Volume 60, Issue 3

Pipelines installed in the seabed for long periods suffer from high stress levels, and the sea mud environment is complex because it contains various microorganisms that make pipelines prone to stress corrosion cracking (SCC). In this study, a self-designed stress electrochemical corrosion test device was adopted to ensure the normal growth and metabolism of sulfate-reducing bacteria (SRB). The effects of strain rate on the SCC behavior of X100 pipeline steel with SRB in a simulation solution of sea mud from the South China Sea were studied using the slow strain rate test, electrochemical impedance spectroscopy, and scanning electron microscopy fractography. Results show that SRB can promote the stress corrosion susceptibility of X100 pipeline steel. As strain rate increases, the stress corrosion susceptibility decreases in general. When the strain rate is 5 × 10 −7 × s −1 , the stress corrosion susceptibility is largest and SCC occurs. Under the impact of SRB and strain rate, the stress corrosion fracture mechanism is hydrogen embrittlement mechanism. With the increase in strain rate, the effect of SRB becomes weak and the stress corrosion susceptibility shows a decreasing trend in general. Consequently, SCC does not occur in the specimen and the fracture is dominated by mechanical factors.

The investigated indefinite chill materials are designed for highest wear resistances for surface-critical applications in hot strip mills. The microstructure consists of tempered martensite together with cementite and MC carbides as well as a certain amount of graphite in different morphologies. These alloys have very high hardness values and a poor toughness which makes it rather difficult to measure the mechanical properties with standard testing methods. These materials were successfully tested with the 4-point bending method and reliable and comprehensible values for the flexural strength and the Young's modulus were generated. A clear correlation between those values and the total amount of carbides and graphite was found. Also, both values are dependent from the shape of the graphite precipitations. The investigations prove that the 4-point bending test is a feasible method to test the mechanical properties of indefinite chill alloys.

Corrosion behavior of 3 wt.-% Chromium (3Cr) tubing steel in CO 2 saturated high-salinity brine was investigated by using an autoclave in the laboratory. The partial pressure of CO 2 and the Cl − concentration were fixed at 0.2 MPa and 139552 mg × l −1 , respectively. The water cut was varied from 20 to 100 vol.-%, and the temperature was varied from 50 to 110 °C. For comparison, the corrosion behaviors of N80 carbon steel and 13 wt.-% Cr (13Cr) martensitic stainless steel were tested in the same conditions. The surface morphologies and chemical composition of corrosion product layers were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometry (EDS) technologies. The results show that the 3Cr steel's corrosion rate increased as water cut increased, especially when the water cut exceeded 70 vol.-%. Serious general corrosion and local attack occurred on the 3Cr samples in a 0.2 MPa CO 2 and 139552 mg × l −1 Cl − corrosion environment. The product layer structure of 3Cr steel in high-salinity brine is demonstrated. When the chloride ion concentration is high enough, the Cr-enriched layer no longer provides sufficient protection against the chloride ion penetration and pitting attacks may occur.

Low-alloyed, high-strength steels with yield strength above 1200 MPa are frequently used in the automotive industry, in order to reduce the weight of the components. However, hydrogen embrittlement susceptibility is often a concern for this group of materials. Hydrogen can be produced on the metal surface, as a result of electrochemical corrosion reaction during service. The aim of this study is to evaluate the impact of the various loading procedures according to the existing technical specifications for environmental hydrogen embrittlement (EHE) testing. The hydrogen embrittlement susceptibility of high strength fasteners (strength class 14.8) was tested according to the well-established testing specifications: DIN 50969-2, DIN EN ISO 7539, ASTM F1624-12 in 5 wt.-% sodium chloride solution acidified to pH 3 with hydrochloric acid. Open circuit potential measurements were carried out during the testing procedure to gain understanding of the damage process in each of the testing approaches. Under the chosen testing conditions, rising step load (RSL) testing approach, specified in ASTM F1624-12, appeared as the most sensitive method for the evaluation of the material's hydrogen embrittlement susceptibility.

Unpigmented HDPE jerrycans filled with nitric acid (55 wt.-%) and water respectively had been exposed to outdoor conditions for one Berlin summer season. As both liquids underwent equal temperature progression, exposure effects of UV radiation and nitric acid as well as of the combination of both can be separated and compared. On the basis of various property changes after these exposures, synergistic action is evaluated and compared to a damaged Intermediate Bulk Container (IBC) from a transport accident. It is found that carbonyl formation accompanies lightness increase in color measurement due to microcracking and with a worsening in mechanical behavior, all of them showing the synergistic effects of UV and nitric acid exposure. By contrast, embedding nitrogen compounds accompanies yellowing of the material but cannot be correlated to oxidation. The reason for intensified damaging is the decomposition of the 55-percent nitric acid and the formation of nitrogen oxides even at ambient temperatures, caused by UV radiation. Thus, damaging effects become similar to those caused by fuming nitric acid exposure at temperatures above 60 °C, resulting in strong oxidative degradation of the polyethylene. By contrast, exclusive exposure to the 55 wt.-% nitric acid at 40 °C does not cause any failure. It can therefore be assumed that the damaged IBC too had been exposed to both UV radiation and nitric acid, probably outdoors.

The tribological behavior of composites based on zinc aluminum ZA27 alloy, reinforced with silicon carbide (SiC) and graphite (Gr) particles is analyzed using the Taguchi method and described in this paper. Two sample composites were tested: the first containing 10 % of SiC and the second containing 10 % of SiC and 3 % Gr particles. They were prepared by the compo-casting procedure. The experiments were carried out using a block-on-disc tribometer under dry sliding test conditions. The tests were conducted with sliding speeds of 0.25, 0.5 and 1.0 m×s −1 , normal loads of 10, 20 and 30 N and a sliding distance of 300 m. The wear surface of the composite material was examined using scanning electronic microscopy (SEM) and energy dispersive spectrometry (EDS). The influence of various parameters on the wear behavior was investigated by means and analysis of variance (ANOVA).

Continuous drive friction welding (CDFW) and magnetic impelled arc butt (MIAB) welding are solid-state welding techniques, in which bonding is achieved at temperatures below the material melting point. Although CDFW welding has been widely used in automotive and aeronautics industry, MIAB welding has not been commonly used yet. The present study involves the comparison of CDFW and MIAB welding for joining medium carbon steel tubes and medium carbon forging brackets together, which are widely used for the construction of drivetrain applications in automotive industry. Optimum parameters are presented for both techniques by using macro- and microstructural analysis, hardness, tensile and petal tests. Based on the analyses presented in this study, MIAB welding can be an alternative to CDFW for structural automobile parts.

Spark plasma sintering provides faster heating that can create fully, or near fully, dense samples without significant grain growth. In this study, pre-alloyed Ti-6Al-4 V powder compact samples produced through field assisted sintering in a spark plasma sintering machine are compared as a function of consolidation temperature. The effect of sintering temperature on the densification mechanism, microstructural evolution and mechanical properties of spark plasma sintered Ti-6Al-4 V alloy compacts was investigated in detail. The compact, sintered at 1100 °C, exhibited near net density, highest hardness and strength as compared to the other compacts processed at a temperature lower than 1100 °C.

The pulverized coal flow in the two-phase gas-solid is monitored based on the ECAH (Epstein, Carhart, Allegra, Hawley) theoretical model. The relationship between the volumetric concentration of the pulverized coal and the ultrasound attenuation coefficient is analyzed. The flow velocity and concentration of the coal particles is measured using two ultrasonic probes at an angle of 45° to the flow direction. The results show that the aberration of the ultrasonic on-line measurements of the pulverized coal flow is less than 3 % compared to the coal flow set by the experimental boiler test platform. The general feasibility and reliability of the ultrasonic method of the flow measurements is verified.

Thermal insulation concrete (TIC) with glazed hollow beads (GHBs) is a new type of building materials meeting the needs of energy-saving building. The TIC is advantageous in applications due to its excellent bearing capacity and thermal insulation properties. This paper discusses the seismic performance of the shear wall with TIC. Based on the seismic tests of two specimens under low frequency cyclic horizontal loads with constant vertical actions, the hysteretic behavior, energy dissipation capacity, stiffness degradation and failure pattern of the shear wall were investigated. A finite element model was developed and nonlinear analyses were made to simulate the quasi-static test of the shear wall using ABAQUS software. Both modal and time-history analyses of a test building with TIC were also performed using SAP2000 software. The test results show that, compared with the normal concrete shear wall (SW), the shear wall with TIC (specimens named GSW) has better energy dissipation capacity and ductility, while the failure pattern is similar.

The metal magnetic memory effect is highly sensitive to stress. This experimental investigation of the magnetic memory signal characteristic of a ferromagnetic material at different stress-strain states has been performed using X80 steel specimens. The magnetic signals were measured in accordance with these procedures at twice the elastic deformation and once the elastic deformation to fracture under the tensile load. The results indicate that magnetic memory signals linearly decrease with increasing tensile load in the elastic state and the reverse in the plastic stage. The intensity clearly increases when damage occurs which can be taken as evidence for damage caused by stress. The test was performed on an actual pipeline with a crack created by a special device. The effect of metal magnetic memory for the evaluation of damage caused by stress has thus been verified by this engineering procedure.

In recent years, there has been a great deal of interest in lightweight vehicle design due to regulations about reducing fuel consumption and emissions. Lightweight design of vehicle components is one of the most important research topics in vehicle design. Developing the optimum structure in the early stages of design process is very important for minimizing the vehicle weight and production costs. In this paper, an automobile hinge component has been developed using PA66 GF60 glass fiber-reinforced polyamide composite materials instead of conventional steel. The automobile hinge component has been conceived using computer aided design software. Topology optimization was made under specific loadings subject to the constraints of finite element method analysis. As a result of this study, optimum dimensions of the component have been obtained and the weight of the component has been reduced via structural topology optimization techniques while satisfying displacement and stress conditions. The results show that composite materials are an important alterative in lightweight vehicle design.

The product design process has a very important effect on product costs. It aims to develop products that are able to compete by achieving an optimum design in the product design process. This research presents the first application in the literature of the grey wolf, whale, water cycle, ant lion and sine-cosine optimization algorithms for the optimum design of vehicle components. In this study, the optimal structural model of a vehicle connecting rod was determined. In the optimization process, various design alternatives were created by using the latin hypercube method. Stress analysis was performed for each of these designs. According to the generated responses, equations for objective and constraint functions were obtained. The optimization problem was solved using the above mentioned algorithms which have been newly developed in the literature, resulting in optimum connection rod design. The results demonstrate that the grey wolf, whale, water cycle, ant lion and sine-cosine algorithms are very important options in optimizing design and manufacturing optimization problems.

In this study, the technique of drilling at stepped feed rate is suggested as a new method for reducing the burr size at the exit of a hole in Al-5005, without prolonging the drilling time. The hole was divided into two regions, which were drilled at different feed rates. As a reference for comparison analysis, Al-5005 was drilled at constant drilling parameters. The smallest burr size with constant drilling parameters was obtained at 140° point angle, 0.1 mm × rev −1 feed rate, and 400 rpm spindle speed. The parameters that mainly effect the burr size were determined to be point angle, feed rate and the spindle speed, respectively. The same material was drilled employing the method of stepped feed rate, where the first region of the hole was drilled at 140° point angle, feed rates of 0.1, 0.2, and 0.3 mm × rev −1 , and spindle speeds of 400, 800, and 1200 rpm. The second region was drilled with a feed rate that was automatically adjusted by the CNC machine to be one tenth of the feed rate in the first region, without removing the drill bit from the hole. It was observed that, using the stepped feed rate method, the burr height and burr thickness were diminished by 35 % and 25 %, respectively, compared to constant drilling parameters.

The extrusion-shear (ES) process for magnesium alloys is a newly developed plastic deformation technique, which combines one step of direct extrusion and two steps of ECAP (equal channel angular pressing). Corrosion resistances of the AZ61 magnesium alloy fabricated by ES with different billet temperatures have been investigated and evaluated through immersion and electrochemical tests. Influences of Cl- concentrations, immersion times and pH values on the corrosion behaviors of samples have been evaluated by analyzing corrosion morphologies and compositions, and phase compositions of corrosive products by using SEM and X-ray diffraction. According to the experimental results, samples processed by ES at 440 °C billet temperature have a higher corrosion resistance than those prepared at a billet temperature of 400 °C, which might be attributed to the grain-size reduction and the redistribution of inter-metallic particles within microstructures.