Biography:

In the past T.S. Srivatsan has collaborated on articles with E.B. Shields and Y.H. Guo. One of their most recent publications is Technical noteCyclic strain resistance and fracture behavior of 7150 aluminum alloy. Which was published in journal Engineering Fracture Mechanics.

More information about T.S. Srivatsan research including statistics on their citations can be found on their Copernicus Academic profile page.

T.S. Srivatsan's Articles: (31)

Technical noteCyclic strain resistance and fracture behavior of 7150 aluminum alloy

AbstractIn this paper the low cycle fatigue properties and cyclic fracture behavior of aluminum alloy 7150 are examined. Test specimens of the alloy were cycled using tension-compression loading, under total strain control, over a range of plastic strains giving lives of less than 104 cycles. The alloy displayed softening in both the longitudinal and transverse orientations of the wrought plate, at all cyclic strain amplitudes. The observed softening behavior is ascribed to contributions from concurrent and synergistic effects involving an interaction of mobile dislocations with matrix precipitates and multiple microscopic crack initiation leading to macroscopic crick growth. Fracture of the alloy samples was predominantly intergranular, for both orientations, with tortuous crack path. The low cycle fatigue properties and cyclic fracture behavior of the alloy are discussed in terms of competing influences of plastic strain amplitude, response stress, intrinsic microstructural effects, dislocation-microstructure interactions and matrix slip characteristics.

Analytical methods for evaluation of stress intensity factors and fatigue crack growth

AbstractThe problem of fatigue has been of major concern in the design of structures for use in engineering applications. The fatigue process is comprised of crack nucleation, crack propagation and final failure. The fatigue crack propagation characteristics of engineering materials have been a topic of considerable research effort with the majority of such investigations focusing on experimental predictions of the behavior of fatigue cracks. This paper reviews the various approaches used for extraction of stress intensity factors and for predicting stable fatigue crack growth under linear elastic fracture mechanics conditions. Problems containing a single crack and multiple cracks are critically examined. Specific approaches discussed are the direct methods, energy methods, singularity function methods, superposition methods and boundary integral equation methods. The implications and characteristics of each method are examined based on the results published in open literature. The salient advantages and limitations of each method are discussed. Also examined in this paper are research efforts on the simulation of fatigue crack growth.

Influence of mixed-mode loading on fatigue-crack propagation

AbstractThe subject of fatigue which comprises crack nucleation, crack propagation and final failure or fracture has, over the years, been the subject of numerous theoretical and experimental studies. These studies have highlighted the extrinsic influence of mixed-mode loading in governing the fatigue behavior of a wide spectrum of engineering materials and structures. In this paper we review the basic criteria and models that have been proposed and used to predict crack behavior and response for structures containing large cracks and subject to mixed-mode loading. Since the aspect of crack growth is the focus of this review, the effects or contributions from intrinsic microstructural effects are largely excluded. Specific criteria discussed are the maximum tangential stress, minimum strain-energy density and the maximum energy-release rate criteria. The use of these criteria to predict the behavior of structures is examined based on results published in the open literature. The characteristics and implications of each criterion are examined and discussed with particular relevance to threshold conditions on crack growth, direction of crack growth and crack-growth rate. The limitations of each criterion are highlighted.

Influence of nitrogen ion implantation on tensile behavior of 1018 carbon steel

AbstractIon implantation is shown to be an effective tool for the modification of surface microstructures such that they can have a profound influence on the mechanical properties of metals and alloys. In this paper, the influence of nitrogen ion implantation on tensile behavior of low carbon steel 1018 is reported. The tensile properties of the implanted material are compared with those of the unimplanted counterpart. Implantation was found to decrease the yield strength and marginally improve the ultimate tensile strength. Environmental influence on tensile elongation was less for the implanted material in comparison with the unimplanted counterpart. Fracture was predominantly ductile with evidence of numerous dimples and microvoids. The degradation in yield strength and the improvement in ultimate tensile strength are rationalized on the basis of free dislocations on the surface which promote early yielding and the additional precipitation of nitride particles in the bulk during “aging” that provides increased strengthening.

Mechanisms of damage in high-temperature, low cycle fatigue of an aluminium alloy

AbstractThe roles of microstructure and environment in influencing mechanisms of damage during high-temperature, low cycle fatigue were investigated in a lithium-containing aluminium alloy in the peak-aged condition, and tested over a range of plastic strains. Reduction in fatigue life and resistance were observed at an elevated test temperature. Localized oxidation and embrittlement at grain boundaries are promoted by the applied stress, and play an important role in accelerating crack initiation and subsequent crack propagation. Evidence is presented to rule out contributions from microstructural changes through the coarsening of precipitate particles and the formation of new precipitate phases, and damage due to creep. The apparent acceleration of crack initiation and enhanced crack propagation are ascribed to a complex interaction of four mechanisms: intrinsic microstructural features, the embrittling effect of the environment, the slip mode arising from a combination of mechanical and microstructural contributions, and applied stress. The abnormal plastic strain-fatigue life by behaviour is attributed to differences in the distribution of deformation as a function of plastic strain amplitude.

Effect of silicon carbide particulate on cyclic plastic strain response characteristics and fracture of aluminium alloy composites

AbstractThe cyclic stress-response characteristics of powder-metallurgy-processed high-purity aluminium alloy 2124 discontinuously reinforced with varying volume fractions of silicon carbide particulates were studied over a range of plastic strains. The specimens were cycled using tension/compression loading under total strain control. The composite material, in the heat-treated condition, displayed cyclic hardening at all cyclic strain amplitudes and for different volume fractions of the ceramic reinforcement in the aluminium alloy matrix. The degree of hardening was observed to be greater at the higher cyclic strain amplitudes than at corresponding lower strain amplitudes. Micromechanisms controlling the hardening response during cyclic straining are highlighted and rationale for the observed hardening behaviour is attributed to concurrent and competing influences of an increase in dislocation-dislocation interaction, dislocation multiplication and dislocation-particle interactions, and is a mechanical effect. The kinetics of the cyclic fracture process of the composite alloy is discussed in light of composite microstructural effects, plastic strain amplitude and concomitant response stress.

Influence of processing and heat treatment on micro structure and tensile properties of copper-lead alloys

AbstractLead is a soft metal that possesses excellent antifriction and lubricating characteristics and is a desired addition to alloys which find use in friction-critical and low load-bearing applications. In this paper, the influence of processing on microstructure and tensile properties of copper-lead alloys is reported. The alloys were continuously cast into ingots by a traditional continuous cast process and also by the use of a die that induced a swirling motion of the molten metal prior to casting. Coarse or fine microstructures were therefore produced in the final ingots. Samples of the alloys were heat treated at 100 and 200 ° C and the microstructure and tensile properties compared with the as-cast ingots.

The tensile behavior of an oxide dispersion strengthened copper-niobium composite

AbstractNiobium particulate reinforced aluminum oxide (Al2O3) dispersion strengthened copper composite is an attractive and emerging engineering material for applications requiring high strength, high thermal and electrical conductivities and resistance to softening at elevated temperatures. In this paper, the microstructure and tensile behavior of the composite is examined. The strength of the material marginally decreases at elevated temperatures with a concomitant improvement in ductility. The composite microstructure maintained a high value of the yield strength/ultimate tensile strength ratio. The fracture behavior of the composite is examined in light of intrinsic microstructural effects, nature of loading and deformation characteristics of the matrix.

Effects of microstructure on the strain-controlled fatigue failure behavior of an aluminium-alloy/ceramic-particle composite

AbstractA study has been made to understand the cyclic fatigue and cyclic fracture characteristics of a cast aluminium alloy metal matrix discontinuously reinforced with particulate silicon carbide. The Al/SiCp composite was strained to failure over a range of strain amplitudes giving lives of less than 104 cycles to failure. The specimens were cycled by using tension-compression loading under total strain control. In the as-cast condition, the aluminum-alloy/ceramic composite displayed combinations of cyclic hardening and softening to failure at higher cyclic-strain amplitudes, and progressive softening to failure at low cyclic-strain amplitudes. The spray-atomized and deposited composite exhibited softening to failure at the higher cyclic-strain amplitudes and combinations of softening and hardening behavior at the lower strain amplitudes. The observed hardening and softening behavior is a mechanical effect and attributed to concurrent and competing influences of interactions between cyclic deformation and composite microstructure during cyclic straining. The processed microstructure exhibited better cyclic ductility and cyclic-strain resistance than the as-cast composite microstructure. The cyclic fatigue behavior of the alloy is briefly interpreted in the light of composite microstructural effects, plastic strain amplitude and concomitant response stress.

Approximation and numerical treatment of an autoregressive equation with stochastic coefficients

AbstractIn this paper, we discuss the relationship between the solution of a random discrete equation that arises in an autoregressive (AR) system and its corresponding deterministic discrete counterpart. To illustrate this relationship both analytical and numerical techniques are used. The statistical properties of the random equation are evaluated numerically. The error expressed as the difference between the mean of the random solution and the deterministic solution is established. Results of this study highlight the ease of using a numerical approach to solve complicated autoregressive equations having stochastic coefficients.

An investigation of cyclic plastic strain response and fracture behavior of steel-based metal-matrix composites

AbstractThis paper summarizes the results of a study to understand the role of composite microstructure and test temperature on cyclic stress response characteristics, cyclic strain resistance, low-cycle fatigue life and mechanisms governing the cyclic fracture behavior of tool-steel metal matrix discontinuously-reinforced with titanium carbide (TiC) particulates. Two different volume fractions of the carbide particulate reinforcement phase, in a tool-steel metal matrix, are considered. The composite microstructure had near similar particle size distribution. The tool-steel/TiCp metal-matrix composites were cyclically deformed under fully-reversed total strain-amplitude control cyclic straining, giving fatigue lives of less than 104 cycles to failure. At both ambient and elevated temperatures, the cyclic strain resistance and resultant low-cycle fatigue life degraded with an increase in the discontinuous particulate reinforcement phase in the tool-steel metal matrix. The stress response characteristics of the composite microstructures are compared in order to rationalize the influence of reinforcement content and test temperature on total strain amplitude-controlled fatigue behavior. The cyclic fracture behavior of the composite is discussed in the light of concurrent and mutually interactive influences of composite microstructural effects, matrix deformation characteristics, cyclic plastic strain amplitude and concomitant response stress.

An investigation of the cyclic fatigue and fracture behavior of a niobium aluminide intermetallic

AbstractThis paper presents the results of a study designed to improve our understanding of the cyclic fatigue and fracture characteristics of a niobium aluminide intermetallic. Specimens of the intermetallic were deformed to failure in uniaxial tension, fully-reversed total strain amplitude control and cyclic stress amplitude control. The alloy exhibited limited plasticity and life under strain amplitude-controlled fatigue. Cyclic stress controlled high-cycle fatigue characteristics were established at ambient temperature. The cyclic stress response and fatigue fracture characteristics of the intermetallic are presented and discussed in the light of concurrent and mutually interactive influences of intrinsic microstructural effects, cyclic strain and stress amplitude, and ductility of the material. The matrix deformation characteristics of the intermetallic during incremental tensile and cyclic loading are presented and discussed in the light of magnitude of load, slip characteristics and intrinsic microstructural effects.

Influence of temperature on cyclic stress response and fracture behavior of aluminum alloy 6061

AbstractThe cyclic stress response and fracture characteristics of aluminum alloy 6061 was studied at different temperatures. The specimens were cyclically deformed using tension-compression loading under total strain-amplitude control. The alloy showed evidence of softening at all test temperatures. The degree of cyclic softening was observed to increase with an increase in test temperature. The presence of shearable matrix precipitates in the alloy results in a local decrease in resistance to dislocation movement, thereby causing a progressive loss of strengthening contribution. At the elevated temperatures, localized oxidation and embrittlement at the grain boundaries are promoted by the applied cyclic stress and play an important role in accelerating crack initiation and subsequent crack propagation. The fracture behavior of the alloy is discussed in terms of competing influences of intrinsic microstructural effects, deformation characteristics arising from a combination of mechanical and microstructural contributions, plastic strain amplitude and concomitant response stress, and test temperature.

The cyclic strain resistance, fatigue life and final fracture behavior of magnesium alloys

AbstractThis paper summarizes the results of a comprehensive study on the cyclic strain resistance, low-cycle fatigue life and fracture behavior of three rapidly solidification processed magnesium alloys. Test specimens of the magnesium alloy were cyclically deformed under fully-reversed total strain amplitude control straining, over a range of strain amplitudes, giving less than 104 cycles to failure. The cyclic stress response characteristics, strain resistance and low-cycle fatigue life of the alloys are discussed in light of alloy composition. All three alloys follow the Basquin and Coffin-Manson strain relationships, and exhibit a single slope for the variation of cyclic elastic and cyclic plastic strain amplitude with reversals-to-fatigue failure. The cyclic stress response characteristics, fatigue life and final fracture behavior of the alloy are discussed in light of competing and synergistic influences of cyclic total strain amplitude, response stress, intrinsic microstructural effects and dislocation-microstructural feature interactions during fully-reserved strain cycling.

Cyclic plastic strain response and fracture behavior of 2009 aluminum alloy metal-matrix composite

AbstractIn this paper the influence of discontinuous ceramic particulate reinforcements on cyclic stress response, cyclic stress versus strain response, cyclic strain resistance, deformation and fracture behavior of 2009 aluminum alloy discontinuously reinforced with silicon carbide particulates are presented and discussed. The cyclic strain amplitude–controlled fatigue properties and fracture characteristics of the 2009/SiC composite specimens are discussed for a range of cyclic strain amplitudes and at two different temperatures. The conjoint influence of test temperature and strain amplitude on cyclic stress response, cyclic stress versus strain response, and cyclic strain resistance is highlighted. The intrinsic mechanisms governing stress response, cyclic deformation and fatigue fracture characteristics are presented and discussed in light of the competing and mutually interactive influences of intrinsic composite microstructural effects, deformation characteristics of the composite constituents, cyclic strain amplitude and concomitant response stress, cyclic ductility, and test temperature.

Influence of titanium dioxide nanopowder addition on microstructural development and hardness of tin–lead solder

AbstractThis paper presents the microstructure and hardness of composite solders obtained by the addition of nanopowders of titanium dioxide to a conventional solder. Titanium dioxide powders-reinforced lead (Pb)–tin (Sn) composite solders were prepared by thoroughly blending nano-sized titanium dioxide powders with powders of a eutectic solder and using a water-soluble flux. The blended solder paste was melted and allowed to re-solidify in a crucible placed on a hot plate and maintained at a constant temperature. Optical microscopy observations revealed that for additions of titanium dioxide up to 1 wt.%, the grain size and width of the grain boundary decreased. For the addition of 2 wt.% of titanium dioxide, nanopowders microporosity was observed both at and along the grain boundary regions coupled with the presence of second-phase particles. Microhardness measurements revealed that the addition of titanium dioxide nanopowders is helpful in enhancing the overall strength of the eutectic solder.

An investigation of fatigue crack nucleation and growth in a Ti–6Al–4V/TiB in situ composite

AbstractThis paper presents the results of an experimental study of fatigue crack nucleation and growth in a Ti–6Al–4V/TiB in situ whisker-reinforced composite. The onset of crack nucleation is shown to correspond to ∼20% of the total life at a stress range of 480 MPa. This is associated with transverse cracking across TiB whiskers, and interfacial decohesion between the TiB whiskers and the Ti–6Al–4V matrix. Subsequent cracking occurs by the formation of multiple cracks across the elongated α grains. These cracks are retarded initially by the β phase. However, subsequent fatigue damage results in transgranular crack growth across α and β phases prior to the onset of catastrophic failure. The long fatigue crack growth rates in the Paris regime in the Ti–6Al–4V/TiB composite are comparable to those of Ti–6Al–4V processed under nominally identical conditions. However, the fatigue crack growth rates in the composite are faster than those in the matrix alloy at lower ΔK values. Cyclic deformation of the composite is associated with strain softening, presumably as a result of progressive interfacial decohesion around the TiB whiskers early in the fatigue deformation process. The implications of the results are assessed for potential structural applications of the Ti–6Al–4V/TiB composite.

The quasi static deformation and fracture behavior of aluminum alloy 7150☆

AbstractThis paper highlights the results of an experimental study aimed at understanding the tensile deformation and fracture behavior of aluminum alloy 7150. Uniaxial tensile tests results reveal the alloy to have acceptable strength and ductility in both the longitudinal and transverse orientations. The ductility in the transverse orientation is inferior to the longitudinal orientation. No drastic change in fracture mode was observed with sample orientation. On a macroscopic scale, tensile fracture surface revealed features reminiscent of locally ductile and brittle mechanisms. The fracture behavior of the alloy is discussed in light of intrinsic microstructural features, deformation characteristics of the alloy, grain boundary failure and local stress state.

A study to evaluate and understand the response of aluminum alloy 2026 subjected to tensile deformation

AbstractThe strain concentration factors were determined for aluminum alloy 2026 in the T3511 temper using multi-hole structural coupon specimens. Samples of the alloy were evaluated for both the 6.25 mm (0.25 in.) thick and 10 mm (0.4 in.) thick specimens and having widths of 50 mm (2 in.) and 100 mm (4 in.), respectively. For the case of the specimens that were 50 mm in width the mechanical tests were conducted for both the open hole and filled hole conditions and the corresponding strain concentration value was determined. Threaded fasteners having collars were used for the case of the filled hole specimens. The fasteners posses a shank diameter that was slightly larger than the nominal hole size in order to provide for some interference. The strain concentration values were evaluated at both the failure strain (εf) and the strain at maximum load (εmax). The average strain concentration value was then used to predict the results for the stack-up tests.

Technical ReportInfluence of microstructure and load ratio on cyclic fatigue and final fracture behavior of two high strength steels

Highlights•The study was aimed at understanding effects of load ratios on fatigue properties.•The steels have better mechanical properties in comparison with rest in this category.•The steels were cyclically deformed at two different load ratios.•SEM was used to characterize the intrinsic features on the fracture surface.

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