Effect of Strain Rate on the Transverse Tension and Compression Behavior of a Unidirectional Non-Crimp Fabric Carbon Fiber/Snap-Cure Epoxy Composite

The strain rate-dependent behavior of a unidirectional non-crimp fabric (UD-NCF) carbon fiber/snap-cure epoxy composite loaded along the transverse direction under quasi-static and dynamic conditions was characterized. Transverse tension and compression tests at quasi-static and intermediate strain rates were performed using hydraulic testing machines, while a split Hopkinson pressure bar (SHPB) apparatus was used for transverse compression tests at high strain rates. A pulse shaper was used on the SHPB apparatus to ensure dynamic equilibrium was achieved and that the test specimens deformed homogenously with a nearly constant strain rate. The transverse tensile strength at a strain rate of 16 s−1 increased by 16% when compared to that at quasi-static strain rates, while distinct localized fracture surface morphology was observed for specimens tested at different strain rates. The transverse compressive yield stress and strength at a strain rate of 325 s−1 increased by 94% and 96%, respectively, when compared to those at quasi-static strain rates. The initial fracture plane orientation for the transverse compression tests was captured with high-speed cameras and found to increase with increasing strain rate. The study provides an important data set for the strain rate-dependent response of a UD-NCF composite material, while the qualitative fracture surface observations provide a deeper understanding of the failure characteristics.

Some Physical Processes Involved in Deformation and Fracture

<p>The effects of strain rate, of moisture content, and of tracheid structure on the transverse fracture properties of Pinus Radiata have been studied. Small rectangular blocks were loaded to failure in transverse tension, with the conditions of fracture being varied as follows: (i) strain raite - at 2 x 10 caret-6 sec caret-1, and from 10 caret-5 to 10 caret 2 sec caret-1 in decade steps , (ii) moisture content - airdry (12.7%) and saturated, and (iii) structure - springwood and summerwood. Microscopical examination (both scanning electron and optical) of the surfaces produced by the facture showed that the cellular level, either of two types of failure could occur. These are called transwall and intrawall; transwall is the longitudinal splitting of a tracheid wall, and intrawall is a splitting between adjacent tracheids.</p>

Some Physical Processes Involved in Deformation and Fracture

<p>The effects of strain rate, of moisture content, and of tracheid structure on the transverse fracture properties of Pinus Radiata have been studied. Small rectangular blocks were loaded to failure in transverse tension, with the conditions of fracture being varied as follows: (i) strain raite - at 2 x 10 caret-6 sec caret-1, and from 10 caret-5 to 10 caret 2 sec caret-1 in decade steps , (ii) moisture content - airdry (12.7%) and saturated, and (iii) structure - springwood and summerwood. Microscopical examination (both scanning electron and optical) of the surfaces produced by the facture showed that the cellular level, either of two types of failure could occur. These are called transwall and intrawall; transwall is the longitudinal splitting of a tracheid wall, and intrawall is a splitting between adjacent tracheids.</p>

IN SITU CHARACTERIZATION OF FIBER-MATRIX INTERFACE DEBONDING VIA FULL-FIELD MEASUREMENTS

Macroscopic mechanical and failure properties of fiber-reinforced composites depend strongly on the properties of the fiber-matrix interface. For example, transverse cracking behavior and interlaminar shear strength of composites can be highly sensitive to the characteristics of the fiber-matrix interface. Despite its importance, experimental characterization of the mechanical behavior of the fibermatrix interface under normal loading conditions has been limited. This work reports on an experimental approach that uses in situ full-field digital image correlation (DIC) measurements to quantify the mechanical and failure behaviors at the fiber-matrix interface. Single fiber model composite samples are fabricated from a proprietary epoxy embedding a single glass rod. These samples are then tested under transverse tension. DIC is used to measure the deformation and strain fields in the glass rod, epoxy, and their interface vicinity. Initiation and propagation of the fiber-matrix debond are discussed. Full-field measurements are shown to facilitate the quantitative analysis of the traction-separation laws at the fiber-matrix interface subjected to transverse tension.

Enhancing the interyarn friction properties of kevlar and glass fabrics through ZnO nanowire coating

The interyarn friction properties of fabrics can be enhanced by appropriate surface treatment of fibers. This study focuses on evaluating the interyarn friction properties of Kevlar and Glass fabrics that were coated with ZnO nanowires through different growth cycles. ZnO nanowires were coated onto woven Kevlar and Glass fabrics through a low temperature hydrothermal solution method. Longer growth time coupled with periodic refreshing of growth solution and washing of fabrics was found to be a favorable condition for uniform and precipitate free growth of ZnO nanowires. The effects of ZnO nanowire coating on the tensile and interyarn friction properties of fabrics were measured. In general, after ZnO nanowire coatings, Kevlar fabrics remained equally flexible as that of bare fabric while Glass fabrics became relatively stiff and brittle. The interyarn friction properties of Kevlar fabrics were found to be high under 100 N transverse tension while the transverse tension was found to have negligible or insignificant effect on the interyarn friction properties of Glass fabrics that were used in this research. Compared to bare fabric, Kevlar fabric coated with ZnO nanowires for extended duration showed 266% and 293% increase in yarn pull out load and energy, respectively under 100 N tension. Compared to bare fabric, Glass fabric coated with ZnO nanowires for extended duration showed 517% and 376% increase in yarn pull out load and energy, respectively under 5 N tension. These significant improvements in interyarn friction properties were attributed to mechanical interlocking and accumulation of ZnO nanowires at the intersection of yarns.

Microstructure Characteristics and Its Effect on the Fracture in the Triple Junction Region of Friction Stir Welded Mg Alloys Subjected to Tension

Because of the tensile strength decreasing of the friction stir welded wrought magnesium (Mg) alloy compared to the base material, the reasons for the failure of weld has been focused on. After the fracture in transverse tension, the crack went through the welded joint from the center of the weld to the transition zone between the thermal-mechanical affected zone and weld zone. In the present study, the microstructure characteristics and its effect on the facture in the triple junction region is investigated. Based on the metallography and the electron back-scattered diffraction (EBSD) technology, it was observed that a twin band extended from the triple junction region to the middle of weld. The profuse twinning in the twin band was considered to play an important role on the crack propagation from the stir zone edge to the crown zone.