Fatigue and Fracture of the FRP-Wood Interface: Experimental Characterization and Performance Limits

A performance-based material evaluation methodology was developed to qualify FRP composite reinforcement bonded to glulam structural members for highway bridge applications. The objectives of this thesis are: a) to implement and correlate two methods to evaluate the fatigue and fracture performance of FRP-wood interfaces with associated performance limits; and b) to provide data and recommendations necessary to develop performance-based material specifications. The first method is based on evaluating the apparent shear strength in a single-lap shear test by fatigue tension loading. The second method is based on evaluating the interface fracture toughness in Mode I or opening-mode using fracture mechanics. ASTM standard test procedures were identified as the basis for each method. However, these test procedures had to be modified and adapted for FRP-wood interfaces. The research approach combined experimental techniques, data reduction methods and analytical tools. A laminating press was designed and calibrated for timedependent effects to fabricate the test samples. Two material systems that passed adhesive screening tests were evaluated: E-glasslurethane pultruded composite sheet with urethane adhesive (material system B) and E-glasslepoxy composite sheet by continuous lamination with epoxy adhesive (material system C). The fatigue performance of FRPwood interfaces using a single-lap shear configuration was characterized by modifying ASTM D2339 standard test procedure. A fatigue performance-based evaluation criteria and associated limits were proposed. It was shown that material system C had higher apparent shear strength and better fatigue resistance than system B. Quality bonding was observed for both material systems in terms of high percentage of wood failure. Finite Element Analysis (FEA) was performed on a model simulating single lap shear specimens loaded in tension to analyze the peeling and shear stress distributions in the overlap area. The Mode I fracture toughness of FRP composite and wood bonded interfaces was evaluated using flat double-cantilever beam (DCB) specimens. ASTM standard test procedure D5528 for unidirectional FRP composites was modified to characterize hybrid FRP-wood materials. Crack lengths and crack opening displacements were monitored during the experiments using a CCD digital camera system with digital image correlation. An important simplification was realized with flat DCB geometry with respect to other methods based on tapered specimens. Three data reduction methods were applied to compute interlaminar fracture toughness: modified beam theory, compliance calibration and shear corrected compliance. The three methods provided similar fracture toughness values. It was found that Mode I fracture toughness of material system C (epoxy adhesive) was significantly higher than that of material system B (urethane adhesive). It was demonstrated that this fracture method could be used to quantitatively discriminate and evaluate FRP-wood bonded material systems

Software for evaluating probability-based integrity of reinforced concrete structures

In recent years, much research work has been carried out in order to obtain a more controlled durability and long-term performance of concrete structures in chloride containing environment. In particular, the development of new procedures for probability-based durability design has proved to give a more realistic basis for the analysis. Although there is still a lack of relevant data, this approach has been successfully applied to several new concrete structures, where requirements to a more controlled durability and service life have been specified. A probability-based durability analysis has also become an important and integral part of condition assessment of existing concrete structures in chloride containing environment. In order to facilitate the probability-based durability analysis, a software named DURACON has been developed, where the probabilistic approach is based on a Monte Carlo simulation. In the present paper, the software for the probability-based durability analysis is briefly described and used in order to demonstrate the importance of the various durability parameters affecting the durability of concrete structures in chloride containing environment

Beam-Induced Damage Mechanisms and their Calculation

The rapid interaction of highly energetic particle beams with matter induces dynamic responses in the impacted component. If the beam pulse is sufficiently intense, extreme conditions can be reached, such as very high pressures, changes of material density, phase transitions, intense stress waves, material fragmentation and explosions. Even at lower intensities and longer time-scales, significant effects may be induced, such as vibrations, large oscillations, and permanent deformation of the impacted components. These lectures provide an introduction to the mechanisms that govern the thermomechanical phenomena induced by the interaction between particle beams and solids and to the analytical and numerical methods that are available for assessing the response of impacted components. An overview of the design principles of such devices is also provided, along with descriptions of material selection guidelines and the experimental tests that are required to validate materials and components exposed to interactions with energetic particle beams.Comment: 69 pages, contribution to the 2014 Joint International Accelerator School: Beam Loss and Accelerator Protection, Newport Beach, CA, USA , 5-14 Nov 201

Healing-on-Demand Polymer Composites Based on Shape Memory Polyurethane Fibers and Polymeric Artificial Muscles

In this dissertation, the healing-on-demand polymer composites based on shape memory polyurethane fibers and artificial muscles are investigated, for understanding and developing a novel healing-on-demand composite so that it would be used for industrial applications that could heal structural-length scale damage and leaking autonomously, repeatedly, efficiently, timely, and molecularly. Firstly, the structural relaxation behavior of shape memory polyurethane (SMPU) fiber was studied by theoretical analysis and experimental test. Then, a self-healing composite based on cold-drawn short SMPU fiber was prepared and tested for evaluating its crack-healing performance. After that, polymer artificial muscle based healing-on-demand composite was developed and characterized. Based on the systematic research results, the study on fishing line artificial muscle reinforced composite for impact mitigation and on-demand damage healing was conducted. Future studies to grow this research area are discussed

Recent Progress in Electrospun Nanofibres: Reinforcement Effect and Mechanical Performance

Composite materials are becoming increasingly important as structural materials for aeronautical and space engineering, naval, automotive, and civil engineering, sporting goods, and other consumer products. Fiber-based reinforcement represents one of the most effective manufacturing strategies for enhancing the mechanical strength and other properties of composite materials. Electrospinning has gained widespread interest in the last two decades because of its ability to fabricate continuous ultrafine nanofibers with unique characteristics. The impact of electrospinning on fiber synthesis and processing, characterization, and applications in drug delivery, nanofiltration, tissue scaffolding, and electronics has been extensively studied in the past. In this article, the authors have focused on a comprehensive review of the mechanical performance and properties of electrospun nanofibers as potential reinforcements as well as their advanced nanocomposites

Elastic wave measurement in rock engineering

Imperial Users onl

MODELING PULL-OUT BEHAVIOR OF THE DEFORMED REBAR EMBEDDED INSIDE THE REINFORCED CONCRETE

Abstract: This study presents the modeling of the pull-out behavior of deformed bars embedded inside the reinforced concrete element. The simulation uses an in-house finite element package called 3D-NLFEA. Sufficiently small solid elements that consider the frictional resistance and mechanical interlocking between the bar thread and the concrete matrix were used in the simulation. The effect of concrete compressive strength, cover thickness, and stirrup configuration on the pull-out capacity of the modeled specimens are investigated thoroughly. The modeling found out that the 3D-NLFEA package can capture the bond-fracture process at the interface between the bars and concrete. The fracture that occurs in the concrete was dominated by tensile splitting failure. The presence of stirrups that confined the concrete and restrained the crack propagation significantly influences the pull-out capacity, cracking pattern, and failure behavior at the bar interface with the concrete. The analysis results from 3D-NLFEA are also compared with the 3D-RBSM analysis results available in the literature. From the comparison between the two packages, it can be concluded that the analysis result from 3D-NLFEA is somewhat more conservative compared to the 3D-RBSM