X-ray microtomographic characterization and quantification of the strain rate dependent failure mechanism in cenosphere epoxy syntactic foams

This work investigates the failure mechanism in cenosphere epoxy syntactic foams at the quasi-static and dynamic strain rates. Split-Hopkinson pressure bar experiments are controlled to stop dynamic deformation of the foams at various strain stages. The internal microstructure at each strain is characterized in the x-ray microtomography and compared to the microstructure in the foams deformed quasi-statically. The microscopic observations reveal that the failure process in syntactic foams at the low and high rates is dominated by the crushing of cenospheres and the cracking of the epoxy matrix. However, the mechanism of failure in the foam is significantly affected by the strain rate. Compared to quasi-static compression, macro-cracks form earlier in the matrix at dynamic rates and can propagate to split cenospheres. The volume of the damage as defined by the failure of both cenospheres and the matrix is calculated from the x-ray microtomographic images. It is found that the damage can be quantitatively related to the strain and the strain rate using an empirical equation

Electromagnetic micropower generation - system design and analyses

There has been a huge reduction in size and power consumption of MEMS devices like transducers and sensors. These devices are usually designed to run on batteries. The limited lifespan of batteries may induce costly maintenance, in the case of contaminated areas for instance. That led to a surge of research in the area of energy harvesting. Sustainable power generation may be achieved in converting ambient energy into electrical energy. Since mechanical vibrations exist in most systems, many works focused on vibration-driven generators. In this field, the electromagnetic induction is well suited for the mechanical to electrical energy conversion. The design of the mechanical system that transmits the surrounding vibratory energy to the electromagnetic generator is a critical importance. This thesis presents an optimization of an electromagnetic microgenerator. It describes the theory, design and simulation of an energy converter based on electromagnetic induction. The objectives of this research are designing, improving the performance and operational reliability of electromagnetic microgenerator. These have been achieved by identifying the desirable design features of the electromagnetic microgenerator. Extensive analytical investigation has been conducted to develop an efficient design of an electromagnetic microgenerator. An analytical model is developed. Numerical analyses using Mat Lab software investigate the optimum design parameters to get maximum power output. This thesis deals with the design and simulation of a number of flat springs to be used for supporting the moving magnet of an electromagnetic microgenerator. The flat spring and moving magnet are equivalent to a basic spring-mass system, in which the moving magnet is attached to a platform suspended by four beams. These flat springs were designed by modelling and finite element method simulation using ANSYS 5.7. A series of structural and vibration analyses were carried out using ANSYS to evaluate the flat spring characteristics and to choose the desirable mode of vibration. Finite element method is also used for the analysis, evaluation and optimization of the electromagnetic design of the electromagnetic microgenerator. The objectives behind this analysis are to characterize the permanent magnet and to investigate the optimum position of the coil relative to the magnet. Output power is estimated using the ANSYS simulation results of the magnetic field induced on the coil. It is also found that the magnetic field of the permanent magnet in the vertical direction is higher in magnitude than the magnetic field in the horizontal direction. Estimated power was calculated for different distance between the coil and the permanent magnet. The methodology and findings in this research provided a number of contributing elements to the field of MEMS power generation, and provided an insight into the development of an electromagnetic microgenerator. This thesis is concluded with a discussion on the performance of the proposed electromagnetic microgenerator and suggestions for further research

Friction and Adhesion of Different Structural Defects of Graphene

Graphene structural defects, namely edges, step-edges and wrinkles are susceptible to severe mechanical deformation and stresses under frictional operations. Applied forces cause deformation by folding, buckling, bending and tearing the defective sites of graphene, which lead to a remarkable decline in normal load and friction bearing capacity. In this work, we experimentally quantified the maximal normal and friction forces corresponding to the damage thresholds of the different investigated defects as well as their pull-out (adhesion) forces. Horizontal wrinkles (with respect to the basal plane, i.e. folded) sustained the highest normal load, up to 317 nN, during sliding, whereas for vertical (i.e. standing collapsed) wrinkles, step-edges and edges, the load bearing capacities are up to 113 nN, 74 nN and 63±5 nN, respectively. The related deformation mechanisms were also experimentally investigated by varying the normal load up to the initiation of the damage from the investigated defects and extended with the numerical results from Molecular Dynamics and Finite Element Method simulations

Optimization of atmospheric plasma treatment of LDPE films: Influence on adhesive properties and ageing behavior

One of the major disadvantages of low density polyethylene (LDPE) films is their poor adhesive properties. Therefore, LDPE films have been treated with atmospheric pressure air plasma in order to improve their surface properties. So as to simulate the possible conditions in an industrial process, the samples have been treated with two different sample distances (6 and 10 mm), and treatment rates between 100 and 1000 mm s-1. The different sample distances are the distance of the sample from the plasma source. The variation of the surface properties and adhesion characteristics of the films were investigated for different aging times after plasma exposure (up to 21 days) using contact angle measurement, atomic force microscopy, weight loss measurements and shear test. Results show that the treatment increases the polar component () and these changes improve adhesive properties of the material. After the twenty-first day, the ageing process causes a decrease of wettability and adhesive properties of the LDPE films (up to 60%).Fombuena Borrás, V.; García Sanoguera, D.; Sánchez Nacher, L.; Balart Gimeno, RA.; Boronat Vitoria, T. (2014). Optimization of atmospheric plasma treatment of LDPE films: Influence on adhesive properties and ageing behavior. Journal of Adhesion Science and Technology. 28(1):97-113. doi:10.1080/01694243.2013.847045S97113281Achilias, D. S., Roupakias, C., Megalokonomos, P., Lappas, A. A., & Antonakou, Ε. V. (2007). Chemical recycling of plastic wastes made from polyethylene (LDPE and HDPE) and polypropylene (PP). Journal of Hazardous Materials, 149(3), 536-542. doi:10.1016/j.jhazmat.2007.06.076Friedman, M., & Walsh, G. (2002). High performance films: Review of new materials and trends. Polymer Engineering & Science, 42(8), 1756-1788. doi:10.1002/pen.11069Wiles, D. M., & Scott, G. (2006). Polyolefins with controlled environmental degradability. Polymer Degradation and Stability, 91(7), 1581-1592. doi:10.1016/j.polymdegradstab.2005.09.010Gao, J., Lei, J., Li, Q., & Ye, S. (2004). Functionalized low-density polyethylene via a novel photografting method and its adhesion properties. Journal of Adhesion Science and Technology, 18(2), 195-203. doi:10.1163/156856104772759403Shenton, M. J., Lovell-Hoare, M. C., & Stevens, G. C. (2001). Adhesion enhancement of polymer surfaces by atmospheric plasma treatment. Journal of Physics D: Applied Physics, 34(18), 2754-2760. doi:10.1088/0022-3727/34/18/307Belgacem, M. N., Salon-Brochier, M. C., Krouit, M., & Bras, J. (2011). Recent Advances in Surface Chemical Modification of Cellulose Fibres. Journal of Adhesion Science and Technology, 25(6-7), 661-684. doi:10.1163/016942410x525867Friedrich, J., Unger, W., & Lippitz, A. (1995). Plasma modification of polymer surfaces. Macromolecular Symposia, 100(1), 111-115. doi:10.1002/masy.19951000118Ladizesky, N. H., & Ward, I. M. (1989). The adhesion behaviour of high modulus polyethylene fibres following plasma and chemical treatment. Journal of Materials Science, 24(10), 3763-3773. doi:10.1007/bf02385768Nardin, M., & Ward, I. M. (1987). Influence of surface treatment on adhesion of polyethylene fibres. Materials Science and Technology, 3(10), 814-826. doi:10.1179/mst.1987.3.10.814Villagra Di Carlo, B., Gottifredi, J. C., & Habert, A. C. (2010). Synthesis and characterization of composite membrane by deposition of acrylic acid plasma polymer onto pre-treated polyethersulfone support. Journal of Materials Science, 46(6), 1850-1856. doi:10.1007/s10853-010-5012-4Matsunaga, M., & Whitney, P. J. (2000). Surface changes brought about by corona discharge treatment of polyethylene film and the effect on subsequent microbial colonisation. Polymer Degradation and Stability, 70(3), 325-332. doi:10.1016/s0141-3910(00)00105-1Novák, I., Pollák, V., & Chodák, I. (2006). Study of Surface Properties of Polyolefins Modified by Corona Discharge Plasma. Plasma Processes and Polymers, 3(4-5), 355-364. doi:10.1002/ppap.200500163Arpagaus, C., Rossi, A., & Rudolf von Rohr, P. (2005). Short-time plasma surface modification of HDPE powder in a Plasma Downer Reactor – process, wettability improvement and ageing effects. Applied Surface Science, 252(5), 1581-1595. doi:10.1016/j.apsusc.2005.02.099Morra, M., Occhiello, E., Marola, R., Garbassi, F., Humphrey, P., & Johnson, D. (1990). On the aging of oxygen plasma-treated polydimethylsiloxane surfaces. Journal of Colloid and Interface Science, 137(1), 11-24. doi:10.1016/0021-9797(90)90038-pKim, K. S., Ryu, C. M., Park, C. S., Sur, G. S., & Park, C. E. (2003). Investigation of crystallinity effects on the surface of oxygen plasma treated low density polyethylene using X-ray photoelectron spectroscopy. Polymer, 44(20), 6287-6295. doi:10.1016/s0032-3861(03)00674-8Kim, S. H., Ha, H. J., Ko, Y. K., Yoon, S. J., Rhee, J. M., Kim, M. S., … Khang, G. (2007). Correlation of proliferation, morphology and biological responses of fibroblasts on LDPE with different surface wettability. Journal of Biomaterials Science, Polymer Edition, 18(5), 609-622. doi:10.1163/156856207780852514Borcia, G., Anderson, C. A., & Brown, N. M. D. (2004). The surface oxidation of selected polymers using an atmospheric pressure air dielectric barrier discharge. Part I. Applied Surface Science, 221(1-4), 203-214. doi:10.1016/s0169-4332(03)00879-1Pascual, M., Calvo, O., Sanchez-Nácher, L., Bonet, M. A., Garcia-Sanoguera, D., & Balart, R. (2009). Optimization of adhesive joints of low density polyethylene (LDPE) composite laminates with polyolefin foam using corona discharge plasma. Journal of Applied Polymer Science, 114(5), 2971-2977. doi:10.1002/app.30906Encinas, N., Díaz-Benito, B., Abenojar, J., & Martínez, M. A. (2010). Extreme durability of wettability changes on polyolefin surfaces by atmospheric pressure plasma torch. Surface and Coatings Technology, 205(2), 396-402. doi:10.1016/j.surfcoat.2010.06.069Takke, V., Behary, N., Perwuelz, A., & Campagne, C. (2009). Studies on the atmospheric air-plasma treatment of PET (polyethylene terephtalate) woven fabrics: Effect of process parameters and of aging. Journal of Applied Polymer Science, 114(1), 348-357. doi:10.1002/app.30618Awaja, F., Gilbert, M., Kelly, G., Fox, B., & Pigram, P. J. (2009). Adhesion of polymers. Progress in Polymer Science, 34(9), 948-968. doi:10.1016/j.progpolymsci.2009.04.007Garcia, D., Sanchez, L., Fenollar, O., Lopez, R., & Balart, R. (2008). Modification of polypropylene surface by CH4–O2 low-pressure plasma to improve wettability. Journal of Materials Science, 43(10), 3466-3473. doi:10.1007/s10853-007-2322-2Guimond, S., & Wertheimer, M. R. (2004). Surface degradation and hydrophobic recovery of polyolefins treated by air corona and nitrogen atmospheric pressure glow discharge. Journal of Applied Polymer Science, 94(3), 1291-1303. doi:10.1002/app.21134Pascual, M., Balart, R., Sánchez, L., Fenollar, O., & Calvo, O. (2008). Study of the aging process of corona discharge plasma effects on low density polyethylene film surface. Journal of Materials Science, 43(14), 4901-4909. doi:10.1007/s10853-008-2712-0Sanchis, R., Fenollar, O., García, D., Sánchez, L., & Balart, R. (2008). Improved adhesion of LDPE films to polyolefin foams for automotive industry using low-pressure plasma. International Journal of Adhesion and Adhesives, 28(8), 445-451. doi:10.1016/j.ijadhadh.2008.04.002Fresnais, J., Chapel, J. P., Benyahia, L., & Poncin-Epaillard, F. (2009). Plasma-Treated Superhydrophobic Polyethylene Surfaces: Fabrication, Wetting and Dewetting Properties. Journal of Adhesion Science and Technology, 23(3), 447-467. doi:10.1163/156856108x370127Abenojar, J., Colera, I., Martínez, M. A., & Velasco, F. (2010). Study by XPS of an Atmospheric Plasma-Torch Treated Glass: Influence on Adhesion. Journal of Adhesion Science and Technology, 24(11-12), 1841-1854. doi:10.1163/016942410x507614Lommatzsch, U., Pasedag, D., Baalmann, A., Ellinghorst, G., & Wagner, H.-E. (2007). Atmospheric Pressure Plasma Jet Treatment of Polyethylene Surfaces for Adhesion Improvement. Plasma Processes and Polymers, 4(S1), S1041-S1045. doi:10.1002/ppap.200732402Balu, B., Berry, A. D., Patel, K. T., Breedveld, V., & Hess, D. W. (2011). Directional Mobility and Adhesion of Water Drops on Patterned Superhydrophobic Surfaces. Journal of Adhesion Science and Technology, 25(6-7), 627-642. doi:10.1163/016942410x525849Bhattacharya, S., Singh, R. K., Mandal, S., Ghosh, A., Bok, S., Korampally, V., … Gangopadhyay, S. (2010). Plasma Modification of Polymer Surfaces and Their Utility in Building Biomedical Microdevices. Journal of Adhesion Science and Technology, 24(15-16), 2707-2739. doi:10.1163/016942410x511105Das, S., Neogi, S., Chainy, G. B. N., & Guha, S. K. (2011). A Novel Two-Step Procedure for Plasma Surface Modification of Low-Density Polyethylene for Improved Drug Adhesion in Intra Uterine Devices (IUDs). Journal of Adhesion Science and Technology, 25(1-3), 151-167. doi:10.1163/016942410x503285Schulz, U., Munzert, P., & Kaiser, N. (2010). Plasma Surface Modification of PMMA for Optical Applications. Journal of Adhesion Science and Technology, 24(7), 1283-1289. doi:10.1163/016942409x12561252292026Silverstein, M. S., Breuer, O., & Dodiuk, H. (1994). Surface modification of UHMWPE fibers. Journal of Applied Polymer Science, 52(12), 1785-1795. doi:10.1002/app.1994.070521213Inagaki, N., Narushim, K., Tuchida, N., & Miyazaki, K. (2004). Surface characterization of plasma-modified poly(ethylene terephthalate) film surfaces. Journal of Polymer Science Part B: Polymer Physics, 42(20), 3727-3740. doi:10.1002/polb.20234Nakamatsu, J., Delgado-Aparicio, L. F., Da Silva, R., & Soberon, F. (1999). Ageing of plasma-treated poly(tetrafluoroethylene) surfaces. Journal of Adhesion Science and Technology, 13(7), 753-761. doi:10.1163/156856199x00983Yun, Y. I., Kim, K. S., Uhm, S.-J., Khatua, B. B., Cho, K., Kim, J. K., & Park, C. E. (2004). Aging behavior of oxygen plasma-treated polypropylene with different crystallinities. Journal of Adhesion Science and Technology, 18(11), 1279-1291. doi:10.1163/1568561041588200Morent, R., De Geyter, N., Leys, C., Gengembre, L., & Payen, E. (2007). Study of the ageing behaviour of polymer films treated with a dielectric barrier discharge in air, helium and argon at medium pressure. Surface and Coatings Technology, 201(18), 7847-7854. doi:10.1016/j.surfcoat.2007.03.018Zhao, B., & Kwon, H. J. (2011). Adhesion of Polymers in Paper Products from the Macroscopic to Molecular Level — An Overview. Journal of Adhesion Science and Technology, 25(6-7), 557-579. doi:10.1163/016942410x52582

Reactive extrusion of polyamide 6 using a novel chain extender

YesPolyamide 6 (PA6) is an important engineering thermoplastic, very widely used but prone to thermal degradation during extrusion at temperature not far from its melt temperature (220 oC). Typically, and as measured in this study, PA6 extruded at temperature of 300 oC shows a 40% decrease in tensile modulus compared to non-extruded PA6. To rebuild PA6 molecular weight, the easiest and cheapest method is to use an appropriate chain extender. Many chain extenders have been used in the past but they are essentially suited to nucleophile induced degradation, targeting split PA6 chains carboxyl COOH and amine NH2 end groups. What has been lacking are effective chain extenders for thermally only induced degradation, i.e. for the practical cases where the PA6 is thoroughly dried before extrusion. For such a case, the degradation reaction mechanism dictates that the solution is to develop chain extenders that target the split PA6 chains amide CONH2 groups not the carboxyl COOH and amine NH2 end groups. As amide groups strongly react with anhydride functionalities, we test the effectiveness of a novel chain extender, Joncryl® ADR 3400, a styrene maleic anhydride copolymer with multiple, repeating anhydride functionality. Assessment of chain extension in this study is done as with previous work, using rheology, mechanical and thermal properties of PA6 extruded on its own and with the chain extender. The viscoelastic data conclusively show the efficacy of such chain extender with more than 10 fold changes in the comparative values of the extruded sample storage modulus G' and as much as an 85% increase in the tensile modulus.Republic of Turkey, Ministry of National Education. University of Bradfor

Cracks, microcracks and fracture in polymer structures: Formation, detection, autonomic repair

The first author would like to acknowledge the financial support from the European Union under the FP7 COFUND Marie Curie Action. N.M.P. is supported by the European Research Council (ERC StG Ideas 2011 n. 279985 BIHSNAM, ERC PoC 2015 n. 693670 SILKENE), and by the EU under the FET Graphene Flagship (WP 14 “Polymer nano-composites” n. 696656)

A fluoride degradable crosslinker for debond-on-demand polyurethane based crosslinked adhesives

The requirement to consider the whole lifecycle of products including disassembly and recycling has resulted in considerable interest in debond-on-demand adhesives. These smart materials undergo controlled loss of adhesive strength when subject to a specific stimulus. This paper reports the design of a crosslinked polyurethane (PU) adhesive which incorporates a fluoride responsive degradable group. The crosslinked PU (CLP) adhesive showed a 28 % increase in adhesive bonding strengths by lap shear testing (14.6 MPa) when compared to structurally analogous linear PU (LPU) adhesive (11.4 MPa). After 3 h in contact with fluoride ions, the CLP exhibited a 55 % loss in adhesive bonding strength (from 14.6 MPa to 6.7 MPa) as a consequence of selective degradation of covalent bonds at the crosslinking sites. This work introduces a new route to dismantle components adhered with the widely used PU adhesives, facilitating recovery of valuable materials, and dramatically reducing waste