Plastic Rupture Research Articles

Mature compost promotes biodegradable plastic degradation and reduces greenhouse gas emission during food waste composting

Mature compost can promote the transformation of organic matter (OM) and reduce the emission of polluting gases during composting, which provides a viable approach to reduce the environmental impacts of biodegradable plastics (BPs). This study investigated the impact of mature compost on polybutylene adipate terephthalate (PBAT) degradation, greenhouse gas (GHG) emission, and microbial community structure during composting under two treatments with mature compost (MC) and without (CK). Under MC, visible plastic rupture was advanced from day 14 to day 10, and a more pronounced rupture was observed at the end of composting. Compared with CK, the degradation rate of PBAT in MC was increased by 4.44 % during 21 days of composting. Thermobifida, Ureibacillus, and Bacillus, as indicator species under MC treatment, played an important role in PBAT decomposition. Mature compost reduced the total global warming potential (GWP) by 25.91 % via inhibiting the activity of bacteria related to the production of CH4 and N2O. Functional Annotation of Prokaryotic Taxa (FAPROTAX) further revealed that mature compost addition increased relative abundance of bacteria related to multiple carbon (C) cycle functions such as methylotrophy, hydrocarbon degradation and cellulolysis, inhibited nitrite denitrification and denitrification, thus alleviating the emission of GHGs. Overall, mature compost, as an effective additive, exhibits great potential to simultaneously mitigate BP and GHG secondary pollution in co-composting of food waste and PBAT.

Study on structural integrity of reactor pressure vessel with various ablation under core meltdown accident

In-vessel retention is an important measure to alleviate the core meltdown accident in the third generation nuclear power plant. External Reactor Vessel Cooling(ERVC) is the key to the successful implementation of IVR. Due to the ablation caused by the molten pool in the lower head, the reactor pressure vessel(RPV) has various wall ablation and thinning, which poses a great threat to the integrity of the pressure boundary of the RPV. Based on the boiling water RPV as the research object, the model is established for the RPV with various ablation and local thinning by finite element method(FEM). The stress/strain response of the structure is calculated and analyzed under the core meltdown accident. The plastic and creep damage are assessed for the RPV in terms of its evolution and distribution with continuum damage mechanics(CDM). Due to the existence of internal pressure within the RPV, the effect of pressure on creep and plastic rupture is also studied within the required 72 h. According to the criterion of ductile exhaustion, the results show that the increase of internal pressure further reduces the load-bearing capacity of RPV.

Creep rupture assessment of cyclically heated 3D pressure pipelines with volumetric defects using a direct numerical approach

Creep rupture assessment is a significant issue in the field of high-temperature structural integrity. In this paper, the creep rupture assessment of 3D pressure pipelines with volumetric defects subjected to cyclic thermo-mechanical loadings is done using a direct numerical approach within the framework of stress compensation method (SCM). For calculation of creep rupture limit, an extended shakedown analysis scheme with yield strength correction is essentially performed, where the revised yield strength is determined as the minimum of the plastic yield strength and the creep rupture strength of material corresponding to a specified elevated temperature and rupture time. This direct numerical approach performs the creep rupture assessment by using the given creep rupture data of material rather than simulating the degenerative process of material based on creep damage constitutive equations under a specified loading history. The numerical approach is incorporated into commercial finite element software of Abaqus. Parametric studies on geometric dimensions of part-through slot affecting the creep rupture limit of 3D pressure pipelines with volumetric defects are conducted. Numerical results shown in this study indicate that the direct numerical approach accurately identifies the creep rupture limit boundary of the pressure pipeline, verified by the elastic-plastic cycle-by-cycle analysis. Failure mechanisms, such as local creep rupture, global creep rupture and global plastic rupture are detected under different loading combinations. These results give the helpful information for in-service integrity assessment of defective pressure pipelines at elevated temperature, and demonstrate the applicability and application prospect of the direct numerical approach in solving questions relevant to design or life assessment of other engineering structures.

Thermomechanical Modeling of a Sleeve Rehabilitation System for Pressure Pipes

Abstract The thermomechanical modeling of a sleeve rehabilitation system for pressure pipes is studied including temperature effect on system behavior. The rehabilitation system consists of a multicylinder axisymmetric layer system, with an intermediate layer of epoxy resins and two outer steel covers that are longitudinally welded forming a sleeve. The analysis is conducted over several stages; initially, the incidence of temperature on the rigidity of three types of resins currently available on the market is experimentally evaluated. Then, nonlinear relationships between rigidity and temperature are established from the evaluation of the resins, which are typical of an inhomogeneous material. The resins exhibit a significant loss of rigidity with temperature, generating a risk of delamination that could drastically reduce the effectiveness of the rehabilitation system in the event of possible temperature rises. An analytical model was developed to calculate contact pressures between the resin layer and the external sleeve, internal pipeline displacements, stresses, and deformations. Finally, contour plots were developed for different temperature, pressure levels, and pipe thickness as a graphics tool to predict pipeline failure due to plastic deformation or rupture.

Stability of Biological Membranes upon Mechanical Indentation.

Mechanical perturbations are ubiquitous in living cells, and many biological functions are dependent on the mechanical response of lipid membranes. Recent force-spectroscopy studies have captured the stepwise fracture of stacks of bilayers, avoiding substrate effects. However, the effect of stacking bilayers, as well as the exact molecular mechanism of the fracture process, is unknown. Here, we use atomistic and coarse-grained force-clamp molecular dynamics simulation to assess the effects of mechanical indentation on stacked and single bilayers. Our simulations show that the rupture process obeys the laws of force-activated barrier crossing, and stacking multiple membranes stabilizes them. The rupture times follow a log-normal distribution which allows the interpretation of membrane rupture as a pore-growth process. Indenter hydrophobicity determines the type of pore formation, the preferred dwelling region, and the resistance of the bilayer against rupture. Our results provide a better understanding of the nanomechanics underlying the plastic rupture of lipid membranes.

Statistical Model of the Explosive Fragmentation of a Ring

A model of the explosive fragmentation of a thin ring is developed which takes into account the statistical dispersion of the relative fracture deformation along the length of the ring. A formula is proposed for calculating the velocity of the boundary of the region near a plastic rupture in which the plastic flow of the ring material ceases. Methods for the numerical and analytical calculation of the average number of fragments of the ring are developed. The calculation results are compared with available experimental data.

The Nanomechanics of Lipid Multibilayer Stacks Exhibits Complex Dynamics.

The nanomechanics of lipid membranes regulates a large number of cellular functions. However, the molecular mechanisms underlying the plastic rupture of individual bilayers remain elusive. This study uses force clamp spectroscopy to capture the force-dependent dynamics of membrane failure on a model diphytanoylphosphatidylcholine multilayer stack, which is devoid of surface effects. The obtained kinetic measurements demonstrate that the rupture of an individual lipid bilayer, occurring in the bilayer parallel plane, is a stochastic process that follows a log-normal distribution, compatible with a pore formation mechanism. Furthermore, the vertical individual force-clamp trajectories, occurring in the bilayer orthogonal bilayer plane, reveal that rupturing process occurs through distinct intermediate mechanical transition states that can be ascribed to the fine chemical composition of the hydrated phospholipid moiety. Altogether, these results provide a first description of unanticipated complexity in the energy landscape governing the mechanically induced bilayer rupture process.

Про пластичні лінії розриву у кутовій точці кусково-однорідного тіла

Про пластичні лінії розриву у кутовій точці кусково-однорідного тіла

Properties of carbon fibre/bismaleimide composites ex situ toughened with phosphorous-containing poly(arylene ether ketone) film

To control the dissolution process of a phosphorous-containing poly(arylene ether ketone) (P-PAEK)/bismaleimide (BMI) resin diphase system, a series of P-PAEKs were synthesized by changing the molar ratio of the reactants through nucleophilic substitution. The U3160/BMI composites toughened with P-PAEK film were manufactured by resin transfer moulding based on the concept of ex situ toughening. In addition, the interlaminar properties of the composites were characterized by applying modes I and II fracture toughness tests. The mode I fracture toughness of the composite was shown to be less improved, whereas the mode II fracture toughness was increased by about 74%. Furthermore, the interlaminar microstructure, which was observed by using a scanning electron microscope (SEM), revealed that reaction-induced phase decomposition and inversion occurred in the interlaminar region. The improvement in fracture toughness was attributed to plastic rupture of the continuous P-PAEK phase and debonding or cavitations of the BMI particle phases. Through the application of ex situ toughening, the compression-after-impact properties of the composite were significantly improved, whereas the thermodynamic properties were well maintained. Besides, optical microscopy images showed more space in the interlayer of the toughened specimens, which contributed to the improvement of damage tolerance.

Microstructure-based analysis of thermal- and mechanical behaviors of W/CuCrZr composites and porous W coating

In this work we applied an advanced simulation procedure on two heterogeneous random materials relevant for fusions, mapping high resolution micrographic images of their microstructures into FEM (finite element method) models. This technique enables one to calculate the local thermal and mechanical responses of a material on his real microstructure. This technique also allows one to interpret experimental observations based on the local effects captured by the simulation (within a two-dimensional approximation). The inputs for the FE simulations were created from SEM (scanning electron microscopy) micrographs using the dedicated software OOF2. In this paper, two examples are presented: tensile deformation up to plastic rupture of the W–CuCrZr particulate composite and thermal conduction of plasma-sprayed porous tungsten taking into account its dual-scale porosity. Essential role of the heterogeneous, random morphology of the microstructures is highlighted. Comparison with experimental measurements is discussed.

Tensile creep fracture of polycrystalline near-stoichiometric NiAl

Tensile creep fracture behavior of polycrystalline near-stoichiometric NiAl has been studied between 700 and 1200 K under initial applied stresses varying between 10 and 200 MPa. The stress exponent for fracture varied between 5.0 and 10.7 while the activation energy for fracture was 250 +/- 22 kJ/mol. The fracture life was inversely proportional to the secondary creep rate in accordance with the Monkman-Grant relation although there was extensive scatter in the data. This observation suggests that the fracture life for near-stoichiometric NiAl was influenced by creep under these stress and temperature conditions. Several different fracture morphologies were observed. Transgranular ductile cleavage fracture occurs at 700 K and at the higher stresses at 800 K. The fracture mode transitions to transgranular creep fracture at 900 and 1000 K and at lower stresses at 800 K, while plastic rupture and grain boundary cavitation occur at 1100 and 1200 K. An experimental fracture mechanism map is constructed for near-stoichiometric NiAl.

Analysis of the High-Temperature Cohesion Behavior of Ash Particles Using Pure Silica Powders Coated with Alkali Metals

This paper analyzes the increasing mechanism of cohesive behavior of ash powders at elevated and high-temperature conditions. Model ash powders were prepared from fine pure amorphous silica powder coated and heat-treated on the surface with 0.5 wt % sodium and/or potassium. The cohesive behavior and deformation properties of model ash powder beds were determined by using a new split-type tensile strength tester of powder beds. The adhesion behavior of fly ash collected in a pulverized coal combustion (PC) and a pressurized fluidized bed combustion (PFBC) system was compared with the results of model ash powder samples. In the high-temperature range above 800 °C, a rapid increase of tensile strength and plastic rupture deformation occurred in both the natural ash samples and the model ash powder samples prepared from alkali metal and pure silica powder. It is suggested that the coating alkali metal reacted with the amorphous silica phase and formed a small amount of low-melting-point eutectic materials, such as K2O·4SiO2. Since these eutectic materials formed a small amount of liquid phase at interparticles at about 800 °C, the tensile strength and plastic rupture deformation rapidly increased at high temperatures above 800 °C.

Deformation and fracture of Al-8Fe rapidly solidified alloys

The effects of the rapid solidification on the deformation and fracture of Al-8Fe alloys, from TEM fracture specimens, have been studied. The most general conclusion which can be drawn in this study is clearly in agreement with a plastic deformation mechanism. Crack propagation occurs by localized plastic rupture mechanisms which result from enhanced slip along {111}σ planes. Crack propagation occurs within the deformed zone either by the nucleation, growth and coalescence of holes ahead of the crack-tip, or through the emission of dislocation from the crack-tip. The resulting fracture is along the active {111}σ slip planes. The principal effect of secondary phases (Al13Fe4) on the fracture propagation in Al-8Fe alloys was that the secondary phases increased the stress level at which plastic deformation occurs at the crack-tip and increased the stress level at which the crack propagates. This work clearly shows that in order to obtain coarse intermetallic precipitates in the specimens after ageing heat treatments the crack propagation and deformation processes occur at lower stresses compared to as-received rapidly solidified samples.

Plastic Deformation and Rupture of Ring-Stiffened Cylinders under Localized Pressure Pulse Loading

An analytical solution for the dynamic plastic deformation of a ring-stiffened cylindrical shell subject to high intensity pressure pulse loading is presented. By using an analogy between a cylindrical shell that undergoes large plastic deformation and a rigid-plastic string resting on a rigid-plastic foundation, one derives closed-form solutions for the transient and final deflection profiles and fracture initiation of the shell. Discrete masses' and springs are used to describe the ring stiffeners in the stiffened shell. The problem of finding the transient deflection profile of the central bay is reduced to solving an inhomogeneous wave equation with inhomogeneous boundary conditions using the method of eigenfunction expansion. The overall deflection profile consists of both global (stiffener) and local (bay) components. This division of the shell deflection profile reveals a complex interplay between the motions of the stiffener and the bay. Furthermore, a parametric study on a ring-stiffened shell damaged by a succession of underwater explosions shows that the string-on-foundation model with ring stiffeners described by lumped masses and springs is a promising method of analyzing the structure.

A survey of toughness in ductile phase composites

The available literature data on toughness in ductile phase composites are overviewed, and the known theoretical toughness models are assessed for their usefulness for predicting fracture toughness in ductile phase composites. It is shown that the predictions of simple equations incorporating ductile phase properties agree with the measured fracture toughness of ductile phase composites. It was found that the fracture toughness of ductile phase composites is governed by the modulus of the composite, the flow stress, and the plastic rupture displacement of the ductile phase. It is suggested that these equations should be useful for the alloy design of high-temperature materials consisting of ductile phases. 32 refs.

The rupture of a thin ligament associated with a part-through crack in a plate subject to tensile deformation

This paper focuses on the criterion for the plastic rupture of a thin ligament associated with a part-through crack in a tensile plate subjected to an applied tensile stress. With a very wide (infinite width) plate, the critical crack length for ligament rupture is shown to decrease with increasing applied stress. At low applied tensile stress levels, i.e. less than 50% of the yield stress, ligament rupture requires a very thin ligament and a very long crack. With a finite width plate, the required crack length for ligament rupture is less than the infinite width plate value, provided that the crack and plate dimensions are such that general yield occurs. The implications of these conclusions with regard to the development of a leak-before-break condition are discussed.

Fracture mechanism maps in stress space

Diagrams can be constructed in stress space which show, for metals and alloys, the competition between the processes which lead to fracture. These include yield, necking, void nucleation, ductile fracture, brittle grain-boundary fracture, cleavage, shear fracture, and plastic rupture. Simplified diagrams are constructed for E.T.P. copper, α-brass, two steels and an aluminium alloy. The diagrams show how the fracture mechanism changes with stress state and help rationalize a number of apparently conflicting observations. They have application in predicting the behaviour of metals under complex stress states.

On optimal plastic anisotropy

An approach is developed for the optimal design of a structure, based on optimization of the anisotropic plastic properties of materials. Problems of maximizing the ultimate plastic rupture load as a result of optimal orientation of the plastic anisotropy axes in the structure elements are formulated. Necessary conditions are presented for optimality in the three-dimensional problem of the theory of ultimate plastic equilibrium. Cases of the torsion and bending of plastic rods are considered. The bilateral achievable estimates of the ultimate loads are obtained. It is noted that the conditions for achieving the upper and lower bounds agree with the necessary optimality conditions. It is proved that the maximum ultimate load is realized in the case when the direction with the greatest yield point of the material agrees with the direction given by the tangential stress vector at the time of exhaustion of the carrying capacity.

Plastic rupture of materials during compression along near-surface fractures

Plastic rupture of materials during compression along near-surface fractures

A theory of pseudo cross-link

Summary The rupture of the polymer solid is classified into three c ategories: 1. A brittle f racture takes place at very rapid or low temperature extension due to the break-down of the pseudo cross-link. Craze or crack occurs. 2. An elastic rupture occurs at ultimate elongation of the chain due to the break-down of the p rimary bond. 5. A plastic rupture occurs at elevated temperature when the resistance due to viscous flow predominates over the elastic f orce. For cases 1 and 2 the elongation at break decreases while the strength increases as the rate of extension increases. For the case 3 both the elongation and strength increases. F ailure envelope, optimum cure, effect of filler, segmented rubber and rupture energy are discussed