Influence Of Material Strength Research Articles

Effects of Fatigue Parameters on Fatigue Crack Growth Rate of Pipe Steels and Girth Weld

Abstract Oil and gas pipeline steels and welds are subjected to a wide variety of cyclic loadings: internal pressure variation, pulsation of gas pressure resulting from the cyclic operation of a reciprocating compressor at a gas compressor station, internal flow-induced vibration resulting from the turbulent flow within the pipe, vortex-induced vibration of a free-spanning section exposed to air (wind) for aboveground pipelines or water for water-crossing pipelines, and cyclic thermal stresses developed by significant changes in temperature due to seasonal changes or changes in operating temperatures. These cyclic loadings are very variable and complex. Considering the fatigue situations, a better understanding of the effects of fatigue test parameters on fatigue behaviors of pipeline steels and welds is required. Hence, in this study, the influences of fatigue test parameters on the Paris law coefficients were studied for pipeline steels and welds. It was analyzed for pipe steels of X65∼X100 and a girth weld of X70. Influences of material strength, crack orientation relative to the pipe axis, and frequency in the range of 1∼30 Hz were insignificant. It was found that the coefficients a1 and b2 of the m-ln(C) relationships linearly relied on the load ratio. The constants (α1, β1, α2, and β2) of these linear relationships between R-ratio and a1 (and b2) were determined for pipe steels.

Dispersion characteristics of surface wave in SCCS: theoretical analysis, numerical simulation and MASW-based NDT

To fully validate the feasibility of multichannel analysis of surface waves (MASW)-based interfacial debonding detection for steel–concrete composite structures (SCCS), dispersion characteristics of surface waves in SCCS are systematically investigated using theoretical analysis and elaborate 3D numerical simulations. First, the influences of material strength and thickness of concrete core, steel plate thickness on the dispersion figures are analyzed based on the theoretical dispersion characteristic of Rayleigh wave. Scientific layering strategy, including single steel plate, double-layer, and three-layer medium assumptions, is investigated using the theoretical dispersion analysis of Lamb wave. Besides, the dispersion characteristics of surface wave in circular steel pipes are calculated to determine the appropriate theoretical dispersion curves for MASW measurement. Finally, the stress wave propagation processes in SCCSs with various internal structures, including stiffeners, studs, and diaphragms, as well as the debonding width, are simulated using 3D numerical simulation to validate the research finding of theoretical analysis and detectability of MASW-based non-destructive testing on interfacial debonding defects in rectangular and circular concrete-filled steel tubulars. Finally, the dispersion characteristics corresponding to displacement, velocity, and acceleration of surface waves are comparatively discussed. The research findings of this study are the cornerstone of experimental study and essential theoretical support for identifying interfacial debonding and bond-slip damage of SCCS components utilizing MASW method.

Study on confinement mechanism of core concrete in steel tubular-corrugated steel plate confined concrete columns

This paper investigated the confinement mechanism of core concrete in steel tubular-corrugated steel plate confined concrete (S-CSC) column. Fourteen S-CSC columns and one CFST column were tested under axial compression, and the corresponding failure modes and load-displacement curves were observed. The strain changes of corrugated steel plate at different positions and square steel tubular were measured. Combined with the test results, the influences of some parameters including the section size, the steel tubular width, the wave height of corrugated steel plate, the thickness of corrugated steel plate and etc. on the strength index of core concrete and the ductility index of the specimens were analyzed. And the confinement mechanism of the core concrete in S-CSC column was studied. It was found that the confinement coefficient ξ which considered the influence of material strength and section size on the confinement effect of core concrete can reflect the confinement mechanism of core concrete effectively. Based on L.-H. Han's model, a constitutive relation for core concrete in S-CSC column by modifying key parameters was proposed and implemented in finite element simulation to predict the mechanical behaviors of axially loaded S-CSC column from the results of the tests. Comparing the test results of S-CSC columns which were described in this paper and the FE results, the satisfactory agreement was observed. Finally, it is verified that the size effect has no effect on the strength index of core concrete in S-CSC column basically.

Influence of Material Strength on the Apparent Cohesion of Unbounded Gravity Dam Joints under Low Normal Stress

AbstractInternational gravity dam design guidelines consider that the different joints of a dam or its foundation (rock–rock, rock–concrete, and concrete–concrete joints) are unbounded and recommen...

Theoretical and experimental study on jet formation and penetration of the liner loaded by electromagnetic force

Jet formation driven by strong magnetic field adopts the electromagnetic force to collapse the liner and breaks through the traditional jet forming mode of shaped charge, which relies on explosive. The influence of material strength on the liner deformation under low current is considered in this work to study the formation characteristics of the jet. Combined with the loading circuit, the jet formation and critical yield current (CYC) models are established. Subsequently, the CQ-4 device with 0.115 MJ energy is used to carry out electromagnetic loading experiments on the conical liners with a diameter of 10 mm and thickness of 1, 1.5, and 2 mm. The static penetration test method was used to test the jet power. The liners were all collapsed, and effective jets were formed by liners with 1 mm and 1.5 mm thickness. The depth of penetration (DOP) to the aluminum and steel targets were 30 mm and 12.5 mm, respectively. However, the 2 mm-thick liner almost did not have the ability to penetrate the steel target. The formation, movement, stretching, and penetration of the jets were calculation by theory and simulation. Results are in good agreement with the experiments. In the scope of this paper, the velocity and power of the jet increase with the decrease in liner thickness. The jet formation under theoretical calculation with and without material strength are compared and analyzed. The results indicated that the material strength cannot be ignored when the loading current is small. The formation characteristics of the liners under different loading currents are also calculated theoretically. The formation of the different liner elements under various currents are also calculated theoretically, and the peak current to CYC ratio is proposed to judge the formation state of the jet.

Surface structure on diamond foils generated by spatially nonuniform laser irradiation

Here we report on the effects of material strength factors on the generation of surface structure due to nonuniform laser irradiation. The influence of material strength on the generation of perturbation on a diamond surface subjected to nonuniform laser irradiation was experimentally investigated. Our previous investigations suggested that stiffer and denser materials reduce surface perturbation due to spatially nonuniform laser irradiation, which was reproduced well by calculations with multi-dimensional hydrodynamic simulation code. In this work, we found that local fractures due to yield strength failure are generated by high degrees of irradiation non-uniformity. A characteristic crack-like surface structure was observed, which was not reproduced by the 2D simulation code calculations at all. The 2D simulations showed that the pressure at the diamond surface locally exceeds the Hugoniot elastic limit due to nonuniform irradiation, implying the potential for development of surface perturbations. We also measured the areal-density distribution of perturbations for single-crystal diamond and diamond with a thin high atomic number (high-Z) coating on its surface. The experimental results imply that the combination of a stiff material and thin high-Z coating can suppress the solid-strength effects caused by large irradiation non-uniformity. The knowledge given here is applicable to inertial confinement fusion target design, laser material processing, and universal problems involving solids and high-energy-density plasmas.

Progressive collapse assessment of friction damped post-tensioned steel frames based on a simplified model

Post-tensioned energy-dissipating (PTED) connections for steel frames have drawn great research attention on account of their good seismic performance. Few studies focus on the progressive collapse of friction damped post-tensioned (FDPT) frame structures. The progressive collapse of FDPT frames exhibits a complex three-dimensional mechanical behavior that is quite different from that of traditional frame structures. In this work, a simplified 3D PTED connection model was first established and then used to investigate the progressive collapse behavior of FDPT frames. The influences of material strength, initial PT force, friction force, and axial and bending stiffness of beams on the collapse behavior of FDPT were studied. Finally, the dynamic response of FDPT frames was compared with that of traditional frame structures (TF).

Ultimate tensile and compressive performances of welded hollow spherical joints with H-beam

Welded hollow spherical joints with H-beam are a new type of spatial grid structural joints. Experiments and numerical simulation were conducted to investigate the axial tensile and axial compressive performances of the welded hollow spherical joints with H-beam. The influences of material strength, size of joint, and stiffening rib on the mechanical properties, were analyzed. The formulas were proposed to calculate the bearing capacity under axial tension and compression. The major conclusions are as follows: (1) Welded hollow spherical joints with H-beam developed strength fracture under axial tensile load, and hollow spheres developed buckling failure under axial compressive load. The failure mode was related to the strength of the material. (2) Proper arrangement of stiffening ribs can increase bearing capacity of welded hollow spherical joints with H-beam. The improvement coefficients were 1.1 under axial tension and 1.4 under axial compression. (3) The compression bearing capacity of welded hollow spherical joints with H-beam increased with the increase in height and flange width of H-beam, as well as wall thickness of the hollow spheres, but it decreased with the increase in diameter of hollow spheres. (4) The formula used to calculate tensile bearing capacity of welded hollow spherical joints with H-beam was proposed according to the punching shear model. (5) The design formula of compressive bearing capacity of welded hollow spherical joint with H-beam was obtained through the linear regression of abundant numerical simulation data.

Analysis of structural damage on the struck ship under side collision scenario

The occurrence of impact needs to be predicted for various cases as it mostly delivers negative to target object and environment. In marine structure, this phenomenon has distributed numerous damages to involved objects, such as can be found in tragedy of the Estonia in 1994. This disaster led to a reassessment of the safety of passenger ships in many country. During impact both of structural and material aspects contributes to responses in form of energy, force, and damage. In present work, consideration of the both aspects would be considered in preparation, analysis, and discussion, to evaluate contribution of considered aspects on failure characteristic. A target subjected to impact load in form of collision so called struck ship which had different hull configuration would be used in analysis as structural behaviour during and after hull structure of the struck ship was penetrated by the striking ship would be observed. In material level, analyses were conducted with applying different mechanical properties on the side structure. The results indicated that the tearing of inner hull was avoided due to size of double hull structure. This condition provided better safety but lower ship capacity. In other hand, strength characteristic of material was proofed dominate difference of internal energy. Finally, the influences of material strength, failure strain, and hardening parameter were evaluated and summarized.

Recent results on fatigue strength improvement of high-strength steel welded joints

Economic considerations push technology towards new lightweight structural solutions. This results in great interest in using high-strength steels (HSS) for structural applications like in railway vehicles, bridges, offshore structure and high-speed ships. In all these applications, welding is the main joining method and fatigue of welds is the major design criterion despite the existence of locally deteriorated microstructure, increased stress concentration and unfavourable tensile residual stresses after welding. Good weld design is a must to ensure the structural durability and performance, however this does not guarantee lightweight design alone. Special applications, such as post-weld treatment methods, can be performed following the welding. Therefore, this study concerns about the recent developments on such improvement techniques by considering two most-commonly used fatigue strength improvement methods; high frequency mechanical impact (HFMI) treatment and tungsten inert gas (TIG) dressing. Evaluations based on more than 1500 fatigue data points extracted from the literature. Investigations include presentation of the individual data analyses and fatigue strength assessment of all the data points by the effective notch stress approach with the reference radius rref=1.00mm. The influence of material strength, residual stress state, weld toe profile and loading conditions on the fatigue strength improvement are all discussed.

The effects of the host-substrate properties on maar-diatreme volcanoes: experimental evidence

While the relationship between the host-substrate properties and the formation of maar-diatreme volcanoes have been investigated in the past, it remains poorly understood. In order to establish the effects of the qualitative host-substrate properties on crater depth, diameter, morphological features, and sub-surface structures, we present a comparison of four campaigns of experiments that used small chemical explosives buried in various geological media to simulate the formation of maar-diatremes. Previous results from these experiments have shown that primary variations in craters and sub-surface structures are related to the scaled depth (physical depth divided by cube root of blast energy). Our study reveals that single explosions at optimal scaled depths in stronger host materials create the largest and deepest craters with steep walls and the highest crater rims. For single explosions at deeper than optimal scaled depths, the influence of material strength is less obvious and non-linear for crater depth, and non-existent for crater diameter, within the range of the experiments. For secondary and tertiary blasts, there are no apparent relationships between the material properties and the crater parameters. Instead, the presence of pre-existing craters influences the crater evolution. A general weakening of the materials after successive explosions can be observed, suggesting a possible decrease in the host-substrate influence even at optimal scaled depth. The results suggest that the influence of the host-substrate properties is important only in the early stage of a maar-diatreme (neglecting post-eruptive slumping into the open crater) and decreases as explosion numbers increase. Since maar-diatremes reflect eruptive histories that involve tens to hundreds of individual explosions, the influence of initial substrate properties on initial crater processes could potentially be completely lost in a natural system.

Experimental and Numerical Determination of the Required Initial Sheet Width in Die Bending

So far, determining the necessary precut dimensions of metal sheets prior to bending has been an unsolved question. During the last decades numerous calculation methods have been suggested. However, comparing these different methods indicates that different calculation methods suggest diverging precut dimensions. Especially in roll-forming, where multiple bend operations occur within the same bend part, these differences between several calculation methods can add up to some millimetres. The accuracy of presently available methods can hardly be compared. Thus an optimized method is needed. One possibility to determine the initial sheet width is identifying the position of the unlengthened layer in the bend zone. This study compares the position of the unlengthened layer determined in experiments and numerical simulations for different bend geometries and materials. The results indicate that even state of the art measuring technique is not accurate enough to determine the position of the unlengthened layer properly. Due to high measurement uncertainties, numerical simulations are required to assess the influence of geometry or material parameters on the position of the unlengthened layer. However, combining numerical and experimental results shows that the geometry of the bend part influences the position of the unlengthened layer and thus the required precut dimension. In contrast, a significant influence of material strength on the position of the unlegthened layer was not found.

G031062 高強度鋼の真空環境下における微小き裂の極低速き裂進展挙動([G031-06]材料力学部門,一般セッション : き裂疲労)

It is known that high strength steel will cause the characteristic internal fracture called Fish eye fracture in very high cycle region. From this, in order to use high strength steel more efficiently and more safely, the elucidation of the mechanism of the Fish eye fracture produced in low stress and long-life and construction of the lifetime evaluation method of Fish eye fracture are desired. In this study, we did ΔK decrease fatigue test under vacuum environment, and examined the relation between internal fracture in very high cycle region and extremely slow fatigue crack growth behavior under vacuum environment. As a result, the influence of material strength was not seen under vacuum environment. Moreover, opening stress increases with increases of maximum stress.

Vibrations of Fiber-Reinforced Laminated Deep Shells

This paper deals with a numerical method for the free vibrational analysis of laminated deep shells. The strain-displacement relations are obtained for a general laminated shell geometry described by orthogonal curvilinear coordinates. Parabolic variation of transverse shear stresses along the thickness and the effects of rotary inertia are included in the formulation. The displacement fields are represented by Bezier patches. The shape and size of these patches are controlled by certain arbitrary points called control points. Owing to the special characteristics of these control points, the treatment of displacements, slopes, curvatures, etc., at a particular edge becomes very simple. Hence, the enforcement of boundary conditions along the edges is straightforward. Ritz-type solution procedure is used for the eigen-analysis of the shell structure. Numerical examples involving laminated spherical, conical, and cylindrical shells are investigated in detail. Such shell geometries usually have planes of symmetry; hence, only one-quarter of the shell is analyzed in this study. Good convergence of the natural frequencies is observed by using eighth-order Bezier functions. The results are compared with the existing sources in the literature. The influences of material strength and number of layers on the natural frequencies are also examined.

A survey of data and some observations about the influence of material strength and surface finish on fatigue properties of steels: Gariboldi, E., Nicodemi, W. and Vedani, M. Proc. Conf. Computer Methods and Experimental Measurements for Surface Treatment Effects II, Milan, Italy, 7–9 June 1995, pp, 217–223

A survey of data and some observations about the influence of material strength and surface finish on fatigue properties of steels: Gariboldi, E., Nicodemi, W. and Vedani, M. Proc. Conf. Computer Methods and Experimental Measurements for Surface Treatment Effects II, Milan, Italy, 7–9 June 1995, pp, 217–223

Application of a new model for fatigue threshold in a structural steel weldment

A new model for fatigue threshold has been proposed. The model takes into consideration the influence of material strength, grain size, and load ratio on fatigue threshold. Fatigue crack growth behavior of a structural steel weldment (ASTM Grade A 514) was investigated to examine the applicability of this model. The investigation also examined the influence of welding procedure [submerged arc welding (SMAW) versus metal inert gas welding (MIG)] on the resultant microstructure and the near threshold fatigue crack growth behavior of the material in room temperature ambient atmosphere. Compact tension specimens were prepared from ASTM Grade A 514 structural steel weldment in such a way that cracks propagated through the heat affected zone (HAZ), base metal and weldments. This arrangement permitted the influence of HAZ on fatigue crack growth rate to be determined in both linear and threshold regions of the Paris curve in room temperature ambient atmosphere. Welding was accomplished by two different techniques, i.e. SMAW and MIG processes. The results of the present investigation demonstrated that the near threshold fatigue crack growth rate was lowest and fatigue threshold was highest when the crack propagated through the weldment. The fatigue threshold values predicted by the model were in good agreement with the experimentally determined values. The MIG welding process was found to be beneficial compared to the SMAW process as far as the fatigue threshold is concerned for weldment.

The effect of overload on corrosion fatigue crack growth behavior of a low alloy steel in threshold region

Influence of tensile overload (stress) on corrosion fatigue crack growth behavior of a low alloy steel in threshold region in 3.5% NaCl solution has been investigated. The investigation also examined the influence of material strength on overload retardation behavior. Compact tension specimens with transverse longitudinal (TL) orientation prepared from SAE 4130 steel in two different heat treated conditions were used. All test specimens used in the present investigation satisfied the test requirements of ASTM Standard E-647. The results of the present investigation demonstrate that in the threshold region, as percentage overload increases more retardation on crack growth rate is produced. This retardation effect on crack growth rate for similar percentage of overload was found to be greater in the annealed condition compared to the hardened and tempered condition. The retardation factor (ϕ) showed a general trend to decrease with increase in ΔK level. This retardation of corrosion fatigue crack growth rate due to tensile overload can be attributed to the effect of crack closure in the crack tip region.