Experimental Study on Chloride-Induced Corrosion of Soil Nail with Engineered Cementitious Composites (ECC) Grout

Conventionally, a soil nail is a piece of steel reinforcement installed inside a hole drilled into the slope and filled with cement paste (CP) grout. Chloride penetration is a major deterioration mechanism of conventional soil nails as the CP grout is easy to crack with an uncontrollable crack opening when the soil nail is subject to loading or ground movements. Engineered Cementitious Composites (ECC) are a class of fiber-reinforced material exhibiting excellent crack control even when loaded to several percent of strain, and therefore, ECCs have great potential to replace traditional CP grout in soil nails for achieving a long service life. In this study, the chloride ion transport characteristics and electrically accelerated corrosion process of steel rebar in ECC and CP grouts are systematically studied. The rapid chloride ion penetration test results showed a reduction of 76% and 58% passing charges in ECC with 0.15% and 0.3% pre-loading strain, respectively, as compared to that in un-cracked CP. Furthermore, the accelerated corrosion experimental data showed that ECC under pre-loading strain still exhibited a coefficient of chloride ion diffusion that is 20–50% lower than CP grout due to the ability to control crack width. Service life calculations based on experimentally measured parameters showed that the predicted corrosion rate and corrosion depth of soil nails in ECC grout were much lower than those in CP grout. The findings can facilitate the design of soil nails with excellent durability and long service life.

Damage Localization in Composite Plates Using Wavelet Transform and 2-D Convolutional Neural Networks

Nondestructive evaluation of carbon fiber reinforced material structures has received special attention in the last decades. Usage of Ultrasonic Guided Waves (UGW), particularly Lamb waves, has become one of the most popular techniques for damage location, due to their sensitivity to defects, large range of inspection, and good propagation in several material types. However, extracting meaningful physical features from the response signals is challenging due to several factors, such as the multimodal nature of UGW, boundary conditions and the geometric shape of the structure, possible material anisotropies, and their environmental dependency. Neural networks (NN) are becoming a practical and accurate approach to analyzing the acquired data using data-driven methods. In this paper, a Convolutional-Neural-Network (CNN) is proposed to predict the distance-to-damage values from the signals corresponding to a transmitter-receiver path of transducers. The NN input is a 2D image (time-frequency) obtained as the Wavelet transform of the acquired experimental signals. The distances obtained with the NN are the input of a novel damage location algorithm which outputs a bidimensional image of the structure’s surface showing the estimated damage locations with a deviation of the actual position lower than 15 mm.

Experimental Characterization of Short Fiber-Reinforced Composites on the Mesoscale by Indentation Tests

Indentation tests are widely used to characterize the material properties of heterogeneous materials. So far there is no explicit analysis of the spatially distributed material properties for short fiber-reinforced composites on the mesoscale as well as a determination of the effective cross-section that is characterized by the obtained measurement results. Hence, the primary objective of this study is the characterization of short fiber-reinforced composites on the mesoscale. Furthermore, it is of interest to determine the corresponding area for which the obtained material parameters are valid. For the experimental investigation of local material properties of short fiber-reinforced composites, the Young’s modulus is obtained by indentation tests. The measured values of the Young’s modulus are compared to results gained by numerical simulation. The numerical model represents an actual microstructure derived from a micrograph of the used material. The analysis of the short fiber-reinforced material by indentation tests reveals the layered structure of the specimen induced by the injection molding process and the oriented material properties of the reinforced material are observed. In addition, the experimentally obtained values for Young’s modulus meet the results of a corresponding numerical analysis. Finally, it is shown, that the area characterized by the indentation test is 25 times larger than the actual projected area of the indentation tip. This leads to the conclusion that indentation tests are an appropriate tool to characterize short fiber-reinforced material on the mesoscale.

Effects of humid and hot environment on fiber composites in cooling towers

Polyvinyl chloride (PVC) materials used in cooling towers always lead to damage and low efficiency due to the hot and humid environment. This paper suggests a glass fiber reinforced material for a better performance. An optimal fractal distribution of glass fibers in the composite matrix is experimentally obtained when the fractal dimensions are between 0.6 and 0.9.

Fractional-Order Thermoelastic Wave Assessment in a Two-Dimensional Fiber-Reinforced Anisotropic Material

The present work is aimed at studying the effect of fractional order and thermal relaxation time on an unbounded fiber-reinforced medium. In the context of generalized thermoelasticity theory, the fractional time derivative and the thermal relaxation times are employed to study the thermophysical quantities. The techniques of Fourier and Laplace transformations are used to present the problem exact solutions in the transformed domain by the eigenvalue approach. The inversions of the Fourier-Laplace transforms hold analytical and numerically. The numerical outcomes for the fiber-reinforced material are presented and graphically depicted. A comparison of the results for different theories under the fractional time derivative is presented. The properties of the fiber-reinforced material with the fractional derivative act to reduce the magnitudes of the variables considered, which can be significant in some practical applications and can be easily considered and accurately evaluated.

Experimental Determinations on Mechanical Properties for Polyester-Glass Fiber Composite Materials

The mechanical characteristics of a fiber reinforced material depend on a number of parameters related to the structure and characteristics of the component materials, the volumetric distribution, orientation, geometry and adhesion of the fibers to the matrix. The modification of these characteristics over time is due to the varied mechanical demands (repeated or lasting), the thermal and humidity demands, the chemical agents and the influence of aging. The paper presents some observations resulting from experimental tests on polyester-glass composite materials developed in the Materiaux Composites laboratory.

Shear deformability characteristics of a rapid-cure woven prepreg fabric

Formability of a continuous fiber-reinforced material is known to be influenced by its intraply shear behavior. This study investigates a 2 × 2 twill weave carbon fabric and the corresponding vinyl-based thermoset prepreg developed for press-cured structural parts. Intraply shear tests of bias-extension and picture-frame were conducted for a range of industrial-relevant processing conditions of temperature and shear rate. The dry fabric was characterized similar to the prepreg to isolate the influence of semi-cured resin on the woven prepreg fabric formability in shear. The shear deformation behavior of the prepreg, usually dependent on the fabric architecture, is found to be controlled by the state of the resin. The results clearly show the significance of the choice of process parameters on the prepreg shear behavior. It is demonstrated that preheating the prepreg to temperatures considerably lower than required to initiate cure can make the shear formability of the woven prepreg equivalent to the constituent (dry) reinforcement fabric. The actual shear angle measurement during the bias-extension tests demonstrates the level of inter-tow slippage for the prepreg fabric at relatively elevated temperatures. The comparison of normalized shear data from the two test methods helps to determine the improved procedure for prepreg fabric testing.

Experimental study of the Poynting effect in a soft unidirectional fiber-reinforced material under simple shear

Shear and normal responses of a soft unidirectional fiber-reinforced material subjected to simple shear.