Cyclic behaviour of materials

1970 ◽  
Vol 5 (3) ◽  
pp. 185-192 ◽  
Author(s):  
K J Miller
Keyword(s):  
Strain Rate ◽  
Strain Curve ◽  
Cyclic Hardening ◽  
Fatigue Behaviour ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Static Tests ◽  
Static Test ◽  
Cyclic Behaviour ◽  
Incremental Step

The effect of strain rate on the cyclic behaviour of two materials is presented. For the material that cyclically hardens (En 32B) a decrease in strain rate decreases the maximum cyclic hardening of the material, whilst for a material that cyclically softens (En 25) a decrease in the rate of deformation increases the maximum cyclic softening. It is concluded that the effect of strain rate on the cyclic stress-strain curve should be more closely studied than the effect of frequency since the frequency may be constant whilst the straining rate may vary considerably in plastically deformed zones. For those zones that suffer low strain rates the inclusion of time-dependent deformation processes can maximize the degree of softening or minimize the degree of hardening, thereby creating a greater localization of the plastic strain which should increase strain-concentration factors. Finally it is argued that it is better to predict fatigue behaviour from an incremental-step high-strain fatigue test on a single specimen than from static-test data. For the same reasons correlations between static tests and fatigue tests should be discouraged, especially for those materials that exhibit marked cyclic softening.

Cyclic Softening of Cu-Ni-Si Alloy Single Crystals under Low-Cycle Fatigue

2010 ◽  
Vol 654-656 ◽  
pp. 1287-1290 ◽  
Author(s):  
Toshiyuki Fujii ◽  
Hiroshi Kamio ◽  
Yoshifumi Sugisawa ◽  
Susumu Onaka ◽  
Masaharu Kato
Keyword(s):  
Plastic Strain ◽  
Single Crystals ◽  
Low Cycle Fatigue ◽  
Strain Curve ◽  
Electron Microscopic Observation ◽  
Cyclic Hardening ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Fatigue Tests ◽  
Electron Microscopic

Cu-2.2wt%Ni-0.5wt%Si alloy single crystals were grown by the Bridgman method and aged at 723 K for 10 h to form Ni2Si precipitates. Fully reversed tension-compression fatigue tests were conducted on the aged single crystals with a single slip orientation under constant plastic-strain amplitudes at room temperature. Cyclic softening occurred at plastic-strain amplitudes between 2.5x10-4 and 2.5x10-2. Using the maximum stress amplitude in each cyclic hardening/softening curve, a pseudo cyclic stress-strain curve (CSSC) was obtained. The CSSC was found to exhibit a plateau region with a stress level of about 167 MPa. Transmission electron microscopic observation revealed the formation of persistent slip bands (PSBs) in the plateau regime. It was found that the Ni2Si precipitate particles were intensively sheared by glide dislocations within the PSBs and were eventually re-dissolved into the Cu matrix. The macroscopic cyclic softening can be attributed to the local softening induced by the re-dissolution of the Ni2Si particles in the PSBs.

Out-of-plane seismic performance of plasterboard partition walls via quasi-static tests

2016 ◽  
Vol 49 (1) ◽  
pp. 125-137 ◽  
Author(s):  
Crescenzo Petrone ◽  
Gennaro Magliulo ◽  
Pauline Lopez ◽  
Gaetano Manfredi
Keyword(s):  
Seismic Performance ◽  
Bending Moment ◽  
Structural Elements ◽  
Nonstructural Components ◽  
Static Tests ◽  
Static Test ◽  
Cyclic Behaviour ◽  
Testing Protocol ◽  
Partition Walls ◽  
Out Of Plane

Internal partitions, as many nonstructural components, should be subjected to a careful and rational seismic design, as is done for structural elements. A quasi-static test campaign aimed at the evaluation of the out-of-plane seismic performance of Siniat plasterboard internal partitions with steel studs was conducted according to FEMA 461 testing protocol. Four tall, i.e. 5 m high, specimens were selected from the range of internal partitions developed in Europe by Siniat, a leading supplier of plasterboard components in Europe. Under the specified testing protocol, a significant nonlinear pinched behaviour of the tested specimen was observed. The pinched behaviour was caused by the damage in the screwed connections, whose cyclic behaviour was strongly degrading. Both stiffness and strength of the specimens are significantly influenced by the board typology and the amount of screwed connections. Finally, it was concluded that Eurocodes significantly underestimate the resisting bending moment of the tested specimens.

Effect of Temperature on the Cyclic Stress Amplitude of ENiCrFe-1 Ni-Based Alloy Electrode and its Mechanism

2021 ◽  
Vol 1035 ◽  
pp. 259-263
Author(s):  
Qun Bing Zhang ◽  
Jian Xun Zhang ◽  
Wen Lan Wei
Keyword(s):  
Stress Amplitude ◽  
Base Alloy ◽  
Fatigue Behavior ◽  
Reference Value ◽  
Cyclic Hardening ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Structural Safety ◽  
Alloy Electrode ◽  
Effect Of Temperature

Ni-based alloy welding material has been widely used in the welding and post-welding repair of high-temperature materials. The effect of temperature on the cyclic stress amplitude of ENiCrFe-1 Ni-base alloy electrode was studied under the same strain condition. The results showed that when the temperature was lower than 400 °C, it presented the characteristics of cyclic hardening and then cyclic softening. When the temperature was higher than 500 °C, it presented the characteristics of cyclic hardening and then cyclic stability. The main reason is that with the temperature increase, the dislocation structure changed more and more stable. The results not only enrich the internal mechanism of fatigue behavior of nickel-based alloy welding materials, but also have important reference value for improving the structural safety of welded joints.

Part 3: Predictions of Deformation and Life under Fatigue/Creep Conditions

1976 ◽  
Vol 190 (1) ◽  
pp. 339-348 ◽  
Author(s):  
A. J. F. Paterson ◽  
E. G. Ellison
Keyword(s):  
Life Prediction ◽  
Strain Curve ◽  
Strain Range ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Virgin Material ◽  
Creep Data ◽  
Stress Strain Curve ◽  
Material Conditions

Predictions of the behaviour of a 1 Cr Mo V steel at 565 °C under cyclic strain plus dwell conditions have been carried out. The strain hardening mechanical equation of state appears to be useful under virgin material conditions but the presence of cyclic softening can cause major errors. Reasonable success was obtained in predicting “softened creep” curves from the virgin creep data and the cyclic stress strain curve. Both strain and time are important in life prediction and a method is proposed which combines the strain range partitioning approach and a modified form of cumulative damage method. Predictions under various combinations of tensile and compressive dwell have been presented.

Cyclic Deformation of a Modern TiAl Alloy at High Temperatures

2014 ◽  
Vol 891-892 ◽  
pp. 1131-1136 ◽  
Author(s):  
Tomáš Kruml ◽  
Alice Chlupová ◽  
Karel Obrtlík
Keyword(s):  
Lamellar Structure ◽  
Tial Alloy ◽  
Low Cycle Fatigue ◽  
Lamellar Microstructure ◽  
Strain Curve ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Fatigue Tests ◽  
Tensile Curve ◽  
Cyclic Straining

Ternary TiAl alloy with 8 at.% Nb and lamellar microstructure is subjected to low cycle fatigue tests at temperatures ranging from room temperature to 800 °C. The aim of the study is to find limit conditions when the microstructure is still stable and to study mechanisms of microstructural degradation when this limit is exceeded. Up to 750 °C, no cyclic softening or hardening is observed and cyclic stress-strain curve follows the tensile curve. Cyclic softening is characteristic for 800 °C. The TEM observation did not reveal any substantial changes in the microstructure due to the cycling up to 700°C. The lamellar structure is altered by cyclic straining at 750 °C and, to a higher extent, at 800°C. In specimens cycled to fracture at 800 °C, the domains without lamellar structure cover about 10% of volume and are almost dislocation free. The destruction of lamellar microstructure is the reason for the marked cyclic softening at 800 °C.

scholarly journals Modification of Charpy machine for the acquisition of stress-strain curve in thermoplastics

DYNA ◽  
2020 ◽  
Vol 87 (213) ◽  
pp. 52-60
Author(s):  
Luis Miguel Zabala Gualtero ◽  
Ulises Figueroa López ◽  
Andrea Guevara Morales ◽  
Alejandro Rojo Valerio
Keyword(s):  
Strain Rate ◽  
Strain Curve ◽  
Strain Rate Range ◽  
Strain Rates ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Static Tests ◽  
Wide Range ◽  
Plastic Components ◽  
Impact Simulations

Simulations of impact events in the automotive industry are now common practice. Vehicle crashworthiness simulations on plastic components cover a wide range of strain rates from 0.01 to 500 s-1. Because plastics mechanical properties are very dependent on strain rate, developing experimental methods for generating stress-strain curves at this strain rate range is of great technological importance. In this paper, a modified Charpy machine capable of acquiring useful information to obtain the stress-strain curve is presented. Strain rates between 300 to 400 s-1 were achieved. Three thermoplastics were tested: high-density polyethylene, polypropylene-copolymer and polypropylene-homopolymer. Impact simulations using LS-DYNA were performed using the acquired high-strain rates stress-strain curves and compared with experimental data. Simulations using stress-strain curves from quasi-static tests were also performed for comparison. Very good agreement between the simulation and experimental results was found when the ASTM D1822 type S specimen was used for testing each material.

scholarly journals Acceleration techniques for the numerical simulation of the cyclic plasticity behaviour of mechanical components under thermal loads

2018 ◽  
Vol 165 ◽  
pp. 19010 ◽  
Author(s):  
Jelena Srnec Novak ◽  
Francesco De Bona ◽  
Denis Benasciutti ◽  
Luciano Moro
Keyword(s):  
Strain Curve ◽  
Cyclic Hardening ◽  
Cyclic Plasticity ◽  
Design Rule ◽  
Plastic Strains ◽  
Thermal Loads ◽  
Small Plastic ◽  
Acceleration Techniques ◽  
Cyclic Behaviour ◽  
Number Of Cycles

Numerical simulations of components subjected to cyclic thermo-mechanical loads require an accurate modelling of their cyclic plasticity behaviour. Combined models permit to capture monotonic hardening as well as cyclic hardening/softening phenomena, that occur in reality. In principle the durability assessment of a component under thermal loads can be performed only if the cyclic behaviour is simulated until complete material stabilization. As materials stabilize approximately at half the number of cycles to failure, it follows that in case of small plastic strains a huge number of cycles must be considered and an unfeasible simulation time would be required. Accelerated models have thus been proposed in literature. The aim of this work is that of comparing the different acceleration techniques in the case a round mould for continuous casting loaded thermo-mechanically. It can be observed that the usual approach of using the stabilized stress-strain curve already from the first cycle could lead to relevant errors. An alternative method is that of increasing the value of the parameter that controls the speed of stabilization in the combined model. This approach permits the number of cycles to reach stabilization to be drastically reduced, without affecting the overall mechanical behaviour. Based on this approach, a simple design rule, that can be adopted, particularly when relatively small plastic strains occur, is finally proposed.

Prediction of settled cyclic behaviour of metals using first cycle data and combined hardening laws for reversed plasticity

1994 ◽  
Vol 29 (2) ◽  
pp. 105-116
Author(s):  
V O A Oloyede ◽  
C E Turner
Keyword(s):  
Hysteresis Loops ◽  
Cyclic Hardening ◽  
Cyclic Stress ◽  
Yield Function ◽  
Stress Strain ◽  
Finite Element Program ◽  
Cyclic Behaviour ◽  
Element Program ◽  
Combined Hardening ◽  
Good Agreement

This paper presents a generalized concept of combined hardening which is examined by experimental and computational methods. A ‘kinematic displacement parameter’, β, relating the movement of the yield function surface to the Bauschinger effect, is defined in terms of its dependence on material properties and loading state. Experimental relations between β and the plastic strain, εp, are prsented for three metals. The monotonic stress-strain and β data are used in a finite element program to show that settled cyclic hysteresis loops are soon established. Settled cyclic stress-strain curves computed in this way are in good agreement with the experimental results for an aluminium alloy, a stainless steel that shows cyclic hardening, and a titanium alloy that shows little cyclic effect.

Overview of Fatigue Behaviour of Ultrafine-Grained Copper Produced by Severe Plastic Deformation

2007 ◽  
Vol 567-568 ◽  
pp. 9-16 ◽  
Author(s):  
Petr Lukáš ◽  
Ludvík Kunz ◽  
Milan Svoboda
Keyword(s):  
Grain Size ◽  
Strain Curve ◽  
Shear Plane ◽  
Fatigue Behaviour ◽  
Cyclic Stress ◽  
Grain Structure ◽  
Temperature Dependent ◽  
Stress Strain Curve ◽  
Ultrafine Grained ◽  
Broad Region

Fatigue behaviour of ultrafine-grained copper of purity 99.9 % produced by ECAP technique was studied in a broad region of stress amplitudes. Fatigue strength is by a factor of about 2 higher than that of conventional-grain-size copper in the broad region of fatigue lives from 6x103 to 2x1010 cycles. The grain structure is stable and undergoes only very marginal changes during cycling. Fatigue slip markings on specimen surface follow the trace of the shear plane of the last ECAP pass. Fatigue notch sensitivity is also higher than that of conventional-grain-size copper, but not dramatically. The cyclic stress-strain curve of studied copper is temperature insensitive, while its S-N curve is temperature dependent.

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