M. W. Tofique, A. Löf, C. Millward, Z. Günther. Testing and calculation of impact fatigue strength of Flap-X and SS 716 flapper valve steel grades / trans from Engl. M. A. Fedorova

During the operation of reciprocating compressors, the flapper valve opens and closes under fluid pressure and flow. As it closes, it strikes against the valve seat, generating stresses and noise. This cycle of loading produces bending and impact fatigue stresses in the reed. This load pattern is repeated billions of times during the service life of a compressor and it defines the service life and reliability. The goal of this study was to calculate the impact fatigue strength of the Flap-X and the SS 716 grades and, to provide the compressor manufacturers with the information they can use to specify a steel grade to be used in their compressors, for reliable service. Impact fatigue tests were conducted on a custom-built impact fatigue test rig that used air pulses to produce movement of the reed valves manufactured by a major European compressor manufacturer Nidec Global appliance GmbH, at a frequency of 315 Hz and pulse width of 2,2 milliseconds. The testing was conducted according to the staircase test method detailed in the International Standard SS-ISO 12107:2012. The impact fatigue strength of the Flap-X and SS 716 steel valves was calculated in terms of the impact velocity according to the modified staircase test method in the standard. The test results and their statistical analysis showed that the impact fatigue strength of the Flap-X grade was higher compared to the SS 716 grade. The calculation and testing of the impact fatigue strength of the flapper valve steel grades could help the compressor designers to select the optimum material for their compressor designs, to provide reliable service. The higher impact fatigue strength of the Flap-X grade, lower failure rate and longer impact fatigue life will allow the compressor manufacturers to design thinner valves, as Flap-X can sustain higher impact fatigue stresses reliably for longer time and, at the same time help reduce noise, as thinner valves produce less noise for a given pressure and frequency.

Fatigue Strength Analysis of S34MnV Steel by Accelerated Staircase Test

This paper presents the reliability estimation of fatigue strength of the material used for crank throw components. The material used for crank throw components is forged S34MnV steel and subsequently heat-treated by normalising and tempering. High cycle fatigue testing under fully reversed cycling (R = −1) was performed to determine the fatigue limit of the material. The staircase test method is used to obtain accurate values of the mean fatigue limit stress until a number of cycles up to 1E7 cycles. Subsequently, the fatigue test results depend strongly on the stress step and are evaluated by the Dixon-Mood formula. The values of mean fatigue strength and standard deviation predicted by the staircase method are 282 MPa and 10.6MPa, respectively. Finally, the reliability of the design fatigue strength in some selected probability of failure is calculated. Results indicate that the fatigue strength determined from accelerated staircase test is consistent with conventional fatigue testing. Furthermore, the proposed method can be applied for the determination of fatigue strength and standard deviation for design optimisation of S34MnV steel.

Motor Skill Training Promotes Sensorimotor Recovery and Increases Microtubule-Associated Protein-2 (MAP-2) Immunoreactivity in the Motor Cortex after Intracerebral Hemorrhage in the Rat

Motor skill learning may induce behavioral and neurophysiological adaptations after intracerebral hemorrhage (ICH). Learning a new motor skill is associated with dendritic reorganization and requires protein synthesis and expression of MAP-2. The purpose of this study was to evaluate motor performance and expression of MAP-2 in the motor cortex of rats submitted to intracerebral hemorrhage model (ICH) and skill task training (SK) or unskilled training (US) during 4 weeks. The Staircase test was used for behavioral evaluation, and relative optical densities and morphometrical analysis were used to estimate MAP-2 immunoreactivity and parameters of brain tissue in both motor cortices. Results show that skill task training performed with the impaired forelimb was able to increase MAP-2 immunoreactivity in the motor cortex either in sham or in ICH groups in both cortices: ipsilesional [F(5,35) = 14.25 (P<0.01)] and contralesional hemispheres [F(5,35) = 9.70 (P<0.01)]. ICH alone also increased MAP-2 immunoreactivity despite the absence of functional gains. Behavioral evaluation revealed that ICH-SK group performed better than ICH and ICH-US animals in the Staircase test. Data suggest that motor skill training induces plastic modifications in both motor cortices, either in physiological or pathological conditions and that skill motor training produces higher brain plasticity and positive functional outcomes than unskilled training after experimental intracerebral hemorrhage.