Position Of Maximum Shear Stress Research Articles

Effect of salt solution wet-dry cycling on the bond behavior of FRP-concrete interface

The strengthening of concrete structures with externally bonded fiber reinforced polymer (FRP) was increasingly being used in marine exposure environments. Marine environment exposure may significantly affect the bonding behavior of FRP externally bonded to concrete. This paper is intended for studying the effect of tidal-like condition such as salt solution wet-dry cycling on the behavior of FRP-concrete interface. Exposure tests and analytical approach are carried out on specimens externally bonded with carbon fiber reinforce polymer (CFRP) and basalt fiber-reinforce polymer (BFRP). Test variable include the types of fiber and the environmental exposure periods (0, 90, 180, 270, 360 cycles). From the bending test results, the bilinear bond stress-slip relationships for different exposure periods are derived. Based on these bond stress-slip relationships, the full-range behavior of shear stress along the bond length and debonding load can be obtained through the analytical solution. The test and numerical results show that salt solution wet-dry cycling can greatly affect the bond behavior of CFRP-concrete and BFRP-concrete interface with the increase of exposure periods. With the increase of exposure periods, the position of maximum shear stress tend to move backward, which indicates the behavior of FRP-concrete interface is weakened due to the salt solution wet-dry cycling. Compared with CFRP-concrete interface, salt solution wet-dry cycling exposure has greater influence on the bond behavior of the BFRP-concrete interface.

Effect of Subtropical Natural Exposure on the Bond Behavior of FRP-Concrete Interface.

Subtropical natural exposure may significantly affect the bonding behavior of fiber reinforced polymer (FRP) externally bonded to concrete. To study the effect of subtropical natural climates on the FRP-concrete interface, natural exposure tests and an analytical approach were carried out on specimens externally bonded with carbon fiber reinforced polymer (CFRP) and basalt fiber reinforced polymer (BFRP). The bilinear bond stress-slip relationships for different exposure periods were derived from the experimental results of the strengthened reinforced concrete (RC) beams. Based on these bond-slip relationships, the full-range behavior of shear stress along the bond length and debonding load can be obtained through the analytical solution. The testing and numerical results showed that subtropical natural exposure can greatly affect the bond behavior of CFRP-concrete and BFRP-concrete interfaces in the early exposure period. In the late exposure period, the bond behavior was basically stable. With the increase of exposure time, the position of maximum shear stress tended to move backward, which indicated that the behavior of the FRP-concrete interface was weakened by natural exposure. Compared to the CFRP-concrete interface, subtropical natural exposure has greater influence on the bond behavior of the BFRP-concrete interface.

Influence of die-shift-distance of overhang dies on residual thermal shear stress in 5-chip SiP after EMC curing

This paper investigates the effects of the die-shift-distance (DSD) of overhang dies on residual thermal shear stress and warpage in a 5-chip stacked-die system-in-packaging (SDSiP) implementation. The proposed 5-chip SDSiP includes a single microprocessor (chip 1) and four pieces of dynamic random access memory (chips 2 to 5) with chip 4 stacked atop chip 2 and chip 5 stacked atop chip 3. Computer software based on finite element method (ANSYS) in conjunction with the measured material properties made it possible to obtain the shear stress, shear strain, warpage, and shear strain energy density (U0) within the chips in the 5-chip SDSiP. We also conducted experiments to obtain the interfacial shear stress as well as U0 between the EMC and die, which was compared with the numerical U0. When the DSD exceeded 0.4mm, the position of maximum shear stress at EMC/die interface in the 5-chip SDSiP changed from chip 4 to chip 1 due to a decrease in the rigidity of the stacked dies. Maximum warpage in the 5-chip SDSiP appeared in the top-left corner with movement in a downward direction. This effect can be attributed to mismatch in the CTE among the various materials in the 5-chip SDSiP.

Effect of elastic modulus and thickness of the interlayer on the bond strength for ceramic coating-substrate system

Finite element method (FEM) was used to investigate the effect of elastic modulus and thickness of the interlayer on the bond strength for ceramic coating-substrate system in contact load condition. The maximum shear stress was acted as the criterion of the bonded strength. Firstly, the FEM simulation results indicate that the sharply changed shear stress (SCSS) can be more obviously decreased by the introduction of a interlayer as compared to by increasing the thickness of coating. Secondly, with the increase in the elastic modulus of interlayer, the SCSS of substrate/interlayer increases, while the SCSS of interlayer/coating decreases. Thirdly, with the increase in the thickness of the interlayer, the SCSS of interlayer/substrate decreases by decreasing rate. The SCSS of coating/interlayer shows the similar trends. Furthermore when the thickness increases to 0.6mm or above, the SCSS of coating/interlayer achieve a platform value and the SCSS of interlayer/substrate do not further decreases. And then, the position of maximum shear stress is moved away from interlayer/substrate to coating/substrate and the maximum shear stress of the interlayer decreases with the increase of thickness. Finally, in present work, the optimal elastic modulus (1×1012Pa) and thickness (0.6mm) of interlayer is summarized.

Burnout conditions for flow of boiling water in vertical rod clusters

AbstractThis paper deals with a new concept for predicting burnout conditions for forced convection of boiling water in fuel elements of nuclear boiling reactors.The concept states the importance of considering the ratio of heated channel perimeter to total channel perimeter.The perimeter ratio concept was arrived at from an experimental study of burnout conditions in rod clusters consisting of three rods of 13 mm. outside diameter and 830 mm. heated length. Data were obtained for pressures between 2.5 and 10 kg./sq. cm., surface heat fluxes between 50 and 120 W./ sq. cm., mass flow rates between 0.03 and 0.33 kg./sec., and steam qualities between 0.01 and 0.52.The rod clearance for the experiment were 2 and 6 mm. The diameter of the channel was 41.3 mm. Additional runs were also performed after unheated displacement rods were introduced in the channel. The rod clearance in this case was 6 mm.In the ranges investigated the measured burnout steam qualities at the outlet of the channel decrease with increasing heat flux and decreasing pressure. Furthermore it has been found that the influence of rod clearance is, in the range investigated, of small significance for engineering purposes.It has also been observed that the present burnout steam quality data for the rod clusters are much lower than those earlier obtained for round ducts. This may be explained physically by means of the perimeter ratio concept.It has also been found that the surface shear stress distribution around the channel perimeter and especially the position of maximum shear stress is of great importance for predicting burnout conditions for flow in channels.Finally the new method has helped in understanding and interpreting experimental results which earlier may have seemed inconsistent.