and 'whole ball' deformation to validate a surface-normal impact finite element method based predictive model as the first step towards a more comprehensive oblique impact model. Accounting for strain rate dependent stiffness and damping material properties has achieved close correlations between model predictions and observed impact behaviour. The propagation of dominant bending and hoop-strain waves through the ball during the impact is revealed to illustrate the methodology's effectiveness in predicting ball performance associated with difficult to observe impact phenomena.     

A study of the effect of PP‐g‐MA and SEBS‐g‐MA on the mechanical and morphological properties of polypropylene/nylon 6 blends

The mechanical and morphological properties of polypropylene/nylon 6 blends compatibilized with PP grafted with maleic anhydride (PP‐g‐MA) and styrene/ethene‐co‐butene/styrene grafted with maleic anhydride (SEBS‐g‐MA) are studied using a special version of a factorial design known as extreme vertices. Properties examined include yield stress, modulus, elongation, toughness, impact strength and morphology. Comparisons are made between various treatment combinations (i.e. a variety of blends) and polypropylene homopolymer using various statistical methods including analysis of variance (ANOVA). Scheffe's Test and Duncan's Multiple Range Test. Significant differences were found for yield stress, modulus, elongation, toughness and impact strength for specific treatment combinations versus PP as well as on average. Ternary diagrams are used to plot response surfaces of the measured data illustrating the main effects and interactions involved, while allowing correlations to be made with blend morphology. Indications from test results and analysis of response surfaces show a strong relationship between nylon/compatibilizer ratio and mechanical properties.     

Parametric numerical simulation of impact response of carbon nanotube/polymer nanocomposites

A numerical model has been developed using the explicit FE code LS-DYNA in order to study the effect of geometrical and material parameters on the low-velocity impact response of carbon nanotube (CNT)/polymer nanocomposites. The model is based on a Representative Volume Element (RVE). The RVE is prismatic with a rectangular cross-section while the impactor is spherical. The simulations show that the presence of CNT significantly enhances the impact stiffness and the energy absorption capacity of the material. The enhancement increases with the CNT's volume fraction and it is larger at larger impact velocities. The effect of CNT's aspect ratio is found to be minor. The orthotropic behaviour of CNT assigns the RVE a higher energy absorption capacity than the isotropic behaviour at small impact velocities. The prediction of impact damage at large impact velocities indicates that the CNT makes the polymer more susceptible to fracture.     

Numerical modeling of the impact response of fiber–metal laminates

This article models the impact response of fiber–metal laminates (FMLs) based on a polypropylene (PP) fiber/PP matrix composite and two types of aluminum alloy. Here, a finite element analysis is used to model the impact behavior of FMLs at velocities up to 150 m/s. The PP‐based composite was modeled as an isotropic material with a specified tensile cut‐off stress to allow for the automatic removal of failed elements. The aluminum was modeled as an elasto‐plastic material with a specified shear failure strain and a tensile failure cut‐off stress. The deformed response of the structures and the resulting failure modes were compared with the experimental data. The variation of the maximum permanent displacement versus normalized impact energy was also predicted and compared with the impact test data and good agreement was observed. Finally, the decay of the kinetic energy of the projectile with time was determined for each of the targets and used to characterize their impact resistance. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Flow‐induced solidification of high‐impact polypropylene copolymer compositions: Morphological and mechanical effects

Polypropylene‐based impact copolymers are a complex composition of matrix material, a dispersed phase and many optional modifiers. The final heterophasic morphology of such systems is influenced significantly by the processing step, adding an additional level of complexity to understanding the structure‐property relation. This topic has hardly been studied so far. The effect of thermal history and shear flow on the solidification process of three different compositions of a polypropylene‐based impact copolymer, i.e., one base material and two compounds with either high density polyethylene or ethylene‐co‐octene added, is investigated. Samples are examined using differential scanning calorimetry, extended dilatometry, transmissions electron microscopy, and finally, tensile testing. With flow, the materials show pronounced flow‐enhanced crystallization of the matrix material and deformed filler content. Compared to the base polymer, the stress–strain response of the compounded samples shows a lower yield stress and more pronounced influence of shear, reflected in the increasing strain hardening modulus. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42040.     

Model for thickness effect with impact testing of viscoelastic materials

Thickness effect on impact parameters is studied and a model is developed for flat‐ended drop weight impact testing of viscoelastic materials. The model represents a relationship of specimen thickness with impact force/stress and impact energy. A polymeric material, ethylene vinyl acetate (EVA), was used for experimental verification. Experimental results for a thickness range of 1–9 mm at impact energy levels of 0.42, 0.96, and 1.54 J have been found to be in reasonable agreement with predictions based on the model with some approximated parameters. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1762–1767, 2001     

Impact characterization of a carbon fiber‐epoxy laminate using a nonconservative model

The study of polymer and composite behavior under high strain rates is of fundamental relevance to determine the material suitability for a selected application. However, the impact phenomenon is a very complicated event, mainly due to the short duration, large deformation, and high stresses developed in the sample. In this work, we have performed impact tests over a carbon fiber reinforced epoxy using low‐energy in the striker. A nonconservative and nonlineal spring‐dashpot series model has been proposed to reproduce the material behavior. The model considers simultaneously both flexural and indentation phenomena accounting for energy losses by means of the restitution coefficient. Using this model, an excellent fit between the predicted and the experimental force‐time trace has been obtained below the composite failure point, which was recognized by a separation of both mentioned curves. As the epoxy‐fiber laminate has a very low viscoelasticity, the high strain rate Young's modulus obtained from the model was compared with that extracted from a conventional three point bending test, finding a very good match between the values. The study of the dashpot coefficients allows concluding that the dominant mechanism is the composite flexion, while the indentation effects contribution takes on importance at low impact velocities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2256–2263, 2005     

Eco‐plastics: Morphological and mechanical properties of recycled poly(carbonate)‐crushed rubber (rPC‐CR) blends

Crushed tire rubber particles (CR) have been dispersed into a recycled poly(carbonate) matrix (rPC) to obtain an eco‐friendly plastic (EFP). A positive synergy was expected from the association of an elastomeric phase to a tough thermoplastic matrix, helping on the other hand to develop a plastic with low impact on the environment. Mechanical melt‐mixing alone cannot provide a suitable interface, and led to blends with poor mechanical properties. Consequently, we have investigated different strategies to improve the EFP properties: First, the rubber surface has been treated by flaming or washing with dichloromethane and second, two copolymers, poly(ethylene‐co‐ethyl acrylate‐tert‐hydroxyl methacrylate) (E‐EA‐MAH) and poly(ethylene‐co‐methyl acrylate‐ter‐glycidyl methacrylate) (E‐MA‐GMA), were used to compatibilize CR particles with rPC matrix by reactive melt‐mixing in an internal mixer. The resulting blends mechanical properties were studied through static tension experiments and interpreted to the light of electronic microscopy fractography analysis and nanoindentation experiments. Significant gain of mechanical properties can be obtained by decreasing CR size under 140 μm (especially for CR contents between 5 and 20% m/m). To reach similar properties with rubber particles of diameter over 140 μm (but under 350 μm), it is necessary to activate their surface by either dichloromethane washing or flaming. Additional use of a compatibilizer extends the plastic behaviour domain of the EFP. rPC‐20% w/w CR is the best alternative material of our study. POLYM. ENG. SCI., 47:1768–1776, 2007. © 2007 Society of Plastics Engineers     

Evidences of solvent‐induced miscibility in polychloroprene‐co‐ethylene‐propene diene terpolymer blends

Solvent dependent changes in the compatibility behavior of Polychloroprene/Ethylene–propylene–diene terpolymer blends (CR/EPDM) have been investigated using dilute solution viscometry and solvent permeability analysis. To predict the compatibility of rubber blends of different compositions in solvents of different cohesive energy densities, Huggins interaction parameter (ΔB), hydrodynamic interaction (Δη) and Sun's parameter (α) were evaluated from the analysis of the specific and reduced viscosity data of two and three‐component polymer solutions. Miscibility criteria were not satisfied for CR/EPDM blends over the entire composition range in toluene, xylene, and carbon tetrachloride (CCl₄), however, a narrow miscibility domain was observed in chloroform (CHCl₃) for CR/EPDM/CHCl₃ system. These results were further corroborated with the analysis of heat of mixing (ΔH_m) and polymer–polymer interaction parameter (χ₁₂), for all rubber blend compositions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Autonomous damage initiated healing in a thermo‐responsive ionomer

The partially neutralised poly[ethylene‐co‐(methacrylic acid)] copolymer Surlyn 8940^® (DuPont) ionomer exhibits damage‐initiated healing during high‐energy impact. This is attributed to the hierarchical structure of ionomers, arising from the presence of ionic aggregates and hydrogen bonding. This work investigates the mechanism of this process using novel techniques developed here. The ionomer's response to penetration has been found to consist of three consecutive events: an initial elastic response, an anelastic response and pseudo‐brittle failure. In addition, the ultimate level of healing has been shown to be dependent upon the elastic response during impact as well as post‐failure viscous flow. Increasing the local temperature at impact consistently increases elastic healing, although further improvements in healing are minor once the local temperature increases beyond the melting point. Below the order‐to‐disorder transition, microscopic investigations reveal severe plastic deformation while the lack of shape memory reduces the comparative level of elastic healing. Above this temperature, healing is facilitated by elastomeric behaviour at the impact site, while above the melting point a combination of elastomeric and viscous flow dominates. This work provides for the first time evidence of the consecutive healing events occurring during high‐impact penetration for ionomers. The hierarchical structure of ionomers and its impact upon the microstructure have been shown to be critical to the process. Comparison of the mechanical response during impact with that of non‐ionic polymers further highlights this. In addition, slow relaxational processes occurring post‐impact are found to facilitate further recovery in mechanical properties. Copyright © 2010 Society of Chemical Industry     

Brittle‐ductile transitions in polyethylene

The failure mode of a number of polyethylenes has been studied under predominantly plane strain conditions. Square section samples, notched on all sides, have been tested in tension to failure over a range of crosshead speeds and temperatures. Integration under the subsequent load displacement curve has allowed the total energy, energy to peak load, and energy after peak load to be determined. The data have been analyzed in terms of the ratio of the energy after the peak load to the total energy. The results show that the material can change from brittle to ductile failure as a function of test speed. At a suitable temperature we have observed brittle‐like failure at the highest and lowest test speeds and ductile failure at intermediate speeds. The resulting failure surface features correlate very strongly with the energy ratio analysis—flat smooth surfaces where low energy ratios are seen and large ductile tearing where high ratios are seen. The effect of molecular weight and polydispersity will be shown and possible failure mechanisms discussed.