Mechanical Engineering Commons^™

Notch Size Effects In Hcf Behavior Of Ti–6al–4v, George Haritos, Theodore Nicholas, David Lanning

Dr. George K. Haritos

The high cycle fatigue (HCF) behavior of Ti–6Al–4V is investigated for cylindrical specimens having three sizes of geometrically similar circumferential V-notches, each with an elastic stress concentration factor, K_t, of approximately 2.78. A step loading technique for obtaining a point on a constant life (10⁶ cycles) Haigh diagram from a single test specimen was implemented. Tests were performed at stress ratios of R=0.1, 0.5, and 0.8 for specimens machined from two different product forms of Ti–6Al–4V, bar and plate forgings. Results indicate that while there is a definite notch size effect in the Ti–6Al–4V bar within …

The Elastic Response Of A Cohesive Aggregate—A Discrete Element Model With Coupled Particle Interaction, George Jefferson, George Haritos, Robert Mcmeeking

Dr. George K. Haritos

A model is presented for the deformation of a cohesive aggregate of elastic particles that incorporates two important effects of large-sized inter-particle junctions. A finite element model is used to derive a particle response rule, for both normal and tangential relative deformations between pairs of particles. This model agrees with the Hertzian contact theory for small junctions, and is valid for junctions as large as half the nominal particle size. Further, the aggregate model uses elastic superposition to account for the coupled force–displacement response due to the simultaneous displacement of all of the neighbors of each particle in the aggregate. …

Osteoarthritis Induced Glenoid Morphology And Bone Quality: An Evaluation Of Augmented Glenoid Components, Nikolas K. Knowles

Electronic Thesis and Dissertation Repository

Osteoarthritis of the glenoid results in regional bone density variations and bone loss that may compromise early component fixation and support. The two common morphologies, symmetric and asymmetric erosion, were characterized by bone density and morphology, and assessed on the basis of bone removal and bone quality in the context of augmented glenoid components. The bone strain field was also compared when different augmented glenoid components underwent simulated joint loading using finite element analysis.

Asymmetrically eroded glenoids were found to have denser bone (p

Mechanical Engineering News, Georgia Southern University

Mechanical Engineering News (2013-2023)

• Eagle Motorspots Places 5th Overall at Auburn

Cerebrospinal Fluid Dynamics In The Cervical Spine: Importance Of Fine Anatomical Structures, S. Pahlavian, T. Yiallourou, R. Tubbs, A. Bunck, M. Goodin, Francis Loth, M. Raisee, Bryn Martin

Dr. Bryn Martin

No abstract provided.

Interactive Behavior Of Internal Resonators In Acoustic Metamaterials Under Impact Pulse Loading, Kwek Tan, C. Sun

Dr. Kwek-Tze Tan

No abstract provided.

Experimental Investigation Of Bridging Law For Single Stitch Fibre Using Interlaminar Tension Test, Kwek Tan, N. Watanabe, Y. Iwahori

Dr. Kwek-Tze Tan

In this study, a novel Interlaminar tension test (ITT) method was performed to experimentally investigate the bridging and fracture process of a single stitch fibre used to improve the delamination strength of composite laminates. Kevlar-29, of various thread thicknesses (44, 66, 88 and 132 tex), was used as the through-thickness stitch fibre in the ITT experiments. Key empirical force and displacement parameters, which governed the stitch fibre bridging law, were characterised and identified. Relationships of such parameters with thread thicknesses were determined. Fibre fracture load and fibre fracture energy are found to increase with increasing thread thickness. Frictional pull-out force …

Stitch Fiber Comparison For Improvement Of Interlaminar Fracture Toughness In Stitched Composites, Kwek Tan, N. Watanabe, Y. Iwahori

Dr. Kwek-Tze Tan

In this study, strain energy release rates are measured and compared for laminated composites reinforced by through-thickness stitching using different stitch fiber materials — Carbon, Kevlar, and Vectran. Strain energy release rates are evaluated experimentally using the DCB test and validated computationally using FEA. The FE model of the stitched composite incorporates a novel four-step stitch fracture process, namely: interfacial debonding, slack absorption, fiber breakage, and pull-out friction. The FE predictions of G_IC show good agreement with the experimental results. It is revealed that the relationship between G _IC and stitch density, or stitch thread volume fraction for all …

Interlaminar Fracture Toughness Of Vectran-Stitched Composites - Experimental And Computational Analysis, Kwek Tan, N. Watanabe, M. Sano, Y. Iwahori

Dr. Kwek-Tze Tan

In this article, mode I interlaminar fracture toughness (GIC) of Vectran-stitched laminated composite is determined experimentally and computa- tionally. Critical strain energy release rates are measured by performing double can- tilever beam test on composites stitched with Vectran as stitch fiber, and are found to increase with increasing stitch thread thickness and stitch density. It is also revealed that the relationship between GIC and stitch density or stitch thread volume fraction appears to be linear. Interlaminar tension test is conducted to identify important fracture behavior of a single Vectran stitch fiber thread. The finite-element (FE) model of the stitched composite …

Effect Of Stitch Density And Stitch Thread Thickness On Damage Progression And Failure Characteristics Of Stitched Composites Under Out-Of-Plane Loading, Kwek Tan, A. Yoshimura, N. Watanabe, Y. Iwahori, T. Ishikawa

Dr. Kwek-Tze Tan

In this paper, the damage progression and failure characteristics of stitched composites under out-of-plane loading are experimentally investigated. Test specimens, stitched with various stitch densities and stitch thread thicknesses, are studied using quasi-static indentation test. Test specimens are loaded and unloaded in 0.5 mm incremental indentation displacement to examine for damage phenomena using non-destructive inspection techniques namely ultrasonic C-scan, X-ray radiography and X-ray micro-computed tomography to elucidate complex damage mechanisms and fracture behavior. Recorded test history of load–displacement curves indicate that damage progression can be characterized into three stages: damage initiation, damage propagation and final damage failure. Results show that …

Understanding Effectiveness Of Stitching In Suppression Of Impact Damage: An Empirical Delamination Reduction Trend For Stitched Composites, Kwek Tan, N. Watanabe, Y. Iwahori, T. Ishikawa

Dr. Kwek-Tze Tan

In this paper, a novel empirical trend has been identified to understand the delamination reduction in stitched composites subjected to impact loading. This empirical-based Delamination Reduction Trend (DRT) is developed based on an extensive series of low-velocity impact tests using specimens of different laminate thicknesses, stitch densities and stitch thread linear (mass) densities, subjected over a range of impact energy levels. The DRT simply relates two parameters: normalized delamination area (Delam_Norm) and stitch fiber volume fraction (V_ft), to characterize the effectiveness of stitching in impact damage suppression. DRT evidently shows a bi-linear behavior: first, …

X-Ray Radiography And Micro-Computed Tomography Examination Of Damage Characteristics In Stitched Composites Subjected To Impact Loading, Kwek Tan, N. Watanabe, Y. Iwahori

Dr. Kwek-Tze Tan

In this study, X-ray radiography and X-ray micro-computed tomography (μCT) are employed to characterise impact damage in stitched composites, paying particular attention to the influence of stitch density and stitch thread thickness. Laminated composites, stitched with varying stitch densities and stitch thread thicknesses, are subjected to low-velocity impact loading at various energy levels. X-ray radiography is used to observe in-plane matrix cracks and overall delamination propagation; whilst μCT is exploited to examine cross-sectional views showing detailed through-thickness matrix cracks distribution and 3D delamination damage pattern. It is revealed that stitches act as crack initiation sites, due to the presence of …

Optimizing The Band Gap Of Effective Mass Negativity In Acoustic Metamaterials, Kwek Tan, H. Huang, C. Sun

Dr. Kwek-Tze Tan

A dual-resonator microstructure design is proposed for acoustic metamaterials to achieve broadband effective mass negativity. We demonstrate the advantage of acoustic wave attenuation over a wider frequency spectrum as compared to the narrow band gap of a single-resonator design. We explicitly confirm the effect of negative effective mass density by analysis of wave propagation using finite element simulations. Examples of practical application like vibration isolation and blast wave mitigation are presented and discussed.

Effect Of Stitch Density And Stitch Thread Thickness On Low-Velocity Impact Damage Of Stitched Composites, Kwek Tan, N. Watanabe, Y. Iwahori

Dr. Kwek-Tze Tan

Effect of stitch density and stitch thread thickness on low-velocity impact damage of stitched composites is investigated experimentally. Physical examination on damage surfaces shows that stitches perform as crack initiators, as well as crack arrestors. Longer matrix cracks are observed in densely-stitched composites, in contrast to isolated matrix cracks found in moderately-stitched composites. Ultrasonic C-scan evidently compares the delamination areas and concludes that specimens with higher stitch density and thread thickness are more capable of impeding delamination growth by effectively bridging delamination cracks. Load–time curves reveal that the onset of delamination is not influenced by stitch density and thread thickness. …

Effect Of Stitch Density And Stitch Thread Thickness On Compression After Impact Strength And Response Of Stitched Composites, Kwek Tan, N. Watanabe, Y. Iwahori, T. Ishikawa

Dr. Kwek-Tze Tan

In this paper, the damage failure and behaviour of stitched composites under compression after impact (CAI) loading are experimentally investigated. This study focuses on the effect of stitch density and stitch thread thickness on the CAI strength and response of laminated composites reinforced by through-thickness stitching. Experimental findings show that stitched composites have higher CAI failure load and displacement, which corresponds to higher energy absorption during CAI damage, mainly attributed to greater energy consumption by stitch fibre rupture. The coupling relationships between CAI strength, impact energy, stitch density and stitch thread thickness are also revealed. It is understood that the …

Blast-Wave Impact Mitigation Using Negative Effective Mass Density Concept Of Elastic Metamaterials, Kwek Tan, H. Huang, C. Sun

Dr. Kwek-Tze Tan

This paper presents the use of elastic metamaterials for impact attenuation and blast-wave mitigation. Metamaterials represent a novel and emerging research area where materials exhibit exceptional properties not commonly found in natural materials. These unique properties are enacted by specifically designed microstructures. In this study, a single-resonator model and a dual-resonator microstructural design are proposed to exhibit negative effective mass density. The effect of negative effective mass density is explicitly confirmed by analysis of wave propagation using numerical simulations. Results evidently show that impact stress wave attenuation occurs over a wider frequency spectrum for the dual-resonator model as compared to …

Impact Damage Resistance, Response, And Mechanisms Of Laminated Composites Reinforced By Through-Thickness Stitching, Kwek Tan, N. Watanabe, Y. Iwahori

Dr. Kwek-Tze Tan

In this article, the study of impact damage of laminated composites reinforced by through-thickness stitching is investigated and presented in threefold. Specimens stitched with varying stitch density and stitch thread thickness are subjected to low-velocity impact via a drop-weight machine. Impact damage resistance is first studied by examining the extent of delamination area in damaged specimens using ultrasonic C-scan analysis. It is revealed that higher stitch density is more capable of impeding delamination growth by arresting cracks at closer interval and suppressing crack propagation. The use of thicker stitch thread offers slight improvement to damage resistance by marginal reduction in …

Autoignition Of N-Decane Under Elevated Pressure And Low-To-Intermediate Temperature Conditions, Kamal Kumar, Gaurav Mittal, Chih-Jen Sung

Dr. Gaurav Mittal

. The current experiments span a temperature range not fully investigated in previous autoignition studies on n-decane. Two-stage ignition, characteristic of large hydrocarbons, is observed over the entire range of conditions investigated, as demonstrated in the plots of raw experimental pressure traces. In addition, experimental results reveal the sensitivity of the first-stage and total ignition delays to variations in fuel and oxygen mole fractions, pressure, and temperature. Predictability of two kinetic mechanisms is compared against the present data. Discrepancies are noted and discussed, which are of direct relevance for further improvement of kinetic models of n-decane at conditions of elevated …

Aerodynamics Inside A Rapid Compression Machine, Gaurav Mittal, Chih-Jen Sung

Dr. Gaurav Mittal

The aerodynamics inside a rapid compression machine after the end of compression is investigated using planar laser-induced fluorescence (PLIF) of acetone. To study the effect of reaction chamber configuration on the resulting aerodynamics and temperature field, experiments are conducted and compared using a creviced piston and a flat piston under varying conditions. Results show that the flat piston design leads to significant mixing of the cold vortex with the hot core region, which causes alternate hot and cold regions inside the combustion chamber. At higher pressures, the effect of the vortex is reduced. The creviced piston head configuration is demonstrated …

Autoignition Of Methylcyclohexane At Elevated Pressures, Gaurav Mittal, Chih-Jen Sung

Dr. Gaurav Mittal

Autoignition of methylcyclohexane (MCH) is investigated in a rapid compression machine (RCM). Experiments are conducted for homogeneous MCH/O₂/N₂/Ar mixtures with equivalence ratios varying from 0.5 to 1.5, at compressed charge pressures of 15.1 and 25.5 bar, and over a compressed gas temperature range of 680–905 K. In the RCM experiments, the mole percentage of MCH is kept constant at 1.047%, while the equivalence ratio is varied through variation in oxygen mole percentage. Ignition delay measurements demonstrate the features of two-stage ignition characteristics and strong negative temperature coefficient (NTC) behavior. The NTC behavior is also noted to …