Predicting bending strength of fire-retardant-treated plywood from screw-withdrawal tests
This report describes the development of a test method and predictive model to estimate the residual bending strength of fire-retardant-treated plywood roof sheathing from measurement of screw-withdrawal force. The preferred test methodology is described in detail. Models were developed to predict loss in mean and lower prediction bounds for plywood bending strength as a function of a screw-withdrawal force. Our analysis of fire-retardant-treated plywood from three different studies, each with various fire-retardant-treatment, processing, plywood thickness, and exposure temperature groupings, clearly indicated that different fire-retardant-treatments and plywood thicknesses could not be grouped into a single “universal” model. Nevertheless, some grouping was possible; parameter estimates for several grouped fire-retardant formulations and plywood thicknesses are reported for mean trends and lower prediction boundaries. Although the models were shown to acceptably predict plywood bending strength, additional work is needed to expand these models to address the effects of plywood quality, wood temperature, and moisture content at time of test.
Effects of a new GUP-B fire retardant on mechanical properties of Korean pine when exposed to elevated temperature
The bending properties of Korean pine (Pinus koraiensis) treated with a newly formulated guanylurea phosphate (GUP) fire re­ tardant were evaluated. The chemical processing method used to formulate this fire retardant (called FRW) results in an organic phosphate fire-retardant system with less acidic pH and fewer impurities. The fire-retardant chemical studied consisted of high pu­ rity GUP, boric acid (B), and a minor amount of additives. The clear specimens of pine treated with FRW were either air-dried after treatment or kiln-dried at 70°C and were then subjected to various durations of a steady-state exposure at 66°C and 75 percent rela­ tive humidity. No significant differences in thermal degradation between the untreated controls and the FRW-treated pine were found regardless of whether it was air-dried or kiln-dried after treatment. However, for other tested fire retardants with much lower pH values, kiln-redrying induced significantly more degradation compared with air-redried material. On exposure to elevated tem­ perature, the strength and stiffness of FRW-treated Korean pine experienced deterioration, but the extent was less than that previ­ ously reported for other GUP-B formulations produced using different manufacturing processes. Because of its milder acidity which results from the modified manufacturing process, enhanced stability related to thermal degradation was noted for this en­ hanced GUP-B (FRW).
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.