Comparative and assessment study of torsional fatigue life for different types of steel
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Abstract
Different types of steel specimens were tested using low cycle torsional fatigue tests to evaluate the torsional behavior. During previous years many authors have developed empirical relationships related to stress amplitude with the life of failure in many types of steel materials. Studies continue to find the best experimental relationships for different subjects. In this study two main problems were considered: torsional fatigue study and comparing the behavior of different steel materials under the influence of torsional fatigue. The effect of temperature on the properties of these substances was also studied. A comparison and evaluation of torsional fatigue for different types of steel were found in this study. Three groups of steel specimen were selected for the present investigation, these included low carbon steel AISI 1020, stainless steel AISI 316L, and cold worked stainless steel AISI 304H. The tests were carried out for each group of the steel specimen using a fatigue machine under fully reversed low cycle at ambient temperature and 100 °C. The temperature range was chosen from room temperature to 100° C because the low carbon steel AISI 1020 material showed high ductility above 100 °C. The shear strain amplitude applied was selected between the max. and min. values of 0.18 and 0.02 respectively. A comparison was carried out between the three steel groups at ambient temperature, it was noticed that the ratio of life to failure for both AISI steels 316L and AISI 304H with respect to AISI 1020 showed an increase of 4 and 2.3 times respectively. Also, the ratio of life to failure showed an increase of 4 and 3.5 times respectively at 100 °C. That is mean the ratio of life to failure for AISI steel 316L with respect to AISI 1020 has no effect with the temperature change because their cycles of life have been affected in the same manner. AISI 304H showed a good withstand to the temperature change because the ratio of life to failure with respect to AISI 1020 has been increased.
Keywords
Torsional fatigue Low-cycle AISI 316L AISI 304H AISI 1020 and fatigue lifeList of symbols
- ε′_{f}
Axial fatigue ductility coefficient
- σ′_{f}
Axial fatigue strength coefficient (MPa)
- c
Axial fatigue ductility exponent
- b
Axial fatigue strength exponent
- e
Elastic modulus (GPa)
- N_{f}
Mumber of cycle to failure
- γ
Shear strain
- Δγ/2
Total torsional strain amplitude
- γ′_{f}
Shear fatigue ductility coefficient (MPa)
- τ′_{f}
Shear fatigue strength coefficient (GPa)
- c_{o}
Torsional fatigue ductility exponent
- b_{o}
Torsional fatigue strength exponent
- G
Shear modulus (GPa)
- σ_{u}
Ultimate tensile strength (MPa)
- σ_{y}
Yield strength (MPa)
- El
Elongation
- RA
Reduction in area
- ν
Poisson’s ratio
1 Introduction
Fatigue of the metal is the phenomenon of failure caused by periodic loading due to movement or rotary parts. It is progressive localized damage due to fluctuating stresses or strains on the material [1]. In case of torsional fatigue failure, the damage to the torque shafts caused by torsional loading which leads to a different form of throwing stress. It is change the breakage level from 90 degrees to 45 degrees from the axis of the shaft [2]. The external observation of failure can be classified into three stages [3]. For explaining the major surface shape that is seen on almost every fatigue face; Origins, peach marks, and Instantaneous zone. In fact, the components fail to adhere to relatively high stress in the low number of cycles. This is called LCF, so the test under LCF is usually used to describe low cycle fatigue resistance in deferent case of loading axial or torsional [4]. The results of the fatigue tests for many authors [5] generally showed an inverse relationship between stress amplitude (or strain) with the overall life of failure. On the other hand, high temperature generally has effects on the stress strain curve [6] by increasing thermal elongation and toughness, while reducing the yield stress, elasticity modulus, hardness and the strain hardening exponent (n). This is also leads to decrease the life to failure. It can be said that the effect of companies to increase the temperature using LCF leads to more periodic dilution behavior throughout life [7]. The Coffin–Manson relationship between fatigue life and total strain [8] consider for low-cycle fatigue because it produces a high-quality value for explaining the nature of fatigue. Several authors were found empirical relations for the steels that related to the amplitude strain and the number of life to failure [9]. The aim of the present study is to find an empirical equation that relates the shear strain amplitude with a number of cycle of failures of three types of steel AISI 1020, AISI 316L and AISI 304H. The prediction equations provided a comparative evaluating to the torsional fatigue behavior for these types of steel in both ambient temperature and 100° C. The number of failure cycles is estimated and found by the S–N curve.
2 Experimental procedures
Compositional analysis results
Steel | C | Si | Mn | P | S | Cr | Mo | IMi | Fe |
---|---|---|---|---|---|---|---|---|---|
316L | 0.02 | 0.42 | 0.81 | 0.043 | 0.019 | 16.55 | 2.04 | 10.09 | 70.00 |
304H | 0.10 | 0.30 | 1.98 | 0.01 | 0.01 | 17.85 | 0.16 | 8.68 | 70.50 |
1020 | 0.20 | 0.27 | 0.50 | 0.003 | 0.002 | 0.13 | 0.004 | 0.096 | 98.46 |
2.1 Axial monotonic properties at ambient temperature
Summary of monotonic axial properties for tested metals at ambient temperature
Steel AISI | σ_{u (MPa)} | σ_{y (MPa)} | E (GPa) | El (%) | RA (%) | G (GPa) | ν |
---|---|---|---|---|---|---|---|
316L | 630 | 435 | 197 | 51 | 72.0 | 77 | 0.28 |
304H | 9S1 | 750 | 196 | 36 | 57.7 | 76.5 | 0.2S |
1020 | 320 | 250 | 200 | 20 | 64.0 | 77.5 | 0.29 |
2.2 Axial monotonic properties at 100 °C
The estimated monotonic axial properties for steels metal at 100° C
Steel AISI | σ_{y (MPa)} | σ_{u (MPa)} | E (GPa) | G (GPa) |
---|---|---|---|---|
316L | 360.3 | 5S6.0 | 189 | 73.8 |
304H | 665.4 | 853.4 | 188 | 73.5 |
1020 | 250.0 | 312.5 | 200 | 77.5 |
2.3 Experimental test
3 Results and discussions
Results regarding fatigue crack growth and fatigue limit show that the impact of biaxial stress on the specimen surface is minimal and that the maximum principal stress governs fatigue behavior under torsional load, Ref [13].
3.1 Torsional fatigue properties
Summary of torsional and axial fatigue properties at room temperature
Material | Torsional cyclic properties | Axial cyclic properties | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
AISI | G (GPa) | τ′_{f}(MPa) | b_{o} | γ′_{f} | c_{o} | E (GPa) | σ′_{f} (MPa) | b | ε′_{f} | c |
316L | 77.0 | 900 | − 0.12 | 2.00 | − 0.56 | 197 | 1152 | − 0.12 | 1.00 | − 0.56 |
304H | 76.5 | 705 | − 0.12 | 1.52 | − 0.56 | 196 | 902.4 | − 0.12 | 0.76 | − 0.56 |
1020 | 77.5 | 270 | − 0.09 | 0.98 | − 0.56 | 200 | 467.6 | − 0.09 | 0.565 | − 0.56 |
Summary of torsional and axial fatigue properties at 100° C
Material | Torsional cyclic properties | Axial cyclic properties | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
AISI | G(GPa) | τ′_{f}(MPa) | b_{o} | γ′_{f} | c_{o} | E(GPa) | σ′_{f} (MPa) | b | ε′_{f} | C |
326L | 73.8 | 700 | − 0.10 | 1.40 | − 0.54 | 189 | 896.0 | − 0.10 | 0.700 | − 0.54 |
304H | 73.5 | 600 | − 0.10 | 1.23 | − 0.53 | 1SS | 768.0 | − 0.10 | 0.615 | − 0.53 |
1020 | 77.5 | 200 | − 0.08 | 0.50 | − 0.50 | 200 | 346.4 | − 0.08 | 0.346 | − 0.50 |
3.2 Axial fatigue properties and verifications
Verifications have been carried out as follows: convert the calculated predicted relations that given in Fig. 5 to axial relations forms as described in Ref [9]. The Tresca, Von Mises and Maximum principal Strain criterion were used to convert the torsional cyclic properties, listed in the Tables 4 and 5, to an axial mode for getting axial fatigue properties at both room temperature and 100 °C. These axial relations forms compared with an another axial relations which calculated from five different methods, Universal Slopes,. Mitchell, Modified universal slopes, Uniform Material Law and Median’s method. These methods described in Ref [14] where used the monotonic properties for steel only.
Verification for axial strain amplitude relations
Steel AISI | Temperature of test | Criteria of Failure | Closer method of verification | Mean percentage error (%) |
---|---|---|---|---|
316L | T room | Maximum principal strain | Mitchell | 0.07 |
100° C | Maximum principal strain | Mitchell | 1.3 | |
304H | T room | Maximum principal strain | Mitchell | 1.1 |
100° C | Maximum principal strain | Mitchell | 0.7 | |
1020 | T room | Von Mises | Uniform material law | 1.5 |
100° c | Von Mises | Median | 3.3 |
After verification the axial properties consider more reasonable to improve the certainty of the experimental torsional properties.
Figures 6 and 7 showed the life curve. Hence, for best comparisons, the applied torsional strain value of 0.1 for three metals was selected. It has been found that the number of cycles to failure for AISI 1020 is 30 cycles, while for 304H stainless steel is 79 cycles. This is mean that the number of fatigue life for 304H is 2.3 times than for AISI 1020. On the other hand, for the stainless steel AISI 316L, the number of fatigue life increased by 4 times than for AISI 1020which is equal to 118.
At 100° C, The AISI 1020 showed the lowest fatigue life to failure compared to other steels. The stainless steel 304H failed at 63 cycles, which means 3.5 times than for AISI 1020. Additionally, the number of fatigue life for the stainless steel 316L increased by 4 times than for AISI 1020 which is equal to 76 cycles approximately at same shear strain amplitude.
Also, From the results and analyzes presented, all three steels tend to become rigid when periodic torsional loading is applied, but the AISI 316L and AISI 304H stainless steels exhibit a longer life span than the AISI 1020 carbon steel. The ratio of life to failure for AISI steel 316L with respect to AISI 1020 has no effect with the temperature change because their cycles of life have been affected in the same manner. AISI 304H showed a good withstand to the temperature change because the ratio of life to failure with respect to AISI 1020 has been increased.
Comparisons of ratio of life to failure
N_{f} _{Stainless steel} | N_{f} _{Stainless steel} (in terms of N_{f} _{Carbon steel}) | |
---|---|---|
Room temperature | T = 100 °C | |
N_{f} AISI 316L | N_{f} AISI 1020 *4 | N_{f} AISI 1020*4 |
N_{f} AISI 304H | N_{f} AISI 1020 * 2.3 | N_{f} AISI 1020 * 3.5 |
4 Conclusions
- 1.
A temperature increase of 100° C leads to a decrease in fatigue life for the three metals tested in the present study as a result of increased plastic stress leading to loss of flexibility and strength.
- 2.
It was observed that both steel AISI 316L and AISI 304H show a high life to failure than for AISI 1020 at both ambient temperature and 100 °C.
- 3.
The ratio of life to failure for AISI steel 316L with respect to AISI 1020 has no effect with the temperature change because their cycles of life have been affected in the same manner
- 4.
AISI 304H showed a good withstand to the temperature change because the ratio of life to failure with respect to AISI 1020 is increased.
- 5.
Finally, it can be noticed that carbon steel AISI 1020 was failed at the lowest value of cycles under fully reversed shear strain compared to stainless steel AISI 316L and AISI 304H, while the steel AISI 316L has a superior number life to failure (Nf) among the other steels in the present investigation.
Notes
Compliance with ethical standards
Conflict of interest
On behalf of all authors, the corresponding author states that there is no conflict of interest.
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