The long term goal of this research is to improve the fire resistance of gypsum wallboard (GWB). Gypsum wallboard consists mainly of gypsum, i.e. calcium sulfate dihydrate, CaSO4•2H2O. In buildings, the chemical, mechanical and thermal properties of gypsum wallboard play an important role in delaying the spread of fire. To build a fire resistant GWB, it is very important to study the thermal, mechanical, physical and chemical properties of regular GWB and various types of fire-resistant wallboards available commercially in the market. Various fire-resistant GWBs have been compared and contrasted with reference to a standard wallboard in this study. Regardless of the type of wallboard, the main component is gypsum. The fire resistance property is mainly attributed to the absorption of energy related with the loss of hydrate water going from the dihydrate (CaSO4•2H2O) form to the hemihydrate (CaSO4•½H2O) and from the hemihydrate to the anhydrous form (CaSO4) in a second dehydration. The present paper is a comparative study of commercially available standard, fire-rated Type X and firerated Type C gypsum wallboards. Type X wallboards are typically reinforced with noncombustible fibers so as to protect the integrity of the wallboard during thermal shrinkage, while the Type C wallboards are incorporated with more glass fibers and an additive, usually a form of vermiculite. These Type C wallboards have a shrinkage adjusting element that expands when exposed to elevated temperature. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), thermomechanical analysis (TMA), scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) were used to characterize and compare the materials. Various properties, such as the heat flow, weight loss, dimensional changes, morphology and crystalline structures of the gypsum wallboards were studied using these techniques.

<p>  </p> <p>Thermal shrinkage in advanced composite manufacturing causes residual stress in a cylindrical anisotropic segment. The residual stress later induces a spring-in angle when  the temperature change is negative. The superposition method in the finite element method (FEM) by ABAQUS©  proves that only the residual stress in the circumferential direction controls the spring-in angle and induces the radial residual stress. To predict the angle change, the residual stress is firstly determined by using the closed-loop geometry in FEM and then implemented into the cylindrical cross-ply symmetric laminate segment. Consequently, the geometry creates the spring-in angle under the traction-free surface. The angle change is in good agreement with the Radford equation and is found to depend on the coefficient of thermal expansion (CTE) in the circumferential and radial directions rather than other material properties and geometry dimensions. </p> <p>The study found a new limitation of the Radford equation, in that it is accurate when the part is anisotropic symmetric laminate, but not when it is unsymmetric. The accuracy of the Radford equation is further explored with the double curve geometry. Using the superposition method, the circumferential residual stress along the major curve is found to have an influence on the angle change not only of the major curve, but also of the minor curve. The negative temperature change produces the spring-in angle on the major curve, and both spring-in and -off angles on the minor curve, which rely on the radius ratio. In addition, the spring-in angle on the major curve is coincident with the Radford equation. In sum, knowing the spring-in angle is very helpful in designing a tool in advanced composite manufacturing, and the superposition method and the Radford equation are applicable to predict the spring-in angle.</p>