Abstract: This paper studies a failure case of a fuel pressure supply tube from an aircraft engine. Multiple fracture cases of the fuel pressure control tube from aircraft engines have been reported. The studied set was composed by the mentioned tube, a welded connecting pipe, where the fracture has been produced, and a union nut. The fracture has been produced in one of the most critical zones of the tube, in a region next to the supporting body of the union nut to the connector. The tube material was X6CrNiTi18-10, an austenitic stainless steel. Chemical composition was determined using an X-Ray fluorescence spectrometer (XRF) and combustion equipment. Furthermore, the material was characterized mechanically, by a hardness test, and microstructurally using a stereo microscope and an optical microscope. The results confirmed that the material was within specifications. To determine the macrofractographic features, a visual examination and an observation using a stereo microscope of the tube fracture surface were carried out. The results revealed a tube plastic macrodeformation, surface damaged and signs of a possible corrosion process. Fracture surface was also inspected by scanning electron microscopy (FE-SEM), equipped with an energy-dispersive X-ray microanalysis system (EDX), to determine the microfractographic features in order to find out the failure mechanism involved in the fracture. Fatigue striations, which are typical from a progressive fracture by a fatigue mechanism, were observed. The origin of the fracture was placed in defects located on the outer wall of the tube, leading to a final overload fracture.
Abstract: Electrochemical impedance spectroscopy (EIS) has been used to detect sensitization in austenitic stainless steels that are heat treated in the temperature regime 600-820 °C to produce different degrees of sensitization in the material. The tests were conducted at five different DC potentials in the transpassive region. The quantitative determination of degree of sensitization has been done using double loop electrochemical potentiokinetic reactivation tests (DL-EPR). The correlation between EIS Nyquist diagrams and DL-EPR degree of sensitization values has been studied. The EIS technique can be used as a qualitative tool in determining the intergranular corrosion in austenitic stainless steels that are heat treated at a given temperature.
Abstract: The present paper aims to investigate the effects of the welding process parameters and cooling state on the weld bead geometry, mechanical properties and microstructure characteristics for weldments of AISI 304L stainless steel. The welding process was carried out using TIG welding with pulsed/non-pulsed current techniques. The cooling state was introduced as an input parameter to investigate the main effects on the structure morphology and thereby the mechanical property. This paper clarifies microstructure- mechanical property relationship of the welded specimens. In this work, the selected pulse frequency levels were 5-500 Hz in order to study the effect of low and high frequencies on the weldment characteristics using filler metal of ER 308LSi. The key findings of this work clarified that the pulse frequency has a significant effect on the breaking of the dendrite arms during the welding process and so strongly influences on the tensile strength and microhardness. The cooling state also significantly affects on the microstructure texture and thereby, the mechanical properties. The most important factor affects the bead geometry and aspect ratio is the travel speed and pulse frequency.
Abstract: This paper reveals the interaction between hydrogen
and surface stress in austenitic stainless steel by X-ray diffraction
stress measurement and thermal desorption analysis before and after
being charged with hydrogen. The surface residual stress was varied
by surface finishing using several disc polishing agents. The obtained
results show that the residual stress near surface had a significant
effect on hydrogen absorption behavior, that is, tensile residual stress
promoted the hydrogen absorption and compressive one did opposite.
Also, hydrogen induced equi-biaxial stress and this stress has a linear
correlation with hydrogen content.
Abstract: The study comprises evaluation of suitability of passive layer created on the surface of AISI 316L stainless steel for products that are intended to have contact with blood. For that purpose, prior to and after chemical passivation, samples were subject to 7 day exposure in artificial plasma at the temperature of T=37°C. Next, tests of metallic ions infiltration from the surface to the solution were performed. The tests were performed with application of spectrometer JY 2000, by Yobin – Yvon, employing Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). In order to characterize physical and chemical features of electrochemical processes taking place during exposure of samples to artificial plasma, tests with application of electrochemical impedance spectroscopy were suggested. The tests were performed with application of measuring unit equipped with potentiostat PGSTAT 302n with an attachment for impedance tests FRA2. Measurements were made in the environment simulating human blood at the temperature of T=37°C. Performed tests proved that application of chemical passivation process for AISI 316L stainless steel used for production of goods intended to have contact with blood is well-grounded and useful in order to improve safety of their usage.
Abstract: Continually increasing working temperature and growing need for greater efficiency and reliability of automotive exhaust require systematic investigation into the thermal fatigue properties especially of high temperature stainless steels. In this study, thermal fatigue properties of 300 series austenitic stainless steels have been evaluated in the temperature ranges of 200-800oC and 200-900oC. Systematic methods for control of temperatures within the predetermined range and measurement of load applied to specimens as a function of temperature during thermal cycles have been established. Thermal fatigue tests were conducted under fully constrained condition, where both ends of specimens were completely fixed. Load relaxation behavior at the temperatures of thermal cycle was closely related with the thermal fatigue property.
Abstract: Simultaneous measurements of the curves for wear versus distance, wear rate versus distance, and coefficient of friction versus distance were performed in situ to distinguish the transition from severe running-in wear to mild wear. The effects of the initial surface roughness on the severe running-in wear volume were investigated. Disk-on-plate friction and wear tests were carried out with SUS304 austenitic stainless steel in contact with itself under repeated dry sliding conditions at room temperature. The wear volume was dependent on the initial surface roughness. The wear volume when the initial surfaces on the plate and disk had dissimilar roughness was lower than that when these surfaces had similar roughness. For the dissimilar roughness, the wear volume decreased with decreasing initial surface roughness and reached a minimum; it stayed nearly constant as the roughness was less than the mean size of the oxide particles.
Abstract: A three-dimensional finite element modeling for austenitic stainless steel AISI 304 annealed condition sheets of 1.0 mm thickness are developed using ABAQUS® software. This includes spot welded and weld bonded joints models. Both models undergo thermal heat caused by spot welding process and then are subjected to axial load up to the failure point. The properties of elastic and plastic regions, modulus of elasticity, fracture limit, nugget and heat affected zones are determined. Complete loaddisplacement curve for each joining model is obtained and compared with the experiment data and with the finite element models without including the effect of thermal process. In general, the results obtained for both spot welded and weld-bonded joints affected by thermal process showed an excellent agreement with the experimental data.
Abstract: Bead-on-plate welds were carried out on AISI 316L
(N) austenitic stainless steel (ASS) using flux cored arc welding
(FCAW) process. The bead on plates weld was conducted as per L25
orthogonal array. In this paper, the weld bead geometry such as depth
of penetration (DOP), bead width (BW) and weld reinforcement (R)
of AISI 316L (N) ASS are investigated. Taguchi approach is used as
statistical design of experiment (DOE) technique for optimizing the
selected welding input parameters. Grey relational analysis and
desirability approach are applied to optimize the input parameters
considering multiple output variables simultaneously. Confirmation
experiment has also been conducted to validate the optimized
parameters.
Abstract: The localized corrosion behavior of laser surface
melted 304L austenitic stainless steel was studied by
potentiodynamic polarization test. The extent of improvement in
corrosion resistance was governed by the preferred orientation and
the percentage of delta ferrite present on the surface of the laser
melted sample. It was established by orientation imaging microscopy
that the highest pitting potential value was obtained when grains were
oriented in the most close- packed [101] direction compared to the
random distribution of the base metal and other laser surface melted
samples oriented in [001] direction. The sample with lower
percentage of ferrite had good pitting resistance.
Abstract: The objective of this research was to study influence
parameters affecting to mechanical property of austenitic stainless
steel grade 304 (AISI 304) with Gas Metal Arc Welding (GMAW).
The research was applying factorial design experiment, which have
following interested parameters: welding current at 80, 90, and 100
Amps, welding speeds at 250, 300, and 350 mm/min, and shield gas
of 75% Ar + 25% CO2, 70% Ar + 25% CO2 + 5% O2 and 69.5% Ar +
25% CO2 + 5% O2 + 0.5% He gas. The study was done in following
aspects: ultimate tensile strength and elongation. A research study of
ultimate tensile strength found that main factor effect, which had the
highest strength to AISI 304 welding was shield gas of 70% Ar +
25% CO2 + 5% O2 at average of 954.81 N/mm2. Result of the highest
elongation was showed significantly different at interaction effect
between shield gas of 69.5%Ar+25%CO2+5%O2+.5%He and
welding speed at 250 mm/min at 47.94%.
Abstract: The modeling of inelastic behavior of plastic materials requires measurements providing information on material response to different multiaxial loading conditions. Different triaxiality conditions and values of Lode parameters have to be
covered for complex description of the material plastic behavior.
Samples geometries providing material plastic behavoiur over the range of interest are proposed with the use of FEM analysis. Round samples with 3 different notches and smooth surface are used
together with butterfly type of samples tested at angle ranging for 0 to
90°. Identification of ductile damage parameters is carried out on
the basis of obtained experimental data for austenitic stainless steel.
The obtained material plastic damage parameters are subsequently applied to FEM simulation of notched CT normally samples used for
fracture mechanics testing and results from the simulation are
compared with real tests.
Abstract: In this study the elastic-plastic stress distribution in
weld-bonded joint, fabricated from austenitic stainless steel (AISI
304) sheet of 1.00 mm thickness and Epoxy adhesive Araldite 2011,
subjected to axial loading is investigated. This is needed to improve
design procedures and welding codes, and saving efforts in the
cumbersome experiments and analysis. Therefore, a complete 3-D
finite element modelling and analysis of spot welded, bonded and
weld-bonded joints under axial loading conditions is carried out. A
comprehensive systematic experimental program is conducted to
determine many properties and quantities, of the base metals and the
adhesive, needed for FE modelling, such like the elastic – plastic
properties, modulus of elasticity, fracture limit, the nugget and heat
affected zones (HAZ) properties, etc. Consequently, the finite
element models developed, for each case, are used to evaluate
stresses distributions across the entire joint, in both the elastic and
plastic regions. The stress distribution curves are obtained,
particularly in the elastic regions and found to be consistent and in
excellent agreement with the published data. Furthermore, the
stresses distributions are obtained in the weld-bonded joint and
display the best results with almost uniform smooth distribution
compared to spot and bonded cases. The stress concentration peaks at
the edges of the weld-bonded region, are almost eliminated resulting
in achieving the strongest joint of all processes.
Abstract: The effect of different tempering temperatures and heat treatment times on the corrosion resistance of austenitic stainless steels in oxalic acid was studied in this work using conventional weight loss and electrochemical measurements. Typical 304 and 316 stainless steel samples were tempered at 150oC, 250oC and 350oC after being austenized at 1050oC for 10 minutes. These samples were then immersed in 1.0M oxalic acid and their weight losses were measured at every five days for 30 days. The results show that corrosion of both types of ASS samples increased with an increase in tempering temperature and time and this was due to the precipitation of chromium carbides at the grain boundaries of these metals. Electrochemical results also confirm that the 304 ASS is more susceptible to corrosion than 316 ASS in this medium. This is attributed to the molybdenum in the composition of the latter. The metallographic images of these samples showed non–uniform distribution of precipitated chromium carbides at the grain boundaries of these metals and unevenly distributed carbides and retained austenite phases which cause galvanic effects in the medium.
Abstract: Primary barrier of membrane type LNG containment system consist of corrugated 304L stainless steel. This 304L stainless steel is austenitic stainless steel which shows different material behaviors owing to phase transformation during the plastic work. Even though corrugated primary barriers are subjected to significant amounts of pre-strain due to press working, quantitative mechanical behavior on the effect of pre-straining at cryogenic temperatures are not available. In this study, pre-strain level and pre-strain temperature dependent tensile tests are carried to investigate mechanical behaviors. Also, constitutive equations with material parameters are suggested for a verification study.
Abstract: The present work is concerned with the effect of turning process parameters (cutting speed, feed rate, and depth of cut) and distance from the center of work piece as input variables on the chip micro-hardness as response or output. Three experiments were conducted; they were used to investigate the chip micro-hardness behavior at diameter of work piece for 30[mm], 40[mm], and 50[mm]. Response surface methodology (R.S.M) is used to determine and present the cause and effect of the relationship between true mean response and input control variables influencing the response as a two or three dimensional hyper surface. R.S.M has been used for designing a three factor with five level central composite rotatable factors design in order to construct statistical models capable of accurate prediction of responses. The results obtained showed that the application of R.S.M can predict the effect of machining parameters on chip micro-hardness. The five level factorial designs can be employed easily for developing statistical models to predict chip micro-hardness by controllable machining parameters. Results obtained showed that the combined effect of cutting speed at it?s lower level, feed rate and depth of cut at their higher values, and larger work piece diameter can result increasing chi micro-hardness.
Abstract: Stainless steel has been employed in many
engineering applications ranging from pharmaceutical equipment to
piping in the nuclear reactors and storage to chemical products. In
this attempt, simulation of fatigue crack growth based on
experimental results of austenitic stainless steel 304L was presented
using AFGROW code when NASGRO mode laws adopted. Double
through crack at hole specimen is used in this investigation under
constant amplitude loading. Effect of mean stress is highlighted.
Results show that fatigue crack growth rate (FCGR) and fatigue life
were affected by maximum applied load and dimension of hole. An
equivalent of Paris law for this material was estimated.