GeoTechnical Investigations for the Dalton Highway Innovation Project As A Case Study of the Ice-Rich Syngenetic Permafrost

INE/AUTC 11.1

Reconsidering laminate nonsymmetry

Nonsymmetric laminates are commonly precluded from composite design due to perceptions of reduced performance arising from in- and out-of-plane coupling. This coupling introduces warpage during cure—leading to raised stresses, together with diminished buckling and load carrying capacity. However, these reduced performance characteristics are rarely quantified and included in the design process; instead the symmetric-only paradigm remains pervasive at the cost of a significantly reduced design space. Warpage is largely driven by mismatch in the coefficients of thermal expansion between sublaminates located above and below the midplane and can be predicted by the classical laminate theory. Acknowledging that all symmetric laminates in multipart structures have build stresses from assembly, it is proposed that subsets of nonsymmetric laminates that translate to similar raised stress levels be considered for design. Challenging this symmetric-only design paradigm would permit greater design freedom and offer new routes to elastically tailor composite structures. Further analysis of structural performance is assessed in terms of reduced loading and buckling capacity

A New kHz Rate Laser-Ultrasound Scanner for Ply-by-Ply Imaging of Defects, Pores and Inconsistencies in Composite Structures

Among NDT methods, only US and X-ray tomography can precisely locate three- dimensional defects regardless of composite type. X-ray systems, however, are very expensive, time-consuming and cumbersome. In addition, the chamber limits the size of the sample to several centimeters and makes it completely unsuitable for field applications. Conventional US pulse-echo techniques usually require couplants or full sample immersion for optimal energy transfer, which can affect overall scan speed and limit the applications where they can be used. Laser-ultrasound (LU) has many advantages over conventional US. First, laser-generated US transients are ultra-wideband, providing at least 3 times better resolution compared to conventional US transducers with the same characteristic frequency [1]. Second, the system is fundamentally non-contact and removes all issues related to US coupling. Its typical disadvantages are low sensitivity, instability, low pulse repetition frequency and high cost. We have recently overcome these limitations with a new kHz rate fiber-optic LU scanner [1-4]. Here we show that the scanner can provide nearly X-ray quality 3D images and locate almost all imperfections in composites: visualize pores [5] and wrinkles, evaluate heat damage [6] and locate impact damage with a sub-ply spatial resolution

Optoacoustic imaging using thin polymer étalon

Optical detection of ultrasound is a promising technique for high frequency imaging arrays. Detection resolution approaches the optical resolution, which can be on the order of the optical wavelength. We describe here an optical technique for ultrasound detection based on a thin (10 μm)(10μm) Fabry–Perot étalon optimized for high resolution imaging. The signal to noise ratio (SNR) approaches that of an ideal piezoelectric transducer over a 100 MHz100MHz bandwidth. Array functionality is demonstrated by scanning a probe beam along a line. Thermoelastic excitation was applied to generate acoustic waves in a test phantom containing a single “pointlike” source. An image of the source was reconstructed using signals acquired from the étalon detector array.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87845/2/134102_1.pd

Non-Contact Evaluation of Residual Stress in Metals with Laser-Generated Surface Acoustic Waves and a Point-Like Fiber-Optic Sagnac Detector

Stress can remain in a material after the original load is removed. It can be purposely introduced to improve the properties of structural components, but can also be undesired, shortening a component’s lifetime, changing its original geometry or even leading to failure. There is a large spectrum of problems where residual stress must be evaluated. An acousto-elastic approach is non-destructive and uses stress-dependent alterations in ultrasound (US) speed of bulk or surface modes [1]. However, these alterations are incredibly small (10-3 ÷ 10-5) and, thus, accurate measurement of both the US wave speed and propagation distance is required. Thickness measurement is not required for surface acoustic waves (SW) as compared to bulk acoustic modes. However, it requires a well determined distance between source and detector and very accurate time-of-flight measurement. Here we show that an approach based on laser-generated SW can solve this problem when a highly sensitive, point-like optical detector [2, 3] is used on receive. Using a laser beam focused to a narrow strip about 100 μm wide as a wave source and a modified Sagnac interferometer [2, 3] with an 8 μm diameter beam on receive, it is possible to use a short propagation path (5-10 mm) to obtain the required accuracy of time-of-flight measurements. For instance, the relative wave speed was estimated with an error of approx. 0.025% (i.e. 2.5*10-4) when only 20 signal averages were applied. The in-plane distribution of relative deviations of SW speed (proportional to stress) can be obtained with 2D scanning over a sample [4]. An example of relative SW speed deviations in one cross-section is shown in Fig.1 for a stainless steel sample

Ultrasound detection using polymer microring optical resonator

Application of polymer waveguide microring resonators for high-frequency ultrasound detection is presented. The device consists of a microring optical resonator coupled to a straight optical waveguide which serves as input and output ports. Acoustic waves irradiating the ring waveguide induce strain modifying the waveguide cross section. As a consequence, the effective refractive index of optical waves propagating along the ring is modified. The sharp wavelength dependence of the high QQ-factor resonator enhances the optical response to acoustic strain. High sensitivity is demonstrated experimentally in detecting broadband ultrasound pulses from a 10 MHz10 MHz transducer. Methods of extending the technique to form multi-element ultrasonic arrays for imaging applications are proposed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70498/2/APPLAB-85-22-5418-1.pd

Optical generation of high frequency ultrasound using two-dimensional gold nanostructure

A two-dimensional (2D) gold nanostructure is used to optically generate high frequency ultrasound. The structure consists of 2D arrangements of gold nanoparticles, sandwiched between a transparent substrate and a 4.5 μm4.5μm thick polydimethylsiloxane (PDMS) layer. The acoustic signal displays significant improvements compared to a bulk black PDMS films (the current state of the art) at frequencies from 50 to 100 MHz50to100MHz. The high optical extinction ratio of the gold nanostructure provides a convenient method to construct an integrated transmit/receive optoacoustic array. These results show that a 2D gold nanostructure can be used to produce high frequency arrays for ultrasound imaging.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87823/2/093901_1.pd

Fluoride-containing bioactive glasses: Effect of glass design and structure on degradation, pH and apatite formation in simulated body fluid

NOTICE: this is the author’s version of a work that was accepted for publication in Acta Biomaterialia. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Acta Biomaterialia, [VOL 6, ISSUE 8, (2010)] DOI: 10.1016/j.actbio.2010.01.04

Clinical Application of Sonographic Elasticity Imaging for Aging of Deep Venous Thrombosis

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135197/1/jum2003225443.pd

Diagnosing Cysts With Correlation Coefficient Images From 2‐Dimensional Freehand Elastography

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135592/1/jum20072691201.pd