A Newly Discovered Relation between the Critical Resolved Shear Stress and the Fatigue Endurance Limit for Metallic Materials

The chapter introduces a valuable new description of fatigue strength in relation to material properties and thus a new perspective on the overall understanding of the fatigue process. Namely, a relation between the endurance limits and the accompanying values of the critical resolved shear stress (CRSS) for various metallic materials has been discovered by means of a multiscale approach for fatigue simulation. Based on the uniqueness of the relation, there is a strong indication that it is feasible to relate the endurance limit to the CRSS and not to the ultimate strength, as often done in the past.

Tension-Torsion Fatigue Tests on the proton Exchange membrane Nafion 115, used in fuel cells

Fatigue tests under tension-torsion have been carried out on the membrane Nafion 115 (Perfluorosulfonic acid, PFSA). This polymeric material is a main component to construct fuel cells, used as proton exchange membrane. These membranes undergo mechanical loading of tension and torsion during its industrial life. A self-designed machine has been constructed to obtain the fatigue endurance on this polymeric material under tension-torsion and the following conditions: one magnitude for the torsion angle, five initial tensile stresses, room temperature, and environmental relative humidity, and frequency of 1.6 Hz. The experimental results show that fatigue endurance decreases with the increase of tensile stress when the torsion angle remains constant, as well as temperature and relative humidity (both taken at environmental conditions). Fracture surfaces were analyzed by SEM, in order to investigate the principal trends of crack initiation and propagation under this modality of fatigue loading. Se han realizado ensayos de fatiga bajo tensión-torsión en la membrana Nafion 115 (ácido perfluorosulfónico, PFSA). Este material polimérico es un componente principal para la construcción de pilas de combustible, utilizado como membrana de intercambio de protones. Estas membranas se someten a cargas mecánicas de tensión y torsión durante su vida industrial. Se ha construido una máquina de diseño propio para obtener la resistencia a la fatiga de este material polimérico bajo tensión-torsión y en las siguientes condiciones: una magnitud para el ángulo de torsión, cinco tensiones iniciales de tracción, temperatura ambiente y humedad relativa ambiental, y frecuencia de 1,6 Hz. Los resultados experimentales muestran que la resistencia a la fatiga disminuye con el aumento de la tensión de tracción cuando el ángulo de torsión se mantiene constante, así como la temperatura y la humedad relativa (ambas tomadas en condiciones ambientales). Las superficies de fractura fueron analizadas por SEM, con el fin de investigar las principales tendencias de iniciación y propagación de grietas bajo esta modalidad de carga de fatiga.

Fretting Fatigue - An Integral Simulation Approach to Strengthening by Shot Peening

Fretting fatigue is a limiting factor in blade attachment de sign for turbomachinery. Shot peening is known to be a strength increasing measure against fatigue. It is applied not only to free surfaces of components under fatigue but also to contacting surfaces subject to fretting fatigue. The present work examines the effect of shot peening on fretting fatigue resistance in fixtures of rotor blades. The chosen integral approach allows the consideration of shot peening and subsequent fretting loading in one simulation. Thus, the residual stresses and material strengthening as well as the surface wavi ness due to the shot peening process are included in the fretting fatigue simulation. To achieve reasonable computation times a 2D model, calibrated to a 3D unit cell model, is employed. A comparative study on fatigue endurance limits is presented for the cases with and without shot peening. With view to the differ ent failure mechanisms met in these two cases, an initiation eval uation is carried out with the Sines criterion for the un-peened condition; a fracture mechanics approach is shown to be neces sary for the evaluation of the shot peened condition.

Contribution In Determining The Fatigue Endurance of Slide Diamond Burnishing AISI52100 Steel Components

The present paper is an investigation on the effect of slide diamond burnishing on the fatigue endurance of a component made of AISI52100 steel. Burnishing operation has been performed on cylindrical specimens using optimal parameters statistically selected such as burnishing force, burnishing feed and number of tool passes. Bending fatigue tests in air at R= -1 and S-N curves have been plotted by incrementing the applied stress from a maximum stress level of about 66% of the ultimate tensile stress to a stress value below which fatigue does not occur. Results show that slide diamond burnishing has increased the fatigue resistance comparing to unburnished specimens. The fatigue endurance is respectively 222 MPa and 190 MPa. At high stress levels, the fatigue resistance improvement is clearly observed and the fatigue trends are in good agreement with those reported in literature. However, the present results are slightly lower and that is attributed to the shoulder fillet value of the specimen. For small fillet radius, fatigue resistance is lowered.

Progress and perspectives in dielectric energy storage ceramics

Dielectric ceramic capacitors, with the advantages of high power density, fast charge-discharge capability, excellent fatigue endurance, and good high temperature stability, have been acknowledged to be promising candidates for solid-state pulse power systems. This review investigates the energy storage performances of linear dielectric, relaxor ferroelectric, and antiferroelectric from the viewpoint of chemical modification, macro/microstructural design, and electrical property optimization. Research progress of ceramic bulks and films for Pb-based and/or Pb-free systems is summarized. Finally, we propose the perspectives on the development of energy storage ceramics for pulse power capacitors in the future.

Features of the electrophysical and mechanical properties of n-component ferroactive solid solutions of composition PZT–PZN–PMN

Study of the fatigue endurance and mechanical strength of solid solutions of the PZT–PZN–PMN system, modified with Ba and Sr, corresponding to the formula (Pb[Formula: see text]Sr[Formula: see text]Ba[Formula: see text] [Ti[Formula: see text]Zr[Formula: see text](Nb[Formula: see text]Zn[Formula: see text] (Nb[Formula: see text]Mg[Formula: see text]]O3, with [Formula: see text] = 0.02 ÷ 0.12; [Formula: see text] = 0.02, [Formula: see text] = 0.0036 ÷ 0.073; [Formula: see text]= 0.385 ÷ 0.430, [Formula: see text]= 0.402 ÷ 0.447 is presented. It is shown that the evolution of the polarization characteristics with an increase in the number of repolarization cycles, [Formula: see text], is characterized by two sections: slow fatigue and logarithmic evolution. It was found that an increase in the strontium content shifts the beginning of the logarithmic stage towards to the large [Formula: see text]. It is shown that an increase in the average grain size decreases the mechanical strength. A conclusion is made about the expediency of using the obtained data in the development of devices operating in power modes.

Fretting Fatigue – An Integral Simulation Approach to Strengthening by Shot Peening

Fretting fatigue is a limiting factor in blade attachment design for turbomachinery. Shot peening is known to be a strength increasing measure against fatigue. It is applied not only to free surfaces of components under fatigue but also to contacting surfaces subject to fretting fatigue. The present work examines the effect of shot peening on fretting fatigue resistance in fixtures of rotor blades. The chosen integral approach allows the consideration of shot peening and subsequent fretting loading in one simulation. Thus, the residual stresses and material strengthening as well as the surface waviness due to the shot peening process are included in the fretting fatigue simulation. To achieve reasonable computation times a 2D model, calibrated to a 3D unit cell model, is employed. A comparative study on fatigue endurance limits is presented for the cases with and without shot peening. With view to the different failure mechanisms met in these two cases, an initiation evaluation is carried out with the Sines criterion for the un-peened condition; a fracture mechanics approach is shown to be necessary for the evaluation of the shot peened condition.