Woonbong Hwang

Fatigue behavior of glass fiber reinforced epoxy composite materials has been studied analytically. A new concept called "fatigue modulus," which is defined as a slope of applied stress and resultant strain at a specific cycle is introduced. Fatigue modulus degradation is studied using an assumption that the fatigue modulus degrada tion rate follows a power function of fatigue cycle. Theoretical equation for predicting fatigue life is formulated using the fatigue modulus and its degradation rate

Cumulative damage during fatigue is studied analytically. Extensive reviews are per formed on the published damage models. Three different cumulative damage models are defined using several physical variables such as fatigue modulus and resultant strain. Proposed model I is defined using fatigue modulus, while models II and III are defined using resultant strains. Proposed models are derived as functions of nor malized applied stress level, r, and number of fatigue cycle, n. It is verified that

With increasing amounts of oily water discharged from industrial and domestic sources, purifying oily emulsions using effective and eco-friendly methods is of great significance. Although functional membranes with selective wettabilities have been extensively explored for the efficient purification of oil-in-water emulsions, the development of functional membranes that use green and inexpensive materials, are simple to fabricate, and are easy to scale up remains very challenging. Herein, we repo

Interlaminar fracture behavior of composite materials under static and cyclic loadings has been studied using a width tapered double cantilever beam specimen. The fracture energy is evaluated by compliance, beam and area methods. The comparison results show that the initial fracture energy could be evaluated either by beam or area method while the crack growth resistance could be calculated by compliance method. Increases in the criti cal load and fracture energy due to fiber bridging are predic

Fatigue life prediction on composite materials is studied analytically using degradation and damage models, resultant strains, and fatigue modulus. Definition of fatigue modulus, new damage models using fatigue modulus and resultant strain, and prediction of fatigue life of composite materials using degradation and damage models are discussed. This approach can predict accurately the multi-stress level fatigue life as well as single-stress level fatigue life of composite materials. Fatigue life

Water waves are a continuously generated renewable source of energy. However, their random motion and low frequency pose significant challenges for harvesting their energy. Herein, we propose a spherical hybrid triboelectric nanogenerator (SH-TENG) that efficiently harvests the energy of low frequency, random water waves. The SH-TENG converts the kinetic energy of the water wave into solid⁻solid and solid⁻liquid triboelectric energy simultaneously using a single electrode. The electrical output

A 5.3 GHz microstrip antenna for use in synthetic aperture radar (SAR) systems was developed with a composite sandwich construction, using composite laminates, Nomex honeycomb and aluminum alloy. This is the surface-antenna-structure (SAS) for application to load-bearing structural surfaces. The design concept originated from a composite sandwich structure and a multi-layer microstrip antenna. Design, fabrication and validation of structural/electrical performances were all demonstrated. To veri