Effect of Barium Titanate Reinforcement on Tensile Strength and Dielectric Response of Electrospun Polyvinylidene Fluoride Fibers

In this study, we used electrospinning to obtain polyvinylidene fluoride (PVDF) fibers reinforced with barium titanate (BaTiO3) and investigated the influence of BaTiO3 concentration on the tensile strength and dielectric behavior of PVDF fibers. X-ray diffraction (XRD) study and infrared spectroscopy revealed that PVDF fibers filled with BaTiO3 possessed higher fraction of ferroelectric β-crystals compared to neat PVDF fibers. Further, incorporation of 40 wt% BaTiO3 within the fibers increased their stiffness and strength by 95 and 38%, respectively. These improvements in tensile properties of BaTiO3 filled PVDF fibers arose from the reinforcement effect of BaTiO3. Also, the dielectric response of the BaTiO3/PVDF fibers was characterized. The effective dielectric constants of PVDF fibers reinforced with BaTiO3 were found to increase consistently with BaTiO3 content at all frequencies. The dielectric loss of the fibers did not show any significant change for all concentrations of BaTiO3 within the fibers

On the environmental fracture of polymethylmethacrylate

Crack propagation of PMMA in some liquid environments is described for various testing conditions, such as fixed load, fixed displacement and monotonically increasing displacement. Fracture mechanics concepts have been used successfully in analysing the results. When continuous stable cracking is achieved, values of fracture toughness ( R ) for PMMA under these loading conditions are obtained as a function of crack velocity ( ŀ ) using the method of Gurney and Hunt [11]. For crack velocities greater than 10 −2 mm sec −1 , the fracture toughness values in the environments are increased when compared with the corresponding air results. Unique relationships between R and ŀ have been shown to exist for cracking in ethanol and carbon tetrachloride.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44666/1/10853_2004_Article_BF00823210.pd

Temperature and rate dependent fracture in glass-filled polystyrene

The rate and temperature dependent fracture behavior of glass-filled polystyrene has been investigated over the crack speed range of 10 13 to 1 mm/sec and in the temperature range 283 to 396°K for three environmental conditions: (i) air; (ii) water; and (iii) hot water exposure at 363°K and subsequent drying. Relationships between fracture toughness ( K c ), crack speed and temperature have been obtained experimentally and analysed according to the concepts of fracture mechanics and reaction rate theories. Crack propagation in air is shown to be controlled by a Β-relaxation process associated with crazing. Activation energies of 200 ∼ 210 kj/mole in air and 80 ∼ 120 kj/mole in water are reported. At a given temperature and crack speed, the glass-filled polystyrene is shown to display smaller crack propagation resistances in a water environment when compared with the air results. Specimens subjected to hot water exposure and then tested after drying also possess less cracking resistance. This toughness degradation phenomenon is a result of the damaging effects of the water which penetrates into the glass-filled composite.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38103/1/760160604_ftp.pd

Fatigue crack propagation of PMMA in organic solvents

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44786/1/10853_2004_Article_BF00541761.pd

Fracture criterion and crack stability in grooved beam-like testpieces

In this paper, the fracture criterion for rectangular grooved beam-like testpieces under several loading conditions has been analysed using a simple beam-on-elastic foundation model. Experiments have shown that the model is adequate for describing quasi-static fracture in such test geometries. In addition, the crack stability conditions under both load-controlled and displacement-controlled testing machines are presented. Dans ce mémoire, le critère de rupture pour des pièces rectangulaires entaillées en forme de poutres soumises à diverses conditions de mise en charge est analysé en recourant à un modèle d'une poutre simple posée sur une fondation élastique.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42759/1/10704_2004_Article_BF00036014.pd

Contoured double cantilever beam specimens for fracture toughness measurement of adhesive joints

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44671/1/10853_2004_Article_BF00540939.pd

Singularities of an interface crack in electrostrictive materials

AbstractIn the present work, the singularities of an interface crack between two dissimilar electrostrictive materials under electric loads are investigated. Within the framework of two-dimensional deformation, the problem is solved using the complex variable method. Three crack models, that is, permeable, impermeable and conducting crack models are considered individually. Complex potentials and intensity factors of total stresses are derived by considering both the Maxwell stresses in the surrounding space at infinity and inside the crack. It is found that, for the above three crack models, the singularities of total stress are the same as those in traditional bi-materials with an interface crack; however, the intensities of the total stress depend on the actual crack model used

Mixed-Mode Fracture Of Adhesively Bonded Joints

The study focuses on using fracture mechanics to evaluate mixed-mode fracture properties of adhesively bonded aerospace material systems. As a part of experimental efforts, mixed-mode fracture tests were performed using modified Arcan specimens consisting of several combinations of adhesive, composite and metallic adherends using a special loading device. By varying the loading angle, alpha from 0 degrees to 90 degrees, mode I, mixed-mode and mode II fracture data were obtained experimentally. Experimental and theoretical studies of mixed-mode fracture behaviour of adhesively bonded aluminium, steel and CF/PEI composite joints were also performed using an adhesive in the aerospace industry. Finite element analyses were carried out on specimens with different adherends. Based on those analyses, mixed-mode fracture criterions for the adhesively bonded systems under consideration have been determined

Effect of hygrothermal ageing on morphology and indentation modulus of injection moulded nylon 6/organoclay nanocomposites

The effect of water immersion on the morphology and indentation modulus of injection moulded nylon 6 and its organoclay nanocomposites was investigated. XRD analysis showed that at 70 °C water promoted further crystallization in the nylon matrix and aided the γ- to α-crystal phase transition in the skin region. However, the presence of organoclay deterred this transformation. The combined actions of water and heat (70 °C) did not further degrade nylon 6 and its nanocomposites compared to water ageing at room temperature (25 °C). In fact, there was relative enhancement of the indentation moduli owing to the beneficial morphological changes induced in the nylon matrix. The largest improvements were found in the skin region of the injection moulded bars.Fil: Seltzer, Rocío. University of Sydney; AustraliaFil: Frontini, Patricia Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Mai, Yiu-Wing. University of Sydney; Australi