Alternating Bending Load Research Articles

Коррозионная усталость меди в водных средах

The failure of the cooling systems of engines and propellers of the ship poses the serious hazard to passengers and crew. Damage to these units is often caused by corrosion, with localized corrosion being the most dangerous. In the case under consideration, when the metal is simultaneously affected by a corrosive environment and alternating mechanical loads, conditions arise for the behaviour (occurrence) of corrosion fatigue. The prospects of cathodic electrochemical protection of these units are considered in the paper. Since the cooling systems and propellers are made of copper alloys, the effect was studied concerning the potential and composition of the solution on the corrosion of the main component of the structural material — copper. Copper samples with a smooth mechanical pressure concentrator cantilevered in a fluoroplastic electrochemical cell were tested. Alternating bending loads were applied to them, and the number of load cycles before the destruction of the sample (durability) was determined. The experiments were carried out in deaerated solutions of the surfactantly inactive electrolyte NaF, as well as fluoride solutions with additives of surfactants and organic surfactants - benzotriazole. At the same time, an interval of potentials was set, in which the only Faraday process is possible — the reduction of traces of dissolved oxygen. It was found that at potentials less than the zero charge potential, the durability of copper increases significantly. And the introduction of chloride ions and benzotriazole into the solution, on the contrary, leads to a strong decrease in its durability. The potential of zero charge of copper was determined from the measurement data of the differential capacitance of the metal in sodium fluoride solutions with different concentrations of fluoride. The increase in the durability of the metal is explained by the occurrence of hydrogen bonds between the water molecules adsorbed by the hydrogen atoms. This manifests the so-called negative Rebinder effect. For electrochemical protection, the potential range is recommended below the potential of zero charge of the metal, but above the potential of water decomposition. For cooling systems, it is recommended to use deionized water as a coolant.

Analysis of injector spring damage to determine maintenance management diesel engine at PLTD Ampenan

The injector spring in cylinder #2 of a diesel engine in Ampenan PLTD which is operated by PT. X damaged. After visual inspection, a helical spring of the injector was broken. The spring broke in the lower part, in winding 2 of the spring. Before the damage was known, with a diesel load of 1100 kW, the exhaust manifold the cylinder #2 was glowing. Root cause analysis of the broken spiral spring was carried out by visual observation, metallography, and maintenance management analysis. Results indicated that the damaged of the broken injector spring based on visual observation of the helical spring was due to alternating bending loads. The fracture angle was at 450 indicated a bending load. Benchmark shows the beginning of the fault, followed by a static fracture. Metallographic and microstructure examination results found too many sulphides possibly making the formation of the onset of the fatigue. To minimize the damage, the sulphide amount of the spring must be reduced, and the spring injector material must be redesigned. Maintenance management must check every time the new spring is received and the cam lobe dimensions and wear of the roller must be lifted every 1000 hours.

Influence of Alternating Short-Cycle Bending on the Mechanical Properties of Copper, α-Titanium and the Mild Steel DC01

The influence of alternating bending loads as they occur during roller levelling on the mechanical properties of sheet metals is not yet fully understood. A detailed knowledge of the influence of the commonly used levelling process on the resulting properties of sheet material is needed in particular for the design of subsequent processes with narrow process windows. To investigate the mechanical property changes during loading conditions similar to roller levelling, sheet samples of mild steel DC01, α-titanium and pure copper (CU-DHP) were subjected to alternating bending loads with different amplitudes for up to 9.5 bending cycles. An isotropic hardening behavior according to a Voce description could be shown for the DC01 deep drawing steel with a strong dependence on the load amplitude applied per cycle. A strengthening behavior that depends on the loading amplitude could be observed for α-titanium as well. In contrast, pure copper featured minor changes with a tendency to soften. For all three materials, changes in springback were present after one bending cycle.

Determination of fatigue resistance characteristics of helicopter rotor blade

This paper presents an investigation of the fatigue resistance testing of structural elements of the helicopter by the example of testing of helicopter rotor blades samples. Endurance tests of components and structural elements of aviation equipment are the laboratory reproduction of external influences corresponding to the typical operating conditions, cyclic loading and functioning. However, these tests do not include research related to the gradual accumulation of damage leading to the emergence and propagation of cracks and construction failure. In this regard, a special interest is learning the process of cracks growth during the specimens’ full-scale tests. A brief description of the blades endurance tests process with simultaneous video shooting has been given. Stretching static load is applied to the samples, after those samples are additionally loaded by alternating bending moment. Videos of the cracks growth are processed and the data about the time of subcritical crack growth are obtained. This information is displayed as a graph. The control and measurement system is considered which is used in the process of testing for recording of values of stress occurring in tested specimens because of alternating bending load applied to them. The characteristics of fatigue strength are determined, fatigue graph is plotted, durability arithmetic mean and standard deviation are determined, assemblage of durability distribution curves, assemblage of fatigue curves and endurance distribution curve are plotted, endurance limit arithmetic mean and standard deviation are determined. The achieved results have importance for the prediction of the safe operation term of the helicopter rotor blades.

Effect of Heat Treatment on the Mechanical Behavior and Fracture of TiNi Alloy

The mechanical properties and fracture of a TiNi alloy (Ti-55.8 wt % Ni) have been investigated under vacuum heat treatment at 700–1200°C. Three-point bending and low cycle fatigue tests were conducted on heat treated wire samples under extreme loading conditions (large strains and alternating bending loads) to determine the effect of the annealing temperature on the superelastic behavior of the alloy. It was found that an increase in the heat treatment temperature leads to grain coarsening in the alloy, but the coarsening effect on its superelastic behavior is insignificant at low bending strains (4.0–4.5%). With heat treatment temperature variation from 700 to 1200°C, the shape of the alloy stress-strain curves remains almost unchanged for all bended samples, but with increasing heat treatment temperature the martensitic shear stress and residual strain slightly increase. In low cycle bending tests, the alloy ductility reduces significantly after heat treatment above 1100°C. Fractographic analysis of the tested alloy samples revealed different fracture surface structures depending on the heat treatment conditions, but the same fracture mechanism. In all cases, fracture occurs by quasi-cleavage, and the microcrack nucleus is associated with Ti2Ni/Ti4Ni2O inclusion particles or surface defects. The general results indicate the possibility of diffusion welding of TiNi alloys at a temperature of 1000–1100°C, without pronounced changes in their mechanical properties and ductility.

Numerical Analysis of ACSR Conductor–Clamp Systems Undergoing Wind-Induced Cyclic Loads

Submitted to wind-induced vibrations, overhead conductors are vulnerable to fatigue damage, especially at restraining fixtures such as the suspension clamp. This paper proposes an efficient finite-element modeling approach providing a full 3-D representation of both the conductor and suspension clamp. Validation based on experimental data shows the precision of the approach. An in-depth model response analysis also demonstrates its ability to describe inter-wire and conductor–clamp contact interactions. Finally, a study of conductor stress distributions reveals that in critical regions, conductor wires mostly sustain alternating bending loads.

Fatigue resonant tests on drill collar rotary shouldered connections and critical thread root identification

A fatigue test series on a drill collar rotary shouldered connection, thread type 5-1/2 FH MOD, was performed with a dedicated alternating bending resonant test rig. Compared to a quasi-static testing approach, the dynamic loading allowed high testing frequency and a relatively light supporting structure. Crack initiation was identified as the onset of a discrepancy between two strain gauge signals which were monitored throughout the test. A through-wall crack condition was assumed as the effective fatigue failure. The stress distribution in the connection was then analysed with a finite element plane harmonic axisymmetric model, taking into account both the initial make-up torque and the alternating bending load during the test. In these simulations, the most critical stress between the pin or box, in terms of fatigue, mainly depended on the preload. The modelled contact behaviour of the incomplete threads of the box played a significant role in predicting the position of the crack initiation thread root, which was then compared with the test results.

An incremental analysis of a deep drawing steel’s material behaviour undergoing the predeformation using drawbeads

Nowadays lightweight design in metal forming processes leads to complex deep drawing geometries, which can cause multiple damages. Therefore, drawbeads are one way to regulate and control material flow during the forming process. Not only in research, but also in industrial practice, it could be determined that material is work hardened passing drawbead geometries. It particularly means when material is pre-deformed with tensile and alternating bending loads. This incident also gives the opportunity to utilize it in a reasonable way if examined properly. To investigate these findings, a process oriented and comprehensive analysis of the material behaviour during these forming operations is needed.In this paper, sheet metal strips are linearly drawn through a drawbead and stopped after passing the drawbead. Within this forming operation, the material undergoes non-linear straining before reaching the in-plane position again. Here, the process will be stopped to investigate a permanent strengthening local along the sheet thickness. Therefore, microhardness measurements are realized before and after passing the drawbead. Because of its common use and its wide known material data, a deep drawing steel DC will be used for these studies. Additionally, the strategy is applied to advanced high strength steel.

Studying and Mastering the Controlled Rolling of Sheet for Side Members

The production of sheet for side members ‐ a product delivered to automobile factories in Russia and Belarus ‐ has been successfully introduced on the 800 mill at the Orsk-Khalilovo Metallurgical Combine (Nosta company). In accordance with the orders the combine has received, the sheet is made in widths of 310‐430 mm from steels 15GYuT, 20GYuT, 17G2(17G1), 13G2AF, 10KhSND, and 10KhSNDA. As is known, sheet produced for the side members of automobiles must have high indices for strength, ductility, cold resistance, and weldability, since the members are subjected to dynamic loads (mainly alternating bending loads) while in service, and needs to meet the requirements of TU 14-1-4632‐93. The technology used to make the sheet involves producing the steel in electric-arc furnaces, rolling ingots on a 1250 blooming mill, heating the blooms in the heating furnaces of an 800 mill, and rolling them on that mill with a force of 8.4 MN. The 800 mill consists of a reversing two-high universal roughing stand, a continuous finishing train of four-high stands, and a water-air cooling unit for accelerated cooling of the sheet. The sheet is heat-treated (normalized) after rolling. The goal of the project we undertook was to develop and successfully introduce a technology for the production of universal sheet that can be used to make automobile side members. We wanted the heat treatment of the sheet to take place during the final stage of the rolling operation in the normalization temperature range ‐ a range of temperatures somewhat higher than the critical temperature (Ac 3  820‐870°C for most low-alloy steels). This would make it possible to obtain a set of properties similar to those of normalized metal [F. Khaisterkamp, K. Khulka, Yu. I. Matrosov, et al., Niobium-Bearing Low-Alloy Steels. “Intermet Engineering,” St. Petersburg, Moscow (1999)]. Studies were performed on steel 20GYuT, which was designed for the fabrication of side members at the Kama River Truck Plant. To obtain rolled products of the desired types, we make steel 20GYuT with a carbon equivalent C e = 0.37‐0.47% (C e = C + Mn/6 + Si/24, where C, Mn, and Si are the mass contents of carbon, manganese, and silicon in the steel, %). The semifinished products are heated in the walking-beam furnaces of the 800 mill to temperatures of 1240‐1260°C and then rolled on the mill (the finishing temperature in the continuous finishing train is no higher than 850°C). The rolled products then undergo forced cooling in a water-air cooling system to a temperature no higher than 760°C. This is done to alleviate striation in the structure of the sheet metal. The rolled products are normalized at 940‐970°C and pickled in the hot-pickling section of the 800 mill. It was found that when the existing regime is used on the 800 mill to roll sheet of steel 20GYuT with a carbon equivalent greater than 0.39%, the strength and hardness properties of the sheet are good but its ductility and toughness characteristics do no satisfy the requirements of TU 14-1-4632‐93. Taking this into account, we used blooms from regular production heats with C e < 0.39% when we devised new regimes for normalization rolling. The blooms were rolled in the continuous finishing train of the 800 mill while varying the finishing temperature within the range from 850 to 950°C and avoiding use of the water-air cooling unit. The results of chemical analyses of the experimental heats are shown in Table 1 in comparison to the requirements of TU 14-1-4632‐93. Figures 1 and 2 show the dependence of the strength, ductility, and toughness properties of steel

Microstructure and mechanical properties of ultrafine-grained hardmetals

The interest in ultrafine-grained hardmetals as woodcutting tool materials derives from their excellent mechanical properties compared with those of conventional hardmetals. The aim of this work was to determine the mechanical properties of ultrafine-grained hardmetals and to correlate the measured effects with microstructural parameters. The ultrafine-grained hardmetals (WC grain size ⩽0.3 μm) investigated consisted of different WC powders and different binder systems: Co and complex binder systems. The mechanical properties of ultrafine-grained hardmetals were tested under two different loading conditions: monotonically increasing and cyclic alternating bending loads. It could be shown that the binder systems of different compositions show different behaviours under cyclic loads. Ultrafine-grained hardmetals with Co binder exhibit high bending strength values, but high fatigue sensitivity. Ultrafine-grained hardmetals with complex binders show lower bending strength values but their sensitivity to fatigue is lower. This implies that different damaging mechanisms exist for ultrafine-grained hardmetals with Co and complex binders.

Crack initiation, crack growth and fracture behaviour of large diameter pipes with circumferential defects under internal pressure and superimposed alternating bending load : Stoppler, W., Sturm, D., Hippelein, K. and de Boer, A. Nucl. Engng Design (1996) 160, (1-2-I), 137–152

Crack initiation, crack growth and fracture behaviour of large diameter pipes with circumferential defects under internal pressure and superimposed alternating bending load : Stoppler, W., Sturm, D., Hippelein, K. and de Boer, A. Nucl. Engng Design (1996) 160, (1-2-I), 137–152

Crack initiation, crack growth and fracture behaviour of large diameter pipes with circumferential defects under internal pressure and superimposed alternating bending load

Pipes made of steel 20 MnMoNi 5 5 and MnMoNiV-special melt having an external diameter of 800 mm, wall thickness of 47 mm, and length of up to 5500 mm were provided with circumferential defects of defined length and depth. They were loaded by internal pressure and a superimposed alternating bending moment. During the tests deformation and crack growth were determined in the wall thickness and circumferential direction. Pipes with an outer diameter of 226 mm and a wall thickness of 20 mm were used to investigate the leak-before-break behaviour in the dynamic sphere. These pipes were also made of steel 20 MnMoNi 5 5 and a MnMoNiV-special melt and were loaded with internal pressure and an alternating bending moment. The excitation took place at the resonance frequency of the pipes. The pipes also contained circumferential defects of defined length and depth.

Crack growth and fracture behaviour of pipes with circumferential defects under internal pressure and superimposed alternating bending load

Pipes made of 20 MnMoNi 5 5 steel and an MnMoNiV special melt, with an external diameter of 800 mm, wall thickness of 47 mm and length of up to 5500 mm, were provided with circumferential defects of defined length and depth. The pipes were loaded by internal pressure and a superimposed alternating bending moment. During the tests, deformation and crack growth were determined in the wall thickness and circumferential direction, and these were compared with calculated values. Pipes with an outer diameter of 226 mm and a wall thickness of 20 mm were used to investigate the leak-before-break behaviour in the dynamic sphere. These pipes also were made of 20 MnMoNi 5 5 steel and an MnMoNiV special melt, and were loaded with internal pressure and an alternating bending moment. The excitation took place at the resonance frequency of the pipes. The pipes also contained circumferential defects of defined length and depth.

Crack growth tests on pipes with circumferential defects under internal pressure and superposed alternating bending load

Abstract Pipes made of steel 20 MnMoNi 5 5 having an external diameter of 800 mm, wall thickness of 47 mm and length of 5 m were provided with circumferential flaws in defined length and depth. They were loaded simultaneously by internal pressure, alternating or pulsating external bending moment. Deformation and the crack growth were determined in the wall thickness and circumferential direction and compared with calculated values.