The main purpose of this search is to study the punching shear behavior of fourteen specimens of Reactive Powder Concrete (RPC) two-way flat plate slabs, half of these slabs have been exposed to a high temperature up to 400 C° by using an electric oven. All slabs have dimensions of (400x400x60) mm, with steel reinforcement mesh of (Ø6mm) diameter. Laboratory tests show that there is an increase in the value of First Crack Loading (FCL) and Ultimate Load (UL) by (208, and 216.67) % and a decrease in deflection by (56.85) % due using slab with complete reactive powder relative to a slap made of normal concrete. The use of the (RPC)mixture in layers in slabs gave results close to the slab which consists of full (RPC) this gives the benefit of more than the use of a slab that contains full reactive powder concrete in terms of cost, the increase was in FCL and UL by (130.8, 169.23, 102.7 and 135.135) % and a decrease in the value of deflection by (37.17, 47.64) %. The use of a partial reactive powder mixture also showed good results, and by increasing the dimensions of the RPC area, the results were better. the increase in FCL and UL by (54, 116, and 185) % and (53, 116.67, and 166.67) % and a decrease in value of deflection by (36.12, 42.4, and 50.26) % from reference slab. When slabs are subjected to high temperatures, there may be a decrease in the value of the FCL and UL and an increase in the value of deflection when compared to models not exposed to high temperature. But when compared to the reference slab with the same circumstance showed an increase in the value of the FCL and the rate ranged between (50- 200) % and the UL was the ratio ranged between (51.35-208.1) % and a decrease in the value of the deflection where the ratio ranged (21-46) %
TMF (thermomechanical fatigue) damage model devoted to prediction of the high temperature fatigue lifetime of navel copper alloy (C46400) , was proposed .This model was built on the basis of the stress –number of cycles curve responsible for damage due to interaction of high temperature and fatigue. This obtained prediction compared was very favorably with the cumulative experimental TMF results.
In this study, silicon and yttrium were simultaneously co-deposited by diffusion into austenitic stainless steel (AISI 316L) substrates, by a single-step pack cementation process. Cyclic oxidation tests were conducted on the siliconized coating and on the yttrium doped siliconized coating of stainless steel in CO2 atmospheric pressure at temperatures 800° C and 900° C for 100h at 10h cyclic. The results show that the initial weight gain is rapid and increased as the temperature increased. The oxidation resistance of the yttrium doped siliconized of stainless steels was significantly improved as compared with the siliconized stainless steels. The scale formed on coated stainless steel after oxidation in CO2 environment was thick and consisted of Y2O3, SiO2, Fe2O3 and chromium oxide. Optical metallography (LOM) and X-ray diffraction (XRD) were used to characterize the resulting coating and cyclic oxidation structures.
Previous studies showed that fire incidents cause a considerable deterioration of limestone samples' engineering and physical properties. Various laboratory tests were used in previous studies to investigate the properties of limestone. These tests included destructive and non-destructive tests like the hammer test, ultrasonic pulse velocity test, water-capillary rise test, and water transfer properties test, as well as destructive tests like the unconfined compression test and Brazilian tensile test. The stones of buildings exposed to fire are occasionally assessed on the site. This study analysed the physical and mechanical changes that occurred to the limestone samples when subjected to high temperatures, the damage mechanism, and laboratory or field damage assessment. This study also includes a review of the most significant studies that looked at how alternative cooling techniques—rapid water cooling or gradual air cooling—affect stone samples subjected to high temperatures and compared the behaviour of the samples in each scenario
In this paper, the hydraulic-thermal performance of a double-pipe heat exchanger equipped with 45°-helical ribs is numerically studied. The ribbed double-pipe heat exchanger is modelled using three heights (H = 0, 2.5, 3.75, 5 mm) of 45°-helical ribs. Two numbers (4-ribs and 8-ribs) of 45°-helical ribs are attached on the outer surface of the inner pipe of the counter-flow double-pipe heat exchanger and compared with a smooth double-pipe heat exchanger. Three-Dimensional computational fluid dynamics (CFD) model for a laminar forced annular flow is performed in order to study the characteristics of pressure drop and convective heat transfer. In addition, the influence of rib geometries and hydraulic flow behaviour on the thermal performance is system-atically considered in the evaluations. The annular cold flow is investigated with the range of Reynolds numbers from 100 to 1000, with three heights of ribs at the same width (W = 2 mm) and inclined angles of (θ = 45°).The results illustrate that the average Nusselt number and pressure drop increase with an in-creasing number of ribs, the height of ribs and Reynold number, while the friction factor decreas-es with increasing Reynolds numbers. The percentage of averaged Nusselt number enhancement for three rib heights (H = 2.5, 3.75 and 5 mm) at 4-ribs is (34%, 65% and 71%), respectively, While for 8-ribs the enhancement percentage is (48%, 87% and 133%) as compared with the smooth double-pipe heat exchanger at Re = 100. The best performance evaluation criteria of (PEC) at (8-ribs, and H = 5 mm) is 2.8 at Re = 750. The attached 45-helical ribs in the annulus path can generate kind of secondary flows, which enhance the fluid mixing operation between the hot surface of the annular gap and the cold fluid in the mid of the annulus, which lead to a high-temperature distribution. Increasing the height of 45°-helical ribs lead to an increase in the sur-face area subjecting to convective heat transfer.
In this study , Silicon and Aluminum with and without cerium were simultaneously co-deposited by diffusion into austenitic stainless steel (AISI 316L) substrates, by a single-step packcementation process. Cyclic hot corrosion tests were conducted on coated and uncoated austenitic stainless steel alloy with 50wt.% NaCl+50wt.%Na2So4 deposits at 750C° for 120h at 10h cycle. The results show that the hot corrosion resistance of both coated stainless steels, was significantly improved as compared with the uncoated steels. The scale formed on coated stainless steel after oxidation in mixture environment was consisted of NiAl2O4, NiFe2O4 and NiCr2O4. Optical metallography (LOM) and X-ray diffraction(XRD) was used to characterize the resulting coating and cyclic hot corrosion structures.
In this study, yttrium and aluminum were simultaneously co-deposited by diffusion into austenitic stainless steel (AISI 316L) substrates, by a single-step pack cementation process. Cyclic oxidation tests were conducted on the aluminide coating and on the yttrium modified aluminide coating of stainless steel in air under atmospheric pressure at temperatures 700 C° and 800 C° for 100h at 10h cyclic. Optical metallography and X-ray diffraction (XRD) techniques were used to characterize the changes in scale morphology and to identify the phases and oxidation products. The yttrium modified aluminde coating showed very good cyclic oxidation resistance compared to aluminide coating