HYDRAULIC BULGE TESTING TO COMPARE FORMABILITY OF CONTINUOUS AND STRETCH BROKEN CARBON FIBER PREPREG LAMINATES

The use of carbon fiber reinforced polymer composites has increased with the increased need for high-strength, low-density materials, particularly in the aviation industry. Stretch broken carbon fiber (SBCF) is a form of carbon fiber created by the randomized breaking of aligned fibers in a tow at inherent flaw points, resulting in a material constituted of collimated fiber fragments longer than chopped fibers. While continuous carbon fibers possess desirable material properties, the limited formability prevents their wider adoption. SBCF composites exhibit pseudo-plastic deformation that can potentially enable the use of traditional metal forming techniques like stamping and press forming well established in mass production applications. To investigate the formability of SBCF composites prepared with either continuous or stretch broken Hexcel IM-7 12K fiber, impregnated with Huntsman RDM 2019-053 resin, hydraulic bulge testing was performed to explore the strain behavior under biaxial stress conditions at elevated temperature under atmospheric pressure. Initial results show better formability of SBCF compared to continuous fiber, characterized by the axisymmetric response to the applied stress.

Analytical Modeling of an Implantable Opto-Mechanical Pressure Sensor to Study Long Term Drift

“Zero-drift” characteristics of an optical intraocular pressure sensor is investigated as a function of membrane dissolution and hygroscopic swelling of the epoxy layer. Both effects were studied using an analytical model based on the deflection of a circular membrane. Results from the analytical model were verified with experimental results from “bulge” testing. The analytical model was used to study the “zero drift” of the sensor as a function of changes in membrane thickness and geometry of the sensor. The results show that dissolution of the membrane and swelling of the spacer layer can contribute to zero-drift over time. The results are useful in guiding design and fabrication optimization to minimize drift in intraocular pressure sensors used for long term implantation.

Hydrodynamic Bulge Testing: Materials Characterization Without Measuring Deformation

Characterizing the elastic properties of soft materials through bulge testing relies on accurate measurement of deformation, which is experimentally challenging. To avoid measuring deformation, we propose a hydrodynamic bulge test for characterizing the material properties of thick, pre-stressed elastic sheets via their fluid–structure interaction with a steady viscous fluid flow. Specifically, the hydrodynamic bulge test relies on a pressure drop measurement across a rectangular microchannel with a deformable top wall. We develop a mathematical model using first-order shear deformation theory of plates with stretching and the lubrication approximation for the Newtonian fluid flow. Specifically, a relationship is derived between the imposed flowrate and the total pressure drop. Then, this relationship is inverted numerically to yield estimates of the Young’s modulus (given the Poisson ratio) if the pressure drop is measured (given the steady flowrate). Direct numerical simulations of two-way-coupled fluid–structure interaction are carried out in ansys to determine the cross-sectional membrane deformation and the hydrodynamic pressure distribution. Taking the simulations as “ground truth,” a hydrodynamic bulge test is performed using the simulation data to ascertain the accuracy and the validity of the proposed methodology for estimating material properties. An error propagation analysis is performed via Monte Carlo simulation to characterize the susceptibility of the hydrodynamic bulge test estimates to noise. We find that, while a hydrodynamic bulge test is less accurate in characterizing material properties, it is less susceptible to noise, in the input (measured) variable, than a hydrostatic bulge test.

Design of Flexible Bulge Testing System for Evaluating the Influence of Size Effect on Thin Metal Sheets

Formability in sheet forming processes are usually analyzed by standardized tests, which often requires different test equipment associated with high initial investment cost. The present study purposes a flexible test tooling system for hydraulic bugle test apparatus that allows to evaluate the impact of size effect on the formability of thin metallic sheets. Finite Element Method was used for concept and design of the tooling system and experimental tests were carried out with thin sheets of SUS316L stainless steel to assess the overall performance of the tooling system.

A microfluidic method to measure bulging heights for bulge testing of polydimethylsiloxane (PDMS) and polyurethane (PU) elastomeric membranes

A unique microfluidic platform to rapidly and accurately measure the bulging heights of polymeric membranes.

In situ synchrotron radiation X-ray diffraction studies on molecular aggregation structure of nylon 12 films during bulge testing

It is desirable to establish a method for evaluating mechanical properties, such as modulus and strength, of micrometer and sub-micrometer thick polymer films.