Experimental and numerical investigation on pure aluminum by ECAP

The equal channel angular pressing(ECAP) experiments were carried out with industrial pure aluminum and an in-house mould. The comparison of material grain size before and after ECAP was performed by applying the technique of electron back scattered diffraction(EBSD). The results show that the grains in the material after ECAP are refined and the yield stress and ultimate strength are increased. In order to investigate the deformation mechanism during ECAP and the reason for driving grain size refinement, three-dimensional numerical simulations of the ECAP process were carried out. Based on the Lode parameter analysis, the deformation of the material sample is found very complicated, not just pure shear during extrusion through the angular channel. The simulation confirms that a strong strain gradient in the sample material is imposed by the ECAP.     

Durability of FRP Composite Bridge Deck Materials under Freeze-Thaw and Low Temperature Conditions

Fiber-reinforced polymer (FRP) composites, especially lightweight sandwich structures, are rapidly finding their way into civil infrastructure application. FRP composite panels are particularly attractive as bridge deck systems due to their high strength, low density, and durability, which are of importance to the bridge industry. Most of the vast amount of durability data for FRP has been generated for aerospace and automotive applications, which involve very different service conditions than civil infrastructure. For civil engineering applications, it is essential to examine the durability performance of FRP materials under weathering conditions. The ultimate goal of this research is to develop a reliable framework for durability assessment of FRP decks, including laboratory testing procedure and finite-element simulation capability. Such a framework should be applicable to all types of FRP deck construction. In this paper, specimens of typical FRP bridge deck skin materials are subjected to freeze-thaw cycling between 4.4 and ?17.8°C in media of dry air, distilled water, and saltwater, and constant freeze at ?17.8°C . The selected deck is used as an example for demonstration purposes. In addition, selected specimens are subjected to simultaneous environmental exposure conditions and sustained loading of 25% ultimate strain. It should be emphasized that most of the environmental conditions reported in the literature produce minor deterioration of a single composite property, and the assessment of such effect on this single property becomes unreliable because of a large property variation. Therefore, in this paper we use multiple mechanical properties as performance indices for damage evaluation. Based on findings from this work, it is concluded that freeze-thaw cycling between 4.4 and ?17.8°C alone and up to 1,250 h and 625 cycles caused very insignificant or no change in the flexural strength, storage modulus, and loss factor of the FRP specimens conditioned in dry air, distilled water, and saltwater. Small reductions in storage modulus (about 1% or less) were observed when specimens were prestrained and subjected to 250 freeze-thaw cycles in distilled water and saltwater. Changes in flexural strength were statistically insignificant, since they were within the data scatter.     

Tensile Behavior of Cement-Based Composites with Random Discontinuous Steel Fibers

In this paper, the tensile properties of cement-based composites containing random discontinuous steel fibers are reported. Direct tensile tests were performed to study the effects of fiber length (hence fiber aspect ratio), interfacial bonding, and processing conditions on composite properties. Composite tensile strength and ductility are highlighted and discussed.     

FEA of Complex Bridge System with FRP Composite Deck

Innovative fiber-reinforced polymer (FRP) composite highway bridge deck systems are gradually gaining acceptance in replacing damaged/deteriorated concrete and timber decks. FRP bridge decks can be designed to meet the American Association of State Highway and Transportation Officials (AASHTO) HS-25 load requirements. Because a rather complex sub- and superstructure system is used to support the FRP deck, it is important to include the entire system in analyzing the deck behavior and performance. In this paper, we will present a finite-element analysis (FEA) that is able to consider the structural complexity of the entire bridge system and the material complexity of an FRP sandwich deck. The FEA is constructed using a two-step analysis approach. The first step is to analyze the global behavior of the entire bridge under the AASHTO HS-25 loading. The next step is to analyze the local behavior of the FRP deck with appropriate load and boundary conditions determined from the first step. For the latter, a layered FEA module is proposed to compute the internal stresses and deformations of the FRP sandwich deck. This approach produces predictions that are in good agreement with experimental measurements.     

Frictional Constraint of Rope Strands

In this study, the slippage criterion and model of synthetic double-braided ropes have been formulated, particularly, for the partial frictional conditions. Such constraint is closest to reality, and contributes to most failure cases in marine service due to abrasion/wear. The slippage criterion proposed is based on the measured frictional resistance of individual rope strands from a newly devised pull-out test. Emphasis is on straight ropes as well as rope terminations, the latter either an eye splice or a continuous loop on a bollard-like pin. The experimental results agree well with the predictions of the partial friction case for small nylon ropes. However, for PET ropes, the predictions of the infinite friction case agree better with the experiments due partially to high frictional constraint. The slippage process is also discussed and this can provide further insight into prevention against abrasion failures which are found to be the major cause of the deterioration of ropes in service.     

Mechanical Interaction between Concrete and FRP Sheet

In this technical note, fiber-reinforced plastics (FRP) strengthening efficiency for reinforced-concrete columns will be examined from a micromechanical point of view by accounting for direct mechanical interaction between FRP sheet and concrete. Concrete compressive failure is initiated by wing-crack propagation. The mechanical interaction dictates the compressive behavior of FRP-wrapped concrete from the first bent-over point to the peak load in the load∕displacement curve. A possible detailed interaction under compression is described.     

Effect of Plasma Treatment of Polyethylene Fibers on Interface and ementitious Composite Properties

It is well known that interfaces in composites play an important role in determining composite properties. In this paper, preliminary results of the improvement in tensile properties of a fiber-reinforced cementitious composite due to plasma treatment of the discontinuous polyethylene fibers are reported. Specific focus is placed on the pseudo strain-hardening composite properties induced by fiber reinforcements and associated load transfer from crackbridging fibers to matrix. Single fiber pullout tests support that the composite property improvement is indeed derived from interfacial property enhancement of the plasma treatment process.     

Snubbing and Bundling Effects on Multiple Crack Spacing of Discontinuous Random Fiber-Reinforced Brittle Matrix Composites

Multiple cracking due to pseudo strain–hardening of fiber-reinforced brittle matrix composites contributes significantly to enhanced composite strain capacity as well as toughness. This unique phenomenon is true for both continuous aligned and discontinuous random fiber composites. Theoretical formulation of multiple crack spacing is reviewed in this paper. In particular, a snubbing effect of fiber pullout and a bundling effect of fiber strands on crack spacing are discussed. Taking account of these effects, expressed via the snubbing coefficient, f , and effective bond strength, τ_eff, a better spacing prediction has been obtained for a discontinuous random glass-strand-reinforced cement composite.