Band 61, Heft 9

Fiber-reinforced polymers show a continuous material degradation under cyclic loading, which is why damage development has to be investigated for an exact assessment of fatigue properties. In order to obtain information on damage in the internal volume, conventional mechanical test methods require accompanying support by further developed techniques. In this study, a methodology for in situ computed tomography has been developed and applied to glass fiber-reinforced polyurethane. Polyurethane has advantages over epoxy in terms of impact strength, damage tolerance and abrasion, which are important for various applications. Fatigue properties, on the other hand, are largely unknown. Optimized imaging parameters for computed tomography have been established in order to obtain detailed 3D volume images suitable for analysis. The 3D volumes of the damage state were recorded according to defined fatigue load steps and used to evaluate and correlate the damage development with the mechanical properties. The results confirm known damage characteristics of fiber-reinforced composites but also show material and structure-related differences in crack formation and propagation.

The objective of the study is to investigate the phase evolution of the aluminized surface of iron-concentrated nickel-based superalloys. Aluminization is carried out via pack cementation at constant temperature of 900 °C at three processing times of 1, 2.25 and 4 h. Backscattered images and X-ray diffractions are used for phase identification. Small incident angle X-ray diffraction applied on the surface and subjected to repetitive polishing elucidate a formation sequence of iron aluminides. The overall thickness of the aluminized layers is proportional to the processing time squared. The samples are composed of 4 zones, identified by elemental concentration profiles. Only iron aluminides are observed which is in agreement with thermodynamic- and atomic diffusion. The results conclude that aluminization on alloys is similar to oxidation and that nickel aluminide forms with great difficulty on the surface of an aluminized Incoloy 825 alloy.

This work aims to determine the material qualification of 13Cr-L80 casing for sour conditions which is of great importance to check the sulfide stress cracking susceptibility, confirm the range of applicable conditions and recommend anti-corrosion materials. First, the casing material was tested to judge whether its properties were normal. Secondly, the testing matrix was defined to determine actual casing exposure conditions. Thirdly, slow strain rate testing was used to screen the conditions. Fourthly, thirty-day tests of uniaxial tensile specimens were conducted to check for SSC susceptibility. The casing material satisfied API 5CT standards and could be used for slow strain rate testing and sulfide stress cracking testing. The testing matrix is intended to distinguish the combined effect of temperatures (41, 75, 140 °F), chloride levels (1000, 13 000 mg × L −1 ), pH (3.5, 5.5) and partial pressures of H 2 S (3.5 psi) in shut-in and flowing conditions. The slow strain rate testing showed a reduction of signs of embrittlement with increased temperature, suggesting that the mechanism is supported by sulfide stress cracking. The 13Cr-L80 passed field-specific qualification tests for sulfide stress cracking resistance in sour wells at maximum H 2 S partial pressures of 3.5 psi in the casing-tubing annulus. The API 5CT 13Cr-L80 casing application is in compliance with ISO15156/NACE MR0175 standards as long as the aggressiveness of the field conditions does not go beyond the envelope conditions tested (3.5 psi of H 2 S, pH 3.5, temperature of 41 or 75 °F).

The demands placed on highly stressed components are constantly increasing. For this reason, components with a higher degree of efficiency are required for the competitiveness of metallic components. Therefore, a comprehensive understanding of the fatigue behavior of metallic materials and components as well as the development of new methods for the reliable calculation of service life are of increasing importance. The fatigue properties of components are multi-parameter sets and are strongly influenced by surface integrity, as surface and near-surface zones are the most stressed regions of a component. Surface integrity is influenced by each individual manufacturing process, its parameters, the process order and the process combination. Due to their high complexity, the influence-cause-effect relationships of process chains have not yet been sufficiently understood. In order to analyze the interactions between manufacturing process chains, their design, variations in material properties, in particular the microstructure and the resulting component properties, specimens were processed with specifically different machining parameters with and without polished surface. The specimens were characterized by different analyzing methods, such as X-ray for residual stress measurements and phase analysis as well as surface characterizations through confocal microscopy. The results from these analytics are used as an input for a semi-empirical model and finite element analysis providing effective stress amplitudes which include factors such as stress concentration and residual stress in order to predict their influence on fatigue life. This additional material information can be used in currently existing short-time procedures or for conventional determined SN curves to expand them to a multi-parameter dataset. The investigations presented in the scope of this paper were performed on specimens made from quenched and tempered steel SAE 4140H (42CrMoS4) machined with various processing parameters.

The resilience of materials from the notch effect together with subsequent operating life and safety are important factors for the choice of material in industrial manufacture as well as for crash scenarios. The aim of this investigation is to study stress caused by the notch effect for HCT780XD and X5CrNi18-10 at different tensile test strain rates as well as due to various stress concentration factors during a high-speed tensile test. The notch geometries chosen are round, trapezoid, sharp and bore. They are compared to a test specimen without notch. The stress distribution analysis of notches was performed by the finite-element-method (FEM) in order to determine stress concentration factors. The high-speed tensile test was recorded with a high-speed camera. For this purpose, the test specimens were marked with a speckle-pattern, essential for the identification of strain rate via Dantec Dynamics Istra 4D. The influence of the stress concentration rate on parameters like energy, strength and the elongation of break was established and will be reported in the following. The level of the concentration factor leads to negative effects while the strain rate level delivers positive results. On other hand, the stress concentration factor is more important on the parameter than the strain rate. By contrast, Poisson's ratio does not affect the parameters observed.

Exposure to a hygrothermal environment would cause severe degradation of the mechanism properties of carbon fiber reinforced polymer (CFRP) laminates. The moisture absorption characteristics of T700/3228 CFRP laminates was studied through moisture absorption tests. The effects on the tensile and compression properties of [0] 16 and [90] 16 specimens under various hygrothermal conditions were comparative analyzed, and the degradation mechanisms of tensile and compression properties were further researched by microstructure characterization. The results show that under dry conditions, matrix strength increases with rising of temperature because of post-curing of epoxy at high temperatures. At 85 % RH (relative humidity), the strength of CFRP laminates decrease entirely with rising temperature because of the thermal and moisture stress generated at the interface. At a water temperature of 70 °C, the proprieties of CFRP laminates decrease severely.

In the present study, the authors investigated the effect of the austenitizing temperature (860 to 1020 °C) on the microstructure evolution, hardness, wear resistance and corrosion resistance of Cu-bearing carbidic austempered ductile iron (CADI) by means of an optical microscope (OM), a scanning electron microscope (SEM), a Rockwell hardness tester, a microhardness tester, an X-ray diffractometer (XRD), a block-on-ring wear testing machine and electrochemical tester. The results show that with an increase in the austenitizing temperature, the amount of acicular ferrite decreases, size expands, and the volume fraction of high-carbon austenite increases gradually as does carbon content. Part of the carbide dissolves into the matrix, and the amount is significantly reduced. The hardness of Cu-bearing CADI first increases and subsequently decreases, and the hardness is highest at 940 °C. With an increase in austenitizing temperature, the wear loss of Cu-bearing decreases and its wear resistance increases. When the austenitizing temperature is 940 °C, wear loss is lowest and wear resistance is optimal. Electrochemical corrosion experiments show that as the austenitizing temperature increases, the corrosion potential of Cu-bearing CADI is slightly improved, the corrosion current density is gradually reduced, and the corrosion resistance of Cu-bearing CADI is improved. Considered comprehensively, the austenitizing temperature of Cu-bearing CADI should be determined to be 940 °C.

In this study, Fe-1Nb, Fe-5Nb and Fe-10Nb (at.-%) binary alloys were boronized by the pack boronizing method at 950 °C for 3 h. The effect on the boride layer of the increasing niobium amount in pure the iron was experimentally investigated. After boron treatment, microstructural changes occurring on the surfaces of the coated alloys were examined by SEM, EDS and XRD analysis. A microhardness test analysis was applied to the coated alloys. Typical saw tooth morphologies were present in all coated alloys. The increasing niobium amount in the pure iron suppressed the appearance of the saw tooth morphologies. In addition, the microhardness of the boron layers was much higher than that of the base metal.

This paper studies the corrosion inhibition of carbon steel in a 0.51 mol × dm −3 sodium chloride solution in the presence of honey. The tests were carried out using the potentiodynamic polarization method, scanning electronic spectroscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared spectroscopy (FTIR). Electrochemical parameters which indicate the corrosion behavior of the steel in the sodium chloride solution in the absence and in presence of honey were calculated based on the experimental results. It was shown that honey acts as a mixed corrosion inhibitor whose efficiency increases with an increasing concentration. The maximum efficiency of inhibition (77.68 %) was maintained through a 1200 ppm concentration of honey. The adsorption of the tested inhibitor is described by Langmuir's isotherm, and the calculated value of free adsorption energy indicates the physical adsorption of the organic components of honey on the steel surface. The results of the SEM, FTIR and EDX analysis show that the honey covers the steel surface and prevents the influence of the aggressive medium.

This paper presents some experimental results on the effect of the notch–depth ratio on intermittent electromagnetic radiation during the progressive plastic deformation of a Cu-Ni alloy sheet specimen under tension. An electromagnetic antenna was used for receiving the electromagnetic waves emitted by the deforming specimen. The specimens (with varied notch-depth ratios) first emit electromagnetic radiation near yield which is always oscillatory in nature. However, the axial strain at the initial emission of the electromagnetic radiation increases with an increase in the notch-depth ratio. The nature of electromagnetic radiation signals changes from oscillatory to exponential until instability is reached. This shows that the viscous coefficient of the material of the specimens increases during strain-hardening. The paper also presents a correlation between electromagnetic radiation emission parameters and the radius of the plastic zone created ahead of the advancing crack tip, an important parameter in fracture mechanics. With an increase in the plastic zone size, the amount of intermittent electromagnetic radiation decreases asymptotically: the first electromagnetic radiation amplitude increases linearly and a maximum energy burst first decreases the electromagnetic radiation frequency parabolically. Initial electromagnetic radiation characteristics differ considerably from optimum electromagnetic radiation emissions within the strain-hardening region. These experimental results show a novel technique for studying various fracture mechanics parameters and also for developing a non-contact crack growth monitor.

In the traditional development of aluminum based composite materials ceramic particles such as SiC, Al 2 O 3 and B 4 C etc. are customarily used as a reinforcement material for the aluminum matrix. Further, industries producing these ceramic particles emit huge amount of greenhouse gases which in turn cause a great amount of environment pollution. Moreover, the production of these ceramic particles is costly. Agro waste groundnut shell ash (GSA) is an agricultural waste product that produces soil and air pollution. In addition, its disposal is costly. In this study, an attempt was made to utilize agro waste GSA as a partial replacement for ceramic particles in the development of AA2024 aluminum based composite. Microstructure results showed a uniform distribution of GSA particles in the aluminum base metal matrix alloy. Maximum tensile strength and hardness were found to be 198 MPa and 64 BHN for 3.75 wt.-% reinforcement of GSA particles in the AA2024 aluminum base matrix material. Porosity and thermal expansion were found to be 12.96 % and 125 mm 3 , respectively for the AA2024/3.75 wt.-% GSA composite. Density, corrosion loss and the cost of the GSA reinforced composite continuously decreased by increasing the percentage of reinforcement. Specific strength and corrosion loss of the AA2024/3.75 wt.-% GSA green metal matrix composite were also found satisfactory.

In recent years, the use of wire electrical discharge machining (WEDM) has gained momentum for processing hardened alloys. The machining of a hardened alloy commonly reveals poor surface finish and poor corner accuracy. In order to improve the machining performance, multi-pass cutting was employed during wire EDM of Monel 400 alloy. In this work, multi- pass cutting is achieved by one rough cut followed by two trim cuts. Control factors such as offset distance, pulse-on time (T on ), corner angle, flushing nozzle height, pulse-off time (T off ), open circuit voltage and wire tension are selected as control factors in so far as the process criteria results in reduced speed, corner error and surface roughness. The experiments were carried out using Taguchi design, and the results were analyzed. These showed that surface finish and corner accuracy were improved if the machining had been performed with a single trim cut. The outcome of the results revealed that the use of a trim cut more than once adversely affects the productivity and accuracy of the products in question. Moreover, a comparative study on (i) a single pass cut versus a trim cut (ii) a trim cut versus path modification was carried out.

The influence of process parameters on thrust force during the drilling of pure and chemically treated Kevlar reinforced epoxy composites has been investigated. Surface treatment has been carried out to enhance the physical bonding between fiber and matrix. Four different drill bits were used for the investigation: standard twist, core, step cone and candle stick drill. Three speed and feed rates were used for the investigation. Our objective was to find the minimum thrust force during the drilling of pure and chemically treated Kevlar reinforced composite using four different drill bits. Optimization of drilling process parameters was performed using the Taguchi method of L 9 Orthogonal Array. We found that among the four drills core and candle stick drills produce a minimum thrust force compared with the twist and step cone drills. Thrust force values produced by a chemically treated specimen is lower than that of a pure composite specimen irrespective of the drill bits used. Chemically treated specimens of the core and candle stick varieties are suitable for lower thrust force and delamination free holes under specified experimental conditions. The significance of feed rate is more important for thrust force during the drilling of composite specimens irrespective of drills.

The present study deals with the synthesis and characterization of Kevlar fibers produced by a condensation reaction of para-phenylenediamine with terephthaloyl chloride. The composites were fabricatedusing a 5 % KFs fiber loading for groundnut/epoxy at varied filler loadings by means of hand lay-up. We have evaluated dynamic mechanical properties such as the tensile, flexural and impact strength ofgroundnut/epoxy composites reinforced with Kevlar fibers. All the dynamic mechanical properties were performed as per the essential American Society of Testing and Methods standards. The Groundnut/epoxy hybrid composite reinforced with synthesized Kevlar fibers has a high tensile, flexural and impact strength. A composite treated in this manner has high dynamic mechanical properties which make it suitable for a number of applications in engineering industries.