introduction - wit press€¦ · boundary element technology 553 fatigue resistance than...

10
Preliminary high-temperature plastic deformations and fatigue resistance of titanium alloy P. D. Zhemanyuk<", V. V. Tkachenko<", I. E. Kovalev<*>, A. P.Petrov^, V.P. Dmitrenko^, S. A. Voitenko^, L. A. Pirogov^, F. P. Banas<*>, and A. E. Kovalev<*> <**Motor Sich JSC, Zaporozhye, Ukraine ™K. E. Tsiolkovsky Moscow State Aviation-Technology University, Moscow, Russia Email: [email protected] Abstract The paper presents the results of investigations of the influence of preliminary plastic deformation at high temperature on the endurance limit of pseudo- -a-titanium alloy. The original method of gauging of specimen transversal deformations during high-temperature deforming is developed. The method differs by the increased accuracy, simplicity and by extended functionalities. It is revealed that the increase of the temperature of preliminary plastic deformations of pseudo-a-titanium alloy up to 500°C results in diminishing of negative influence of plastic deformations on fatigue resistance. However, on the whole, the effect of sharp decrease of fatigue resistance in the field of deformations, which are transient from elastic to elastic-plastic, persists. The results obtained make itpossible to make prognosis of the service life of products, operating under fatigue, manufacturing process of which is connected with hot plastic deformations of the material. Transactions on Modelling and Simulation vol 22, © 1999 WIT Press, www.witpress.com, ISSN 1743-355X

Upload: others

Post on 09-Aug-2020

2 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Introduction - WIT Press€¦ · Boundary Element Technology 553 fatigue resistance than deformation in critical cross-section equal to 1.0%. The endurance limit, corresponding to

Preliminary high-temperature plastic

deformations and fatigue resistance of titanium

alloy

P. D. Zhemanyuk<", V. V. Tkachenko<", I. E. Kovalev<*>,

A. P. Petrov , V.P. Dmitrenko , S. A. Voitenko ,

L. A. Pirogov , F. P. Banas<*>, and A. E. Kovalev<*>

<**Motor Sich JSC, Zaporozhye, Ukraine™K. E. Tsiolkovsky Moscow State Aviation-Technology University,

Moscow, RussiaEmail: [email protected]

Abstract

The paper presents the results of investigations of the influence of preliminaryplastic deformation at high temperature on the endurance limit of pseudo--a-titanium alloy. The original method of gauging of specimen transversaldeformations during high-temperature deforming is developed. The methoddiffers by the increased accuracy, simplicity and by extended functionalities.It is revealed that the increase of the temperature of preliminary plasticdeformations of pseudo-a-titanium alloy up to 500°C results in diminishing ofnegative influence of plastic deformations on fatigue resistance.However, on the whole, the effect of sharp decrease of fatigue resistance in thefield of deformations, which are transient from elastic to elastic-plastic, persists.The results obtained make it possible to make prognosis of the service life ofproducts, operating under fatigue, manufacturing process of which is connectedwith hot plastic deformations of the material.

Transactions on Modelling and Simulation vol 22, © 1999 WIT Press, www.witpress.com, ISSN 1743-355X

Page 2: Introduction - WIT Press€¦ · Boundary Element Technology 553 fatigue resistance than deformation in critical cross-section equal to 1.0%. The endurance limit, corresponding to

550 Boundary Element Technology

Introduction

Taking into account the influence of preliminary plastic deformation on fatigueresistance of materials is necessary when evaluating the strength of manymachine parts and structural members, which during manufacturing weresubjected to plastic deformations. The great many of technological processes, forexample, hot rolling and forge-rolling, quenching, electron-beam welding, isconnected with plastic deformations of metals at high temperature. However, inthe literature practically there are no data concerning relation of endurance limitof materials to a degree of preliminary high-temperature deformation. It isobviously caused by large methodical complexities of experimental activities atmeasurement of elastic - plastic deformations of specimens during theirpreliminary high-temperature deforming.Due to increase of light alloys application in engineering industry the problem ofinfluence of preliminary plastic deformations at high temperature on fatigueproperties of titanium alloys becomes very actual. The importance of this problemis underlined in a number of works, devoted to IIT-3B pseudo-a-titanium alloy*,which make it possible to assume, that small plastic deformations, arising duringtechnological process (for example, electron-beam welding) at temperature of500 C result in essential decrease of fatigue resistance.Proceeding from it, the study of influence of preliminary plastic deformation athigh temperatures on endurance limit of pseudo-a-titanium alloy was carried out,the technique of measurement of magnitudes of elastic-plastic deformations ofspecimens during their preliminary high-temperature deforming was developed.

Technique of realization of experiments

The investigation of fatigue resistance was carried out with technique, permittingto determine automatically the most unfavourable value of preliminary plasticdeformation for endurance limit of a material*. The application of this techniquerequires first of all a provision for imparting plastic deformations of specificvalue to the test portion of researched specimen. It sets a problem of measurementof high-temperature deformations of specimens during their preliminary staticloading.The review of the literary data concerning this problem, has shown, that untilrecently there were no rather reliable and simple methods and means of gaugingof elastic-plastic deformations of specimens during their preliminary deforming athigh temperature.In our researches the problem was set, taking into consideration the merits ofknown engineering solutions *'*'*, to improve techniques and means ofmeasurement of a specimen transversal deformations at high temperatures (up to600'C). The special device was developed, with the purpose of increasing theaccuracy of measurements and simplification of the design by elimination of thenecessity of cooling the device, provision of the possibility to maintain the devicein standard testing machines, in particular in the YM3-10T machine.

Transactions on Modelling and Simulation vol 22, © 1999 WIT Press, www.witpress.com, ISSN 1743-355X

Page 3: Introduction - WIT Press€¦ · Boundary Element Technology 553 fatigue resistance than deformation in critical cross-section equal to 1.0%. The endurance limit, corresponding to

Boundary Element Technology 551

The YM3-IOT testing machine has an appliance for measurement ofdeformations only at normal temperatures. At the same time its heating device ofthe yH2C-1100 type is designed for carrying out tests without a shield up to700°C. An easy access to the specimen at these temperatures permits to measuretransversal deformations directly on the test part of the specimen.To expand functionalities of the YM3-10T machine the device for measurementof deformations at high temperatures is offered. The device is actually a brace,intended to embrace the specimen. The brace is cut out integrally from a plate ofa heat resisting material as two simultaneously manufactured symmetrical annularelastic elements, jointed to each other with parallel bars (Fig. 1). The measurementof elastic-plastic deformations of a specimen during the process of deforming isbased on the transformation of displacement of the body points, being plasticallydeformed, into deformations of elastic elements. The deformations of elasticelements are measured with the help of bonded resistance strain gauges andappropriate instrumentation which is included in the kit of the YM3-10Tmachine. The design of the brace allows to remove resistance strain gauges fromthe operative area of the YH2C-1100 heating device.Manufacture of the brace integrally from a plate of a heat resisting material astwo simultaneously manufactured annular elastic elements, jointed with parallelbars, and pasting on resistance strain gauges, jointed in four-arm bridge, promotesself-compensation of thermal deformations, therefore it does not require cooling.If the brace had consisted of separate elements, its joints (for example, welded,riveted, bolted etc.) would have caused non-uniformity of distribution of thermaldeformations, causing distortion of the readings of the device.In the offered device the arrangement of annular elements symmetrically withregard to each other and the connection of them with parallel bars permits toavoid non-uniformity of thermal expansion of the brace, thus considerablyreducing distorting influence of temperature deformations of the device itself.The removal of resistance strain gauges from the operative area of heatersprovides their protection from an overheating and preservation of linear relationbetween electrical resistance and deformation.When the cooling fluid circulates inside Strain Gauge for measurement of largedeformations at elevated temperatures *, the irregular deformation of levers takesplace due to temperature gradient. It results in distortion of the readings of thedevice and, hence, in significant errors in measurement of deformations of aspecimen (5-10~* units of relative deformation). Strain Gauge permits to measureat elevated temperatures only large deformations.The design features and dimensions of the new Device permit to use it in theYM3-10T testing machine and to investigate insufficiently studied problems ofalterations of material properties due to high-temperature deformation (up to600%).The device has the following advantages:

increased accuracy owing to elimination of influence of thermalexpansion of the device itself (error is 5-10"* units of relativedeformation);capability to measure high-temperature deformations of specimens of

Transactions on Modelling and Simulation vol 22, © 1999 WIT Press, www.witpress.com, ISSN 1743-355X

Page 4: Introduction - WIT Press€¦ · Boundary Element Technology 553 fatigue resistance than deformation in critical cross-section equal to 1.0%. The endurance limit, corresponding to

552 Boundary Element Technology

variable cross-section;simplicity of the design owing to elimination of such technically complexappliance, as cooling device,capability to evaluate local transversal deformations both for the case oftension and for the case of compression.

On the given Device for measurement of deformations at high temperatures theAuthor's Certificate of Russian Federation JV« 1668851 * was obtained.

Realization of experiments and their discussion

The study of influence of small preliminary plastic deformations at hightemperature (500°C) on fatigue resistance was carried out onTTT-3B pseudo-a-titanium alloy.For determination of dependence of the alloy endurance limit from degree ofpreliminary deformation, three sets of specimens were tested with maximum(along the axis) transversal plastic deformation 0 % (set 1), 0.5 % (set 2), 1 0 %(set 3). The round specimens of variable cross-section with minimum diameter oftest portion of 10 mm were tested. Each set consisted from 10 to 15 specimens.Deforming of specimens up to specific value of deformation was carried out instandard YM3-10T testing machine. The gauging of deformations wasimplemented with the help of Device for measurement of deformations at hightemperatures; the material of the brace is 3H-395 heat resisting steel. Thespecimen was heated in air within 40 minutes to temperature of 500% by meansof heat radiation created by YH2C-1100 standard device. Temperature of thespecimen test portion was monitored by a thermocouple with accuracy of ±5°C.The assembled installation for high-temperature deforming is shown in Figure2.The plastic tension of a specimen at temperature 500% up to specific value ofresidual deformation was carried out at travel speed of grips (loading rate) equalto 0.5 mm / min The kit of the VM3-IOT machine includes sensors of force,which made it possible to plot the stress-strain diagram for each specimen.After deforming the specimens were subjected to rotating bending fatigue testswith cantilever loading at frequency of 33Hz, using "up - down" method. Thebase of the tests was equal to 10^ cycles.The specimens of the sets 1 and 2 failed at critical cross-section.By results of the tests of these sets the mean value and root-mean-squaredeviation of endurance limit of the alloy was determined. For the sets 1 and 2the values of endurance limit made up 278 and 163 MPa respectively.During investigation of fractures of specimens of the third sets it was revealed,that the fatigue failures occurred outside of critical cross-section. The values ofpreliminary transversal plastic deformation in the place of crack initiation,determined by the individual S-N curves of the specimens, appeared to be equalto 0.5%. Mean values of endurance limits of specimens of this sets weredetermined by nominal stresses in cross-sections of fractures, which appeared tobe on the average by 7 % less than those in reference cross-sections. Hence,preliminary plastic deformations by value of 0.5 % cause the greater decrease of

Transactions on Modelling and Simulation vol 22, © 1999 WIT Press, www.witpress.com, ISSN 1743-355X

Page 5: Introduction - WIT Press€¦ · Boundary Element Technology 553 fatigue resistance than deformation in critical cross-section equal to 1.0%. The endurance limit, corresponding to

Boundary Element Technology 553

fatigue resistance than deformation in critical cross-section equal to 1.0%. Theendurance limit, corresponding to J .0 %, exceeds 175 MPa.The results of investigations of influence of preliminary plastic deformation athigh temperature (500 **C) on fatigue resistance of FFT-3B pseudo-a-titaniumalloy are represented on Fig.3 and in the table.

Table.Relationship between fatigue limit o./ of the alloy ETT-3B and degree of

preliminary deformation e' at high temperature

£•', %

0

0.5

1.0

cr.ie, MPa278

163

>175

Ky

1

0.59

>0.63

On the grounds of experimental data it is possible to conclude, that preliminaryplastic deformation at high temperature (500°C) considerably reduces fatigueresistance of the IIT-3B alloy. The curve of relationship of endurance limit anddegree of preliminary hot deformation has a minimum at deformation value equalto 0.5%. The endurance limit is reduced by maximum 41%The comparison of test results at normal (20°C)* and high (SOO C) temperatures(Fig.4) permits to note, that preliminary cold deforming of the TTT-3B alloy ismore unfavorable for fatigue resistance as comparative to hot deforming.However effect of a sharp drop of endurance limit in the region of minimumplastic deformations, distinctive for cold deforming , persists at hot deforming .The value of critical deformation, which mostly decreases endurance limit at hotdeforming, gets displaced in the direction of increase (from 0.2% up to 0.5 %) incomparison with cold deforming.As it is visible, the increase of temperature of preliminary deforming of pseudo--a-titanium alloy leads to diminishing of adverse influence of plasticdeformations on fatigue resistance. This regularity is in good compliance withresults ofstudy\ where it was established, that heating of the riT-3B alloy withinthe interval of temperatures from 650°C up to 1050°C entirely eliminatesinfluence of preliminary plastic deformations on endurance limit Thus, from thepoint of view of the influence of preliminary deforming on fatigue resistance ofpseudo-a-titanium alloy, the temperatures, which are lower than 650 C areunfavorable, and temperatures, over 650 °C and up to 1050 °C are favorable.The detected regularities permit to make the important practical conclusion: themanufacturing operations, causing the occurrence of small plastic deformations inpseudo-a-titanium alloy at temperature lower 650 C, adversely influence fatigueproperties. In order to increase fatigue strength of products, subjected to plasticdeforming, optimum temperature is 650 C.With reference to electron-beam welding of products from ITT-3B titanium alloy,it is possible to consider as established the fact, that sharp decrease of fatiguestrength of welded joints* is explained mainly by imparting minimum plastic

Transactions on Modelling and Simulation vol 22, © 1999 WIT Press, www.witpress.com, ISSN 1743-355X

Page 6: Introduction - WIT Press€¦ · Boundary Element Technology 553 fatigue resistance than deformation in critical cross-section equal to 1.0%. The endurance limit, corresponding to

554 Boundary Element Technology

deformations at temperature 50(fC in the cooling down metal after a cycle ofwelding.

Conclusions

1. The influence of preliminary plastic deformation at high temperature (500 C)on the endurance limit of FIT-SB pseudo-a-titanium alloy is investigated. Theoriginal method of gauging of specimens transversal deformations duringhigh-temperature deforming is developed; the method is distinguished by theincreased accuracy, simplicity and by extended functionalities.

2. It is revealed, that the effect of sharp decrease of resistance to fatigue in thefield of deformations which are transient from elastic to elastic-plastic,distinctive for cold deformation (20°C), persists during hot deformation(500 C). However, increase of temperature from 20° up to 500°C results indiminishing of adverse influence of plastic deformations on fatigue resistanceof the material. From the point of view of fatigue strength decrease, thetemperatures of preliminary deforming, which are lower than 650 C, areunfavorable.

3 The greatest decrease of endurance limit of the investigated alloy duringhigh-temperature deforming is caused by preliminary plastic deformationequal to 0.5%. The value of the decrease makes 135 MPa (41 %).

4. The described phenomena have practical importance when evaluating theservice life of products, subjected to hot plastic deformations duringmanufacturing or operation. Particularly important is the established fact, thatthe reason of significant decrease of resistance to fatigue of welded jointsfrom the IIT-3B alloy, made by electron-beam welding, is imparting smallplastic deformations to metal at temperature of 500°C.

References

1. Gladkovsky V. A., Vasserman N.N., Fatiyev IS et al. Strength ofelectron-beam welded joints of titanium alloy with aluminium andvanadium, Automatic Welding, 7, pp. 38-41, 1986.

2. Boguslayev V A., Kovalev I.E., Banas P.P., Kovalev AE On effectproduced by residual stresses and deformed surface properties on thefatigue strength of components, hardened by surface plasticdeformation. Computer Methods and Experimental Measurementsfor Surface Treatment Effects II (z<\. M.H. Aliabadi &A.Terranova), Computational Mechanics Publications, pp. 103-108,1995.

3. Jur T A Diameter gauge for use at elevated intermediate tensilestrain rates, Trats. ASME, H96, Jfs3, pp. 195-200, 1974.

4. Khristov G.P., Kiselevsky V.N., Samigullin B. A.et al. Strain-measuringdevice for measurement of transversal deformation, Authors Certificate813124, USSR.

5. Kramarev L.N. Strain Gauge for measurement of large

Transactions on Modelling and Simulation vol 22, © 1999 WIT Press, www.witpress.com, ISSN 1743-355X

Page 7: Introduction - WIT Press€¦ · Boundary Element Technology 553 fatigue resistance than deformation in critical cross-section equal to 1.0%. The endurance limit, corresponding to

Boundary Element Technology 555

deformations at elevated temperatures, Factory Laboratory, 5, pp.625-626, 1977.Ragozin U.I., Vasserrnan N.N., Gladkovsky V.A., Makarov IV,Kovalev I.E. High Temperature Strain-Measuring Device,Author's Certificate 1668851, Russia.Subbotin V.A., Nemanov AM Influence of heat treatment onmechanical characteristics and structure of welded joint of FIT3Balloy, Dynamics and Strength of Mechanical Systems, Perm,pp. 12-17, 1985.

Figure 1: Device for measurement of deformations at high temperatures

Transactions on Modelling and Simulation vol 22, © 1999 WIT Press, www.witpress.com, ISSN 1743-355X

Page 8: Introduction - WIT Press€¦ · Boundary Element Technology 553 fatigue resistance than deformation in critical cross-section equal to 1.0%. The endurance limit, corresponding to

556 Boundary Element Technology

Figure 2: Assembled installation for high-temperature deforming

Transactions on Modelling and Simulation vol 22, © 1999 WIT Press, www.witpress.com, ISSN 1743-355X

Page 9: Introduction - WIT Press€¦ · Boundary Element Technology 553 fatigue resistance than deformation in critical cross-section equal to 1.0%. The endurance limit, corresponding to

Boundary Element Technology 557

180

160

0 0.2 O.M 0.6 0.8 10 C 7L»j *O

Figure 3: Influence of preliminary plastic deforming at high temperature(500°C) on fatigue resistance of HT-3B titanium alloy

Transactions on Modelling and Simulation vol 22, © 1999 WIT Press, www.witpress.com, ISSN 1743-355X

Page 10: Introduction - WIT Press€¦ · Boundary Element Technology 553 fatigue resistance than deformation in critical cross-section equal to 1.0%. The endurance limit, corresponding to

558 Boundary Element Technology

0,55

0.50

0.2 O.M 0.6 0.8 -1.0 £, %

Figure 4: Influence of preliminary deforming at temperatures 20°C (I) and500°C (2) on fatigue resistance of FIT-IB titanium alloy

Transactions on Modelling and Simulation vol 22, © 1999 WIT Press, www.witpress.com, ISSN 1743-355X