Digital image correlation for non-homogeneous biomaterials

The Digital Image Correlation (DIC) is the optical and noncontact method to measure deformation and full- field strain of a loaded object. In general, DIC method is used for homogenous materials, whose composition, shape, and texture are the same throughout the materials like aluminum, copper. There is no established DIC method for a non- homogenous material, which is not uniform, such as bi-material interface surfaces. The goal of this study is to apply DIC method to a non-homogeneous system to evaluate the mechanical response due to applied load. In this study, DIC method was applied to three different non-homogeneous systems: metal/cement, bone/cement and multi-layers' fiber cloth. The first objective was to measure the strain at the interface of aluminum and cement by using DIC method. In order to understand the deformation characteristics, a series of images were taken by high speed camera, Phantom V641. Using a Matlab program of DIC method, the full-strain at the interface was found. The second objective was to find the full strain at the interface of bone-cement-aluminum in a knee replacement surgery. The third objective was to find the strain of the rolled fiber cloth that can be used for biomedical applications. The fiber was obtained from the existing electrospinning system and the procedure was repeated to find the strain value of the fiber. The research successfully measured the deformation characteristics of aluminum - cement interface using DIC method and compared the values with mechanical of materials theoretical values. This study also measured deformation characteristics of bone-cement- aluminum interfaces for a total knee replacement system and compared the values with the computer model. Finally, the strain field of rolled fiber was measured and compared the values with a plastic material model. The DIC protocol developed in this study can be used to measure the properties of the materials around the interface of two bi-materials and multi-layers fibrous materials. The developed techniques will be useful for the development and design of orthopedic biomaterials

An optical coherence tomography (OCT)-based air jet indentation system for measuring the mechanical properties of soft tissues

2008-2009 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

The emergence of optical elastography in biomedicine

The authors thank their colleagues past and present who have contributed to the evolution of optical elastography; in particular, S. Adie, W. Allen, L. Chin, B. Quirk, A. Curatolo, S. Es'hagian, K. Kennedy, R. Kirk, R. McLaughlin and P. Munro. This work has been supported in part by the Australian Research Council, the National Health and Medical Research Council, the National Breast Cancer Foundation, and the Western Australian Department of Health. P.W. thanks the Schrader Trust for a studentship.Optical elastography, the use of optics to characterize and map the mechanical properties of biological tissue, involves measuring the deformation of tissue in response to a load. Such measurements may be used to form an image of a mechanical property, often elastic modulus, with the resulting mechanical contrast complementary to the more familiar optical contrast. Optical elastography is experiencing new impetus in response to developments in the closely related fields of cell mechanics and medical imaging, aided by advances in photonics technology, and through probing the microscale between that of cells and whole tissues. Two techniques-optical coherence elastography and Brillouin microscopy-have recently shown particular promise for medical applications, such as in ophthalmology and oncology, and as new techniques in cell mechanics.PostprintPeer reviewe

The development of an experimental technique to measure the influence of temperature on the mechanical properties of weldments

In large industries, such as in power stations, welds are widely employed to join different components together to meet various property requirements. The thermal gradient that develops during welding causes an inhomogeneous distribution of material properties, in areas adjacent to the weld, known as the Heat Affected Zones (HAZ). Welded joints subjected to elevated temperatures and loads during operations often experience a degradation of mechanical properties and performance of the joint. Studies have found that mechanical phenomena’s such as, fatigue and creep have compromised the structural integrity of weld zones. In essence a welded component acts as a composite material, for which it’s overall performance is dependent on its weakest material component. This study focuses on developing an experimental technique that is capable of measuring the influence of temperature on the mechanical and material properties across a weldment. The development of the experimental technique includes the design and optimisation of the hot zone of a welded tensile specimen, identification and characterisation of the different weld zones as well as, refining a strain recording strategy to detect the localised strains in each of the different weld zones. The application of the experimental technique is applied to welded components from turbine steam penetrations, which were extracted from a coal fired power station. The steam penetrations are a low Cr structural steel; (Cr 0.66, C 0.24 by wt. %) and have been in service for approximately 24 year (± 212 000 hrs). Two primary systems namely the Gleeble 3800 thermo-mechanical simulator and digital image correlation are used in this study. In order to accurately map the in-service evolution of material properties, each of the welds were mechanically loaded in tension and exposed to elevated operating temperatures. To induce mechanical loading at constant elevated temperatures, a Gleeble 3800 thermo-mechanical simulator with a tensile module was used to deform specimens at a strain rate of 50 µε.s1 . Experiments were conducted at various temperatures, ranging from room temperature (RT) to 535 o C. The evolution of material properties across the weldment was evaluated using Digital Image Correlation (DIC). DIC is a non-contact digital technique, capable of measuring localized strain during mechanical loading at elevated temperatures. In order to investigate the localized strain across the different weld zones, virtual strain gauges of one millimetre in length were simulated at intervals of one millimetre. It was found that there was a continuous accumulation of strain from the Fusion Line (FL) into the Parent Material (PM). This finding suggested that the HAZ nearest to the PM; which was the Fine Grained Heat Affected Zone (FGHAZ) was the weakest zone as it strained the most. The FL was found to be the least ductile region of the weld as most of the absorbed thermal energy provided during the welding process was used for strain hardening. At elevated temperatures, localised strain occurred at lower strain values than those at RT. This finding suggested that at elevated temperatures there was more thermal energy available for dislocation activation and mobilization. The influence of temperature on the local weld zones were evaluated by extending a specimen, containing just the parent material. A simulation of a virtual strain gauge across the monolithic specimen’s gauge length, revealed that necking occurred at the centre of the specimen which corresponded to the hot zone. In contrast, a simulation of virtual strain gauges across both welds revealed that necking occurred in the region between the HAZ and weld material. This finding inferred that the presence of a weld reduced the strength of the component, as the weld material was the weakest material. Furthermore, the in-service operating conditions was found to have significantly influenced the material behaviour of the welds. A weld that was exposed to a more elevated temperatures and loads, was found to have undergone a higher degree of material degradation, and strained to a larger extent when compared to a weld that was exposed to a more moderate operating environment

A novel method to obtain modulus image of soft tissues using ultrasound water jet indentation : a phantom study

2006-2007 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Simultaneous measurement of temperature and strain in electronic packages using multi-frame super-resolution infrared thermography and digital image correlation

For microelectronic components and systems, reliability under thermomechanical stress is of critical importance. Experimental characterization of hotspots and temperature gradients, which can lead to deformation in the component, relies on accurate mapping of the surface temperature. One method of non-invasively acquiring this data is through infrared (IR) thermography. However, IR thermography is often limited by the typically low resolution of such cameras. Additionally, the unique surface finish preparations required to infer physical deformation using digital image correlation (DIC) generally interferes with the ability to measure the temperature with IR thermography, which prefers a uniform high emissivity. This work introduces a one-shot technique for the simultaneous measurement of surface temperature and deformation using multiframe super-resolution-enhanced IR imaging combined with digital image correlation (DIC) analysis. Multiframe super-resolution processing uses several sub-pixel shifted images, interpolating the image set to extract additional information and create a single higher-resolution image. Measurement of physical deformation is incorporated using a test sample with a black background and low-emissivity speckle features, heated in a manner that induces a non-uniform temperature field and stretched to induce physical deformation. Through processing and filtering, data from the black surface regions used for surface temperature mapping are separated from the speckle features used to track deformation with DIC. This method allows DIC to be performed on the IR images, yielding a deformation field consistent with the applied tensioning. While both the low- and super-resolution data sets can be successfully processed with DIC, super-resolution helps reduce noise in the extracted deformation fields. As for temperature measurement, using super-resolution is shown to allow for better removal of the speckle features and reduce noise, as quantified by a lower mean deviation from the spatial moving average

Mechanochemical Investigation of a Glassy Epoxy-Amine Thermoset Subjected to Fatigue

Covalent bonds in organic molecules can be produced, altered, and broken through various sources of energy and processes. These include photochemical, thermochemical, chemical, and mechanochemical processes. Polymeric materials derive their physical properties from the time scale of motion, summation of intermolecular forces, and number of chain entanglements and crosslinks. Glassy thermoset polymers experience mechanical fatigue during dynamic stress loading and properties diminish with inevitable material failure at stress levels below the ultimate tensile strength (UTS). Damage modeling has been successful in predicting the number of cycles required to induce failure in a specimen due to stress. However, it does not directly provide an explanation of the origin of fatigue in polymers. It is hypothesized herein that mechanical failure at stress levels below the ultimate strength property is due to the accumulation of mechanically induced homolytic chain scission events throughout the glassy thermoset network. The goal of this research will be to quantify homolytic chain scission events with fatigue cycles with the ultimate goal of correlating mechanical property loss with degradation of covalent network structure. To accomplish this goal, stable free nitroxyl radicals were incorporated into an epoxy-amine matrix to detect homolytic chain scission resulting from fatigue. Chapter II discusses a successful synthesis and characterization of the nitroxyl radical molecule, a product of 4-hydroxy-2,2,5,5-tetramethylpiperdin-1-yl-oxyl (TEMPO) and isophorone diisocyanate designated as BT-IPDI. In Chapter III, the epoxy-amine reaction was determined to be unaffected by incorporation of up to 5 wt% of BT-IPDI. Although 50% UTS fatigue studies produced property degradation and fatigue failure as shown in Chapter IV, analysis of BT-IPDI through EPR did not detect homolytic chain scission. Chapter V reveals that mechano-radicals were produced from cryo-grinding the glassy epoxy-amine thermoset, and although the mechano-radicals reacted through recombination at elevated temperatures, the reaction between mechano-radicals and the BT-IPDI was not detected to occur within the glassy state. During mechanical testing, observations of unusual tensile yield behavior were coupled with production of atypical fracture surfaces. In Chapter VI, physical aging was used as an investigative tool to verify that viscous deformation (plastic flow) was required to produce the atypical fracture surfaces. Atomic force microscopy and scanning electron microscopy of the fracture surface both revealed a tendril nodule morphology. It is our hypothesis that this morphology produces the unusual mechanical behavior. In Chapter VII, NIR, AFM, and SEM were used to measure the conversion and morphology of the epoxy-amine thermoset correlated with mechanical properties. The thermal cure profile of the epoxy-amine thermoset affects the size and formation of the nodular nanostructure. Eliminating vitrification during thermoset polymerization forms a more continuous phase, reduction in size of the nodules, and eliminates the capacity of the material to yield in plastic flow. Specific findings of this research reveal that morphology control through thermal cure design may indicate a route in which thermoplastic type failure mechanisms can be incorporated into glassy epoxy thermosets

A Study on Residual Compression Behavior of Structural Fiber Reinforced Concrete Exposed to Moderate Temperature Using Digital Image Correlation

Fire ranks high among the potential risks faced by most buildings and structures. A full understanding of temperature effects on fiber reinforced concrete is still lacking. This investigation focuses on the study of the residual compressive strength, stress strain behavior and surface cracking of structural polypropylene fiber-reinforced concrete subjected to temperatures up to 300 A degrees C. A total of 48 cubes was cast with different fiber dosages and tested under compression after exposing to different temperatures. Concrete cubes with varying macro (structural) fiber dosages were exposed to different temperatures and tested to observe the stress-strain behavior. Digital image correlation, an advanced non-contacting method was used for measuring the strain. Trends in the relative residual strengths with respect to different fiber dosages indicate an improvement up to 15 % in the ultimate compressive strengths at all exposure temperatures. The stress-strain curves show an improvement in post peak behavior with increasing fiber dosage at all exposure temperatures considered in this study

A New Experimental Approach for In Situ Damage Assessment in Fibrous Ceramic Matrix Composites at High Temperature

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112011/1/jace13538.pd