Effects Of Material Strain Hardening Research Articles

A response prediction method for clamped circular plates subjected to repeated blast loading

The aim of the present investigation is to study the behavior of metal circular plates that are clamped under the repeated blast loading at stand-off distances. In this paper, the Johnson-Cook constitutive equation involving the effects of material strain hardening and strain rate sensitivity is introduced into the empirical analysis equations used to predict the midpoint displacement of circular plates. Thus, a group of non-dimensional empirical equations are proposed for predicting the midpoint displacement of clamped metal circular plates subjected to both single and repeated blast loading. The proposed non-dimensional empirical analysis equations are verified with the simulation analysis and experimental results of previous papers. It indicates that the proposed non-dimensional midpoint displacement prediction equations demonstrate good consistency in predicting the deformation of clamped metal circular plates under both single and repeated blast loading conditions.

Material response and local stability of high-chromium stainless steel welded I-sections

The present paper describes a thorough testing and finite element modelling programme on the material characteristics and local stability of welded I-sections made of a new high-chromium grade EN 1.4420 stainless steel. Structural testing was conducted on four GMA (gas metal arc) welded I-sections, and involved material testing, residual stress measurements, initial geometric imperfection measurements, eight stub column tests and eight four-point bending tests, with four for each axis of bending. A parallel numerical modelling study was then carried out, in which numerical models were developed and validated against the obtained experimental results and afterwards utilised to perform numerical parametric studies to generate additional data to supplement the test results over a broader spectrum of cross-section geometric dimensions. The experimentally and numerically obtained data were employed to evaluate the suitability of the codified slenderness limits for cross-section classification and local buckling design provisions in both Europe and America to welded I-sections made of the new high-chromium grade EN 1.4420 stainless steel. The results of the comparisons generally indicated that the established cross-section slenderness limits are applicable to the new high-chromium stainless steel welded I-sections, while the codified local buckling design rules, based on an elastic, perfectly plastic material model without taking into account the material strain hardening effect of stainless steel and the effective width method without considering the element interaction effect within the cross-section, yield safe but unduly conservative and scattered cross-section local buckling resistance predictions. The accuracy of a recently proposed continuous strength method to the design of this new type of stainless steel welded I-sections was also evaluated, indicating a substantial improvement over the established design codes, mainly owing to the rational consideration of the favourable effects of material strain hardening and element interaction in the calculation of cross-sectional capacities.

Numerical modelling and design of hot-rolled and cold-formed steel continuous beams with tubular cross-sections

The structural behaviour and design of hot-rolled and cold-formed steel continuous beams with square and rectangular hollow sections are studied in the present paper, with a focus on the beneficial effects of material strain hardening and moment redistribution. Finite element (FE) models were first developed and validated against existing test results on hot-rolled and cold-formed steel square and rectangular hollow section continuous beams. Upon validation against the experimental results, parametric studies were carried out to expand the available structural performance data over a range of cross-section geometries, cross-section slendernesses, steel grades and loading conditions. Representative material properties and residual stress patterns were incorporated into the FE models to reflect the two studied production routes – hot-rolling and cold-forming. The experimental results, together with the parametric numerical results generated herein, were then used to evaluate the accuracy of the design provisions of EN 1993-1-1 (2005) as well as the continuous strength method (CSM) for indeterminate structures, the latter of which is extended in scope in the present study. It was shown that the current provisions of EN 1993-1-1 (2005) for the design of hot-rolled and cold-formed steel continuous beams are rather conservative, while the proposed CSM yields a higher level of accuracy and consistency, due to its rational consideration of both strain hardening at the cross-sectional level and moment redistribution at the global system level. Finally, statistical analyses were carried out to assess the reliability level of the two design methods according to EN 1990 (2002).

Effect of substrate structure on properties of nitrided layers formed on pure iron

PurposeThis paper aims to investigate the structure and scratch resistance properties of gas nitrided pure iron samples.Design/methodology/approachThe effects of material strain hardening and amount of grain boundaries exposed on nitriding surface were evaluated by cold rolling the starting samples to different reduction levels before gas nitriding.FindingsThe study finds that nitriding without any prior cold rolling produced a comparatively wide compound layer with a large fraction of porous zone featuring low scratch hardness values but no evidence of damage. On the contrary, cold rolling before nitriding led to a more irregular and thinner compound layer with reduced amount of porous zone and much finer nitrides in the diffusion zone. Scratch hardness was increased but failure mechanism changed by generation of conformal cracks within the track groove and the appearance of discontinuous spallation at high loads.Originality/valueOne of the issues of great industrial importance concerning nitriding of steels is the need to predict the extent of the nitrided layer in products showing small variations in microstructure or in extent of cold working due to complex manufacturing cycles. Despite the practical importance, relatively little information is available in literature about these issues. The present paper is therefore aimed at investigating the structure and mechanical properties of pure iron samples, gas nitrided with different amounts of cold working and microstructural conditions.

The analysis of the bending stiffness and intensity of cylindrical tubes

Based on the mechanics of material, the bending stiffness and intensity of cylindrical bar and tube are analyzed. By comparing the cylindrical tube whose ratio of outside diameter to internal diameter is 0.7 with the cylindrical bar, it is concluded that when both of them have the same mass, the section stiffness of the cylindrical tube is three times that of the cylindrical bar; when both of them have the same external diameter, the mass of the cylindrical tube is only 1/2 that of the cylindrical bar, but the section stiffness of the cylindrical tube is 3/4 that of the cylindrical bar. By virtue of the elemental elastic-plastic theory, the yield stress of the liquid-filled cylindrical tube is investigated. Due to the incompressibility of liquid and the strain hardening effect of material, the yield stress of the liquid-filled tube is enlarged compared with the hollow tube, thus raising its bending intensity. Under the dynamic load, compared with the hollow tube, the impact resistance of the liquid-filled tube is also raised due to elastic recovery. Because the hydraulic pressures perpendicular to the inner surface are identical everywhere, the local stress concentration resulting from the ovalisation of the tube would be decreased, and the resistance to buckling would be improved.

Relationship between the CTOD and the J-integral for stationary and growing cracks. Closed-form solutions

A modified line-plasticity model, involving concept of structured nonlinear zone coupled with the final stretch criterion governing the crack propagation, is used to show the effects of material strain-hardening and the redistribution of strain caused by an advancing quasi-static crack, on the essential parameters pertinent to a mathematical description of elasto-plastic fracture process including its ductile limit. The model links micro-structural and continuum aspects of ductile fracture occurring in dissipative solids equipped with an ability to strain-harden. Attention has been focused on the crack tip opening displacement ( δ_t ) and the J-integral, both associated with either stationary of quasi-static crack contained in a power-hardening material of the Ramberg–Osgood type. The ratios of δ_t and J for a stationary and moving crack are represented via closed-form solutions and then compared against the earlier numerical results of Shih (1981), based on the finite element analyses. Expressions derived here, apart from having a theoretical merit, address an issue of significant interest to the researchers involved in the field of the Experimental Fracture Mechanics.

Analysis of buckle propagation in marine pipelines

Abstract This paper shows how the analysis of minimum, quasi-static, buckle propagation pressures for subsea pipelines may be exactly formulated in terms of the characteristics of ring collapse. A simple mechanistic approach to ring collapse is described which enables the rational incorporation of the effects of material strain hardening. Theoretical predictions resulting from this analysis are shown to reproduce past empirically observed propagation pressures; they also successfully predict the variations in the forms of ring collapse modes resulting from differing strain-hardening properties. Upon suitable non-dimensionalisation this analysis shows how predicted propagation pressures may be represented in terms of just one composite material and geometric ‘propagation parameter’. This eliminates the need for recourse to empirically fitted design curves and allows resolution of certain anomalies experienced in past analyses. It emphasises the need for more complete information regarding material strain-hardening properties if test results are to be properly interpreted. Most importantly, the present analysis offers the potential for future design of pipelines being at once more rationally and parametrically complete, and yet compact and simple to apply.

A numerical method of analysis for the mushrooming of flat-ended projectiles impinging on a flat rigid anvil

The theories of Taylor, and Lee and Tupper use conservation of momentum across the plastic wave front to determine the strain distribution in a flat ended projectile impinging on a flat rigid anvil. In Hawkyard's theory conservation of energy is used across the plastic wave and some account of projectile strain hardening is incorporated. The present study replaces the projectile with a lumped parameter model which consists of a number of concentrated masses connected to each other by massless links. The equation of motion is applied to each concentrated mass and a solution for the dynamic behaviour of the connected mass system is obtained using a numerical technique. This method of approach is capable of incorporating the effects of material strain hardening and strain rate on the final shape of the projectile, it enables the distribution of strain in the projectile to be determined.

Plastic Collapse Loads for Pipe Elbows Using Inelastic Analysis

The results of an inelastic analysis are used to predict plastic collapse loads for in-plane bending of several pipe elbows. The analysis is made using a nonlinear finite element computer program which takes into account the effects of material strain hardening, stress redistribution, and ovalization of the elbow cross section. Various methods are used to determine plastic collapse loads based on the calculated load-deformation curves. The predicted collapse loads are compared to collapse loads determined by limit analysis and the method described for plastic analysis in Section III, Appendix F, of the ASME Boiler and Pressure Vessel Code. It is concluded that the current Code definition of collapse load is overly conservative for structural materials typical of high temperature application, and that the 0.2 percent offset method or the 2 times the angle of linear response method produce more realistic results.