Matching Items (10)

155692-Thumbnail Image.png

Experimental investigations and modeling of the strain sensing response of matrices containing metallic inclusions

Description

This study explores the possibility of two matrices containing metallic particulates to act as smart materials by sensing of strain due to the presence of the conducting particles in the

This study explores the possibility of two matrices containing metallic particulates to act as smart materials by sensing of strain due to the presence of the conducting particles in the matrix. The first matrix is a regular Portland cement-based one while the second is a novel iron-based, carbonated binder developed at ASU. Four different iron replacement percentages by volume (10%, 20%, 30% and 40%) in a Portland cement matrix were selected, whereas the best performing iron carbonate matrix developed was used. Electrical impedance spectroscopy was used to obtain the characteristic Nyquist plot before and after application of flexural load. Electrical circuit models were used to extract the changes in electrical properties under application of load. Strain sensing behavior was evaluated with respect to application of different stress levels and varying replacement levels of the inclusion. A similar approach was used to study the strain sensing capabilities of novel iron carbonate binder. It was observed that the strain sensing efficiency increased with increasing iron percentage and the resistivity increased with increase in load (or applied stress) for both the matrices. It is also found that the iron carbonate binder is more efficient in strain sensing as it had a higher gage factor when compared to the OPC matrix containing metallic inclusions.

Analytical equations (Maxwell) were used to extract frequency dependent electrical conductivity and permittivity of the cement paste (or the host matrix), interface, inclusion (iron) and voids to develop a generic electro-mechanical coupling model to for the strain sensing behavior. COMSOL Multiphysics 5.2a was used as finite element analysis software to develop the model. A MATLAB formulation was used to generate the microstructure with different volume fractions of inclusions. Material properties were assigned (the frequency dependent electrical parameters) and the coupled structural and electrical physics interface in COMSOL was used to model the strain sensing response. The experimental change in resistance matched well with the simulated values, indicating the applicability of the model to predict the strain sensing response of particulate composite systems.

Contributors

Agent

Created

Date Created
  • 2017

150889-Thumbnail Image.png

Characterization of local deformation in Pb-free solder joints using three dimensional (3D) X-ray microtomography

Description

Pb-free solder joints are commonly used as interconnects in semiconductor packaging. One of the major defects affecting the mechanical performance of solder joints are reflow pores that form during processing.

Pb-free solder joints are commonly used as interconnects in semiconductor packaging. One of the major defects affecting the mechanical performance of solder joints are reflow pores that form during processing. These pores exhibit significant variability in size and distribution, and understanding the effects of pore geometry on failure is an important reliability concern. In this thesis, the pore microstructures of solder joint samples and the localized plastic deformation around individual pores was characterized in 3D using lab scale X-ray Microtomography. To observe the deformation of a solder joint in 3D, a solder joint was imaged with Microtomography after reflow and then deformed in shear in several loading steps with additional tomography data taken between each. The 3D tomography datasets were then segmented using the 3D Livewire technique into regions corresponding to solder and pores, and used to generate 3D models of the joint at each strain value using Mimics software. The extent of deformation of individual pores in the joint as a function of strain was quantified using sphericity measurements, and correlated with the observed cracking in the joint. In addition, the error inherent in the data acquisition and 3D modeling process was also quantified. The progression of damage observed with X-ray Microtomography was then used to validate the deformation and failure predicted by a Finite Element (FE) simulation. The FE model was based on the as-reflowed tomography data, and incorporated a ductile damage failure model to simulate fracture. Using the measured sphericity change and cracking information obtained from the tomography data, the FE model is shown to correctly capture the broad plastic deformation and strain localization seen in the actual joint, as well as the crack propagation. Lastly, Digital Image Correlation was investigated as a method of obtaining improved local strain measurements in 3D. This technique measures the displacement of the inherent microstructural features of the joint, and can give localized strain measurements that can be directly comparable to that predicted by modeling. The technique is demonstrated in 2D on Pb-Sn solder, and example 3D data is presented for future analysis.

Contributors

Agent

Created

Date Created
  • 2012

155622-Thumbnail Image.png

Strain concentrations in polyethylene geomembranes adjacent to seams and scratches

Description

Laboratory testing was conducted to quantify strain concentrations adjacent to seams and scratches in high density polyethylene (HDPE) geomembranes. The tensile strain profile of remnants meeting the ASTM criteria for

Laboratory testing was conducted to quantify strain concentrations adjacent to seams and scratches in high density polyethylene (HDPE) geomembranes. The tensile strain profile of remnants meeting the ASTM criteria for wide-width tensile testing from samples of field seams recovered for construction quality assurance testing was evaluated using digital image correlation (DIC). Strains adjacent to scratches on laboratory prepared samples loaded in tension were also measured using DIC. The tensile strain in the zone adjacent to a seam and the tensile strain adjacent to a scratch were compared to the tensile strains calculated using theoretical strain concentration factors. The relationship between the maximum tensile strain adjacent to a seam and the global nominal strain in the sample was quantified for textured and smooth geomembranes of common thicknesses. Using statistical analysis of the data, bounds were developed for the allowable nominal tensile strain expected to induce maximum tensile strains adjacent to the seam less than or equal to the typical yield strain of HDPE geomembranes, at several confidence levels. Where nominal strain is the global or average strain applied to the sample and maximum strain is the largest tensile strain induced in the sample.

The reduction in the nominal yield strain due to a scratch in a HDPE geomembrane was also quantified. The yield strain was approximately the same as predicted using theoretical strain concentration factors. The difference in the average measured maximum strains adjacent to the seams of textured and smooth HDPE geomembranes was found to be statistically insignificant. However, maximum strains adjacent to extrusion welded seams were somewhat greater than adjacent to fusion welded seams for nominal strains on the order of 3% to 4%. The results of the testing program suggest that the nominal tensile strain should be limited to 4% around dual hot wedge seams and 3% around extrusion fillet seams to avoid maximum strains equal to 11%, a typical yield strain for HDPE geomembranes.

Contributors

Agent

Created

Date Created
  • 2017

153275-Thumbnail Image.png

Highly sensitive in-plane strain mapping using a laser scanning technique

Description

In this work, a highly sensitive strain sensing technique is developed to realize in-plane strain mapping for microelectronic packages or emerging flexible or foldable devices, where mechanical or thermal strain

In this work, a highly sensitive strain sensing technique is developed to realize in-plane strain mapping for microelectronic packages or emerging flexible or foldable devices, where mechanical or thermal strain is a major concern that could affect the performance of the working devices or even lead to the failure of the devices. Therefore strain sensing techniques to create a contour of the strain distribution is desired.

The developed highly sensitive micro-strain sensing technique differs from the existing strain mapping techniques, such as digital image correlation (DIC)/micro-Moiré techniques, in terms of working mechanism, by filling a technology gap that requires high spatial resolution while simultaneously maintaining a large field-of-view. The strain sensing mechanism relies on the scanning of a tightly focused laser beam onto the grating that is on the sample surface to detect the change in the diffracted beam angle as a result of the strain. Gratings are fabricated on the target substrates to serve as strain sensors, which carries the strain information in the form of variations in the grating period. The geometric structure of the optical system inherently ensures the high sensitivity for the strain sensing, where the nanoscale change of the grating period is amplified by almost six orders into a diffraction peak shift on the order of several hundred micrometers. It significantly amplifies the small signal measurements so that the desired sensitivity and accuracy can be achieved.

The important features, such as strain sensitivity and spatial resolution, for the strain sensing technique are investigated to evaluate the technique. The strain sensitivity has been validated by measurements on homogenous materials with well known reference values of CTE (coefficient of thermal expansion). 10 micro-strain has been successfully resolved from the silicon CTE extraction measurements. Furthermore, the spatial resolution has been studied on predefined grating patterns, which are assembled to mimic the uneven strain distribution across the sample surface. A resolvable feature size of 10 µm has been achieved with an incident laser spot size of 50 µm in diameter.

In addition, the strain sensing technique has been applied to a composite sample made of SU8 and silicon, as well as the microelectronic packages for thermal strain mappings.

Contributors

Agent

Created

Date Created
  • 2014

154263-Thumbnail Image.png

Stress and strain propagation in soft viscoelastic tissue while tracking microscale targets

Description

Tracking microscale targets in soft tissue using implantable probes is important in clinical applications such as neurosurgery, chemotherapy and in neurophysiological application such as brain monitoring. In most of these

Tracking microscale targets in soft tissue using implantable probes is important in clinical applications such as neurosurgery, chemotherapy and in neurophysiological application such as brain monitoring. In most of these applications, such tracking is done with visual feedback involving some imaging modality that helps localization of the targets through images that are co-registered with stereotaxic coordinates. However, there are applications in brain monitoring where precision targeting of microscale targets such as single neurons need to be done in the absence of such visual feedback. In all of the above mentioned applications, it is important to understand the dynamics of mechanical stress and strain induced by the movement of implantable, often microscale probes in soft viscoelastic tissue. Propagation of such stresses and strains induce inaccuracies in positioning if they are not adequately compensated. The aim of this research is to quantitatively assess (a) the lateral propagation of stress and (b) the spatio-temporal distribution of strain induced by the movement of microscale probes in soft viscoelastic tissue. Using agarose hydrogel and a silicone derivative as two different bench-top models of brain tissue, we measured stress propagation during movement of microscale probes using a sensitive load cell. We further used a solution of microscale beads and the silicone derivative to quantitatively map the strain fields using video microscopy. The above measurements were done under two different types of microelectrode movement – first, a unidirectional movement and second, a bidirectional (inch-worm like) movement both of 30 μm step-size with 3min inter-movement interval. Results indicate movements of microscale probes can induce significant stresses as far as 500 μm laterally from the location of the probe. Strain fields indicate significantly high levels of displacements (in the order of 100 μm) within 100 μm laterally from the surface of the probes. The above measurements will allow us to build precise mechanical models of soft tissue and compensators that will enhance the accuracy of tracking microscale targets in soft tissue.

Contributors

Agent

Created

Date Created
  • 2015

153411-Thumbnail Image.png

Gallium-based room temperature liquid metals and its application to single channel two-liquid hyperelastic capacitive strain sensors

Description

Gallium-based liquid metals are of interest for a variety of applications including flexible electronics, soft robotics, and biomedical devices. Still, nano- to microscale device fabrication with these materials is challenging

Gallium-based liquid metals are of interest for a variety of applications including flexible electronics, soft robotics, and biomedical devices. Still, nano- to microscale device fabrication with these materials is challenging because of their strong adhesion to a majority of substrates. This unusual high adhesion is attributed to the formation of a thin oxide shell; however, its role in the adhesion process has not yet been established. In the first part of the thesis, we described a multiscale study aiming at understanding the fundamental mechanisms governing wetting and adhesion of gallium-based liquid metals. In particular, macroscale dynamic contact angle measurements were coupled with Scanning Electron Microscope (SEM) imaging to relate macroscopic drop adhesion to morphology of the liquid metal-surface interface. In addition, room temperature liquid-metal microfluidic devices are also attractive systems for hyperelastic strain sensing. Currently two types of liquid metal-based strain sensors exist for inplane measurements: single-microchannel resistive and two-microchannel capacitive devices. However, with a winding serpentine channel geometry, these sensors typically have a footprint of about a square centimeter, limiting the number of sensors that can be embedded into. In the second part of the thesis, firstly, simulations and an experimental setup consisting of two GaInSn filled tubes submerged within a dielectric liquid bath are used to quantify the effects of the cylindrical electrode geometry including diameter, spacing, and meniscus shape as well as dielectric constant of the insulating liquid and the presence of tubing on the overall system's capacitance. Furthermore, a procedure for fabricating the two-liquid capacitor within a single straight polydiemethylsiloxane channel is developed. Lastly, capacitance and response of this compact device to strain and operational issues arising from complex hydrodynamics near liquid-liquid and liquid-elastomer interfaces are described.

Contributors

Agent

Created

Date Created
  • 2015

154753-Thumbnail Image.png

Stress-responsive nano- and microcomposites featuring mechanophore units

Description

The problem of catastrophic damage purveys in any material application, and minimizing its occurrence is paramount for general health and safety. Thus, novel damage detection schemes are required that can

The problem of catastrophic damage purveys in any material application, and minimizing its occurrence is paramount for general health and safety. Thus, novel damage detection schemes are required that can sense the precursors to damage. Mechanochemistry is the area of research that involves the use of mechanical force to induce a chemical change, with recent study focusing on directing the mechanical force to embedded mechanophore units for a targeted chemical response. Mechanophores are molecular units that provide a measureable signal in response to an applied force, often in the form of a visible color change or fluorescent emission, and their application to thermoset network polymers has been limited. Following preliminary work on polymer blends of cyclobutane-based mechanophores and epoxy, dimeric 9-anthracene carboxylic acid (Di-AC)-based mechanophore particles were synthesized and employed to form stress sensitive particle reinforced epoxy matrix composites.

Under an applied stress, the cyclooctane-rings in the Di-AC particles revert back to their fluorescent anthracene form, which linearly enhances the overall fluorescence of the composite in response to the applied strain. The fluorescent signal further allows for stress sensing in the elastic region of the stress-strain curve, which is considered to be a form of damage precursor detection. This behavior was further analyzed at the molecular scale with corresponding molecular dynamics simulations. Following the successful application of Di-AC to an epoxy matrix, the mechanophore particles were incorporated into a polyurethane matrix to show the universal nature of Di-AC as a stress-sensitive particle filler. Interestingly, in polyurethane Di-AC could successfully detect damage with less applied strain compared to the epoxy system.

While mechanophores of varying chemistries have been covalently incorporated into elastomeric and thermoplastic polymer systems, they have not yet been covalently incorporated a thermoset network polymer. Thus, following the study of mechanophore particles as stress-sensitive fillers, two routes of grafting mechanophore units into an epoxy system to form a self-sensing nanocomposite were explored. These involved the mechanophore precursor and mechanophore, cinnamamide and di-cinnamamide, respectively. With both molecules, the free amine groups can directly bond to epoxy resin to covalently incorporate themselves within the thermoset network to form a self-sensing nanocomposite.

Contributors

Agent

Created

Date Created
  • 2016

150697-Thumbnail Image.png

Mechanical shock behavior of environmentally-benign Pb-free solders

Description

The mechanical behavior of Pb-free solder alloys is important, since they must maintain mechanical integrity under thermomechanical fatigue, creep, and mechanical shock conditions. Mechanical shock, in particular, has become an

The mechanical behavior of Pb-free solder alloys is important, since they must maintain mechanical integrity under thermomechanical fatigue, creep, and mechanical shock conditions. Mechanical shock, in particular, has become an increasing concern in the electronics industry, since electronic packages can be subjected to mechanical shock by mishandling during manufacture or by accidental dropping. In this study, the mechanical shock behavior of Sn and Sn-Ag-Cu alloys was systematically analyzed over the strain rate range 10-3 - 30 s-1 in bulk samples, and over 10-3 - 12 s-1 on the single solder joint level. More importantly, the influences of solder microstructure and intermetallic compounds (IMC) on mechanical shock resistance were quantified. A thorough microstructural characterization of Sn-rich alloys was conducted using synchrotron x-ray computed tomography. The three-dimensional morphology and distribution of contiguous phases and precipitates was analyzed. A multiscale approach was utilized to characterize Sn-rich phases on the microscale with x-ray tomography and focused ion beam tomography to characterize nanoscale precipitates. A high strain rate servohydraulic test system was developed in conjunction with a modified tensile specimen geometry and a high speed camera for quantifying deformation. The effect of microstructure and applied strain rate on the local strain and strain rate distributions were quantified using digital image correlation. Necking behavior was analyzed using a novel mirror fixture, and the triaxial stresses associated with necking were corrected using a self-consistent method to obtain the true stress-true strain constitutive behavior. Fracture mechanisms were quantified as a function of strain rate. Finally, the relationship between solder microstructure and intermetallic compound layer thickness with the mechanical shock resistance of Sn-3.8Ag-0.7Cu solder joints was characterized. It was found that at low strain rates the dynamic solder joint strength was controlled by the solder microstructure, while at high strain rates it was controlled by the IMC layer. The influences of solder microstructure and IMC layer thickness were then isolated using extended reflow or isothermal aging treatments. It was found that at large IMC layer thicknesses the trend described above does not hold true. The fracture mechanisms associated with the dynamic solder joint strength regimes were analyzed.

Contributors

Agent

Created

Date Created
  • 2012

150098-Thumbnail Image.png

Nonlinear inelastic mechanical behavior of epoxy resin polymeric materials

Description

Polymer and polymer matrix composites (PMCs) materials are being used extensively in different civil and mechanical engineering applications. The behavior of the epoxy resin polymers under different types of loading

Polymer and polymer matrix composites (PMCs) materials are being used extensively in different civil and mechanical engineering applications. The behavior of the epoxy resin polymers under different types of loading conditions has to be understood before the mechanical behavior of Polymer Matrix Composites (PMCs) can be accurately predicted. In many structural applications, PMC structures are subjected to large flexural loadings, examples include repair of structures against earthquake and engine fan cases. Therefore it is important to characterize and model the flexural mechanical behavior of epoxy resin materials. In this thesis, a comprehensive research effort was undertaken combining experiments and theoretical modeling to investigate the mechanical behavior of epoxy resins subject to different loading conditions. Epoxy resin E 863 was tested at different strain rates. Samples with dog-bone geometry were used in the tension tests. Small sized cubic, prismatic, and cylindrical samples were used in compression tests. Flexural tests were conducted on samples with different sizes and loading conditions. Strains were measured using the digital image correlation (DIC) technique, extensometers, strain gauges, and actuators. Effects of triaxiality state of stress were studied. Cubic, prismatic, and cylindrical compression samples undergo stress drop at yield, but it was found that only cubic samples experience strain hardening before failure. Characteristic points of tensile and compressive stress strain relation and load deflection curve in flexure were measured and their variations with strain rate studied. Two different stress strain models were used to investigate the effect of out-of-plane loading on the uniaxial stress strain response of the epoxy resin material. The first model is a strain softening with plastic flow for tension and compression. The influence of softening localization on material behavior was investigated using the DIC system. It was found that compression plastic flow has negligible influence on flexural behavior in epoxy resins, which are stronger in pre-peak and post-peak softening in compression than in tension. The second model was a piecewise-linear stress strain curve simplified in the post-peak response. Beams and plates with different boundary conditions were tested and analytically studied. The flexural over-strength factor for epoxy resin polymeric materials were also evaluated.

Contributors

Agent

Created

Date Created
  • 2011

149553-Thumbnail Image.png

Predictive modeling for extremely scaled CMOS and post silicon devices

Description

To extend the lifetime of complementary metal-oxide-semiconductors (CMOS), emerging process techniques are being proposed to conquer the manufacturing difficulties. New structures and materials are proposed with superior electrical properties to

To extend the lifetime of complementary metal-oxide-semiconductors (CMOS), emerging process techniques are being proposed to conquer the manufacturing difficulties. New structures and materials are proposed with superior electrical properties to traditional CMOS, such as strain technology and feedback field-effect transistor (FB-FET). To continue the design success and make an impact on leading products, advanced circuit design exploration must begin concurrently with early silicon development. Therefore, an accurate and scalable model is desired to correctly capture those effects and flexible to extend to alternative process choices. For example, strain technology has been successfully integrated into CMOS fabrication to improve transistor performance but the stress is non-uniformly distributed in the channel, leading to systematic performance variations. In this dissertation, a new layout-dependent stress model is proposed as a function of layout, temperature, and other device parameters. Furthermore, a method of layout decomposition is developed to partition the layout into a set of simple patterns for model extraction. These solutions significantly reduce the complexity in stress modeling and simulation. On the other hand, semiconductor devices with self-feedback mechanisms are emerging as promising alternatives to CMOS. Fe-FET was proposed to improve the switching by integrating a ferroelectric material as gate insulator in a MOSFET structure. Under particular circumstances, ferroelectric capacitance is effectively negative, due to the negative slope of its polarization-electrical field curve. This property makes the ferroelectric layer a voltage amplifier to boost surface potential, achieving fast transition. A new threshold voltage model for Fe-FET is developed, and is further revealed that the impact of random dopant fluctuation (RDF) can be suppressed. Furthermore, through silicon via (TSV), a key technology that enables the 3D integration of chips, is studied. TSV structure is usually a cylindrical metal-oxide-semiconductors (MOS) capacitor. A piecewise capacitance model is proposed for 3D interconnect simulation. Due to the mismatch in coefficients of thermal expansion (CTE) among materials, thermal stress is observed in TSV process and impacts neighboring devices. The stress impact is investigated to support the interaction between silicon process and IC design at the early stage.

Contributors

Agent

Created

Date Created
  • 2011