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The Manufacture and Physical Properties of Rubber-Toughened Styrenics
Published in Charles B. Arends, Polymer Toughening, 2020
David E. Henton, Robert A. Bubeck
The tensile test [110] is also commonly used to measure the toughness of styrenic resins. The absolute strain to failure is used as a measure of the toughness as well as the energy to failure. The rate of the test can be varied to determine the sensitivity of the material to strain rate in a tensile mode. The measured toughness of a sample is a function not only of the type of test used, but also of test temperature, test deformation rate, and sample thickness. As the temperature of the test approaches the glass transition of the elastomer phase, the cavitation process becomes suppressed, thus limiting the mechanical response of the modified styrenic to a greatly reduced amount of crazing. Consequently, the material fractures in a brittle manner with a fracture toughness that is close to that of the unmodified matrix. Such behavior is typical for polybutadiene-modified polystyrene and SAN [3]. The thickness effect on fracture in HIPS with about 7% rubber has been determined by Yap et al. [111]. For thicknesses below about 10 mm, plane stress ductile tearing occurs, whereas above a thickness of 10 mm mixed-mode plane strain-plane stress fracture predominates. Although increasing the deformation rate can be and often has much the same effect as lowering temperature, this need not always be the case for ABS resins. For example, Kobayashi and Broutman [112] have reported nonmonotonically increasing fracture energies for poly(styrene-co-acrylate-co-methyl methacrylate) AMBS copolymers at higher rubber levels.
Stress-Strain Behavior Investigation by Molecular Dynamic (MD) Simulation
Published in Snehanshu Pal, Bankim Chandra Ray, Molecular Dynamics Simulation of Nanostructured Materials, 2020
Snehanshu Pal, Bankim Chandra Ray
In conventional polycrystalline metals, the nucleation of dislocation ensues from Frank-Read sources, but when the grain size decreases to the nanoscale regime, grain boundary or grain junction acts as a dislocation source. The nucleation of the first dislocation is aided by the shuffling of atoms in the near vicinity of triple junction, attributed to the excess free volume associated with the triple junction. The NC FCC metals initially emit partial dislocation; however, as the stress value increases, high-stacking-fault-energy metals such as Al emit second partials to form complete dislocations. Nevertheless, in low-stacking-fault-energy metals, for instance, in Cu, such closing partials cannot be formed, owing to the equal lengths of the stacking fault. Under such circumstances, the stacking fault aggrandizes via gliding of the partial dislocations, thereby transacting the grain and consequently restricting any further propagation of stacking faults, leading to strain hardening. Figure 6.24 illustrates the variation in the deformation behavior of the FCC metals with stacking fault energy. Both the metals deform identically at lower strain values (~0.4% strain), but the deviation in the deformation behavior is observed at a higher strain rate. The high-stacking-fault-energy metal forms complete dislocation, thereby entering the “perfect dislocation slip” regime [52]. On the other hand, the low-stacking-fault-energy metal exhibits sluggish deformation behavior attributed to strain hardening due to the inability of generation of full dislocation [53].
Mechanics of Cutting
Published in David A. Stephenson, John S. Agapiou, Metal Cutting Theory and Practice, 2018
David A. Stephenson, John S. Agapiou
The shear flow stress of the work material in the primary deformation zone is usually larger than that measured in low-speed tension or torsion tests [93,95,96]. Figure 6.19 illustrates this effect for free-machining steel [97]. A number of unusual mechanisms, such as dependence of the flow stress on hydrostatic pressure [98,99], have been proposed to account for the increase, but it now seems to be plausibly explained by strain and strain rate hardening. The strains in the primary deformation zone are sufficient to produce saturation strain hardening, and most metals also exhibit strain rate hardening, especially at strain rates over 10s−1. Flow stresses measured in low-speed cutting tests appear to be consistent with those measured high-speed compression tests when strain, strain rate, and temperature effects are accounted for (Figure 6.20) [100].
Residual performance and damage mechanism of prestressed concrete box girder bridge subjected to falling heavy object impact
Published in Structure and Infrastructure Engineering, 2023
Jingfeng Zhang, Rui Wang, Zhichao Zhang, Chaokang Tong, Yu Zhang, Liang Feng, Wanshui Han
Figure 1(b) shows the FE model of the PC beam. The concrete and supports were modeled with eight-node hexahedron element. The reinforcements in the PC beam were simulated by using three-node Gauss integral algorithm based beam element. The mesh size was set to 10 mm. The detailed material parameters are presented in Table 1. Specifically, the constitutive model of the concrete adopted the continuous surface cap model (*MAT_CSCM_CONCRETE) with rate effects in LS-DYNA, and the reinforcement and prestressed tendons employed the *MAT_PLASTIC_KINETIC material model that was suited to model isotropic and kinematic hardening plasticity. The strain rate effect of material has significant influence on the structural responses under impact. In concrete material constitutive model *MAT_CSCM_CONCRETE, the strain rate effect can be easily considered by turning on the rate effect option. The strain-rate effect for steel reinforcement was accounted by the Cowper and Symonds model and the relationship between static yield strength σs and dynamic yield strength σd is described by: where is the strain rate, while C and P are the parameters for Cowper Symonds strain rate mode.
Study of microstructure and mechanical properties of 17-4 PH stainless steel produced via Binder Jetting
Published in Powder Metallurgy, 2023
Lorena Emanuelli, Giacomo Segata, Matteo Perina, Martin Regolini, Valentina Nicchiotti, Alberto Molinari
According to the void bands theory of ductile fracture [31] necking is caused by the multiple gliding of dislocations on several slip planes. Fracture starts when a cavity forms in the centre of the necked region due to the presence of any discontinuity in the metallic matrix that opposes the motion of dislocations. On increasing deformation, the cavity grows and transforms in the ductile crack, orthogonal to the loading direction. Then deformation propagates being localised at the crack tips, causing the formation of the so-called void sheets, whose failure supports the propagation of the fracture until the final collapse. Voids are still caused by obstacles to the motion of dislocations. The uniform deformation is then the deformation required for the formation of the ductile crack, and the non-uniform deformation is the deformation required to propagate the crack to fracture. In ductile metals, uniform deformation is correlated to strain hardenability, whilst non-uniform deformation is correlated to strain-rate sensitivity, that is, to the increased resistance to plastic flow when the strain rate increases. In porous materials, the strain rate increases because of the localisation of deformation at the pores edges.
Experimental study on flexural fatigue behavior of self-compacting concrete with waste tire rubber
Published in Mechanics of Advanced Materials and Structures, 2021
Chen Chen, Xudong Chen, Jinhua Zhang
As shown in Figure 6(a), it can be found that the secondary strain rate per cycle has a logarithmic linear relationship with fatigue life of SCRC, and stress level has no effects on the relationship. The fitting parameters are shown in Table 6. It can be found that the slopes for SCRC with different rubber content are very close, and the intercept increases with the increase of rubber content. The maximum strain corresponding to the last cycle in the fatigue process is defined as the fatigue failure strain [40], and the strain corresponding to the monotonic curve under the same stress level is close to the fatigue failure strain, which is shown in the compressive fatigue test of ordinary concrete and steel fiber reinforced concrete (SFRC) [40, 42], respectively. As shown in Figure 7, fatigue failure strain under different stress levels and loading frequencies of SCRC with different rubber contents are close to that in the monotonic curve. And under the same stress level, the strain corresponding to monotonic curve of SCRC increase with the increases of rubber content. As a result, when the secondary strain rate per cycle is the same, then the larger the fatigue failure strain is, the longer the fatigue life would be. Therefore, in the relationship between secondary strain rate per cycle and fatigue life, the intercept increases with the increase of rubber content.