RESUMO
The elastic-plastic properties of mesoscale electrodeposited LIGA Ni alloy specimens are investigated as a function of specimen size, strain rate, and material composition. Two material compositions are studied: a high-strength fine-grained Ni-Fe alloy and a high-ductility coarse-grained Ni-Co alloy. The specimens have thicknesses of approximately 200 µm and gauge widths ranging from 75 µm to 700 µm. Tensile tests are conducted at strain rates of 0.001/s and 1/s using tabletop loading apparatuses and digital image correlation (DIC) for strain measurement. For each test condition, the apparent Young's modulus, yield strength, ultimate tensile strength, and strain hardening exponent and strength coefficient are extracted from the tensile tests. The true strains to failure are also assessed from fractography. Size, rate, and composition effects are discussed. For most properties, the statistical scatter represented by the standard deviation exceeds the measurement uncertainty; the notable exceptions to these observations are the apparent Young's modulus and yield strength, where large measurement uncertainties are ascribed to common experimental factors and material microplasticity.
RESUMO
Photolithographically defined thin film Au dots were used as micro fiducial markers for digital image correlation (DIC), to enable two-dimensional strain measurement of 200 µm-thick LIGA (Lithographie, Galvanformung, Abformung) nickel alloys. Due to the sensitivity of electrodeposited films' microstructure and properties on the processing conditions, characterization of LIGA mechanical properties continues to be necessary for microsystems commercialization. DIC offers advantages over laser-based strain measurement techniques but creating suitable speckle patterns on specimens with dimensions under a millimeter is challenging. The material surface roughness itself is often used as the speckle pattern, or micro- or nanoparticles are applied to the surface. But for materials with highly polished surfaces, such as commercial LIGA alloys, the surface roughness is not always suitable, while application of particles still poses technical challenges in uniformity and reproducibility. We fabricated freestanding tensile specimens, with gauge sections 700 µm wide × 3 mm long × 200 µm thick, from electrodeposited Ni-10% Co using a commercial LIGA process, and conducted microtensile tests at strain rate 0.001 s-1. Designing and fabricating arrays of randomly oriented 1.5 µm-thick Au dots on the specimens provided a suitable way to obtain full-field surface strains over the entire gauge lengths and was reproducible from one specimen to another. Microfabricated fiducial markers therefore can be a useful surface-preparation approach for investigating micromechanical behavior, particularly plasticity and fracture, of LIGA films using DIC.
RESUMO
Two different LIGA electrodeposited nickel alloys displayed distinct fracture modes after meso-scale tensile testing. The Ni-Co alloy failed in a ductile manner, while the Ni-Fe alloy failed in a more brittle-appearing manner. Various factors affecting the fracture are discussed; it was determined that the fracture mode did not depend upon the strain rate but did depend upon the sample geometry. The difference in the microstructure is likely the cause of the difference in fracture mode, as the Ni-Co alloy is fine-grained, while the Ni-Fe alloy is nano-grained and likely failed by a creep-like mechanism.
RESUMO
This article examines the intersection of workers' compensation laws with the Americans with Disabilities Act (ADA) and the Family and Medical Leave Act (FMLA). Much ADA and FMLA litigation stems from work-related injuries or illnesses. Knowledge of the ADA and FMLA may help prevent workers' compensation cases from resulting in costly employment litigation. Employees who are absent from work for a work-related condition often have rights under other laws, besides workers' compensation laws, such as the ADA and FMLA. Employers need to be cognizant of this while addressing these cases. First, the goals of state workers' compensation laws and the ADA and FMLA are reviewed. Then specific issues involving the intersection of workers' compensation, ADA,and FMLA are discussed.
