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3D deformation field throughout the interior of materials

Jin, Huiqing J.; Lu, Wei-Yang L.

This report contains the one-year feasibility study for our three-year LDRD proposal that is aimed to develop an experimental technique to measure the 3D deformation fields inside a material body. In this feasibility study, we first apply Digital Volume Correlation (DVC) algorithm to pre-existing in-situ Xray Computed Tomography (XCT) image sets with pure rigid body translation. The calculated displacement field has very large random errors and low precision that are unacceptable. Then we enhance these tomography images by setting threshold of the intensity of each slice. DVC algorithm is able to obtain accurate deformation fields from these enhanced image sets and the deformation fields are consistent with the global mechanical loading that is applied to the specimen. Through this study, we prove that the internal markers inside the pre-existing tomography images of aluminum alloy can be enhanced and are suitable for DVC to calculate the deformation field throughout the material body.

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TYPE SAND Report YEAR 2013
OSTIDOI

Modeling interfacial fracture in Sierra

Brown, Arthur B.; Ohashi, Yuki O.; Lu, Wei-Yang L.; Nelson, Stacy M.; Austin, Kevin N.; Margolis, Stephen B.

This report summarizes computational efforts to model interfacial fracture using cohesive zone models in the SIERRA/SolidMechanics (SIERRA/SM) finite element code. Cohesive surface elements were used to model crack initiation and propagation along predefined paths. Mesh convergence was observed with SIERRA/SM for numerous geometries. As the funding for this project came from the Advanced Simulation and Computing Verification and Validation (ASC V&V) focus area, considerable effort was spent performing verification and validation. Code verification was performed to compare code predictions to analytical solutions for simple three-element simulations as well as a higher-fidelity simulation of a double-cantilever beam. Parameter identification was conducted with Dakota using experimental results on asymmetric double-cantilever beam (ADCB) and end-notched-flexure (ENF) experiments conducted under Campaign-6 funding. Discretization convergence studies were also performed with respect to mesh size and time step and an optimization study was completed for mode II delamination using the ENF geometry. Throughout this verification process, numerous SIERRA/SM bugs were found and reported, all of which have been fixed, leading to over a 10-fold increase in convergence rates. Finally, mixed-mode flexure experiments were performed for validation. One of the unexplained issues encountered was material property variability for ostensibly the same composite material. Since the variability is not fully understood, it is difficult to accurately assess uncertainty when performing predictions.

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TYPE SAND Report YEAR 2013
OSTIDOI

Transverse impact response of a linear elastic ballistic fiber yarn

Journal of Applied Mechanics, Transactions ASME

Song, Bo; Park, Hwun; Lu, Wei-Yang L.; Chen, Weinong

Transverse impact response of a linear elastic Kevlar® KM2 fiber yarn was determined at various striking speeds from Hopkinson bar and gas gun experiments incorporated with high-speed photography techniques. Upon transverse impact, a triangle shape was formed in the fiber yarn. Both longitudinal and transverse waves were produced and propagated outwards the fiber yarn. Both the angle of the triangle and Euler transverse wave speed vary with striking speeds. The relationship between the Euler transverse wave speed and the striking speed was determined. The transverse impact response of the fiber yarn was also analyzed with a model, which agrees well with the experimental results. The model shows that the longitudinal wave speed is critical in the ballistic performance of the fiber yarn. At a certain striking speed, a higher longitudinal wave speed produces a higher Euler transverse wave speed, enabling us to spread the load and dissipate the impact energy faster, such that the ballistic performance of the fiber yarn is improved. © 2011 American Society of Mechanical Engineers.

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TYPE Journal Article YEAR 2011
ScopusOSTI

Raman and infrared thermometry for microsystems

Phinney, Leslie M.; Lu, Wei-Yang L.; Serrano, Justin R.

This paper compares measurements made by Raman and infrared thermometry on a SOI (silicon on insulator) bent-beam thermal microactuator. Both techniques are noncontact and used to experimentally measure temperatures along the legs and on the shuttle of the thermal microactuators. Raman thermometry offers micron spatial resolution and measurement uncertainties of {+-}10 K; however, typical data collection times are a minute per location leading to measurement times on the order of hours for a complete temperature profile. Infrared thermometry obtains a full-field measurement so the data collection time is much shorter; however, the spatial resolution is lower and calibrating the system for quantitative measurements is challenging. By obtaining thermal profiles on the same SOI thermal microactuator, the relative strengths and weaknesses of the two techniques are assessed.

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TYPE Conference YEAR 2011
OSTI
Results 51–100 of 168
Results 51–100 of 168