Claims:1. A method for low cycle fatigue testing of a new nickel base casting material, Alloy 625M under total axial stain controlled condition using a modified clevis mounting system and evaluation of its fatigue life comprising steps of:
mounting of Test specimen constituting a nickel based casting material in sample mounting system, wherein the sample mounting clevises are modified with inner threading of 26 mm from top to bottom level to hold the specimen threaded end straight, to align the specimen more stable with the loading axis and to avoid twisting of specimen;
wherein specimens are fabricated with gauge length twice the test diameter as per the standard ASTM E 606;
wherein the nickel base casting material, Alloy 625M comprising of Chromium [Cr]: 20wt%-23wt%, Molybdenum [Mo]: 8wt%-10wt%, Titanium [Ti]: 0.1wt%-0.35wt%, Aluminium [Al]: 0.1wt%-0.35wt%, Iron [Fe]: 3.5wt% , Manganese [Mn]:0.2wt%-0.5wt%,Silicon [Si]: 0.2wt%-0.4wt%,Carbon[C]: 0.05wt%., Phosphorus [P]: 0.01wt% , Sulfur [S]: 0.01wt%, Niobium and Tantalum [Nb+Ta]: 3.15wt%-3.6wt% and Nickle[Ni], wherein Aluminium and Titanium [Al+Ti] is 0.2wt%-0.7wt%;
wherein a 12.5mm gauge length extensometer is mounted on the gauge length of the test specimen;
wherein an electrical resistance furnace is fixed around the test specimen to conduct a high temperature fatigue test;
wherein an R-Type thermocouple is fixed in the vicinity of the test specimen;
wherein a strain rate of 0.0029 s-1 is applied during each test;
wherein four levels axial strain (strain range: 0.5%, 0.8% 1.2% and 1.6%) controlled condition tests are carried out at a temperature of 600 Deg. C;
wherein each test is conducted in full reversal condition with strain ratio (minimum strain to maximum strain), R = -1.
2. The method as claimed in claim 1, wherein data collected from each test condition comprise of half-life plastic strain, half-life elastic strain and the plurality of measured cycles to 20% stress drop from half-life stress amplitude.
3. The method as claimed in claim 1or 2, wherein the plurality of cycles to failure data are collected at 20% stress drop from half-life stress amplitude.
4. The method as claimed in claims 1 - 3, wherein elastic strain vs. plurality of cycles to failure and plastic strain vs. plurality of cycles to failure best fit curves are generated.
5. The method as claimed in claims 1-4, wherein the best fit curve equations of elastic and plastic strain with plurality of cycles to failure best fit curves are evaluated.
6. The method as claimed in claims 1-5, wherein the curves and data of elastic and plastic strain components are superimposed to get a strain range vs. plurality of cycles to fatigue failure graph and data for the nickel base alloy, Alloy 625M and it is mentioned as follows:
Total strain range, ?? = 15.696*Nf-0.69 + 4.3905*Nf -0.195
, Description:TITLE: METHOD OF TESTING AND FATIGUE LIFE EVALUATION OF A NEW MATERIAL FOR HIGH TEMPERATURE APPLICATIONS

FIELD OF INVENTION:

[001] This invention relates to method for low cycle fatigue testing a new nickel base casting material, Alloy 625M under total axial stain controlled condition using a modified clevis mounting system and evaluation of its fatigue life.

[002] General area of invention is a method of low cycle fatigue (LCF) testing of a new nickel base super alloy casing material using a modified sample mounting system. The test is conducted under full reversal and strain controlled conditions at high temperature. Evaluation of fatigue life is done using the LCF test data. In particular, the invention relates to LCF testing of a new nickel base supper alloy, Alloy 625M material using a modified clevis mounting system and then evaluation of its fatigue life. The material is the candidate material for advanced thermal power plant turbine casing components which experience a low cycle fatigue phenomena in start-up, transient and shut down conditions.

BACKGROUND OF INVENTION/PRIOR ART:

[003] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[004] These days, around the world, inventers are putting their effort to minimize the environment pollution by optimizing the efficiency of thermal power plant like equipment. Higher efficiency of the power plants necessitates the development of high temperature fatigue and creep strength materials with high temperature corrosion resistance. Nickel base alloys are considered as the candidate materials for high temperature advanced thermal power plant turbine components. Among nickel base alloys, Inconel 625 alloy is a candidate material for turbine casing component which is subjected to a fatigue damage action during start-up, transient and shut down conditions. In India, the chemical elements of Inconel 625 are tightened and some minor elements are added and the customized version is named as Alloy 625M. This alloy is considered as the candidate alloy for Indian AUSC high pressure (HP) and intermediate pressure (IP) turbine casings applications. Therefore, it was proposed to develop a method of testing and evaluation of fatigue life of Alloy 625M at 600 deg. C temperature of AUSC HP/IP turbine casing design application.

[005] Now, reference may be made to the following patents:

S.No. Patent No. Title
1. 8532941 Fatigue life estimation method and system

2. 10094751 System and method for determining direct damage tolerance allowables

3. 10126201 Fatigue testing of a test specimen

4. 6880401 Fatigue test device and method for testing the thin plate

[006] In 8532941 patent, a method to estimate the fatigue life of a component operable under cyclic stress is provided. A system including testing device for performing a strain controlled test of a component or a representative specimen of the component, to obtain therefrom a first set of data samples including measured stress amplitude values for varying applied strain levels, and a second set of data samples including measured number of cycles to crack initiation for varying applied strain levels is also provided.

[007] The system further includes a modeling device for fitting a first low cycle fatigue material curve on the first set of data samples and a second low cycle fatigue material curve on the second set of data samples.

[008] Limitation: Sample mounting system is not disclosed. Specimen dimension and material composition details is not disclosed. Further, detailed testing method including strain rate and high temperature ambient conditions applications are not described in the cited patent.

[009] In 10094751 patent, a method of determining damage tolerance allowables in a specimen is described. The method includes applying a cyclic load to a specimen until a first crack emanates from a notch in the specimen, the cyclic load having a maximum load and a minimum load. The method also includes applying a subsequent cyclic load to the specimen until the first crack grows to form a second crack emanating from the first crack, the subsequent cyclic load having the same maximum load but a greater minimum load.

[0010] Limitation: The test method does not include cyclic fatigue testing under strain controlled conditions. The test method discloses the testing of notched specimen under load control. The method does not include high temperature and strain rate applications. Also, life evaluation method is not included.

[0011] In 10126201 patent, the invention pertains to a combination of a test rig and test specimen for performing a fatigue test, wherein the test specimen is non-axisymmetric and comprises:—a central element,—a first branch element, which has a longitudinal axis that extends at an angle to the longitudinal axis of the central element,—a joint connecting the first branch element to the central element, which has an in plane bending resonance frequency with an associated in plane bending mode shape, and an out of plane bending resonance frequency with an associated out of plane bending mode shape, wherein the in plane bending resonance frequency and the out of plane bending frequency are substantially the same, wherein the first node of the in plane bending mode shape and the first node of the out of plane bending mode shape are substantially at the same position at the first branch element and wherein the test rig comprises:—a support for supporting the test specimen,—an excitator for subjecting the test specimen to forced vibration.

[0012] Limitation: Specimen used is non-axisymmetric wherein in the present invention, a round axis symmetric specimen is used. The test has been performed in forced vibration control and hence, the testing method is different from the present invention. Life evaluation method is not discussed.

[0013] In 6880401 patent, the invention discloses a fatigue test device for testing thin plates. The fatigue test device has a rod having ends in a longitudinal direction thereof; a vibration source for excitating a longitudinal end of the rod in the longitudinal direction thereof so as to form a standing wave having node portions and antinode portions formed there between and a mounting means for mounting a test piece having a longitudinal direction at one of the antinode portions, the test piece being positioned such that the longitudinal direction thereof is perpendicular to the longitudinal direction of the rod.

[0014] Limitation: This patent discloses a fatigue test method and system for testing thin plates which is different test from the present invention. Material of testing is not disclosed. Life evaluation method is also not mentioned.

[0015] The present invention proposes Nickel based super alloy turbine casing material and method of testing thereof for high-temperature applications, which can address the drawbacks of the prior arts and serve the purpose of the invention for which it is devised.

OBJECTS OF THE INVENTION:

[0016] Primary object of the present invention is to provide method for low cycle fatigue testing a new nickel base casting material, Alloy 625M under total axial stain controlled condition using a modified clevis mounting system and evaluation of its fatigue life.

[0017] An object of the present invention is to develop a method of testing and evaluation of fatigue life of a new nickel base material for advance ultra-super critical thermal power plant HP/IP turbine casings design applications.

[0018] Another object of the invention is to modify the sample mounting system, wherein the clevises for specimen mounting is to be modified to ensure stable alignment of the test samples with the axis of loading and avoiding twisting.

[0019] Another object of the invention is to fabricate the test samples as per the standard ASTM E 606.

[0020] Yet another object is to test the nickel base alloy under strain controlled fatigue regime, wherein extensometer, strain rate, strain range and temperature for the test are to be selected.

[0021] A further object is to collect the data of half-life plastic strain, half-life elastic strain and plurality of measured cycles to 20% drop from half-life stress amplitude.

[0022] A further object is to generate elastic strain vs. plurality of cycles to failure and plastic strain vs. plurality of cycles to failure best fit curves.

[0023] A further object is to generate the best fit curves of elastic and plastic strain components of low cycle fatigue testing with popularity of cycles to failure.
[0024] A further object is to evaluate the constants and equations of curves of elastic and plastic strain components of low cycle fatigue testing with popularity of cycles to failure.

[0025] A further object is to superimpose the elastic and plastic strain range data and curves to get a total strain range vs. plurality of cycles to failure data and curve.

[0026] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF INVENTION:

[0027] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.

[0028] The present invention discloses a method of testing, low cycle fatigue of a new nickel base alloy, Alloy 625M using a modified mounting system. The clevises of sample mounting was fabricated with complete inner hole threading to support full threading portion of the specimen. The sample gauge length was considered as twice the specimen diameter. The samples were tested under full reversal and strain control. The tests were conducted at temperature, 600 degree C for four strain ranges. An electrical resistance furnace was used for high temperature application. An axial extensometer was mounted on the test specimen for conducting a strain controlled test. All fatigue tests were carried out on a servo electric 100kN Universal Testing Machine (UTM). After each test, data were collected for strain range-fatigue life evaluation. Strain vs. plurality of cycles to failure data were evaluated and curve was generated for Alloy 625M material. The fatigue life curve and data generated will be used for Advanced Ultra Super Critical HP/IP turbine casings design applications.

[0029] The objective of the present invention is achieved by the features of principal claims 1 and 2 followed by subsequent claims 3-7.

[0030] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[0031] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[0032] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0033] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:-
[0034] Figure 1 shows: Sample mounting clevise with threaded inner hole depth of 26 mm from top to bottom level according to the present invention.

[0035] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAIL DESCRIPTION OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS OF PREFERRED EMBODIMENTS

[0036] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[0037] The present invention makes a disclosure regarding a technology pertaining to method for low cycle fatigue testing a new nickel base casting material, Alloy 625M under total axial stain controlled condition using a modified clevis mounting system and evaluation of its fatigue life.

[0038] In this invention, a material, Alloy 625M (nickel base alloy) casting is provided for low cycle fatigue testing samples preparation. The alloy is chemically customized Indian version of Inconel 625 material. This material is designed to use for Indian Advanced Ultra Super Critical (AUSC) HP/IP turbine casing design applications.

[0039] Test specimen constitutes a nickel base casting material comprising of Chromium [Cr]: 20wt%-23wt%, Molybdenum [Mo]: 8wt%-10wt%, Titanium [Ti]: 0.1wt%-0.35wt%, Aluminium [Al]: 0.1wt%-0.35wt%, Iron [Fe]: 3.5wt%, Manganese [Mn]:0.2wt%-0.5wt%,Silicon [Si]: 0.2wt%-0.4wt%,Carbon[C]: 0.05wt%., Phosphorus [P]: 0.01wt% , Sulfur [S]: 0.01wt%, Niobium and Tantalum [Nb+Ta]: 3.15wt%-3.6wt% and Nickle[Ni]. Here in this composition Aluminium and Titanium [Al+Ti] is[ 0.2wt%-0.7wt%.

[0040] Before application, various mechanical and fatigue design data were required. Therefore, it is proposed to carry out low cycle fatigue testing on Alloy 625M and evaluate its fatigue life for AUSC HP/IP turbine casings design applications.

[0041] For this, M12 samples are prepared as per the standard ASTM E 606. The gauge length of the sample is taken as twice the test specimen diameter.

[0042] According to this invention, the sample mounting system is modified. The clevises of sample mounting is fabricated with complete inner hole threading (top-to-bottom) with inner hole threading depth 26mm to support full threading portion of the specimen as shown in Figure – 1.

[0043] The instant invention proposes method for low cycle fatigue testing a new nickel base casting material, Alloy 625 under total axial stain controlled condition using a modified clevis mounting system and evaluation of its fatigue life comprising following steps of:
• mounting of Test specimen constituting a nickel based casting material in sample mounting system, wherein the sample mounting clevises are modified with inner threading of 26 mm from top to bottom level to hold the specimen threaded end straight, to align the specimen more stable with the loading axial and to avoid twisting of specimen;
• wherein specimens are fabricated with gauge length twice the test diameter as per the standard ASTM E 606;
• wherein a 12.5mm gauge length extensometer is mounted on the gauge length of the test specimen;
• wherein an electrical resistance furnace is fixed around the test specimen to conduct a high temperature fatigue test;
• wherein an R-Type thermocouple is fixed in the vicinity of the test specimen;
• wherein a strain rate of 0.0029 s-1 is applied during each test;
• wherein four levels axial strain (strain range: 0.5%, 0.8% 1.2% and 1.6%) controlled condition tests are carried out at a temperature of 600 Deg. C;
• wherein each test is conducted in full reversal condition with strain ratio (minimum strain to maximum strain), R = -1.

Testing Procedure

[0044] The new mounting clevis keeps the specimen well aligned and stable to the loading axis as compared to the old clevis. The samples are tested under full reversal and strain control with a strain rate of 0.0029 s¬¬-1. The tests are conducted at temperature, 600 degree C for the strain ranges of 0.5%, 0.8%, 1.2% and 1.6%. An electrical resistance furnace is used to apply 600 degree C temperature as ambient temperature condition of the test specimen each time. The temperature is maintained within the range from – 2 degree C to + 2 degree C. R-type thermocouple is fixed in the vicinity of each test specimen. An extensometer with 12.5mm gauge length is mounted on the test specimen for conducting a strain controlled test for the above four strain ranges. The all tests are carried out on a servo electric 100kN UTM. After each test, data are collected for half-life plastic strain amplitude, half-life elastic strain amplitude and plurality of cycles to drop 20% of half-life stress amplitude. Based on these data, plastic strain vs. plurality of cycles to sample failure and elastic strain vs. plurality of cycles to sample failure curves are plotted. Best fit curve functions of both the graphs are evaluated. The two curves data are superimposed to get total strain range values and its equation is mentioned as follows for Alloy 625M material.

[0045] Total strain range, ?? = 15.696Nf-0.69 + 4.3905 Nf -0.195

[0046] Where, ‘Nf’ is the popularity of cycles to failure

[0047] The fatigue strain range -life curve and data generated are used for Advanced Ultra Super Critical HP/IP turbine casings design applications.

[0048] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[0049] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

[0050] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogues to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[0051] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.

[0052] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.

[0053] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.

[0054] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.