Low Frequency Fatigue Tests Research Articles

Corrosion resistance and other utility properties of selected austenitic nodular cast irons

This study deals with the evaluation of corrosion resistance and other utility properties of selected austenitic nodular cast irons and their comparison with other (non-austenitic) nodular cast irons. For the investigations, two types of austenitic nodular cast iron were selected: nickel-manganese nodular cast iron EN-GJSA-XNiMn13-7 and nickel-chromium nodular cast iron EN-GJSA-XNiCr20-2. Basic mechanical properties, such as yield strength, tensile strength, elongation, absorbed energy and hardness, were evaluated using mechanical tests. The fatigue limit was determined using low-frequency fatigue tests. Corrosion properties, such as average corrosion rate, corrosion potential and corrosion current density, were determined by the exposure immersion test and the electrochemical potentiodynamic polarisation test. Both corrosion tests were performed in a 3.5% NaCl solution (to simulate seawater) at room temperature. The results of mechanical, fatigue and corrosion tests show that austenitic nodular cast irons have lower strength and fatigue properties but significantly higher plastic properties and corrosion resistance compared to non-austenitic nodular cast irons.

ANALYSIS OF THE CAUSES OF DEGRADATION PRESTRESSED REINFORCED CONCRETE RAILWAY SLEEPERS

Railway sleepers are a very important component of the transport infrastructure, they are dynamically loaded and subject to many stresses that can cause degradation, shorten their service life and also reduce the safety of rail transport. The subject of the study was damaged-highly cracked prestressed concrete railway sleepers, 10 years old, sampled on the railway line route. The results of the investigations carried out to determine the characteristics of the concrete are presented. In order to determine the cause of the damage, low-frequency fatigue tests were also carried out in the laboratory to measure vibrations and to check for cracks. By checking the microstructure of the concrete with SEM-SEI and EDS electron microscopy, we found that the cracks were caused by chemical reactions in the hydrated concrete. The results of the analyses carried out can improve the criteria for the inspection and assessment of the serviceability of degraded railway sleepers during their service life.

Study of the fatigue behaviour of synthetic nodular cast irons at low and high frequency cyclic loading

The paper presents the results of low and high frequency fatigue tests carried out on nodular cast iron. The specimens of synthetic nodular cast irons from three different melts were studied in the high cycle fatigue region (from 105 to 108 cycles) using fatigue experimental equipments for low and high frequency cyclic loading. Low frequency fatigue tests were carried out at frequency f ≈ 120 Hz using the fatigue experimental machine Zwick/Roell Amsler 150HFP 5100. High frequency fatigue tests were carried out at frequency f ≈ 20 kHz using the ultrasonic fatigue testing device KAUP-ZU. Both of them were carried out at sinusoidal cyclic push-pull loading (stress ratio R = -1) at ambient temperature (T ≈ 20 °C). The relationship σa = f (N) and fatigue strengths were determined experimentally; mechanical properties, microstructures and fracture surfaces were investigated.

Comparison of low and high frequency fatigue tests

Abstract The paper presents the results of low and high frequency fatigue tests carried out on nodular cast iron. The specimens of synthetic nodular cast irons from three different melts were studied in the high cycle fatigue region (from 105 to 108 cycles) using fatigue experimental equipments for low and high frequency cyclic loading. Low frequency fatigue tests were carried out at frequency f ≈ 120 Hz using the fatigue experimental machine Zwick/Roell Amsler 150HFP 5100; high frequency fatigue tests were carried out at frequency f ≈ 20 kHz using the ultrasonic fatigue testing device KAUP-ZU. Both fatigue tests were realised at sinusoidal cyclic push-pull loading (stress ratio R = −1) at ambient temperature (T = 20 ± 5 °C).

Comparison of Fatigue Properties of Nodular Cast Iron at Low and High Frequency Cyclic Loading

The paper deals with comparison of the fatigue properties of nodular cast iron at low and high frequency fatigue testing. The specimens from three melts of nodular cast iron with different microstructure and mechanical properties were used for experiments. Fatigue tests were carried out at low and high frequency sinusoidal cyclic push-pull loading (stress ratio R = –1) at ambient temperature (T = 20 ± 5°C). Low frequency fatigue tests were carried out using the fatigue experimental machine Zwick/Roell Amsler 150HFP 5100 at frequency f≈ 120 Hz; high frequency fatigue tests were carried out using the ultrasonic fatigue testing device KAUP-ZU at frequency f≈ 20 kHz.

Fatigue tests of nodular cast iron at low and high frequency cyclic loading

The paper presents the results of fatigue tests of nodular cast iron at low and high frequency cyclic loading. For comparison of fatigue properties, the specimens from three melts of nodular cast iron with different microstructure and mechanical properties were used. Fatigue tests were carried out at low and high frequency sinusoidal cyclic push-pull loading (stress ratio R = –1) at ambient temperature (T = 20 ± 5°C). Low frequency fatigue tests were carried out at frequency f ≈ 120 Hz; high frequency fatigue tests were carried out at frequency f ≈ 20 kHz.

Fatigue Resistance of Low Alloy Steel after Shot Peening

It is well known that shot peening is able to increase the fatigue strength and endurance of metal parts, especially with a steep stress gradient due to a notch. This positive effect is mainly put into relation with the ability of this treatment to induce a compressive residual stress state in the surface layer of material and to cause surface work hardening [1]. In this paper shot peening is applied on the 40NiCrMo7 low alloy steel and subsequently the surface was re-peened with glass beads to decrease the final surface roughness. Roughness, hardness and residual stress analysis were used for characterizing the strongly deformed surface layer. Low frequency fatigue tests were carried out to evaluate the effect of the applied treatment on fatigue life in the high cycle region. Results show fatigue strength increase in the high cycle region after the shot peening surface treatment.

Strain-induced corrosion cracking behaviour of low-alloy steels under boiling water reactor conditions

The strain-induced corrosion cracking (SICC) behaviour of different low-alloy reactor pressure vessel (RPV) and piping steels and of a RPV weld filler/weld heat-affected zone (HAZ) material was characterized under simulated boiling water reactor (BWR)/normal water chemistry (NWC) conditions by slow rising load (SRL) and very low-frequency fatigue tests with pre-cracked fracture mechanics specimens. Under highly oxidizing BWR/NWC conditions (ECP ⩾+50 mV SHE, ⩾0.4 ppm dissolved oxygen), the SICC crack growth rates were comparable for all materials (hardness <350 HV5) and increased (once initiated) with increasing loading rates and with increasing temperature with a possible maximum/plateau at 250 °C. A minimum K I value of 25 MPa m 1/2 had to be exceeded to initiate SICC in SRL tests. Above this value, the SICC rates increased with increasing loading rate d K I /d t, but were not dependent on the actual K I values up to 60 MPa m 1/2. A maximum in SICC initiation susceptibility occurred at intermediate temperatures around 200–250 °C and at slow strain rates in all materials. In contrast to crack growth, the SICC initiation susceptibility was affected by environmental and material parameters within certain limits.

Corrosion fatigue crack growth behaviour of low-alloy reactor pressure vessel steels under boiling water reactor conditions

The corrosion fatigue crack growth behaviour of different low-alloy reactor pressure vessel (RPV) steels and weld filler/heat-affected zone materials was systematically characterized under simulated boiling water reactor normal water and hydrogen water chemistry conditions by low-frequency fatigue tests with pre-cracked fracture mechanics specimens. The experiments were performed in oxygenated or hydrogenated high-purity or sulphate/chloride containing water at temperatures from 150 to 288 °C. In this paper, the observed synergistic effects of environmental, material and loading parameters on the environmental acceleration of fatigue crack growth in low-alloy RPV steels are discussed in the context of the Ford–Andresen model. Additionally, the adequacy and conservatism of the current “ASME XI reference fatigue crack growth curves” of the ASME Boiler & Pressure Vessel Code are critically reviewed and assessed on the basis of the gathered experimental data base and this model. Based on the observed cracking behaviour and the Ford–Andresen model, a simple time-domain superposition model is suggested, which could reduce most of the undue conservatism and eliminate uncertainties of the existing codes and therefore serve as a basis for the development of improved reference fatigue crack growth curves.

Low cycle fatigue and fatigue crack growth behaviour of Sn–Ag eutectic solder

Low cycle fatigue tests on as‐cast Sn–Ag eutectic solder (96.5Sn–3.5Ag) were carried out using a non‐contact strain controlled system at 20°C with different frequencies (10−3–1 Hz). Steps at the boundaries of Sn‐dendrites were found to be the initiation sites for microcracks in the case of low frequency fatigue tests, while for high frequency tests, cracks predominantly initiated at the boundaries of subgrains formed within Sn‐dendrites. The link up of these cracks and the propagation of cracks inside the specimen occurred both transgranularly through Sn–Ag eutectic phases, and intergranularly along Sn‐dendrite boundaries and/or subgrain boundaries. Propagation of stage II cracks for various frequencies could be characterized by theC*‐parameter.

Influence of frequency on low cycle fatigue behavior of Pb-free solder 96.5Sn–3.5Ag

Low cycle fatigue (LCF) tests on as-cast Sn–Ag eutectic solder (96.5Sn–3.5Ag) were carried out using the non-contact strain controlled system at 20 °C with different frequencies (10 −3 –1 Hz). The LCF behavior in this frequency range followed the Coffin–Manson equation. The fatigue ductility coefficient was found to be influenced by frequency. Frequency-modified Coffin–Manson model successfully described frequency effects on the fatigue behavior. Steps at the boundaries of Sn-dendrites were the initiation sites for microcracks in the case of low frequency fatigue tests, while for high frequency tests, cracks predominantly initiated at the boundaries of subgrains formed in Sn-dendrites. The link up of these cracks and the propagation of cracks inside the specimen occurred both transgranularly through Sn–Ag eutectic phases, and intergranularly along Sn-dendrite boundaries and/or subgrain boundaries. The dislocation rearrangement (polygonization) is considered to be the cause of this small grain formation.

The Effect of Sulfate on Environmental Cracking in Boiling Water Reactors Under Constant Load or Fatigue

Abstract Low-frequency fatigue tests at load ratios 0.8 and 0.9 and constant load tests were run on sensitized type 304 (UNS S30400) stainless steel (SS), type 316 nuclear grade (NG) SS and the nickel-base alloy 600 (UNS N06600) in simulated boiling water reactor (BWR) environments. The environments simulated normal water chemistry (NWC) and hydrogen water chemistry (HWC) with 15 or 5 ppb O2, clean or with sulfate. Oxygen enhanced cracking of type 304 SS and alloy 600, but not type 316 NG, under fatigue load conditions. Under constant load conditions, crack propagation was always very low in clean environments. Sulfate enhanced cracking in all three materials, most in type 304 SS and least in type 316 NG. Crack enhancement due to 0.1 ppm sulfate was worse under constant load than under fatigue load conditions, for type 304 SS in NWC up to a factor of 100 in constant load and up to a factor of 10 in fatigue.

短繊維強化アイオノマー複合材料の引張および疲労特性

A study has been made on the tensile and fatigue properties of discontinuous carbon fiber reinforced ionomer composites oriented unidirectionally by hand-alignment technique.The fiber-matrix interfacial shearing strength calculated from the rule of mixture showed considerably lower value than that expected from the good adhesive ionomer matrix. The interfacial shearing strength decreased remarkably with increasing fiber length. It is considered that the fiber-matrix interfacial debonding can arise from the stress concentration at the fiber end, since the fiber overlaps are not perfectly in discontinuous fiber composites, and consequently, the interfacial shearing strength takes a very low value. It seems that the fiber-matrix contacts and the fiber overlaps decrease with increasing fiber length in discontinuous fiber composites oriented unidirectionally by hand-alignment technique.The low frequency fatigue tests on the unidirectionally oriented composites showed an excellent fatigue strength without braking for N=4×103 at 65% of ultimate tensile strength.The dynamic modulus of the fatigued Zn-type ionomer composite showed a 50% decrease against the virgin dynamic modulus at room temperature. The reduction of dynamic modulus may be related to the fiber-matrix debonding. On the other hand, the residual strength retained 90% of the virgin ultimate tensile strength. Even if the interfacial debonding occurs, the fiber could still carry load by the interfacial friction.