scholarly journals Interaction of Migrating Twin Boundaries with Obstacles in Magnesium

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 154
Author(s):  
Andriy Ostapovets ◽  
Konstantin Kushnir ◽  
Kristián Máthis ◽  
Filip Šiška
Keyword(s):  
Shear Stress ◽  
Finite Elements ◽  
Twin Boundary ◽  
Computer Simulations ◽  
Bulk Material ◽  
Twin Boundaries ◽  
Twin Growth ◽  
Critical Resolved Shear Stress

Interaction of migrating {101¯2} twin boundary with obstacles was analyzed by atomistic and finite elements computer simulations of magnesium. Two types of obstacles were considered: one is a non-shearable obstacle and another one is the void inside bulk material. It is shown that both types of obstacles inhibit twin growth and increased stress is necessary to engulf the obstacle in both cases. However, the increase of critical resolved shear stress is higher for the passage of the twin boundary through raw of voids than for interaction with non-shearable obstacles.

Strengthening effect of twin boundaries in bcc crystal evaluated through a micro-bending test

2011 ◽  
Vol 1297 ◽  
Author(s):  
Yuki Karasawa ◽  
Tso-Fu Mark Chang ◽  
Akinobu Shibata ◽  
Masato Sone
Keyword(s):  
Shear Stress ◽  
Type Specimen ◽  
Bending Test ◽  
Displacement Curve ◽  
Strengthening Effect ◽  
Body Centered Cubic ◽  
Twin Boundaries ◽  
Bending Deformation ◽  
Nano Scale ◽  
Critical Resolved Shear Stress

ABSTRACTIn the present study, the strengthening effect of nano-scale twins in body-centered cubic (bcc) crystal was evaluated using micro-sized cantilever type specimen which contained the nanotwinned region (midrib) in ferrous lenticular martensite. The SEM observations of the micro-sized specimen after bending deformation indicated that midrib can act as barriers against dislocations, resulting in slip localization and non-localization across midrib. The load-displacement curve obtained by bending test showed that twin boundaries significantly enhance the critical resolved shear stress of bcc.

scholarly journals Modelling the nucleation and propagation of cracks at twin boundaries

2021 ◽  
Author(s):  
Nicolò Grilli ◽  
Alan C. F. Cocks ◽  
Edmund Tarleton
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Cohesive Zone Model ◽  
Bulk Material ◽  
Zone Model ◽  
Fracture Path ◽  
Twin Boundaries ◽  
Interface Elements ◽  
Local Term ◽  
Good Agreement

AbstractFracture arising from cracks nucleating and propagating along twin boundaries is commonly observed in metals that exhibit twinning as a plastic deformation mechanism. This phenomenon affects the failure of macroscopic mechanical components, but it is not fully understood. We present simulations in which a continuum model for discrete twins and a cohesive zone model are coupled to aid the understanding of fracture at twin boundaries. The interaction between different twin systems is modelled using a local term that depends on the continuum twin variables. Simulations reveal that the resolved shear stress necessary for an incident twin to propagate through a barrier twin can be up to eight times the resolved shear stress for twin nucleation. Interface elements are used at the interfaces between all bulk elements to simulate arbitrary intragranular cracks. An algorithm to detect twin interfaces is developed and their strength has been calibrated to give good agreement with the experimentally observed fracture path. The elasto-plastic deformation induced by discrete twins is modelled using the crystal plasticity finite element method and the stress induced by twin tips is captured. The tensile stress caused by the tip of an incident twin on a barrier twin is sufficient to nucleate a crack. A typical staircase fracture path, with cracks propagating along the twin interfaces, is reproduced only if the strength of the twin interfaces is decreased to about one-third of the strength of the bulk material. This model can be used to help understand fracture caused by the activation of multiple twin systems in different materials.

Non-Schmid Phenomena in HCP Materials

2016 ◽  
Vol 258 ◽  
pp. 29-32
Author(s):  
Andriy Ostapovets ◽  
Olena Vatazhuk
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Computer Simulations ◽  
Slip Plane ◽  
Critical Value ◽  
Deformation Twinning ◽  
Twin Boundaries ◽  
Stress Components ◽  
Hcp Materials

The Schmid law says that yielding takes place when resolved shear stress on slip plane reaches the critical value. It is valid for wide variety of materials. However, it is well known that breaking of Schmid law takes place in bcc materials due to non-planar splitting of dislocation cores. The non-Schmid behavior is also possible for plastic deformation of fcc and hcp materials. Particularly, it is sometimes reported for deformation twinning. Present paper demonstrates the non-Schmid phenomena in hcp magnesium by means of computer simulations. We consider influence of non-glide stress components on motion of screw <a> dislocation as well as migration of twin boundaries.

scholarly journals Enhanced lattice distortion, yield strength, critical resolved shear stress, and improving mechanical properties of transition-metals doped CrCoNi medium entropy alloy

RSC Advances ◽  
2021 ◽  
Vol 11 (38) ◽  
pp. 23719-23724
Author(s):  
Md. Lokman Ali
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Transition Metals ◽  
Yield Strength ◽  
Lattice Distortion ◽  
Critical Resolved Shear Stress

The effect of transition-metals (TM) addition on the mechanical properties of CrCoNi medium entropy alloys (MEAs) was investigated.

On the Critical Resolved Shear Stress and its Importance in the Fatigue Performance of Steels and other Metals with Different Crystallographic Structures

2022 ◽  
pp. 37-65
Author(s):  
M. Mlikota
Keyword(s):  
Shear Stress ◽  
Fatigue Life ◽  
Fatigue Limit ◽  
High Fatigue ◽  
Steel Aisi ◽  
Crystallographic Structures ◽  
Face Centered ◽  
Set Up ◽  
Number Of Cycles ◽  
Critical Resolved Shear Stress

This study deals with the numerical estimation of the fatigue life represented in the form of strength-life (S-N, or Wöhler) curves of metals with different crystallographic structures, namely body-centered cubic (BCC) and face-centered cubic (FCC). Their life curves are determined by analyzing the initiation of a short crack under the influence of microstructure and subsequent growth of the long crack, respectively. Micro-models containing microstructures of the materials are set up by using the finite element method (FEM) and are applied in combination with the Tanaka-Mura (TM) equation in order to estimate the number of cycles required for the crack initiation. The long crack growth analysis is conducted using the Paris law. The study shows that the crystallographic structure is not the predominant factor that determines the shape and position of the fatigue life curve in the S-N diagram, but it is rather the material parameter known as the critical resolved shear stress (CRSS). Even though it is an FCC material, the investigated austenitic stainless steel AISI 304 shows an untypically high fatigue limit (208 MPa), which is higher than the fatigue limit of the BCC vanadium-based micro-alloyed forging steel AISI 1141 (152 MPa).

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