9th International Conference on Quantitative InfraRed Thermography

July 2-5, 2008, Krakow - Poland

Thermomechanical properties of shape memory polymer SMP subjected to tension and simple shear process

by E.A. Pieczyska*, W.K. Nowacki*, H. Tobushi** and S. Hayashi***

*Institute of Fundamental Technological Research, PAS, Warsaw, Poland

**Department of Mechanical Engineering, AIT, Toyota-city, Japan

*** DiAPLEX Co., Tokyo, Japan, Ltd

Abstract Thermomechanical and functional properties of shape memory polymer (SMP) have been presented. A

background of the polymer shape memory effects was described. Taking advantages from high quality testing machine and infrared camera, mechanical characteristics and temperature changes of the shape memory polyurethane specimens subjected to tension and simple shear processes were clarified and discussed. Basing on the mechanical characteristics and the relevant temperature changes, the shape memory polyurethane thermomechanical properties have been studied. Taking into account the tests carried out with various strain rates, the influence of the strain rate on the polymer mechanical behavior was discussed.

1. Introduction - description of shape memory polyurethane properties

The material is said to demonstrate a shape memory properties since it can be deformed, fixed into a

temporary shape, and recover its original shape, during exposure to an external stimulus. The shape memory property of polymer is related to the change of its elastic modulus under various conditions; however the most common activator is a heat. Elastic modulus differs at temperatures above and below the glass transition temperature Tg , and therefore the rigidity of SMP elements vary depending on temperature. Shape memory polymer processed into permanent shape is deformed and fixed with this shape [1]. After heating above its glass transition temperature, the parent shape is recovered, as it was schematically shown in Fig.1.

Loading ! Glass state Rubber state Fixed shape Recover shape

T < Tg T> Tg T< Tg T> Tg

Fig. 1. Scheme of shape memory phenomena activated by heat in shape memory polymer These characteristics can be applied to intelligent elements in various fields. In order to use them to design

intelligent systems properly, it is important to understand their thermomechanical properties. The relationship between elastic modulus E and temperature T obtained by the dynamic mechanical tests

on SMP is shown in Figure 2(a). In the figure, E is expressed in logarithmic scale and T in a reciprocal normalized by Tg. As seen in Figure 2(a), E varies markedly in the glass transition region but is almost constant above and below the glass transition region (T=Tg±15K). As shown in Figure 2(b), the relationship between log E and Tg/T is approximately represented by a straight line with a slope of a.

The relationship in the glass transition region wgwg TTTTT +≤≤− is expressed as follows:

−=− 1 log log

T

TaEE

g

g (1)

Thus E becomes

E E aT

Tg

g= −

exp 1 (2)

where Eg is the value of E at T=Tg. As seen in Figure 2(b), Eh and El denote the values of E above and below the glass transition region, respectively [1, 2].

2. Experimental procedure

The main reason why the shape memory polyurethane is drawing attention is its low weight, high in shape

recoverability and fixity, easy production techniques, the phase transition temperature around the room and body temperature and low cost, in comparison to shape memory alloys. Since the SMP characteristics are being used

9th International Conference on Quantitative InfraRed Thermography

for design of temperature sensors and actuators working in various regimes, the above described properties are investigated in various conditions.

In the presented below research, the shape memory polyurethane properties have been investigated in two ways:

1. comparison of results of tensile tests carried out in the region above and below the polyurethane glass transition temperature Tg .

2. tensile and simple shear tests carried out in room conditions, followed by the specimen heating above the polyurethane glass transition temperature Tg. 2.1. Investigation of the polyurethane shape fixity and shape recovery

Ad. 1. The goal of the shape memory polyurethane tensile tests performed at various temperatures, in the

regions above and below the Tg, was obtaining material parameters, important for the practical applications, called shape fixity and shape recovery.

0.9 0.95 1 1.05 1.1

T g /T

E M

Pa

104

103

102

101

T g +15K T g T g -15K

T g /T

E (

log

sca

le)

E l

E g

E h

T g /(T g +T w ) T g /(T g -T w )1

a

T g

1

(a) Experimental result (b) Approximate curve

Fig. 2. Relationship between elastic modulus and temperature of shape memory polyurethane

The stress-strain curves and strain-temperature curves obtained from the test are shown in Figure 3. As

seen in Figure 3(a), during the loading process (1) up to maximum strain mε at temperature Th=Tg+20K, the strain

increases nonlinearly when stress becomes large. In the cooling process (2) from Th to Tl=Tg-20K under

constant mε , stress increases. In the unloading process (3), the slope of the curve is steep and the strain uε at a

termination point of unloading is close to mε . The ratio mu εε / represents the rate of shape fixity and approaches

1 if mε becomes large. The ratio mirm εεε /)( − represents the rate of shape recovery, where mε and irε

represent the strain obtained after holding no-load condition below Tg and the strain obtained after heating up to above Tg under no-load condition, that is, irrecoverable strain, respectively.

Elastic modulus of SMP is large at the low temperature Tl and small at the high temperature Th. We can use excellent shape fixity of shape memory polyurethane elements by applying the difference of elastic modulus between Tl and Th. As seen in Figure 3(b), during the heating process (4) under no-load, strain is recovered. Strain is markedly recovered in the vicinity of Tg.

The polymer behavior in the changing temperature conditions can be explained like this. Shape memory polyurethane is composed of soft segments and hard segments. Micro-Brownian motion of soft segments is frozen at the temperatures below Tg but it is activated at the temperatures above Tg. Therefore the amount of strain recovery is small at low temperature, but becomes large in the vicinity of Tg due to the activated micro-Brownian motion [1, 2].

SOLID MECHANICS

0

1

2

3

4

5

0 5 10 15 20 25

Strain %

Str

ess

MP

aεεεεm=20%

�

�

�

�

Experimental

Calculated

0

5

10

15

20

25

300 310 320 330 340 350 360

Temperature K

Str

ain

%

T gεεεεm=20%

Experimental

Calculated

(a) Stress-strain curves (b) Strain-temperature curves

Fig. 3. Stress-strain curves and strain-temperature curves in tension

2.2. Experimental details for tension and simple shear performed in room conditions

Ad. 2. The goal of the investigations performed at room temperature was to check and to reveal that the strain

and the accumulated defects, introduced to the shape memory polyurethane even in its glass state, can be removed during the following heating above the glass transition temperature Tg. In addition, the obtained stress-strain curves and related to them, temperature changes accompanying the polymer tension and simple shear, allowed to estimate the polymer mechanical properties.

Tension tests and simple shear tests have been performed in quasistatic range of the strain rate: 10-2

s-1

, 10

-1s

-1, 10

0s

-1. The methodology applied for investigation into thermomechanical properties of the shape memory

polymers is based on the scheme shown in Fig. 4. A specimen with the shape designed according to the program of investigation, was fixed in the testing

machine with hydraulic drive, allowing for obtaining the required kind of the test with the proper strain rate. On the other hand, a infrared camera (ThermaCAM

tm PM 695) was used in order to find the temperature distributions of the

material subjected to study, i.e. thermograms, stored in a digital form with a maximal frequency of 50Hz. That allows for reproduction and calculation of the specimen temperature variation in contact-less way, straightforward, as a function of time or other parameters of the deformation process.

For the investigations three kinds of temperature registration were applied: 1. temperature distribution on the specimen surface, 2. average temperature taken from the chosen specimen area, 3. change in temperature in a chosen point on the specimen surface.

Fig. 4. Scheme and photograph of the experimental set-up The average temperature was calculated over the area located in the central part of the specimen, the

same for particular kind of the test. The average temperature is usually used in the curves and the graphs showing thermomechanical coupling analysis. The accuracy of the average temperature measurement was up to 0.02K. All tests were performed at room temperature 295 K and at the air humidity of 60%.

INFRARED

CAMERA

G

L

TESTING MACHINE

SMP SPECIMEN

εεεε

T

εεεε

�

9th International Conference on Quantitative InfraRed Thermography

3. Theoretical framework of thermomechanical coupling analysis Effects of thermomechanical coupling in solids that are of frequent occurrence in nature have had a long

history in both theoretical and experimental works. The problem has been started to be develop by Kelvin [3]. The coupling effects accompanying the initial elastic deformation are related to the pressure or volume change of the body subjected to loading:

± ∆p → ± ∆T or ± ∆V → ± ∆T ; where: p is the pressure, V is the volume and T is the absolute temperature of the body.

The temperature change of a specimen subjected to adiabatic uniaxial elastic deformation ( ∆Tel ), related

to the pure volumetric deformation and called the thermoelastic (piezocalorimetric) effect can be derived from the first law of thermodynamics, and defined as follows:

∆∆

TT

cel

s

p

= −α σ

ρ, (3)

where: α - the coefficient of thermal expansion, T - the absolute temperature, ∆σ s - the isentropic stress

change, cp - the specific heat per unit volume at constant pressure, ρ - the material density.

The temperature changes can be positive, negative or equal zero, according to the kind of deformation (compression, elongation, shear, torsion), and while for the metals do not exceed 0.2 K with initial reversible deformation ranges, for polymers are significantly higher [4-6].

4. Simple shear test – introduction

Idea of simple shear test technique and measurement of the specimen temperature during the shear

process is described in Fig. 5. A specially designed grip enables to replace the compression into the simple shear according to the innovative technique, elaborated by W.K. Nowacki [7]. Construction of the shear grip allows for observation the shear zones during the deformation process. Thermovision camera was used to register the distribution of the infrared radiation emitted by the shear zones of the specimen in order to obtain the temperature changes accompanying the deformation process. The temperature changes cab be presented as a function of time or various mechanical parameters.

(a) (b)

F-force, ∆l- displacement of grips, ao - width of shear band, d - thickness of specimen, l -length of shear

zone (c)

Fig. 5. Analysis of process of simple shear; scheme of the specimen before (a) and after the shear process (b) and photograph of the shear device in grips of the testing machine (c)

30

Shearzones

42.333

42.3

30

Shearzones

33

Grips of testing machine

Shear device with SMP specimen inside

Infrared camera

oS

F

212=σ

oa

l∆=γ

SOLID MECHANICS

Investigations of shear are very important for both the research and applications, since: - machine parts during normal work and damage usually work in such conditions - this kind of deformation allows for obtaining homogeneous stress and strain state in wider range of

deformation without any localization, in comparison to tension - thermoelastic, i.e. Kelvin effect does not occur during the shear process, since here is no volume change.

5. Shape memory polyurethane specimens Two plates of shape memory polyurethane, with the sizes 150x10 x3.4 mm and Tg=328K, for the joint

research carried out in IFTR PAS, according to the Agreement with Mitsubishi Heavy Industries, Ltd, were obtained. The specimens for the tension tests and the specimens for the simple shear tests were cut off from the materials, respectively. Unfortunately, the sheet width of the obtained material was not uniform - it was changing from 3.4 mm to 4 mm. Therefore, the mechanical characteristics could not be obtained with the highest accuracy and the conditions for the stress and strain localization were not only caused by the pure deformation process but also due to the geometrical variations.

a) b)

Fig. 6. Shape memory polyurethane specimens for tension (1) – before test; (2), (3), (4) – after deformation; (5), (6) – after tension test and heating above glass transition Tg temperature

a) b)

Fig. 7. Shape memory polyurethane specimens for shear test; a),b) (1)– before test, (4) after shear test, a) (2),(3),(4) – after test; b) (2),(3) after shear test and heating above Tg temperature

The sizes of the specimens were as follows: 150 mm x 10 mm x 3.4 mm for tension tests (Fig. 6), 42 mm x

30 mm x 3.4 mm for shear tests (Figs 5 and 7).

6. Tension tests of shape memory polyurethane - experimental results During the tension tests an extensometer was used in order to register the specimen strain with higher

accuracy. From the beginning of the SMP deformation, almost a linear dependence between the stress and the strain is observed, Fig. 8a. At the strain of about 25%, a band of localized deformation appears, inclined by about 50 degree to the tension direction. Initially, the localization was noticed only by infrared camera due to the higher temperature, Fig. 8b; next it was more significant and noticeable also by naked eye due to some bands and white color (polymer crazing phenomena), and finally development of significant necking was observed, in particular by infrared camera, Fig. 9.

2

2 2 2 2

2

9th International Conference on Quantitative InfraRed Thermography

a) b)

Fig. 8. a) Stress σ and average temperature vs. time T∆ , b) stress σ and average T∆ and the point of

localization temperature locT∆ vs. time for SMP tension test at room temperature with the strain rate 0.77x10-2

s-1

.

Fig. 9. Thermogram showing localized band of deformation beyond the G.L. in SMP One can notice that the thermoelastic effect, i.e. drop in the average temperature up to 1.5K, related to the

pure elastic deformation is observed till the onset of localization, Fig. 8a. This means that the material as the whole specimen did not enter the next, plastic stage of deformation, always accompanied by the temperature increase. It was confirmed by Fig. 10, since almost linear dependence between the temperature change and the stress values up to 60 MPa has been recorded, according to the Kelvin law.

Fig. 10. Temperature vs. stress for SMP tension test at room temperature with the strain rate 0.77x10

-2s

-1

On the other hand, in the area of the localized band, a very high temperature rise, up to 20K, has been

recorded by the infrared camera (Fig. 8b). In order to avoid the strain localization, during the following test, the SMP specimen was deformed with the

higher strain rate, till fixed strain limit, and unloading.

0 5 10 15 20Time (s)

0

20

40

60

80

Str

ess (

MP

a)

SMP1 ε = 0.77 * 10-2

s-1.

-2.0

-1.5

-1.0

-0.5

0.0

Te

mpera

ture

va

riation (

K)σ

∆Τ

0 5 10 15 20Time (s)

0

15

30

45

60

75

Str

ess (

MP

a)

SMP1

ε = 0.77 * 10-2

s-1.

-5.0

0.0

5.0

10.0

15.0

20.0

Tem

pera

ture

va

riation (

K)σ

∆Τ

∆Τλοχ

0 20 40 60 80

True stress (MPa)

-1.5

-1.0

-0.5

0.0

Tem

pera

ture

vari

ation (

K)

SMP1 ε = 0.77 * 10-2

s-1.

>

<

SOLID MECHANICS

a) b)

Fig. 11. Stress vs. true strain (a) and stress σ and temperature change T∆ vs. time (b) for SMP tension

test at room temperature with the strain rate 0.82x10-2

s-1

The stress vs. strain curve for this test is shown in Fig. 11a, while the specimen stress and the average

temperature changes during the time are presented in Fig. 11b, respectively. The both curves confirm that the elongation occur in almost reversible strain range. Similar conclusions can be drawn from the temperature vs. true stress graph, shown in Fig.12.

Fig. 12. Temperature vs. stress for SMP tension test at room temperature with the strain rate 0.82x10-2

s-1

. The next test (Fig. 13) was performed for the same strain limit, up to 3 mm, however with significantly

lower strain rate. At the end of the straining, 2 bands of cross-shape localization appear, at the gage lengths border of the SMP specimen.

a) b)

Fig. 13. a) Stress σ and average temperature variation T∆ and the point of localization temperature locT∆ vs.

time; b) temperature vs. true stress, obtained for SMP tension test

0.00 0.01 0.02 0.03 0.04True strain

0

20

40

60

80S

tre

ss (

MP

a)

SMP2 ε = 0.82 * 10-2

s-1.

0 20 40 60 80

True stress (MPa)

-1.5

-1.0

-0.5

0.0

Tem

pera

ture

varia

tion

(K

)

SMP2 ε = 0.82 * 10-2

s-1.

>

<0.0 2.5 5.0 7.5 10.0

Time (s)

0

20

40

60

80

Str

ess (

MP

a)

SMP2

ε = 0.82 * 10-2

s-1.

-2.0

-1.5

-1.0

-0.5

0.0

Te

mp

era

ture

va

ria

tio

n (

K)

σ

∆Τ

0 20 40 60 80Time (s)

0

20

40

60

Str

ess (

MP

a)

SMP3

ε = 0.77 * 10-2

s-1.

-2.0

0.0

2.0

4.0

Tem

pera

ture

varia

tion (

K)

σ

∆Τ

∆Τloc

0 20 40 60

True stress (MPa)

-1.0

-0.5

0.0

0.5

Tem

pera

ture

variation (

K)

SMP3 ε = 0.77 * 10-3

s-1.

>

<

9th International Conference on Quantitative InfraRed Thermography

In the localization area, the temperature decrease up to 1.7 K followed by the increase in temperature above 2K was observed, while the whole specimen did not enter the plastic deformation stage (Fig. 13 a). After the test was completed, the specimen was heated in the temperature 343 K during 20 min. The specimen length completely returns to his previous state and the cross-bands almost disappeared; Fig. 6; specimens (5), (6).

In order to investigate the material behavior after performing the test and subsequent heating beyond the glass transition temperature Tg, the next test was carried out with similar strain rate on the specimen used in the former tension test followed by the heating. The mechanical and temperature results are shown in Figs. 14 and 15.

a) b)

Fig. 14 a) Stress vs. strain, b) stress σ �and temperature variation T∆ vs. time for the specimen subjected to

similar test and next heating with strain rate 0.81x10-2

s-1

Fig. 15. Temperature vs. stress for SMP tension test with strain rate 0.81x10-2

s-1

performed on the specimen subjected to similar test and next heating above Tg.

The obtained graphs indicate on not exactly the same thermomechanical behavior of the shape memory

polyurethane after the straining and subsequent heating processes, namely the maximal stress is significantly lower and the residual strain is higher, in comparison to the thermomechanical behavior of the virgin specimen.

7. Simple shear tests of shape memory polyurethane - experimental results

The obtained mechanical and temperature results for the shape memory polyurethane subjected to simple

shear deformation with various strain rates are shown in next figures, Figs 16-19. After significant range of the elastic deformation, quite long range of almost uniform shear deformation is observed (Fig. 16). The higher the strain rate, the higher value of the stress level was achieved, like for other kinds of polymers [5, 6], while for metals no difference in this range of the strain rates had been observed [7].

Looking at the mechanical characteristics one can notice that even for the complete shear limit chosen, i.e. up to 65%, irrespectively of the strain rate applied the stress-strain curves are smooth and any macroscopic shear localization is recorded. Moreover, for the higher strain rates more pronounced yield point appears (Fig. 16).

0.00 0.01 0.02 0.03 0.04True strain

0

20

40

60

80

Str

ess (

MP

a)

SMP2w1 ε = 0.81 * 10-2

s-1.

0.0 2.5 5.0 7.5 10.0 12.5Time (s)

0

20

40

60

Str

ess (

MP

a)

SMP2w1

ε = 0.81 * 10-2

s-1.

-1.5

-1.0

-0.5

0.0

Te

mp

era

ture

va

riatio

n (

K)σ

∆Τ

0 20 40 60

True stress (MPa)

-1.2

-0.8

-0.4

0.0

Tem

pera

ture

varia

tion (

K)

SMP2w1 ε = 0.81 * 10-2

s-1.

>

<

SOLID MECHANICS

Fig. 16. Shear stress vs. strain obtained for SMP subjected to shear with strain rates: 10

-2s

-1 , 10

-1s

-1, 10

0s

-1.

The graphs shown in Fig. 17 presents stress and temperature variation vs. time obtained for the strain rate

10-2

s-1

, 10-1

s-1

, 100s

-1 , respectively. The temperature characteristic was obtained as an average temperature of

segments of line in central part of two shear specimen zones. One can notice that the temperature decreases in the initial, completely reversible part of the curve. It never occurs during the shear process registered for metals and alloys; however it was also recorded during the former tests performed on polyamide and copolymer [5, 6]. The decrease in temperature is probably caused by the straightening of the polymer chains in the initial stage of loading and deformation, related to the drop of the polymer entropy.

After the reversible elastic deformation, a temperature increase is observed. For the strain rate100s

-1 a

localized deformation along the shear zones was recorded by the infrared camera, i.e. thermographs shown in Fig. 18. Also the point temperature variation presented in Fig. 17c manifests this localization showing why the shear stress decreases in spite of the fact that the run of the average temperature is similar to those observed for the strain rate10

-1s

-1 when any macroscopic localization was noticed.

a) b) c)

Fig. 17. Stress σ and temperature variation T∆ vs. time obtained for SMP subjected to simple shear with strain

rate 10-2

s-1

, 10-1

s-1

, 100s

-1 . mT∆ denotes temperature from the shear zone borders, in the area where the higher

temperature related to the strain localization was observed.

Shear

zones

Fig. 18. Thermograph of shear grip and SMP specimen during the shear process with strain rate100s

-1

0.0 0.2 0.4 0.6 0.8Shear strain

0

10

20

30

40

She

ar

str

ess (

MP

a)

SMP-sc γ =100s

-1.

Simple shear

γ =10-2

s-1.

γ =10-1

s-1.

0 25 50 75 100Time (s)

0

10

20

30

40

Str

ess (

MP

a)

SMPsc1 γ = 10-2

s-1.

-1.0

-0.5

0.0

0.5

1.0

Te

mp

era

ture

vari

ation (

K)

σ

∆Τ

0 4 8 12Time (s)

0

10

20

30

40

Str

ess (

MP

a)

SMPsc2 γ = 10-1

s-1.

-2

-1

0

1

2

Te

mpera

ture

variation (

K)σ

∆Τ

0 1 2 3 4 5Time (s)

0

10

20

30

40

Str

ess (

MP

a)

SMPsc3 γ = 100s

-1.

-1

0

1

2

3

Te

mp

era

ture

vari

ation

(K

)

σ

∆Τ

∆Τm

9th International Conference on Quantitative InfraRed Thermography

The results of thermomechanical couplings, i.e. the temperature variations presented as a function of

stress for the SMP subjected to simple shear tests with various strain rates are shown in Figs. 19 a, b, c. a) b) c)

Fig. 19. Temperature variation vs. stress obtained during SMP simple shear with strain rates 10-2

s-1

, 10-1

s-1

,100s

-1

At the beginning of the loading, the drop in temperature is observed, followed by the temperature increase,

always accompanied the process of plastic deformation in any solids. During the unloading, an increase in temperature, very small and followed by the temperature decrease due to the heat exchange for the lowest strain rate was observed (Fig. 19a), while for the higher strain rates quite significant increase in temperature was recorded (Figs. 19 b, c), related to effects of relaxation and thermoelastic unloading [5, 6]. For the highest shear rate, equal to 10

0s

-1, the thermomechanical coupling characteristics even as the average temperature vs. stress

curve (Fig. 19c) manifests the strain localization - the curve is not smooth.

8. Summary High values of shape fixity and shape recovery enable diversity of the polyurethane practical applications. The shape memory polyurethane is characterized by good mechanical properties which were confirmed by

both the tension and the shear tests. The stress-strain curves for the shape memory polyurethane are very sensitive to the strain rate, in quasi-

static range of the strain rates applied, for both the tension and shear tests. The strain localization during tension test performed with low strain rates has been observed, while for

higher strain rates the process is much more homogeneous. On the other hand, during the shear test the localization was observed for higher strain rates. Infrared technique is very useful in monitoring of the localized strain nucleation and its further developing, since it was not always detected by traditional techniques.

During heating above the polymer glass transition temperature, the localized deformation bands vanishes which confirms good shape memory properties. However, the mechanical properties found for the specimen with an material history are lower and the residual stress is higher in comparison to the shape memory virgin material.

Acknowledgments: The research has been carried out with the support of the Japan Society for the Promotion of Science;

Post-doc ID No. P04774, and by the Polish Ministry of Science and Higher Education under Grant No. N N501 0106 33. The assistance of Dr. S.P. Gadaj in obtaining the experimental results is greatly appreciated. Authors also wish to express the gratitude to the Mitsubishi Heavy Industries Ltd., for providing them with shape memory polyurethane specimens for the joint research carried out in IFTR PAS (Poland) and AIT (Japan).

REFERENCES:

[1] Hayashi S. Properties and Applications of Polyurethane-series Shape Memory Polymer, Int. Progress in

Urethanes, Vol. 6 (1993) 90 – 115. [2] H. Tobushi, K. Okumura, S. Hayashi and N. Ito. Thermomechanical constitutive model of shape memory

polymer, Mechanics of Materials, 33, (2001) 545-554. [3] W. Thomson, (Lord Kelvin). Quart. J. Pure and Appl. Math, 1, 57, 1857; Math. and Phys. Papers, v.1,

291,1882. [4] E.A. Pieczyska, S.P. Gadaj. Thermoelastic Effect during Tensile Cyclic Deformation, Engin. Trans., 45, 2

(1997) 295- 303. [5] E.A. Pieczyska, S.P. Gadaj, W.K. Nowacki. Thermoelastic and thermoplastic effects investigated in steel,

polyamide and shape memory alloys; Proc. of SPIE, Thermosense XXIV, USA, 4710 (2002) 479-497. [6] E.A. Pieczyska, S.P. Gadaj, W.K. Nowacki. Temperature changes in polyamide subjected to tensile

deformation; Infrared Physics and Technology, 43/3-5 (2002) 183-186. [7] S.P. Gadaj, W.K. Nowacki, E.A. Pieczyska. Changes of temperature during the simple shear test of

stainless steel, Arch. Mech., 48-4 (1996) 779-788.

0 10 20 30 40

Stress (MPa)

-0.5

0.0

0.5

1.0

1.5

Te

mp

era

ture

vari

ation

(K

)

SMPsc2 γ = 10-1

s-1.

>

0 10 20 30 40

Stress (MPa)

-0.5

0.0

0.5

1.0

Te

mp

era

ture

vari

ation

(K

)

SMPsc3 γ = 100s

-1.

>

0 10 20 30 40

Stress (MPa)

-0.5

0.0

0.5

1.0

Tem

pe

ratu

re v

ariation

(K

)

SMPsc1 γ = 10-2

s-1.