M. L. Peterson

Ultrasonic investigation of concrete with distributed damage

Bridge decks deteriorate due to many causes including low level fatigue cycling, thermal loading, chemical attack, and reinforcing steel corrosion. This deterioration takes the form of distributed microscopic damage that may evolve into large defects such as cracks, delaminations, spalling, and scaling. An experimental program was conducted to evaluate ultrasonic techniques for measuring distributed cracking in concrete structures. Distributed cracking refers primarily to microcracking and other high porosity regions that generally precede large cracks. An investigation of distributed cracking yields information on weaknesses in the materials that may ultimately lead to major cracking and failure, but also can be used to evaluate distress mechanisms that do not necessarily result in large cracks. Distributed cracking in concrete was induced by freeze-thaw cycling and salt-scaling. Ultrasonic tests were used to measure changes in attenuation, pulse velocity, and peak frequency of the ultrasonic waves due to the distributed damage. The ultrasonic measurements were correlated with damage observed using optical microscopy. It was found that ultrasonic pulse velocity was not very sensitive to changes caused by distributed microcracking. The change in signal amplitude (a measure of ultrasonic attenuation) was quite sensitive to changes caused by microcracking, although the measurements showed considerable scatter. The peak frequency of the ultrasonic signal was also quite sensitive to the condition of the concrete. These results must be considered in the development field tests for evaluation of concrete structures.

COMPOSITE REPAIR OF TIMBER STRUCTURES

Abstract An approach, using pultruded composites, to rejuvenate low aspect ratio timber beams, which model railroad bridge span timbers, is described. The approach focuses on overcoming the loss of shear properties by inserting fiberglass pultruded rods from the bottom to the top of the beam, through areas of damage. The concept includes the incorporation of an adhesive during the process of insertion, which not only bonds the reinforcing rods in-place, but also, fills adjacent cracks. Scale beam testing, with a variety of reinforcement cases, has been performed and the overall results are extremely positive, with test beams showing strong recovery of flexural properties and improvement in the strain to failure.

Characterization of carbons derived from cellulose and lignin and their oxidative behavior.

In this study the oxidative behavior of carbons derived from cellulose and lignin were compared using thermogravimetric analysis (TGA). Specific surface area and chemical composition of the two types of carbon were analyzed using nitrogen adsorption at 77K and infrared spectroscopy respectively. The results demonstrate that cellulose carbon has a higher reaction order and lower activation energy than lignin carbon under identical experimental conditions when they were prepared at temperatures lower than 500 degrees C. However, such differences were considerably reduced for the carbon samples prepared at temperatures greater than 700 degrees C. It was verified that lignin carbon is more stable than cellulose carbon due to its higher content of aromatic structures when they are prepared at lower temperature. The specific surface area and porosity have a more limited contribution to the differential oxidative behaviors of the two types of carbon. This research has significance related to the formation of carbon nanotubes from plant materials during low temperature carbonization.

The role of mechanics in biological and biologically inspired materials

In the development of new materials, researchers have recently turned to nature for inspiration and assistance. A special emphasis has been placed on understanding the development of biological materials from the traditional correlation of structure to property, as well as correlating structure to functionality. The natural evolution of structure in biological materials is guided by the interaction between these materials and their environment. What is most notable about natural materials is the way in which the structure is able to adapt at a wide range of length scales. Much of the interaction that biological materials experience occurs through mechanical contact. Therefore, to develop biologically inspired materials it is necessary to quantify the mechanical behavior of and mechanical influences on biological structures with the intention of defining the natural structure-property-functionality relationship for these materials. In particular, the role mechanics has assumed in understanding biological materials, and the biologically inspired materials developed from this knowledge, will be clarified. The following will serve to elucidate on this role: the helical structure of fibrous tissue, the multi-scale structure of wood, and the biologically inspired optimal structure of functionally graded materials.

Biomechanical and Mechanical Investigations of the Hoof-Track Interface in Racing Horses

The aim of this article is to review current knowledge of kinetic variables of the hoof-track interaction and track properties relevant to the objective of minimizing injuries to horses at racing tracks. In each phase of the stance--primary impact, secondary impact, support, and breakover, the hoof experiences different combinations of force and acceleration. The role of each combination, and of measured track properties, in causing catastrophic and chronic injuries to the limbs of racing horses is unknown. Limited data of this type have been provided in previous epidemiologic studies of risk factors for breakdown. Future epidemiological studies should include characterization of the track surfaces and a more complete description of the kinematics of the hoof and surface. Consideration of an appropriate range of physical properties is necessary in track design, testing, and maintenance.

A simple scheme for self-focusing of an array

A self-focusing technique and its application to a linear array system are presented in this paper. By application of the technique the system is capable of both sonification and reception focusing. The array is first excited as an unfocused array. Next a cross-correlation technique is used to determine time delays of reception of the largest amplitude backscattered signals at the elements of the array. The original transducer signal is then reemitted with the appropriate time delays to achieve sonification focusing on the scatterer producing the largest signal. This process is repeated in an iterative mode to focus energy on the strongest scatterer. Once insonification focusing has been achieved the last time-delay calculations are used once more for reception focusing, i.e., to correct the signals received by the individual elements for differences in arrival times. A low cost linear array has been constructed to implement the self-focusing technique. Examples demonstrate the capability of the technique to focus on the largest hole of sets of three holes in an aluminum specimen.

Inertial effects on mechanically braked Wingate power calculations

PURPOSE The standard procedure for determining subject power output from a 30-s Wingate test on a mechanically braked (friction-loaded) ergometer includes only the braking resistance and flywheel velocity in the computations. However, the inertial effects associated with accelerating and decelerating the crank and flywheel also require energy and, therefore, represent a component of the subjects power output. The present study was designed to determine the effects of drive-system inertia on power output calculations. METHODS Twenty-eight male recreational cyclists completed Wingate tests on a Monark 324E mechanically braked ergometer (resistance: 8.5% body mass (BM), starting cadence: 60 rpm). Power outputs were then compared using both standard (without inertial contribution) and corrected methods (with inertial contribution) of calculating power output. RESULTS Relative 5-s peak power and 30-s average power for the corrected method (14.8 +/- 1.2 W x kg(-1) BM; 9.9 +/- 0.7 W x kg(-1) BM) were 20.3% and 3.1% greater than that of the standard method (12.3 +/- 0.7 W x kg(-1) BM; 9.6 +/- 0.7 W x kg(-1) BM), respectively. Relative 5-s minimum power for the corrected method (6.8 +/- 0.7 W x kg(-1) BM) was 6.8% less than that of the standard method (7.3 +/- 0.8 W x kg(-1) BM). The combined differences in the peak power and minimum power produced a fatigue index for the corrected method (54 +/- 5%) that was 31.7% greater than that of the standard method (41 +/- 6%). All parameter differences were significant (P < 0.01). The inertial contribution to power output was dominated by the flywheel; however, the contribution from the crank was evident. CONCLUSIONS These results indicate that the inertial components of the ergometer drive system influence the power output characteristics, requiring care when computing, interpreting, and comparing Wingate results, particularly among different ergometer designs and test protocols.

Monitoring fungal degradation of E-glass/phenolic fiber reinforced polymer (FRP) composites used in wood reinforcement

The susceptibility of E-glass fiber reinforced polymer (FRP)/phenolic pultruded composite plates to fungal degradation was examined. Interlaminar shear strength (ILSS) by short-beam testing and ultrasonic non-destructive evaluation (NDE) techniques were applied to monitor fungal degradation of E-glass fiber reinforced polymer composites. Since the FRP material was designed for use as reinforcement with wood, the FRP material was exposed to two common wood decay fungi, a brown rot fungus and a white rot fungus. Light and scanning electron microscopy indicated that both wood decay fungi actively grew and penetrated into the FRP material, especially in high-void content areas. The reduction in apparent ILSS of the brown rot-exposed FRP material was not statistically significant at a 95% confident level. A weak relationship between decay exposure and ILLS strength loss, however, was observed. The experimental results indicate that both mechanical property evaluation techniques (ILSS and NDE) may be sensitive enough to detect the effects of fungal degradation in FRP materials.

Instrumented bicycle pedals for dynamic measurement of propulsive cycling loads

A system was developed for measuring and analyzing the forces placed on a bicycle pedal during operation of a stationary ergometer. Forces are measured in the plane parallel to the ergometer in directions normal and tangential to the surface of the pedals, encompassing the plane of propulsive forces. The pedals are designed to be structurally and functionally equivalent to standard clipless pedals. The stock pedal spindle and bearing assembly was replaced with a new spindle that was instrumented with two Wheatstone bridges of foil strain gauges. The bearings were relocated to the crank-arm/pedal-spindle interface. The original pedal body was then pinned to the new spindle. Additionally, the pedals were instrumented with optical encoders to measure the pedal angle relative to the crank arm. An optical encoder was also mounted near the bottom bracket to measure crank-arm angle. Signals were transmitted via a cable tethered to the cyclist’s leg from the pedals to an instrumented chassis, where the strain gauge signals were conditioned and the digital optical encoder signals converted to analogue signals. From the instrumented chassis, seven signals are ready for standard analogue data collection. Data collected from this new system has proved to be both comparable with previously published literature and accurate when compared with expected power output values.

Radiated noise from commercial ships in the Gulf of Maine: Implications for whale/vessel collisions

To understand mysticete acoustic-based detection of ships, radiated noise from high-speed craft, cruise ships, catamarans and fishing vessels was recorded June-September 2009. Calibrated acoustic data (<2500 Hz) from a vertical hydrophone array was combined with ship passage information. A cruise ship had the highest broadband source level, while a fishing vessel had the lowest. Ship noise radiated asymmetrically and varied with depth. Bow null-effect acoustic shadow zones were observed for all ship classes and were correlated with ship-length-to-draft-ratios. These shadow zones may reduce ship detection by near-surface mysticetes.