On the Viscoelastic Response of Composite Laminates

The present work deals with the determination of theviscoelastic properties of composite laminates based on the viscoelasticbehaviour of the single lamina. A viscoelastic lamination theory isdeveloped assuming that the lamina stiffness matrix is fully complex andfrequency dependent.For the measurement of the complete setof frequency dependent viscoelastic properties of the single lamina(i.e. complex moduli and Poisson's ratio) a new methodology has beenintroduced, based on the free and forced vibration of unidirectional and[45/–45] _ns composite laminates.Allmeasurements have been performed both in air and in vacuum. Since thevibration amplitude was very small, in order to fulfil linearityrequirements, the results do not show any significant difference due toair damping.The effects of experimental errors on theevaluation of the viscoelastic properties of the single lamina have alsobeen discussed.     

The origin of androgen and estrogen in a virilized postmenopausal woman with bilateral benign cystic teratomas

Clitoromegaly was observed in a 73-year-old woman who had bilateral ovarian benign cystic teratomas that contained only epithelial derivatives. Scattered in the stroma of these ovaries were clusters of hyperplastic cells. The plasma testosterone production rate was 2.4 mg/day, a value that is ten times greater than that of normal postmenopausal women. The elevated plasma concentrations of testosterone and androstenedione decreased to normal by the second day after bilateral oophorectomy. Ovarian venous concentrations of testosterone and androstenedione were also increased and were considerably greater than those in peripheral blood. Estrone production was 68 microng/day, most of which could be accounted fo by the extraglandular formation from androstenedione. Estradiol production was 71 microng/day, of which 75% was computed to arise from extraglandular formation and the remainder likely arose by ovarian secretion. The modest increase in estrogen production was associated with slight cystic hyperplasia of the endometrium. From this study we conclude that the hyperplastic ovarian stroma was the source of the excessive androgen production.     

The role of Fe and Ti additions in the microstructure of Nb–18Si–5Sn silicide-based alloys

The effects of Fe and Ti on the microstructure and hardness of the as cast and heat treated Nb–24Ti–18Si–5Fe–5Sn (NV8) and Nb–45Ti–15Si–5Fe–5Sn (NV4) alloys were studied. The microstructure of NV8-AC consisted of (Nb,Ti)_ss, (Nb,Ti)₃Sn, (Nb,Ti)₅Si₃, (Nb,Ti)₃Si, FeNb₄Si, and Fe₂Nb₃ and a Ti rich oxide. The microstructure of NV8-HT consisted of (Nb,Ti)₃Si, (Nb,Ti)₃Sn and the Ti rich oxide. In NV8 the formation of Nb₅Si₃ was destabilised, the stability of Nb₃Si was enhanced and the eutectic between Nb₅Si₃ and the solid solution was suppressed. The microstructure of NV4-AC contained Ti rich and Nb rich solid solutions, 3-1 and 5-3 silicides. The FeNb₄Si and Fe₂Nb₃ phases and the Ti rich oxide observed in NV8-AC were not formed in NV4-AC. The microstructure of NV4-HT consisted of (Ti,Nb)₃Sn, β(Ti,Nb)_ss, (Ti,Nb)₃Si and (Ti,Nb)₅Si₃ phases. The solubility of Fe in the Ti-based 3-1 silicide was significantly lower than in the Nb-based 3-1 silicide. The β(Ti,Nb)_ss + (Ti,Nb)₅Si₃ → (Ti,Nb)₃Si transformation was enhanced in NV4. The effects of Fe and Ti on the hardness of Nb–18Si–5Sn-based alloys, and of alloying elements on the hardness of Nb₃Sn, Ti₃Sn, and Nb₃Si, Ti₃Si, and Ti and Nb base 5-3 silicides are discussed.     

The role of Sn and Ti additions in the microstructure of Nb–18Si base alloys

The effects of Sn and Ti on the microstructure and hardness of the as cast and heat treated Nb–18Si–5Sn (NV9) and Nb–24Ti–18Si–5Sn (NV6) alloys were studied. In both alloys the phases present in the as cast and heat treated microstructures were Nb_ss, Nb₃Sn and Nb₅Si_3. In NV9, Sn suppressed the formation of Nb₃Si, partitioned in Nb_ss stronger than in Nb₅Si₃ and did not affect significantly the solubility of Si in the Nb_ss. In NV6, the solubility of Ti in (Nb,Ti)_ss increased in the presence of Sn, the concentration of Ti in Nb₅Si₃ was sensitive to cooling rate and the solubility of Sn in Nb₅Si₃ decreased as the concentration of Ti increased. The Ti controlled the partitioning of Si between (Nb,Ti)_ss and Nb₃Sn and was considered responsible for the macrosegregation of Si in the as cast ingot. The transformation of β to Nb₅Si₃ was enhanced by the synergy of Sn and Ti. The addition of Ti did not destabilise the Nb₃Sn. Silicon increased the hardness of Nb₃Sn significantly, Sn did not affect the hardness of Nb₅Si₃ and Ti reduced the hardness of Nb₃Sn and Nb₅Si₃ significantly. The hardness of NV9 and NV6 decreased and increased, respectively, by heat treatment. The reduction of the hardness of NV6-AC compared to NV9-AC is attributed to the strong effect of Ti on the hardness of Nb₃Sn and Nb₅Si₃.     

Dynamic mechanical analysis of a two-dimensional carbon-carbon composite

A two-dimensional carbon-carbon composite material consisting of stacked carbon cloths densified with a carbon matrix has been characterized with respect to its dynamic mechanical properties. Unprotected specimens and some protected against oxidizing conditions were investigated over the temperature range of subambient (–100°C) to 500°C. The reproducibility of the calculated storage modulus as well as the loss factor was within 5% at any one temperature over the entire temperature range. Results concerning protected and unprotected specimens were compared analytically and the difference of the relative plots above 400°C reflects the bad corrosion resistance of the unprotected samples under oxidizing conditions, where the carbon matrix material is more sensitive to oxidation than the fibre. The transition regions which appeared on the loss factor plots are strongly connected with the relevant secondary transition regions of the antioxidation protected material used. This technique, which has been demonstrated to be non-destructive for the sample analysed, proved that no differences exist in the dynamic mechanical properties of the specimens with respect to fibre orientation (warp or weft direction). Details of the experimental technique and assumptions made are also presented.     

Origin of estrogen in a postmenopausal woman with a nonendocrine tumor of the ovary and endometrial hyperplasia

The origin and quantity of estrogen and androgen were measured in a postmenopausal woman with clinical signs of estrogen excess and a nonendocrine tumor of the ovary. The plasma androstenedione production rate was elevated 5-fold. The estrone production rate was also five times that normally expected for a postmenopausal women and could be accounted for totally by the extraglandular conversion of plasma and androstenedione. Following removal of the tumor, the concentration of plasma androstenedione and the estrone production rate fell dramatically to normal postmenopausal levels. It is concluded that this markedly increased androstenedione production was the result of excessive secretion of androstenedione by the hyperplastic stromal cells of the ovary containing the mucinous cystadenocarcinoma. The excessive prehormone production together with its normal extraglandular conversion to estrone resulted in the massive increase in endogenous estrogen formation.     

Covert bilaterality of mature ovarian teratomas

Over a 21-year period, 213 women with mature teratoma of the ovary were operated on at Parkland Memorial Hospital. Twenty-seven had bilateral tumors. In 22 of these 27 patients, bilateral involvement was evident on clinical examination, and in 5, biopsy of an abnormal but nonteratoid appearing ovary was required to make the diagnosis. Ninety patients with a visually normal opposite ovary had no identifiable tumor in that ovary by investigative incision or incidental excision. Neither incision nor excision of the normal contralateral ovary was performed in 58 cases, and subsequently, one of these women is known to have developed a teratoma in that ovary. We conclude that synchronous covert bilaterality of mature teratomas is not common, and a visually normal contralateral ovary should not routinely be bivalved or wedge biopsied.