Fatigue Behaviour of GFRP Reinforced Beams

This article deals with the influence of fatigue loading on the behaviour of GFRP (Glass Fibre Reinforced Polymers) reinforced concrete elements. The aim of the experimental programme is to quantify the effect of fatigue loading on the mechanical properties of GFRP reinforced beams subjected to flexure. The proposed element was a beam simulating the cut-out part of a reinforced concrete slab directly subjected to traffic loading. The dimensions and the amount of reinforcement were adjusted regarding the possibilities of the testing laboratory and to ensure the repeatability of the test. Two different fatigue loading schemes were experimentally verified: a) a constant load amplitude, b) a gradually increasing amplitude. The applied fatigue load with a constant amplitude was designed to achieve a fatigue life of the element ≥ 2×106 cycles. In the case of fatigue loading with an increasing amplitude, the load was increased every 50,000 cycles by 5% of the maximum load in the cycle. The resulting fatigue life was compared to the expected fatigue life determined according to Miner's rule on linear fatigue summation.

Analysis of the Deceleration Methods of Fatigue Crack Growth Rates under Mode I Loading Type in Pearlitic Rail Steel

The paper presents a comparison of the results of the fatigue crack growth rate for raw rail steel, steel reinforced with composite material—CFRP—and also in the case of counteracting crack growth using the stop-hole technique, as well as with an application of an “anti-crack growth fluid”. All specimens were tested using constant load amplitude methods with a maximum loading of Fmax = 8 kN and stress ratio R = smin/smax = 0.1 in order to analyze the efficiency of different strategies of fatigue crack growth rate deceleration. It has been shown that the fatigue crack grows fastest in the case of the raw material and slowest in the case of “anti-crack growth fluid” application. Additionally, the study on fatigue fracture surfaces using light and scanning electron (SEM) microscopy to analyze the crack growth mechanism was carried out. As a result of fluid activity, the fatigue crack closure occurred and significantly decreased crack driving force and finally resulted in fatigue crack growth decrease.

Static and Flexural Fatigue Behavior of GFRP Pultruded Rebars

This paper presents the experimental results of composite rebars based on GFRP manufactured by a pultrusion system. The bending and radial compression strength of rods was determined. The elastic modulus of GFRP rebars is significantly lower than for steel rebars, while the static flexural properties are higher. The microstructure of the selected rebars was studied and discussed in light of the obtained results—failure processes such as the delamination and fibers fracture can be observed. The bending fatigue test was performed under a constant load amplitude sinusoidal waveform. All rebars were subjected to fatigue tests under the R = 0.1 condition. As a result, the S-N curve was obtained, and basic fatigue characteristics were determined. The fatigue mechanism of bar failure under bending was further analyzed using SEM microscopy. It is worth noting that the failure and fracture mechanism plays a crucial role as a material quality indicator in the manufacturing process. The main mechanism of failure under static and cyclic loading during the bending test is widely discussed in this paper. The results obtained from fatigue tests encourage further analysis. The diametral compression test reflects the weakest nature of the composite materials based on the interlaminar compressive strength. The proposed methodology allows us to invariantly describe the experimental transversal strength of the composite materials. Considering the expected durability of the structure, the failure mechanism is likely to significantly improve their fatigue behavior under the influence of cyclic bending. The reasonable direction of searching for reinforcements of composite structures should be the improvement of the bearing capacity of the outer layers. In comparison with steel rebars (fatigue tensile test), the obtained results for GFRP are comparable in the HCF regime. It is worth noting that in the near fatigue endurance regime (2–5 × 106 cycles) both rebars exhibit similar behavior.

An Investigation on Flexural Fatigue Behavior of CFRP Quasi-Isotropic Laminates

In this study, AS4/914 grade carbon fibre reinforced plastic (CFRP) laminates with two different quasi-isotropic (QI) layup sequences are compared for their performance under four point bend flexure fatigue loads. The QI laminates were designated and fabricated as Laminate-1 (L1) [0/45/-45/90]2S and Laminate-2 (L2) [0/90/45/-45]2S, respectively. These laminates were designed, such that the 0° layers are placed at a similar position in both the laminate systems by changing the other layers. During the test, load and displacement data was monitored online along with instantaneous number of constant load amplitude (CLA) fatigue cycles to calculate the stiffness degradation. Three load levels of 90%, 80%, and 70% of the ultimate flexure strength (UFS) were chosen for assessing the flexure fatigue behavior of the laminates. A few tests were also attempted under variable amplitude loads: (i) high amplitude cycles followed by low amplitude and (ii) low amplitude cycles followed by high amplitude to examine load sequence effect on fatigue life, if any, as compared to the fatigue life under CLA. It has been observed that the laminate L1 performs better under higher amplitudes, while the laminate L2 shows increased life under lower load and variable amplitudes. The results obtained in the form of data plots and failure modes, supported by microscopic images, are discussed in the paper.

Fatigue Life for Type 316L Stainless Steel under Cyclic Loading

The paper presents the determination of fatigue life of 316L stainless steel at room temperature. Plenty of steel in the world has been investigated for a lot of application in the science and technology market. The mechanisms of fatigue of 316L stainless steels were studied and investigated. Fatigue tests of specimens were performed in accordance with ASTM E466-96. The fatigue tests were performed in constant load amplitude, constant frequency of 5 Hz with load ratio R=0.1. Fracture surface of specimens were examined by using Scanning Electron Microscope (SEM). The results showed that the endurance fatigue limit of 316L stainless steel was 146.45 MPa.

Fatigue Crack Growth of Duplex Stainless Steel Castings at 4 K

Constant-load-amplitude stage II fatigue crack growth rates at 4 K were measured for duplex stainless steel castings. The results show that at a ΔK of 60 MPa•m1/2, da/dN = 7.6 × 10−4 mm/cycle for an alloy with 1 percent ferrite. For an alloy with 8 percent ferrite, da/dN is 35 percent, and for an alloy with 29 percent ferrite, da/dN is 260 percent greater than for the 1 percent ferrite alloy. However, the exponent in the Paris equation does not change appreciably (less than 18 percent) as the ferrite content changes from 1 to 29 percent.