Plastic Deformation In Shear Bands Research Articles

Infrared thermographic assessment of heat release phenomena in steel parts subjected to quasi-static deformation

The paper describes the mechanism of heat release during deformation and main features of passive infrared thermographic diagnostics of steel parts subjected to elastic, elastic–plastic and plastic deformation under quasi-static loading. A basic equation for evaluating temperature signals caused by quasi-static deformation is derived. It is stated that the evaluation of steel structures by passive thermal methods should be performed when the heat is generated by mechanical stresses appearing in structures subjected to mechanical loading. The analysis of the loading kinetics and temperature anomalies has shown that thermal nondestructive testing technique is a useful tool for determining stress state in steel structures during the initiation and evolution of fracture. It is shown that the quasi-static deformation of steel structures is accompanied by the formation of elastic clusters separated by shear bands, and the plastic deformation in shear bands causes heat release resulting in a temperature increase of 4–12.5 °C.

Cyclic deformation behavior of austenitic Cr–Ni-steels in the VHCF regime: Part II – Microstructure-sensitive simulation

In Part I – Experimental study, the cyclic deformation behavior of two austenitic stainless steel grades (AISI 304, AISI 316 L) were experimentally investigated at low stress amplitudes in the very high cycle fatigue (VHCF) regime. The observations indicate that during VHCF the metastable austenitic stainless steel (304 grade) performs a pronounced localization of plastic deformation in shear bands followed by a deformation-induced martensitic phase transformation. The 316 grade undergoes only a very limited local plastic deformation in shear bands with almost no phase transformation. Consequently, both materials exhibit distinctly different cyclic softening and hardening characteristics during VHCF. In order to provide a more detailed knowledge about the individual deformation mechanisms and their effect on the cyclic softening and hardening behavior the experimental study is extended by microstructure-sensitive modeling and simulation. Two-dimensional (2-D) microstructures consisting of several grains are represented using the boundary element method and plastic deformation within the microstructure is considered by a mechanism-based approach. Specific mechanisms of cyclic plastic deformation in shear bands and deformation-induced martensitic phase transformation – as documented by experimental results and based on well-known model approaches – are defined and implemented into the simulation. The fatigue behavior at low stress amplitudes observed in experiments can be well represented in simulations so that the underlying model helps to understand the cyclic deformation behavior of austenitic stainless steels at low stress amplitudes in the regime of VHCF strength. In a comparative study based on the resonant behavior the effect of certain deformation mechanisms on the global cyclic softening and hardening characteristics is pointed out for both materials.

Modeling and simulation of temperature-dependent cyclic plastic deformation of austenitic stainless steels at the VHCF limit

The exploration of fatigue mechanisms in the VHCF regime is gaining importance since many components have to withstand a very high number of loading cycles due to high frequency or long product life. In this regime, the period of fatigue crack initiation and thus the localization of plastic deformation play an important role. The material that was investigated in this study is the metastable austenitic stainless steel AISI 304 in the initially purely austenitic condition. The experimental investigations during quasi-isothermal fatigue tests revealed that a moderate increase of temperature from room temperature up to 150°C led to a reduced VHCF strength. At both temperatures the 304 grade still undergoes a pronounced localization of plastic deformation in shear bands accompanied by a deformation-induced martensitic phase transformation from the γ-austenite to the α’-martensite during VHCF loading. In the present study, the experimental study is extended by modeling and simulation of the relevant temperature-dependent VHCF deformation mechanisms in order to provide a more profound understanding of the observed cyclic deformation. For this purpose, two-dimensional (2-D) morphologies of microstructures are modeled in the mesoscopic scale by the use of the boundary element method (BEM), and cyclic plastic deformation is considered by certain mechanisms defined in a simulation model. It describes the localization of plastic deformation in shear bands taking into account the formation, plastic sliding deformation and cyclic slip irreversibility of each shear band. The deformation-induced martensitic phase transformation is represented by introducing martensitic nuclei into the modeled microstructure depending on the plastic deformation in shear bands. The influence of temperature is incorporated into the simulation model by the use of empirical data and a kinetic model, each related to the tensile test. The simulated cyclic deformation and phase transformation is compared to experimental observations and allows for assessing the individual influence of deformation mechanisms on the temperature-dependent fatigue behavior. Finally, a temperature-independent ‘limit curve’ for the accumulated irreversible plastic sliding deformation regarding failure in the VHCF regime is proposed.

Simulation of the Interaction of Plastic Deformation in Shear Bands with Deformation-Induced Martensitic Phase Transformation in the VHCF Regime

The experimental observation of the microstructural deformation behavior of a metastable austenitic stainless steel tested at the real VHCF limit indicates that plastic deformation is localized and accumulated in shear bands and martensite formation occurs at grain boundaries and intersecting shear bands. Based on these observations a microstructure-sensitive model is proposed that accounts for the accumulation of plastic deformation in shear bands (allowing irreversible plastic sliding deformation) and considers nucleation and growth of deformation-induced martensite at intersecting shear bands. The model is numerically solved using the two-dimensional (2-D) boundary element method. By using this method, real simulated 2-D microstructures can be reproduced and the microstructural deformation behavior can be investigated within the microstructural morphology. Results show that simulation of shear band evolution is in good agreement with experimental observations and that prediction of sites of deformation-induced martensite formation is possible in many cases. The analysis of simulated shear stresses in most critical slip systems under the influence of plastic deformation due to microstructural changes contributes to a better understanding of the interaction of plastic deformation in shear bands with deformation-induced martensitic phase transformation in the VHCF regime.

Shear Band Creation in Amorphous Ribbon under Bending

Metallic glasses subjected to bending loads often exhibit the significant strength through the creation of multiple shear bands. Amorphous metallic glasses in the form of thin ribbon (about 40 μm in thickness) can be bent to large curvatures without the failure. The thickness of metallic glass is also an important factor that influences the exceptional properties of these materials. The shear bend formation under bending of Fe40Ni40B20 (at. %) amorphous ribbon was studied. There is highly localized plastic deformation in shear bands as a function of the curvature radius. The development of primary and secondary shear bands is related to the inhomogeneous plastic deformation that occurs at the room temperature. The total deformation increases with the decreasing the bending radius. Shear bands in the bent ribbons were observed using scanning electron microscopy.

Numerical investigation of the influence of shear band localization on the resonant behavior in the VHCF regime

The monitored resonant behavior of fatigue specimens of metastable austenitic stainless steel (AISI304) is correlated with its damage accumulation in the very high cycle fatigue (VHCF) regime. The resonant behavior is studied experimentally and shows a distinct transient characteristic. Microscopic examinations indicate that during VHCF a localized plastic deformation in shear bands arises on the specimen surface. Hence, this work focuses on the effect of damage accumulation in shear bands on the resonant behavior of AISI304 in the VHCF regime. A microstructural simulation model is proposed that takes into account specific mechanisms in shear bands proven by experimental results. The simulation model is solved numerically using the two-dimensional boundary element method and the resonant behavior is characterized by evaluating the force-displacement hysteresis loop. Simulation of shear bands agrees well with microscopic examinations and plastic deformation in shear bands influences the transient characteristic of the resonant behavior.

Simulation of Deformation-induced Martensite Formation and its Influence on the Resonant Behavior in the Very High Cycle Fatigue (VHCF) Regime

The exploration of fatigue mechanisms in the VHCF regime is gaining importance since many components have to withstand a very high number of loading cycles due to high frequency or long product life. In this regime, particular attention is paid to the period of fatigue crack initiation and thus the localization of plastic deformation. The resonant behavior of a metastable austenitic stainless steel (AISI304) is studied experimentally in the VHCF regime and shows a distinct transient characteristic. The major contribution of this work is to obtain a physically-based understanding of this characteristic by modeling the underlying microstructural mechanisms and their influence on the resonant behavior. Microscopic examinations indicate that AISI304 undergoes deformation-induced martensite formation starting mostly at intersecting shear bands during fatigue. Therefore, a microstructural shear band model [Hilgendorff et al. (2013)] is extended regarding the mechanism of deformation-induced martensite formation. The model accounts for the microstructural mechanisms occurring in shear bands as documented by experimental results, and nucleation of martensite is assumed to occur at intersecting shear bands following the Olsen-Cohen nucleation model (1972) in combination with the Bogers-Burgers mechanism (1964). The simulation model is numerically solved using the two-dimensional (2-D) boundary element method. By using this method, a 2-D microstructure can be modeled considering grain orientations as well as individual anisotropic elastic properties in each grain. The resonant behavior is characterized by evaluating the force-displacement hysteresis loop. Results show that plastic deformation in shear bands and deformation-induced martensite formation have a major impact on the resonant behavior in the very high cycle fatigue (VHCF) regime.

Structure vs Chemistry: Friction and Wear of Pt-Based Metallic Surfaces

In comparison of a Pt57.5Cu14.7Ni5.3P22.5 metallic glass with a Pt(111) single crystal we find that wearless friction is determined by chemistry through bond formation alloying, while wear is determined by structure through plasticity mechanisms. In the wearless regime, friction is affected by the chemical composition of the counter body and involves the formation of a liquid-like neck and interfacial alloying. The wear behavior of Pt-based metallic surfaces is determined by their structural properties and corresponding mechanisms for plastic deformation. In the case of Pt(111) wear occurs by dislocation-mediated homogeneous plastic deformation. In contrast the wear of Pt57.5Cu14.7Ni5.3P22.5 metallic glass occurs through localized plastic deformation in shear bands that merge together in a single shear zone above a critical load and corresponds to the shear softening of metallic glasses. These results open a new route in the control of friction and wear of metals and are relevant for the development of self-lubricated and wear-resistant mechanical devices.

The effect of grain size on the localization of plastic deformation in shear bands

The strain localization of plastic deformation in slip bands may induce damage on the specimen surface, characterized by critical values of extrusion height and local irreversible plastic strain accumulated in the band. The functional dependency of the grain size on critical values of these parameters is investigated for nickel-based superalloys. It is confirmed that cracking occurs when certain conditions are fulfilled at the microscopic scale and that the critical value of local irreversible plastic strain accumulated in slip bands is independent of grain size.

Molecular dynamics simulation of deformation and fracture of a “copper - molybdenum” nanocomposite plate under uniaxial tension

The paper presents the results of molecular dynamics simulation of deformation and fracture of a “copper - molybdenum” nanocomposite plate under uniaxial tension. It is shown that plastic deformation in shear bands in the copper culminates in the pore formation at the Cu-Mo contact boundary. In the molybdenum, deformation develops through martensite transformation and formation of a new phase.

Defect Analyses of Deformed Zr-Cu-Ni-Al Bulk Metallic Glasses

In Zr-Cu-Ni-Al bulk metallic glasses where there are no dislocations, localized plastic deformation in shear bands occurs largely by the formation and migration of defects such as voids, micropores, shear bands and local variations in composition. Thus, the investigation on defects is critical for the understanding and improvement of plastic deformation in metallic glasses. In this study, microstructures and nano defects in the Zr-Cu-Ni-Al BMGs are characterized by variety of techniques, such as X-ray diffractometry, high resolution transmission electron microscopy, scanning transmission electron microscopy and electron holography.

Structure and peculiarities of nanodeformation in Ti–Zr–Ni quasi-crystals

Ti–Zr–Ni samples with a substantial predominance of icosahedral quasicrystalline phase were produced by the melt-spinning technique. Their structure and mechanical properties were studied by X-ray diffraction and nanoindentation methods. The quasicrystalline phase was found to have a primitive lattice with the quasicrystallinity parameter a q = 0.5200–0.5210 nm. Quasicrystalline deformation behaviour under nanoindentation versus phase composition and structure is discussed in comparison with single crystal W–12 wt% Ta. The estimated elastic modulus E of the quasicrystalline phase shows no correlation with the element composition. The nanohardness was shown to increase with increasing quasicrystalline-phase perfection. Load–displacement curves of Ti–Zr–Ni quasicrystals (QCs) show stepwise character with alternation of elastic and plastic sections. Such non-uniform plastic flow in QCs might be caused by the localization of plastic deformation in shear bands. The non-uniformity of the plastic deformation increases with the increasing quasicrystalline phase perfection.

The composite-like structure formation of lead brass by heterogenization of deformation at high temperature

The heterogenization of plastic deformation in shear bands creates a possibility to control the spatial distribution of precipitated phases by their preferential nucleation and growth on structural defects inside the shear bands. Basing on such a concept an experiment has been carried out on lead brass to check the possibility of the redistribution of α and β phases from a chaotic to ordered, composite-like form. The results reveal a significant effect of shear banding at high temperature on the spatial distribution of phases in the alloy. The yield point of material with composite-like structure is almost by 40% greater when compared with that of material treated in the conventional way, while ductility remains the same.

Interaction of high-cycle fatigue with high-temperature creep in two creep-resistant steels: Lukas, P., Kunz, L. and Sklenicka, V. Mater. Sci. Eng. A Nov. 1990 A129 (2), 249–255

In Part I – Experimental study, the cyclic deformation behavior of two austenitic stainless steel grades (AISI 304, AISI 316 L) were experimentally investigated at low stress amplitudes in the very high cycle fatigue (VHCF) regime. The observations indicate that during VHCF the metastable austenitic stainless steel (304 grade) performs a pronounced localization of plastic deformation in shear bands followed by a deformation-induced martensitic phase transformation. The 316 grade undergoes only a very limited local plastic deformation in shear bands with almost no phase transformation. Consequently, both materials exhibit distinctly different cyclic softening and hardening characteristics during VHCF. In order to provide a more detailed knowledge about the individual deformation mechanisms and their effect on the cyclic softening and hardening behavior the experimental study is extended by microstructure-sensitive modeling and simulation. Two-dimensional (2-D) microstructures consisting of several grains are represented using the boundary element method and plastic deformation within the microstructure is considered by a mechanism-based approach. Specific mechanisms of cyclic plastic deformation in shear bands and deformation-induced martensitic phase transformation – as documented by experimental results and based on well-known model approaches – are defined and implemented into the simulation. The fatigue behavior at low stress amplitudes observed in experiments can be well represented in simulations so that the underlying model helps to understand the cyclic deformation behavior of austenitic stainless steels at low stress amplitudes in the regime of VHCF strength. In a comparative study based on the resonant behavior the effect of certain deformation mechanisms on the global cyclic softening and hardening characteristics is pointed out for both materials.