Low Carbon Steel Specimens Research Articles

Experimental Energy Balance During the First Cycles of Cyclically Loaded Specimens Under the Conventional Yield Stress

This paper, as an extension of Maquin and Pierron (Mech Mater 41(8):928–942, 2009), presents an experimental procedure developed to macroscopically estimate the energy balance during the very first cycles of a uniaxially loaded metallic specimen at low stress levels. This energy balance is performed by simultaneously measuring the plastic input energy using a load cell and a strain gauge, and the dissipative energy using the temperature field provided by an infrared camera. Some experimental limitations led to restrain the present procedure to positive stress ratios, and to complement this energy balance by a second measurement while the material plastic work per cycle is negligible compared to the dissipative energy. Some results obtained on a cold rolled low carbon steel specimen are presented. First, a sensitivity study is undertaken to precisely determine the detection threshold on both thermal and plastic energies. Then, after having verified the homogeneity of the dissipative source fields, energy balances have been performed at different stress levels. It was thus confirmed that the slow variations of the dissipative sources occurring during the first cycles are due to micro-plastic adaptation, and that the dissipative sources remaining after some hundreds of cycles are due to viscoelastic (internal friction) phenomena. This procedure provides a better understanding of dissipation based approaches to fatigue found in the literature and an advanced tool to study viscoelastic phenomena in uniaxial loading.

1107 水素チャージした低炭素鋼予ひずみ材の疲労き裂伝ぱ速度および破面形態に及ぼす繰返し速度の影響(OS11-2 材料の疲労挙動と損傷評価-き裂発生・進展-)

Loading frequency effects on FCGR and fracture surface morphology were investigated on a hydrogen-charged specimen of a pre-strained low carbon steel. Test results showed difference tendency of loading frequency effects between charged-hydrogen and hydrogen environment. Tests in a low pressure nitrogen showed that decreasing loading frequency revealed increasing FCGR. However, in a hydrogen gas FCGR revealed decreasing tendency as well as an uncharged specimen. Fracture surface morphology showed that the change of FCGR in this region related to the transition of ductile to brittle-like fracture surface or the reverse.

Effect of Microstructure Changes on Barkhausen Noise Properties and Hysteresis Loop in Cold Rolled Low Carbon Steel

Low carbon steel specimens cold rolled at ratios of 0-40% have been examined comprehensively by means of magnetic Barkhausen noise (MBN) method and a physical parameter obtained from a hysteresis loop, and their microstructures were studied by a transmission electron microscope. The behaviors of MBN and coercive force with reduction ratio were discussed in relation to microstructure changes. The MBN energy rises rapidly with cold rolling below 10% reduction, and saturates at higher reduction ratio. The peak in averaged rms voltage exhibited the same behavior as that of the MBN energy, whereas the coercive force and the magnetizing current when the averaged rms showed a peak increased monotonically with increasing reduction ratio. These phenomena are attributed to the combined effects of cell texture and dislocation density.

Thermo-Mechanical Coupled Problems at Finite Strains

This paper discusses some thermodynamic aspects in association with a large strain/large displacement elastic-plastic formulation aiming at application to metal forming problems. The mechanical solution adopts the multiplicative decomposition of the gradient of deformation into elastic, plastic and thermal components. The approach is illustrated by analysing the thermal effects in the plastic deformation of low-carbon steel specimens subject to tensile loading.

A numerical simulation of the nucleation and evolution of localized plastic deformation in welded low-carbon steel specimens

A numerical simulation of the nucleation and evolution of localized plastic deformation in welded low-carbon steel specimens was performed. A mathematical model based on a double-limit yield criterion was constructed to describe the propagation of Liiders bands. The behavior of 3D welded specimens characterized by a gradual or a stepwise change in the mechanical properties of the material in the heat-affected zone was investigated. The plastic deformation evolution pattern in the welded specimens was shown to depend on the mechanical characteristics of the material in the heat-affected zone and on the stress level near the grips of the testing machine and at the interfaces between the weld, heat-affected zone and base metal.

Experimental investigation of fatigue performance of spot welded dual phase sheet steels

Spot weld fatigue performance of dual phase steels is of great interest to worldwide automotive manufacturers due to their expanding use in automotive industry. Given that the majority of the fatigue life is spent propagating the crack through the microstructure, changes in microstructure of welding steels could result in significant changes in spot weld fatigue life compared to that of low carbon steel spot weld. In the present study, tensile shear spot welds of DP600GI, DP780GI with different thickness were used for fatigue test under various amplitude tensile loads. For comparison tensile shear fatigue test was also conducted for spot welds of low carbon steel. Microhardness was measured for spot weld of dual phase steels to study the hardness change across the weld nugget. Failure mechanism and crack propagation path of dual phase steel spot weld was studied. For spot welds of low thickness, the fatigue strength of dual phase steel spot weld is higher than that of low carbon steel specimen in high cycle fatigue test. When thickness increases, the fatigue strength of dual phase steel spot weld and low carbon steel spot weld are almost the same, and fatigue strength of dual phase spot welds also increases with the thickness. And it is also shown in the present study that static tensile interfacial fracture of spot weld does not necessarily lead to interfacial fracture of high cycle fatigue tests. Crack propagation path of tensile shear spot weld of dual phase sheet steels under fatigue test was examined. Crack initiates at the faying surface around the weld nugget, and then passes through the thickness of sheet, which leads to the failure of specimens.

A statistical study of the coefficient of friction under different loading regimes

Shrink-fits are common engineering fastening systems that comprise a cylindrical hub and shaft locked together by a radial pressure due to interference in size at their interface diameter. Frictional forces at the interface allow the transmission of a torque or resistance to axial movement in the assembly. The measurement of the coefficient of friction under simulated shrink-fit conditions is difficult and time consuming. A flexible experimental approach is presented that can test over a range of pressures, sizes, loading directions, i.e. torsion, compression and tension, and which has the ability to detect changes in the normal load applied due to loading direction. A series of statistical validation studies are conducted on 15 mm diameter low carbon steel specimens to verify theoretical formulations that suggest the coefficient of friction is different for the different loading regimes, and also identifies the surface roughness measured axially or radially as being contributory to the final coefficient of friction value. The experimental approach is applied to a novel laminate sleeve for an electrical machine in order that high confidence is achieved in measuring the coefficient of friction under realistic service conditions.

Anticorrosive behaviour of alkyd paints formulated with ion-exchange pigments

Hexavalent chromium compounds (chromates) have been widely used as inhibitive pigments in the formulation of anticorrosive paints. However, their high toxicity and carcinogenic effects are forcing the development of effective chromate-free organic coatings. One such alternative, which is very attractive from a scientific point of view, is the use of ion-exchangeable pigments (IEPs). The few studies conducted with this type of pigment are not conclusive about their anticorrosive efficiency and controversy surrounds their functioning mechanisms, interchange capacity and anticorrosive performance. In the present research, which focuses on the anticorrosive protection of this type of pigment, alkyd paint coatings formulated with vanadate-hydrotalcite (HT/V) (anionic) and calcium/silica (Ca/Si) (cationic) IEPs have been applied on low carbon steel specimens. A traditional zinc chromate pigment has also been used for comparative purposes. The effect of these non-toxic pigments on the protective properties of coatings has been tested by means of natural and accelerated corrosion tests (humidity, salt spray and Kesternich, 0.2 l SO 2) and electrochemical impedance spectroscopy (EIS). None of the IEPs equalled the anticorrosive behaviour of the zinc chromate in the different tests. The anionic pigment (HT/V) seems to present good behaviour in chloride environments (salt spray, NaCl solutions, etc.) while the cationic pigment (Ca/Si) performs well in the humidity condensation and SO 2 tests.

Effect of Annealing Temperature on Microstructure and Properties of Surface Nanocrystalline Structure in Low Carbon Steel Specimen

Nanostructure surface layer was fabricated on a low carbon steel cylinder specimen by means of circulation rolling plastic deformation (CRPD), and the effect of annealing temperature on microstructure and properties of surface nanocrystalline structure was studied. The microstructure of the surface layer on the samples was observed by transmission electron microscopy and the microhardness variation along the depth was measured on the cross-sectional samples by using microhardness instrument. After CRPD treatment for 250min, the average grain size was about 10nm in the top surface layer and increased with an increment of the distance from the top surface. The surface nanocrystallization samples were annealed at 200°C, 300, 400°C and 500°C for 30min respectively. The nanocrystallization grain of surface layer did not grow for samples after annealed at 200°C and 300°C. After surface nanocrystallization by CRPD treatment the microhadness of top surface obviously increase from 220HV0.1 to 520HV0.1.

Fatigue strength and fracture behavior of steels with and without interstitial carbon at room temperature in air

Abstract In this study, fatigue performance and fracture behavior of interstitial-free, low carbon and phosphorus-added low carbon steels have been investigated by plane bending fatigue tests at room temperature in air. For all steels, fatigue tests were carried out at a frequency of 1000 cycles per minute, however, a limited number of specimens of low carbon steel were also tested at frequencies of 500 and 1500 cycles per minute. After all mechanical tests, fracture surfaces were cut and examined using scanning electron microscopy to identify the fracture features. At any applied stress level, low carbon steel showed better fatigue performance than interstitial-free steel, and phosphorus addition further improved the fatigue life of low carbon steel. Fractographic observations on fatigue fracture surfaces revealed transgranular fracture for low carbon steel and intergranular fracture for interstitial-free steel. Interestingly, addition of 0.12 wt.% of phosphorus in low carbon steel could not change the dominant transgranular fracture behavior of the steel.

Comprehensive analysis of Barkhausen noise properties in the cold rolled mild steel

Low carbon steel specimens cold rolled at ratios of 0%, 5%, 10%, 20% and 40% have been comprehensively investigated by magnetic Barkhausen noise method, and their microstructures were studied by transmission electron microscope. A broad peak formed between 15 and 60 kHz in the fast Fourier transformation spectrum increases with rolling ratio. Barkhausen noise energy and rms voltage rise rapidly with cold rolling below 20%, and saturate at higher rolling ratio. This phenomenon is attributed to the combined effects of cell texture and dislocation density.

Modeling of a scan type magnetic camera image using the improved dipole model

The scan type magnetic camera is proposed to improve the limited spatial resolution due to the size of the packaged magnetic sensor. An image of the scan type magnetic camera, ∂B/∂x image, is useful for extracting the crack information of a specimen under a large inclined magnetic field distribution due to the poles of magnetizer. The ∂B/ ∂x images of the cracks of different shapes and sizes are calculated by using the improved dipole model proposed in this paper. The improved dipole model uses small divided dipole models, the rotation and relocation of each dipole model and the principle of superposition. Also for a low carbon steel specimen, the experimental results of nondestructive testing obtained by using multiple cracks are compared with the modeling results to verify the effectiveness of ∂B/∂x modeling. The improved dipole model can be used to simulate the LMF and ∂B/∂x image of a specimen with complex cracks, and to evaluate the cracks quantitatively using magnetic flux leakage testing.

High-cycle fatigue crack paths in specimens having different stress concentration features

This paper summarises an attempt to study the high-cycle fatigue cracking behaviour in specimens of low carbon steel weakened by U-notches. The specimens were tested under uniaxial fatigue loading with a load ratio equal to 0.1, and the considered K t values, calculated with respect to the gross area, ranged from 3.8 up to about 25. The generated crack paths were quite irregular showing a propagation occurring in alternate trans- and intra-crystalline mode: in many cases, this made difficult to unambiguously measure orientation and length of Stage 1 planes. In spite of these experimental difficulties, the observed material cracking behaviour seemed to suggest that a Stage 1-like process could always be assumed to be representative of the crack initiation phenomenon, and this held true independently of the notch sharpness. In light of the fact that, at a mesoscopic level, crack initiations never occurred on material planes parallel to the notch bisector, we attempted to investigate whether it was possible to use a critical plane approach to estimate high-cycle fatigue damage in notched components under uniaxial fatigue loading. In more detail, the generated results have initially been re-analysed by using the Modified Wöhler Curve Method re-interpreted in terms of the Theory of Critical Distances [Susmel L. A unifying approach to estimate the high-cycle fatigue strength of notched components subjected to both uniaxial and multiaxial cyclic loadings. Fatigue Fract Eng Mater Struct 2004;27:391–411]. The accuracy in predicting the high-cycle fatigue behaviour of the considered multiaxial fatigue method was then compared to the accuracy of two other uniaxial approaches: the classical one by Smith and Miller [Smith RA, Miller KJ. Prediction of fatigue regimes in notched components. Int J Mech Sci 1978;20:201–206] and the one recently proposed by Atzori and co-workers [Atzori B, Lazzarin P, Meneghetti G. A unified treatment of the mode I fatigue limit of components containing notches or defects. Int J Fract 2005;133:61–87] and based on the use of some classic LEFM concepts. In particular, this comparison was performed considering virtual specimens having the same geometries as the ones investigated in the present study, but assuming that they were made of materials having mechanical properties known from the literature. This exercise allowed us to see that the high-cycle fatigue damage in notched specimens under uniaxial fatigue loading can satisfactorily be predicted not only using Mode I-crack based methods, but also using multiaxial fatigue criteria modelling the crack initiation phenomenon.

Thermal Shock Cracking: Design and Assessment Guidelines

Repeated thermal shock cracking is common in the operation of pressure equipment where water and steam are present. Surprisingly, it is not fully covered in the ASME Boiler and Pressure Vessel code nor in fitness-for-purpose recommended practice such as API 579. An example of thermal shock stresses occurs when hot surfaces are exposed to splashing of cold water. This eventually may lead to crack nucleation and crack growth. However, not all thermal shock cracks lead to failures (such as rupture, leak, or, in more brittle material, fragmentation), indeed the most frequent situation is that the cracking arrests at a depth of a few millimeters. This paper presents a unique experimental study and analysis of the information being gained from this study in terms of design guidelines and crack growth mechanisms. In the experiments, cracks are initiated and then grown in low carbon steel specimens exposed to repeated thermal shock. The test-rigs achieve large thermal shocks through the repeated water quenching of heated flat plate specimens. The effect of steady state loads on the growth and environmental effects due to the aqueous nature of the testing environment are found to be major contributors to the crack growth kinetics. The most important findings are that the conditions leading to both the initiation and the arrest of cracks can be identified and that the depth of a starter notch contributes little to the crack propagation.

Reference Impact Specimens Made from Low Carbon Steel: Report on Production and Use

Abstract This paper describes a method of producing reference specimens from low carbon steel and reports the results of a national proficiency testing by 45 laboratories. The reference impact specimens of low carbon steel are much cheaper than the traditional ones, and the proficiency testing proved that the specimens are valid for finding out the problems of impact machines. Furthermore, the data showed that an impact machine would represent the similar relative bias at a different energy level of reference specimen, so it is sufficient to use reference specimens with one absorbed energy level to verify impact machines annually.

A fatigue crack growth model for spot welds under cyclic loading conditions

Based on the experimental results for spot welds in square-cup, lap-shear and coach-peel specimens of dual phase, low carbon and high strength steels, kinked fatigue crack paths near spot welds are first examined. A fatigue crack growth model is then developed for spot welds based on the local stress intensity factor solutions for kinked cracks. Various global stress intensity factor solutions for spot welds in the three types of specimens are used to obtain the local stress intensity factor solutions with the experimentally determined kink angles. The predicted fatigue lives based on the fatigue crack growth model are then compared with the experimental data. The results indicate that the fatigue crack growth model can predict reasonably well the fatigue lives of spot welds based on the global stress intensity factor solutions and the assumed material constants in the Paris law for fatigue crack growth.

Microstructure, Microhardness, and Residual Stress Analysis of Laser Surface Cladding of Low-Carbon Steel

This article describes online measurement of thin and flat specimen changes during laser alloying and of the alloyed specimen after treatment. Laser remelting of SiC, Stellite 6, and Stellundum 481 powder was performed on a specimen of low-carbon steel. Experiments were performed with high-temperature resistance-measuring rosettes. Strain was monitored from the beginning to the end of the cladding process (i.e., to a temperature 50°C at the backside of the specimen). Therefore, during the cladding process, the changes in temperature at the backside of the specimen were measured with two Ni-NiCr thermocouples. Other important properties are the size and distribution of residual stresses in the thin cladded specimen (i.e., machine part), because they strongly affect its operational efficiency. Results obtained are analyzed from the viewpoint of minimum final strain of the specimen with the desired variation of residual stresses.

Shape anisotropy of magnetic field generation during tensile fracture in steel

Magnetic field generated by low carbon steel specimens during crack propagation and fracture has been discussed in this paper. Different specimen cross-section viz. cylindrical, square, rectangular, and thin sheet have been considered for the investigation. Magnetic field generated have been found to be strongly dependent on the degree of necking. Cylindrical specimens, which undergo large necking, show more magnetic fields generated than sheets/strips, which undergo less necking.

The effect of ultrasonic treatment on mechanical behavior of titanium and steel specimens

The effect of surface ultrasonic treatment on plastic deformation and mechanical properties of polycrystalline titanium and low-carbon steel specimens under tension was studied. The deformation pattern was investigated using optical, transmission electron, scanning electron and scanning tunneling microscopy. It was shown that the material within hardened surface layers is characterized by ultrafine-grained structure. This structure results in plastic flow localization at different scale levels. Localized deformation meso-bands induce weak work hardening of the material. Plastic flow macro-localization causes a drop of the external deforming stress. The peculiar mechanisms of deformation localization within the specimen surface layer govern formation of a banded dislocation substructure in the bulk of the specimen.

Detection of plastic deformation and estimation of maximum value of residual stress in low carbon steel by X-ray stress analysis using statistical techniques

Residual stress distribution on plate-type tensile specimens of low carbon steel with applied plastic strains up to 6.45% has been measured by X-ray stress analysis. Standard deviation for the frequency distribution profile of the residual stress was calculated by statistical processing to estimate the amount of macroscopic plastic strain applied on the specimen. Since adequate understanding of the maximum value of the residual stress ( σ max) has been important for the maintenance of the nuclear power reactor components, the σ max was also estimated from the limited number of the experimental data by statistics of extreme. It was found from above estimation that the X-ray stress analysis supported by the statistical techniques was a promising non-destructive evaluation (NDE) method to detect the plastic deformation and to estimate the σ max in S25C low carbon steel.