Papers by Keyword: PbO

Abstract: Fiber-reinforced cementitious matrix (FRCM) composites have been increasingly used to strengthen existing concrete and masonry structures in the last decade. Two guidelines are available for the design and construction of FRCM strengthened members: ACI 549.4R (2013) and CNR-DT 215 (2018). Both these guidelines employ the effective strain, i.e. the strain at which the composite action is lost, as key parameter for the evaluation of the capacity of FRCM strengthened members. The American guideline ACI 549.4R (2013) employs the results of clevis-grip tensile tests on FRCM coupons to determine the composite effective strain. Such strain is determined by the Italian guideline CNR-DT 215 (2018) combining the results of direct shear tests on FRCM-substrate joints and of tensile test of bare fiber textile. The effective strain is strictly related to the matrix-fiber bond behavior, which can be expressed by the interface shear stress-slip relationship, i.e. the cohesive material law (CML). The effective strain is not sufficient for a full understanding of the structural response of strengthened members, since the knowledge of the CML is needed to predict important parameters such as the crack pattern or the location where debonding occurs in beams strengthened in flexure. This paper provides a simple procedure to obtain the CML from the load response obtained by direct shear tests of FRCM-substrate joints. The procedure is discussed and applied to the case of poliparaphenilene benzobisoxazole (PBO) FRCM-concrete joints previously tested by the authors.

Abstract: This study addresses a numerical investigation of the bond behaviour exhibited by an FRCM system when subject to tensile and single direct shear tests. A reinforcement system, based on a polyparaphenylene benzobisoxazole (PBO) bi-directional fibre mesh and a mixed cement-pozzolanic mortar is selected. The system is characterized by the presence of coated glass-fibre yarns and dry polypropylene yarns alternated to the PBO yarns in the warp and weft directions, respectively. The mechanical characterization of composite constituent materials is carried out together with tensile and direct shear tests. Concerning mechanical interpretation of the tests, within a mode II fracture mechanics, and assuming a trilinear cohesive material law (CML), the stress transfer law between the fibre and the matrix is back calibrated from single direct shear test results. The CML obtained is employed into a finite-difference model developed for the purpose. Tensile tests are modelled providing adequate boundary conditions. Results satisfactorily agree with the tested behaviour of the FRCM system.

Abstract: Polybenzoxazole (PBO) fiber membranes with submicron-scale diameter were fabricated from the polyhydroxyamide (PHA) precursor by electrospinning and thermal cyclization processes. In order to improve the strength of the membrane MWCNTs was blended with PHA in the mixture solvent of dimethylacetamide (DMAc) and THF. The morphology, thermal stability, mechanical properties and dielectric constant of MWCNTs / PHA and MWCNTs / PBO membranes were characterized. For MWCNTs/PBO membranes, improved mechanical property and low dielectric constant could be achieved.

Abstract: As a kind of rig-rod-like polymer, poly(p-phenylene benzobisoxazole) (PBO) has received great interest because of its excellent mechanical properties and good thermal stability. The use of PBO materials, however, is limited due to its low sunlight stability. In this study, photolysis of PBO films was studied by infrared spectroscopy and molecular mass determination. It found that at the beginning of photolysis, the I.V. values of PBO almost did not changed. Then, it underwent fast decrease stage. Moreover, PBO degrade slowly in N2 atmosphere than in air atmosphere. The most likely photo-degradation mechanism was put forward. Attempts to stabilize PBO from photolysis were also investigated. It found that heat treatment could alleviate photo-degradation speed of PBO. Traditional light stabilizers showed a marginal effect on photolysis of PBO, whereas ferrocene dimethanol behaved better effect on the photo-stabilization of PBO.

Abstract: We have developed a large area, flat panel detector for general applications to digital radiology. This paper presents the x-ray detection characteristics with various semiconductor radiation detectors (HgI2, PbI2, PbO, CdTe) derived by a novel wet coating process for large area deposition. The wet coating process could easily be made from large area films with printing paste mixed with semiconductor and binder material at room temperature. X-ray performance data such as dark current, sensitivity and signal to noise ratio (SNR) were evaluated. The HgI2 semiconductor was shown in much lower dark current than the others, and also has the best sensitivity. In this paper, reactivity and combination characters of semiconductor and binder material that affect electrical and x-ray detection properties would be verified through our experimental results.

Abstract: Wet chemistry produced niobium modified PZT 95/5 was synthesised and processed for use in a ferroelectric power supply. The electrical performance of ferroelectric power supply components can be characterised by the remnant polarisation for the material, which is found to follow closely with density. The effects of doping the wet chemistry derived oxide powder with additional PbO via a traditional mixed oxide route were assessed as a function of density and remnant polarisation. The results have shown a gradual improvement followed by a sharp deterioration in density and electrical properties as PbO additions increase and exceed a certain level. As a result of lead volatilisation during subsequent processing steps, the actual lead content for the optimum PbO dopant level was in the region of theoretical stoichiometry, which in part concludes the findings of this study. Further conclusions are made in reference to the effect of excessive PbO on the material’s processing characteristics.