This paper presents the current understanding relating to fatigue response of materials that are small in volume and tested through cyclic automated ball indentation and cyclic small punch test methods. The paper covers both the experimentation and numerical simulation aspects. Recently, researchers have proposed the hydraulic bulge test as another test method for fatigue life evaluation. All these test methods provide an indication of failure due to fatigue loading. For any given material, each one of the test methods causes its own state of stress (bi-axial or tri-axial), which is different from the uni-axial state of stress for a standard specimen, which makes the correlation of strain-life data between test methods to be difficult. In view of this, a numerical simulation of cyclic ball indentation, cyclic small punch test, and hydraulic bulge test has been carried out. The results of numerical simulation suggest that the mean stress for cyclic ABI and cyclic SPT tests are different, but the failure life data can be corrected using Goodman or similar mean stress correction methods. © 2019 Elsevier Ltd

Raghu V. Prakash

Department of Mechanical Engineering

Pankaj Dhaka

Computer simulation

Fatigue of materials

Fatigue testing

Numerical methods

Numerical models

Plastic deformation

Strain

BALL INDENTATION

FATIGUE LIFE EVALUATION

Fatigue test method

HYDRAULIC BULGE TEST

Mean stress

MEAN STRESS CORRECTION

SMALL PUNCH TEST

STANDARD SPECIMENS

Indentation

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IIT Madras

Theoretical and Applied Fracture Mechanics

Extraction of mechanical properties of in-service materials through small specimen test techniques has become attractive in the recent years. Of the available small specimen test techniques, automated ball indentation (ABI) and small punch test (SPT) methods have proved to be more promising. These test methods are basically non-destructive in nature and are proficient enough to extract the flow properties of the materials using small volume specimen. In this work, tensile properties of a pressure vessel steel (P12) have been estimated through ABI and SPT. The objective is to compare the capability of these test methods in determining the tensile properties. The influence of lubrication (between the indenter and the specimen) on the ABI response is also investigated. The ABI response is found to be similar and the effect on the tensile properties was under 2 %. The tensile properties estimated from ABI and SPT are found to be in good agreement with conventional tensile test results. Nevertheless, in case of SPT, the error in the estimation of yield strength and ultimate tensile strength using empirical correlations is significantly high. However, the use of analytical formulations to convert the SPT load–displacement response to stress–strain curve are found to be reliable, since the error in the estimated properties is considerably less. The ABI process is numerically simulated to study the stress–strain field beneath the indenter. The maximum strain occurs at the edge of the contact indicating the material displacement along the radial direction. The plastic zone beneath the indenter resemble hemispherical shape which is in agreement with the expanding cavity model. The nature of stress changes from compressive (right below the indentation axis) to tensile at the edge of contact. This indicates that radial cracks may initiate on the specimen and propagate outwards. The pile-up is significantly higher in the case of frictionless contact between the indenter and the specimen but found to converge for a value of around 0.2. © 2015, The Indian Institute of Metals - IIM.

Transactions of the Indian Institute of Metals

Estimation of Tensile Properties of Pressure Vessel Steel Through Automated Ball Indentation and Small Punch Test

An experimental investigation of cyclic indentation testing to characterize the fatigue response of three different metallic materials: two aluminum alloys (2014-T651 and 7175-T7351) and a duplex stainless steel (2205), was carried out. The force-displacement response during cyclic loading was logged continuously throughout the entire duration of the test and the data were analyzed to identify parameters such as change in total depth of penetration, change in loading and unloading slopes, change in unloading intercept as a function of number of cycles, and change in displacement range as a function of number of cycles. From the results, one could identify the transient response of the material during cyclic loading, and identify some specific points relating to fatigue failure life, such as knee-point response in depth of penetration as a function of number of cycles of loading. It was observed that data on unloading slope plotted as a function of number of cycles also provide an indication of specimen failure in compression-compression fatigue. The responses were found to be similar for all the three materials tested at different maximum compressive force levels. Failure life data in the low cycle fatigue (LCF) region was evaluated for Al-Cu-Mg alloy 7175-T7351 and the data compared with the failure indicators (knee point) during cyclic indentation testing. A reasonable correlation was established between failure life, as indicated by LCF testing and knee point indicated by cyclic indentation. Experiments were also carried out on virgin material of 7175-T7351 alloy and plastically deformed material of the same alloy. Both static and cyclic indentation tests show a difference in material behavior before and after residual plastic deformation. Further work is required to correlate failure life data as obtained from cyclic indentation with specimens having controlled damage levels, before this technique can be used for residual life estimation purposes. Copyright © 2008 by ASTM International.

ASTM Special Technical Publication

Investigation of material fatigue behavior through cyclic ball indentation testing

Materials Science and Engineering: A

Development of a novel methodology to study fatigue properties using the small punch test

Ubiquity Proceedings

Fatigue strength assessment of SUS316 by small bulge fatigue (SBF) test

304L stainless steel fatigue evaluation using dynamic mechanical analysis

Understanding the fatigue response of small volume specimens through novel fatigue test methods – Experimental results and numerical simulation

Journal	Data powered by TypesetTheoretical and Applied Fracture Mechanics
Publisher	Data powered by TypesetElsevier B.V.
ISSN	01678442
Open Access	No