Mechanical Engineering Commons^™

Experimental And Computational Study On Fracture Mechanics Of Multilayered Structures, Hai Thanh Tran

USF Tampa Graduate Theses and Dissertations

Many devices in electronics are in the form of multilayered structures. These structures can fail catastrophically if they contain defects or cracks. Enhancing their fracture properties is therefore critical to improve the reliability of the systems. The interface-dominated fracture mechanics of multilayered structure was studied using experiments and finite element (FE) modeling by considering two examples: thin films on polymer substrates in flexible electronics and Cu leadframe/epoxy molding compound (EMC) in micro-electronics packaging.

In the first example, aluminum-manganese (Al-Mn) thin films with Mn concentration up to 20.5 at.% were deposited on polyimide (PI) substrates. A variety of phases, including supersaturated …

Effect Of Void Fraction On Transverse Shear Modulus Of Advanced Unidirectional Composites, Jui-He Tai

USF Tampa Graduate Theses and Dissertations

In composite materials, transverse shear modulus is a critical moduli parameter for designing complex composite structures. For dependable mathematical modeling of mechanical behavior of composite materials, an accurate estimate of the moduli parameters is critically important as opposed to estimates of strength parameters where underestimation may lead to a non-optimal design but still would give one a safe one.

Although there are mechanical and empirical models available to find transverse shear modulus, they are based on many assumptions. In this work, the model is based on a three-dimensional elastic finite element analysis with multiple cells. To find the shear modulus, …

Al/Ti Nanostructured Multilayers: From Mechanical, Tribological, To Corrosion Properties, Sina Izadi

USF Tampa Graduate Theses and Dissertations

Nanostructured metallic multilayers (NMMs) are well-known for their high strength in smaller bilayer thicknesses. Six Al/Ti (NMM) with different individual layer thickness were tested for their mechanical hardness using a nanoindentation tool. Individual layer thicknesses were chosen carefully to cover the whole confined layer slip (CLS) model. Nano-hardness had a reverse relation with the square root of individual layer thickness and reached a steady state at ~ 5 nm bilayer thickness. Decreasing the layer bilayer thickness from ~ 104 nm to ~ 5 nm, improved the mechanical hardness up to ~ 101%. Residual stresses were measured using grazing incident X-ray …

Hydrogen Effects On X80 Steel Mechanical Properties Measured By Tensile And Impact Testing, Xuan Li

USF Tampa Graduate Theses and Dissertations

The effect of hydrogen charging current density and tensile strain rate on the mechanical properties of X80 pipeline steel were investigated by slow strain rate test (SSRT), Charpy impact test, and scanning electron microscopy (SEM) in this thesis. The results show that both the ultimate tensile strength and elongation to failure of X80 steel were deteriorated significantly after charging with hydrogen. With a strain rate of 5 x 10^-5 s^-1, the relative tensile strength and plasticity loss of X80 steel had no significant change within the range of assumed hydrogen partial pressures at room temperature. At room …