Experimental Investigation Of Fatigue Behavior Of Carbon Fiber Composites Using Fully-Reversed Four-Point Bending Test

Carbon fiber reinforced polymers (CFRP) have become an increasingly notable material for use in structural engineering applications. Some of their advantages include high strength –to–weight ratio, high stiffness-to-weight ratio, and good moldability. Prediction of the fatigue life of composite laminates has been the subject of various studies due to the cyclic loading experienced in many applications. Both theoretical studies and experimental tests have been performed to estimate the endurance limit and fatigue life of composite plates. One of the main methods to predict fatigue life is the four–point bending test. In most previous works, the tests have been done in one direction (load ratio, R, \u3e 0). In the current work, we have designed and manufactured a special fixture to perform a fully–reversed bending test (R = −1). Static four–point bending tests were carried out on three (0°/90°)15 and (± 45°)15 samples to measure the mechanical properties of CFRP. Testing was displacement–controlled at the rate of 10 mm/min until failure. In (0°/90°)15 samples, all failed by cracking/buckling on the compressive side of the sample. While in (± 45°)15 all three tests, no visual fracture or failure of the samples was observed. 3.4 times higher stresses were reached during four–point static bending test of (0° /90°)15 samples compared to (± 45°) 15 Same trend was seen in literature for similar tests. Four–point bending fatigue tests were carried out on (0° /90°) 15 sample with stress ratio, R = −1 and frequency of 5 Hz. Applied maximum stresses were approximately 45%, 56%, 67%, 72% and 76% of the measured yield stress for (0° /90°) 15 samples. There was visible cracking through the thickness of the samples. The expected downward trend in fatigue life with increasing maximum applied stress was observed in S–N curves of samples. There appears to be a threshold for ‘infinite ’ life, defined as 1.7 million cycles in the current work, at a maximum stress of about 200 MPa. The decay in flexural modulus of the beam as it goes under cyclic loading was calculated and it was seen that flexural modulus shows an exponential decay which can be expressed as: E = E0eAN. Four–point bending fatigue tests were carried out on three (±45°)15 samples with stress ratio, R = −1 and frequency of 5 Hz. Maximum applied stress was 85% of the measured yield stress of (±45°)15 samples. None of the samples failed, nor any sign of crack was seen. Tests were stopped once the number of cycles passed 1·7×106. In general, current study provided additional insight into the fatigue and static behavior of polymer composites and effect of fiber orientation in their mechanical behavior

Vertex Disjoint Path in Upward Planar Graphs

The $k$-vertex disjoint paths problem is one of the most studied problems in algorithmic graph theory. In 1994, Schrijver proved that the problem can be solved in polynomial time for every fixed $k$ when restricted to the class of planar digraphs and it was a long standing open question whether it is fixed-parameter tractable (with respect to parameter $k$) on this restricted class. Only recently, \cite{CMPP}.\ achieved a major breakthrough and answered the question positively. Despite the importance of this result (and the brilliance of their proof), it is of rather theoretical importance. Their proof technique is both technically extremely involved and also has at least double exponential parameter dependence. Thus, it seems unrealistic that the algorithm could actually be implemented. In this paper, therefore, we study a smaller class of planar digraphs, the class of upward planar digraphs, a well studied class of planar graphs which can be drawn in a plane such that all edges are drawn upwards. We show that on the class of upward planar digraphs the problem (i) remains NP-complete and (ii) the problem is fixed-parameter tractable. While membership in FPT follows immediately from \cite{CMPP}'s general result, our algorithm has only single exponential parameter dependency compared to the double exponential parameter dependence for general planar digraphs. Furthermore, our algorithm can easily be implemented, in contrast to the algorithm in \cite{CMPP}.Comment: 14 page

Ultra-short of pico and femtosecond soliton laser pulse using microring resonator for cancer cells treatment

A system of microring resonators (MRRs) incorporating with an add/drop filter system is presented in which ultra-short single and multi temporal and spatial optical soliton pulses can be simulated and used to thermalbased killing of abnormal cells, tumor and cancer, applicable in nanomedical treatments. This proposed system uses chaotic signals generated by a bright soliton pulse within a nonlinear MRRs system. Interaction between gold nanoparticles and ultra-short femtosecond and picosecond laser pulses holds great interest in laser nanomedicine. By using the appropriate soliton input power and MRRs parameters, required spatial and temporal signals are generated spreading over the spectrum. Results obtained show that smallest single temporal and spatial soliton pulse with FWHM = 712 fs and FWHM = 17.5 pm could be generated respectively. The add/drop filter system is used to generate high capacity ultra-short soliton pulses in the range of nanometer/second and picometer/second