Determination of Fracture Toughness From Small Punch Test Using Inverse Finite Element Method for In-Service Equipment

2017 ◽  
Author(s):  
Kaishu Guan ◽  
Tong Xu ◽  
Linling Guo ◽  
Mingxue Fu ◽  
Huadong Zhu
Keyword(s):  
Mechanical Properties ◽  
Finite Element Method ◽  
Fracture Toughness ◽  
Finite Element ◽  
Displacement Curve ◽  
Small Punch Test ◽  
Small Punch ◽  
Punch Test ◽  
Inverse Finite Element Method ◽  
Load Displacement

Fracture toughness is the most important reference index in safety assessment, life prediction of nuclear reactor, pressure equipment, and risk assessment of pressure equipment containing defects. Conventional mechanical test specimens require a large amount of materials and cannot be carried out on in-service pressure equipment. The specimen of small punch test (SPT) is much smaller than conventional one, and can be sampled from the surface of pressure equipment. Repair is not acquired after sampling. Many mechanical properties parameters of the material can be determined from the load-displacement curve of test. SPT makes up the deficiencies of conventional mechanical properties test. In this paper, an innovative approach, inverse finite element method (IFEM), is proposed to deal with the load-displacement curve. The procedure of IFEM can be divided into 3 steps. Step 1, a database containing a variety set of material parameters and their corresponding load-displacement curve will be built using FEM. Step 2; a set of matched material parameter of test load-displacement curve will be selected from the database by artificial neutral network (ANN). Step 3, a numerical simulation of fracture toughness test will be performed and fracture toughness Jic will be determined from the result of simulation. Compared with empirical correlation method, IFEM is much more theoretical and needs not to perform a large number of small punch tests and conventional mechanical tests to create a correlation equation between the mechanical property and load-displacement curve. So IFEM is more efficiency and accurate.

Determination and Validation of Gurson-Tvergaard Model Parameters for Finite Element Simulation of Small Punch Test

2015 ◽  
Vol 750 ◽  
pp. 59-68 ◽  
Author(s):  
Yan Yan Lu ◽  
Liang Chen ◽  
Kai Shu Guan
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Model Parameters ◽  
Displacement Curve ◽  
Small Punch Test ◽  
Test Technique ◽  
Small Punch ◽  
Punch Test ◽  
Element Simulation ◽  
Load Displacement

Small punch test (SPT) is a miniature sample test technique which can evaluate in-service material properties with an almost non-destructive method. Since the deformation behavior of the small punch specimen is complicated, finite element simulation embedded with Gurson-Tvergaard (GTN) model is adopted to simulate elastic-plastic behaviour until fracture. Choosing the proper GTN parameters is crucial for the small punch simulation, which directly influence the precision of load-displacement curve obtained from simulation. In this paper, load-displacement curve is divided into five stages and the parameters identification process is done by adjusting the simulation curve with experimental load-displacement curve in different stages which controlled by separately parameters. The results show that the parameters determined based on this criterion are not unique. In order to validate the reliability of this method, specimen’s minimum thickness of cross-section after fracture was introduced as an extra criterion which turned out to be feasible. Load-displacement curves cannot serve as the only criterion to verify the GTN parameters.

scholarly journals Equivalent biaxial strain evaluation in small punch testing using acoustic emission

2020 ◽  
pp. 030932472094406
Author(s):  
Rhys Pullin ◽  
Ifan Jenkins ◽  
Anghel Cernescu ◽  
Allen Edwards
Keyword(s):  
Fracture Toughness ◽  
Acoustic Emission ◽  
Fracture Strain ◽  
Fracture Initiation ◽  
Unstable Fracture ◽  
Displacement Curve ◽  
Small Punch Test ◽  
Acoustic Emission Technique ◽  
Small Punch ◽  
Punch Test

The small punch test initially used mainly in the nuclear sector proved to be an efficient method of estimating the mechanical properties of materials, including fracture toughness. In general, the fracture toughness is estimated based on a correlation with equivalent biaxial fracture strain. However, the latter depends on knowing the onset of the unstable fracture. In this article, the acoustic emission technique is used within the small punch test for estimating the unstable fracture initiation and determining the corresponding punch displacement from the load–displacement curve. Although, the acoustic emission signal can be slightly altered due to the location of the sensor, the results confirm the potential of the acoustic emission technique for detecting the onset of the unstable cracking and thus accurately estimating the equivalent biaxial fracture strain. The accumulated energy during the small punch test is one of the relevant acoustic emission parameters in estimating the fracture onset since it can be associated with the accumulated strain energy released by the deformed material.

Application of Small Punch Test to Evaluate Tensile Properties of SA213T22 Grade Boiler Steel

2015 ◽  
Vol 830-831 ◽  
pp. 191-194
Author(s):  
M. Venkateswara Rao
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Tensile Properties ◽  
Test Methods ◽  
Uniaxial Tensile ◽  
Test Results ◽  
Small Punch Test ◽  
Small Punch ◽  
Punch Test ◽  
Aging Phenomena

Conventional tensile test methods are used for service exposed high temperature boiler tubes to evaluate the deterioration in mechanical properties such as tensile strength, yield strength and percentage elongation. The mechanical properties are required to be evaluated periodically as the boiler components undergo material degradation due to aging phenomena. The aging phenomena occurs due to continuous exposure of tubes to high temperature & pressure steam prevailing inside the tubes and high temperature exposure to corrosive combustible gases from the external surfaces within the boiler.A recent developed new technique called small punch testing has been used to evaluate the tensile properties of SA 213T22 grade steel predominantly exists in super-heater and re-heater sections of boiler. The small punch tests have been carried out on the miniature disk shaped specimens of diameter of 8.0 mm and 0.5 mm thickness extracted from both the new and service exposed tubes. Conventional uniaxial tensile tests on standard specimens from the same tube material have also been performed for comparison. The service exposed tubes showed considerable loss in mechanical properties in both the conventional and small punch test results. Correlations of tensile properties have been obtained based on the comparative analysis of both small punch and uniaxial tensile test results. Further, the study showed that an appropriate empirical relation could be generated for new and service exposed materials between both the techniques. Conventional test methods require large quantity of material removal for test samples from in-service components whereas small punch test method needs only a miniature sample extraction. This small punch test technique could also be extended to evaluate the thicker section boiler components such as pipelines and headers in the boiler as a part of remaining life assessment study. Also this technique could be a useful tool to any metallic component where large quantity of sample removal may be difficult or may not be feasible.

scholarly journals Possibility to Estimate Fracture Toughness of Ductile Steel Materials from Small Punch Test Data

2015 ◽  
Vol 130 ◽  
pp. 1029-1038
Author(s):  
J.-Y. Jeon ◽  
Y.-J. Kim ◽  
J.-W. Kim ◽  
S.-Y. Lee
Keyword(s):  
Fracture Toughness ◽  
Test Data ◽  
Small Punch Test ◽  
Small Punch ◽  
Punch Test ◽  
Ductile Steel
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