Kavan Hazeli

Mechanical properties and biomineralization of multifunctional nanodiamond-PLLA composites for bone tissue engineering.

Multifunctional bone scaffold materials have been produced from a biodegradable polymer, poly(L-lactic acid) (PLLA), and 1-10% wt of octadecylamine-functionalized nanodiamond (ND-ODA) via solution casting followed by compression molding. By comparison to pure PLLA, the addition of 10% wt of ND-ODA resulted in a significant improvement of the mechanical properties of the composite matrix, including a 280% increase in the strain at failure and a 310% increase in fracture energy in tensile tests. The biomimetic process of bonelike apatite growth on the ND-ODA/PLLA scaffolds was studied using microscopic and spectroscopic techniques. The enhanced mechanical properties and the increased mineralization capability with higher ND-ODA concentration suggest that these biodegradable composites may potentially be useful for a variety of biomedical applications, including scaffolds for orthopedic regenerative engineering.

An integrated structural health monitoring approach for crack growth monitoring

A novel structural health monitoring approach consisting of guided ultrasonic waves, acoustic emission, and digital image correlation, as well as real-time and postmortem analyses, was implemented to monitor and quantify crack growth in Al 2024 compact tension specimens, designed, and precracked according to ASTM E647-08. Tensile loads were applied according to ASTM E1290-08. Guided ultrasonic waves were generated with pulses centered at three different frequencies and were recorded using piezoelectric transducers. Guided ultrasonic waves were also modeled using finite element wave propagation models. The same transducers were further used for online acoustic emission monitoring. A digital image correlation system continuously monitored the crack growth and provided full-field surface strains. The application of this integrated structural health monitoring approach resulted in reliable damage detection and quantified crack growth measurements. In addition, a novelty detector based on the Mahalanobis distance was implemented in a data fusion scheme to assess the extent of damage. The reported results constitute a proof-of-concept investigation of a novel structural health monitoring approach based on the combination of real-time optical and acoustic nondestructive testing.

Acoustic Emission of Deformation Twinning in Magnesium

The Acoustic Emission of deformation twinning in Magnesium is investigated in this article. Single crystal testing with combined full field deformation measurements, as well as polycrystalline testing inside the scanning electron microscope with simultaneous monitoring of texture evolution and twin nucleation were compared to testing at the laboratory scale with respect to recordings of Acoustic Emission activity. Single crystal testing revealed the formation of layered twin boundaries in areas of strain localization which was accompanied by distinct changes in the acoustic data. Testing inside the microscope directly showed twin nucleation, proliferation and growth as well as associated crystallographic reorientations. A post processing approach of the Acoustic Emission activity revealed the existence of a class of signals that appears in a strain range in which twinning is profuse, as validated by the in situ and ex situ microscopy observations. Features extracted from such activity were cross-correlated both with the available mechanical and microscopy data, as well as with the Acoustic Emission activity recorded at the laboratory scale for similarly prepared specimens. The overall approach demonstrates that the method of Acoustic Emission could provide real time volumetric information related to the activation of deformation twinning in Magnesium alloys, in spite of the complexity of the propagation phenomena, the possible activation of several deformation modes and the challenges posed by the sensing approach itself when applied in this type of materials evaluation approach.

Acoustic Emission and Digital Image Correlation as Complementary Techniques for Laboratory and Field Research

This article presents the advantages of combining Acoustic Emission (AE) and Digital Image Correlation (DIC) in nondestructive testing (NDT) applications focusing on in situ damage monitoring. This data-fusion approach is used herein to characterize the mechanical and damage behavior of a fiber metal laminate (Glare 1A) tested in both tension and fatigue. Furthermore, the approach is used to investigate the structural behavior of partially grouted reinforced masonry walls. The obtained AE datasets were post-processed, in combination with DIC and mechanical information, using signal processing and pattern recognition techniques to investigate progressive failure of the Glare 1A. In the case of the masonry wall specimens, DIC clearly identified critical damage areas as a function of applied loading, while AE was capable to monitor the damage process and reveal changes in the overall behavior. The presented analysis demonstrates the potential of integrating AE and DIC in data-driven damage mechanics investigations at multiple time and length scales.

In-situ acousto-ultrasonic monitoring of crack propagation in Al2024 alloy

A data fusion technique implementing the principles of acoustic emission (AE), ultrasonic testing (UT) and digital image correlation (DIC) was employed to in situ monitor crack propagation in an Al 2024 alloy compact tension (CT) specimen. The specimen was designed according to ASTM E647-08 and was pre-cracked under fatigue loading to ensure stable crack growth. Tensile (Mode I) loads were applied according to ASTM E1290-08 while simultaneously recording AE activity, transmitting ultrasonic pulses and measuring full-field surface strains. Realtime 2D source location AE algorithms and visualization provided by the DIC system allowed the full quantification of the crack growth and the cross-validation of the recorded non-destructive testing data. In post mortem, waveform features sensitive to crack propagation were extracted and visible trends as a function of computed crack length were observed. In addition, following a data fusion approach, features from the three independent monitoring systems were combined to define damage sensitive correlations. Furthermore a novelty detector based on the Mahalanobis outlier analysis was implemented to quantify the extent of crack growth and to define a more robust sensing basis for the proposed system.

Micro Characterization of Mg and Mg Alloy for Biodegradable Orthopedic Implants Application

Magnesium as a candidate metallic biomaterial for biodegradable orthopedic implants was evaluated in-vitro in terms of degradation behavior, biocompatibility and mechanical property both in macro- and micro-scale. Micro structure of pure Mg and AZ61 after degradation in both simulated body fluid (SBF) and cell culture environment were analyzed. Different from AZ61, pure Mg degraded at a higher rate and attracted large amount of salt precipitation which formed a layer covering the surface. Much less pitting degradation and salt deposition were observed on both pure Mg and AZ61 in cell culture environment compared to in SBF. After culturing for 7 days, EAhy926 cells growing on AZ61 showed significant higher proliferation rate as of cells growing on pure Mg. Higher proliferation rates indicated that cells grew better on slow-degrading AZ61 than on fast-degrading pure Mg. Cells growing on AZ61 proliferated much better and assembled together to form a consistent tissue-like micro-structure, while cells spread and reached out on the surface of pure Mg, possibly due to low cell density and lack of cellular communication. The elastic modulus and tensile yield strength of magnesium are closer to those of natural bone than other commonly used metallic biomaterials. It was shown that Mg was biodegradable, biocompatible and had appropriate mechanical strength, thus Mg and its alloys showed great potential for deployment in a new generation of biodegradable orthopedic implants.Copyright

The Effect of \{ 10\bar{1}2\} Twin Boundary on the Evolution of Defect Substructure

Pure Mg single crystals were deformed at room temperature along two orientations in sequence, in order to activate a specific dislocation slip mode followed by \( \left\{ {10\bar{1}2} \right\} \) twinning. The defects in both the matrix and twin crystals were analyzed with a transmission electron microscope (TEM). This study reveals the collective evolution of the defect substructure when a dislocated crystal is “invaded” by a moving twin boundary. When primarily \( \left[ c \right] \)-containing defects in the matrix were incorporated by a moving twin boundary, including \( \langle c + a\rangle \), pure \( \left[ c \right] \) dislocations and \( I_{1} \) stacking faults, the twin contains homogeneously distributed \( I_{1} \) stacking faults, which in some instances appear to be connected on twin boundary to the faults in the matrix.

In-situ X-ray CT results of damage evolution in L6 ordinary chondrite meteorites

These are slides about in-situ X-ray CT results of damage evolution in L6 ordinary chondrite meteorites. The following topics are covered: mechanical and thermal damage characterization, list of Grosvenor Mountain (GRO) meteorite samples, in-situ x-ray compression test setup, GRO-chipped reference at 0 N - existing cracks, GRO-chipped loaded at 1580 N, in-situ x-ray thermal fatigue test setup, GRO-B14 room temperature reference, GRO-B14 Cycle 47 at 200°C, GRO-B14 Cycle 47 at room temperature, conclusions from qualitative analysis, future work and next steps. Conclusions are the following: Both GRO-Chipped and GRO-B14 had existing voids and cracks within the volume. These sites with existing damage were selected for CT images from mechanically and thermally loaded scans since they are prone to damage initiation. The GRO-Chipped sample was loaded to 1580 N which resulted in a 14% compressive engineering strain, calculated using LVDT. Based on the CT cross sectional images, the GRO-B14 sample at 200°C has a thermal expansion of approximately 96 μm in height (i.e. ~1.6% engineering strain).

Quantification of Microstructure‐Properties‐Behavior Relations in Magnesium Alloys Using a Hybrid Approach

This study presents a hybrid experimental mechanics approach combining multi-scale mechanical testing, in situ nondestructive evaluation and targeted microscopic quantification to identify and quantify critical micro structural parameters that affect properties and overall plasticity of Mg alloys. Room temperature monotonic and cyclic experiments monitored by Digital Image Correlation (DIC) coupled with Acoustic Emission (AE) of Mg Alloys of the AZ series were used for this investigation. Data obtained using the optico-acoustic nondestructive system revealed for the first time the direct connection between surface strain localization effects similar to Luder’s bands and pronounced twin activity. Electron Back Scatter Diffraction (EBSD) measurements showed the profuse and spatially inhomogeneous nature of twinning at early stages of plasticity which is related with the onset of yielding and the macroscopic plateau region in the stress-strain curve. Furthermore, twinning/detwinning activity was identified in several grains of tested specimens and during characteristic points of fatigue cycles.

Data-Fusion NDE for Progressive Damage Quantification in Composites

The objective of this article is to present a progressive damage quantification framework for fiber reinforced polymer composites (FRPC) that have widespread use in aerospace and wind-turbine applications. To this aim, a novel optico-acoustic nondestructive evaluation (NDE) setup is presented based on integration of Digital Image Correlation (DIC), Acoustic Emission (AE), and Infrared Thermography (IRT). DIC and IRT full-field strain and temperature maps reveal early development of structural hot spots, associated with locations where inelastic strains accumulate, damage initiates, and final fracture occurs in both tensile and fatigue experiments. Damage quantification is further related to: (i) energy dissipation, (ii) residual stiffness, (iii) average both temporal and spatial temperature variations, and (iv) AE features in time and frequency domains. The extracted NDE parameters suggest three characteristic stages of fatigue life that can be used to construct appropriate models for reliable remaining life-predictions.