Plastic Hardening Research Articles

COMPARISON BETWEEN JOHNSON COOK’S PLASTICITY WITH DAMAGE MODEL AND ISOTROPIC HARDENING PLASTICITY WITH DUCTILE DAMAGE MODEL ON ALUMINIUM ALLOY SHEET 2024 T3 TENSILE TEST IN CORRELATING THE FINITE ELEMENT METHOD (FEM) TO THE EXPERIMENT TEST RESULT

Sometimes students and/or researchers are faced with a limited sample and data issue and need to choose carefully which approaches to be used, especially in performing analysis with numerical analysis. As there are a lot of numerical analysis approaches that are having similar purposes and the approaches can be used depending on the analysis cases and objectives. For example, Johnson Cook’s plasticity model and isotropic plasticity hardening model are the common approaches available and used in ABAQUS software to determine the metal and metal alloy plasticity or inelastic mechanical properties. Therefore, in this paper, two approaches – Johnson Cook’s plasticity with damage model and isotropic plasticity hardening with ductile damage model which is used to define the metal and metal alloy mechanical properties and performance are studied using ABAQUS Computer Aided Engineering (CAE) software and compared accordingly. In this study, the experimental result of the tensile test was used to determine the mechanical properties of the Aluminium alloy 2024 T3 sheet with 0.29mm thickness. Then the experiment test data are used to correlate the finite element method (FEM) model and the experimental test result by using Johnson Cook’s plasticity hardening with damage model approach and the isotropic hardening plasticity with ductile damage model approach. Based on the comparison with the experiment failure sample mode, both FEM model failure mode is closely identical to the experiment failure sample. From the mechanical properties comparison, Johnson Cook’s model shows a bigger deviation compared to the isotropic plasticity with ductile damage model in comparison to the experiment value. From this paper, it can be concluded that the ductile damage model is more appropriate to be used when the sample and data are limited.

Ultrahigh deformability of Ti-6Al-4V assisted by high-density pulsed electric current treatment

In this study, the mechanical properties and microstructural evolution of the pre-strained titanium alloy Ti‐6Al‐4V under high-density pulsed electric current (HDPEC) treatment were investigated. The results showed that the HDPEC treatment successfully restored the plastic deformation or strain hardening of the pre-strained Ti‐6Al‐4V without deteriorating its strength. In addition, multi-HDPEC treatments were conducted to examine the cumulative effect on plastic recovery, and ultrahigh deformability with an increasing rate of 287% was achieved at a current density of 250 A/mm2 for 20 ms. Microstructural characterization indicated that dislocations and the associated sub-grain boundaries were remarkably reduced after the HDPEC treatment, contributing to ductility enhancement. Additionally, the rapidly heat-treated sample with a thermal history curve similar to that of the HDPEC-treated samples did not show obvious microstructural changes, indicating that the athermal effect of the HDPEC treatment plays an important role in modifying the microstructure of the material. The α'/α'' martensite phases were formed in the β phase after the HDPEC treatment, which is possibly related to the high cooling rate and diffusion of the V element (β phase stabilizer element). Specifically, at the current condition of 250 A/mm2 for 20 ms, some tiny martensite phases precipitated in the β phase without heavily deteriorating the microstructure and mechanical properties. Therefore, owing to its low cost and high efficiency, the HDPEC treatment can be applied to Ti-alloy components with internal plastic deformation to realize rapid restoration or achieve long service periods without significantly altering the microstructure.

The 2-layer elasto-visco-plastic rheological model for the material parameter identification of bone tissue extended by a damage law

The response of bone tissue to mechanical load is complex and includes plastic hardening, viscosity and damage. The quantification of these effects plays a mayor role in bone research and in biomechanical clinical trials as to better understand related diseases.In this study, the damage growth in individual wet human trabeculae subjected to cyclic overloading is quantified by inverse rheological modeling.Therefore, an already published rheological material model, that includes linear elasticity, plasticity and viscosity is extended by a damage law. The model is utilized in an optimization process to identify the corresponding material parameters and damage growth in single human trabeculae under tensile load.Results show that the damage model is leading to a better fit of the test data with an average root-mean-square-error (RMSE) of 2.52 MPa compared to the non-damage model with a RMSE of 3.03 MPa. Although this improvement is not significant, the damage model qualitatively better represents the data as it accounts for the visible stiffness reduction along the load history. It returns realistic stiffness values of 11.92 GPa for the instantaneous modulus and 5.73 GPa for the long term modulus of wet trabecular human bone. Further, the growth of damage in the tissue along the load history is substantial, with values above 0.8 close to failure. The relative loss of stiffness per cycle is in good agreement with comparable literature.Inverse rheological modeling proves to be a valuable tool for quantifying complex constitutive behavior from a single mechanical measurement. The evolution of damage in the tissue can be identified continuously over the load history and separated from other effects.

Computationally efficient simulation methodology for railway repair welding: Cyclic plasticity, phase transformations and multi-phase homogenization

The in-situ railway repair welding process consists of multiple weld passes, which makes it significantly different from other rail welding processes. In this study, finite element simulations of repair welding are performed to predict the resulting microstructure and residual stresses. To accurately simulate the material behavior, the modeling includes phase transformation kinetics, cyclic hardening plasticity, transformation induced plasticity, and multi-phase homogenization. More specifically, four different homogenization methods are investigated: isostrain, isostress, self-consistent and linear mixture rule. The performance of the material modeling is demonstrated by simulating multiple weld passes using a classical three-bar welding experiment. Based on the results, the self-consistent method and linear mixture rule are used in a 3D full-scale railhead repair weld simulation, in which the former generates a more realistic mechanical response. The immense computational cost associated with 3D full-scale, full-detail multi-pass welding simulations is addressed by exploring different model reduction schemes. From this study, a 2D generalized plane strain model, extended with out-of-plane axial and bending stiffness, is found to replicate the full-scale model at a mere fraction of the computational cost. Finally, the longitudinal residual stress distribution obtained from the reduced model is shown to correlate well with experimental measurements.

Unraveling the effects of Cr interface segregation on precipitation mechanism and mechanical properties of MC carbides in high carbon chromium bearing steels

This study explored the influence of Cr interfacial segregation on the precipitation mechanism and mechanical properties of MC carbides in high-carbon chromium bearing steels. The precipitation of Cr-doped MC carbides at different concentrations was investigated using microscopic morphological characterization (SEM, EDS and HR-TEM) alongside first principles calculations. The results indicated that both the austenite matrix and MC carbides exhibited, FCC structures, and the following orientation relationships of crystal planes in high-carbon chromium bearing steels were as follows: MC (010)//FCC-Fe (100) and MC (111)//FCC-Fe (111). Initially, Cr atoms adsorbed on the Fe-top site of the MC carbide (010) crystal plane, maintaining a distance of 2.5 Å from the Fe atom. Notably, when the Cr atom doping amount was 0.5, the Cr–Fe metallic bond exhibited a long bond length, large bond angle and low bond strength in the MC transition state (TS), resulting in a reduced, reaction barrier (908.08 kcal/mol), thus promoting the precipitation of MC carbide in bearing steel. However, at a Cr atom doping amount level of 1, the shorter bond length, small bond angle, and higher bonding strength of the Cr–Fe metallic bond in the MC TS, elevated the reaction barrier (49709.72 kcal/mol), inhibiting the precipitation of MC carbide in bearing steel. Additionally, this study quantitatively analyzed the effect of Cr atom content on the brittle plastic properties and hardness of MC carbides. At Cr atom contents of 0.23 and 1, the MC carbide hardness reached a minimum value of 3.0 GPa and a maximum value of 17.1 GPa, respectively. This investigation not only elucidated the atomic scale effects of Cr interfacial segregation on the precipitation mechanism and mechanical properties of MC carbides but also provided new ideas for controlling carbide precipitation in high-carbon chromium bearing steels.

Unstable stress-triaxiality development and contrasting weakening in two types of high-strength transformation-induced plasticity(TRIP) steels: Insights from a new compact tensile testing method

The impact of high stress triaxiality on work hardening in transformation-induced plasticity (TRIP) steel has been widely acknowledged, particularly through measurements of the austenite fraction. Understanding this TRIP behavior is crucial for predicting material fracture in press-forming processes. However, the actual flow stresses under high-stress-triaxiality conditions remain largely undetermined. To address this gap, we developed a new tensile testing method using tiny notched round bars to investigate stress-triaxiality-induced work hardening in TRIP steels. The specimens were analyzed using two-dimensional micrometry to allow finite element analyses to identify the flow stress. Additionally, we conducted in situ tensile tests in which their crystal lattice stresses were monitored using synchrotron X-ray diffraction (XRD) to realize mechanism analyses of the unexpected work-hardening behavior identified by the developed tensile testing method. Our combined approach revealed a mutual, unstable increase in the flow stress and stress triaxiality in the TRIP-aided bainitic ferrite steel, which reduced the hardening exponent coefficients and thus induced a higher stress triaxiality. In contrast, the TRIP-aided martensitic steel exhibited a weakening behavior, characterized by a significant decrease in the hardening exponent coefficients in the case of the sharpest notch. XRD analyses showed that microstructural heterogeneity led to an extraordinarily high hydrostatic stress in the austenite phase, accounting for these contrasting behaviors. This finding challenges the established consensus on TRIP steels and suggests the need for a revised framework for their application in press-forming, taking into account stress-triaxiality conditions.

Grain-Scale Study of SAC305 Oligocrystalline Solder Joints: Anisotropic Elasto-Plastic Constitutive Properties of Single Crystals

Abstract This paper focuses on anisotropic elastic-plastic constitutive modeling of SAC (SnAgCu) solder grains because of their importance in modeling the behavior of oligocrystalline (few-grained) micron-scale solder joints that are increasingly common in heterogeneous integration. Such grain-scale anisotropic modeling approach provides more accurate assessment of the mechanical response of solder interconnects in terms of predicting different failure modes, failure sites, and variability in time-to-failure. Anisotropic plasticity is represented using Hill–Ramberg–Osgood (RO) continuum plasticity model, which utilizes Hill's anisotropic plastic potential along with a RO power-law plastic hardening flow rule. Mechanistically motivated empirical scaling factors are proposed to extrapolate the stress–strain response for different grain sizes/shapes and for different coarseness of microstructures within each grain (generated with different cooling rates). This scaling factor can therefore also capture the effects of microstructural coarsening due to isothermal aging. This goal is achieved by first conducting monotonic tensile and shear tests on monocrystalline and oligocrystalline SAC305 solder joints containing grains of various geometries and also intragranular microscale (dendritic and eutectic) structures of various coarseness. The grain structures are characterized for each tested specimen using electron backscattered diffraction (EBSD). The Hill–RO model constants and the empirical scaling factors are then estimated by matching grain-scale anisotropic elastic-plastic finite element models of each tested specimen to the measured stress–strain behavior, using an inverse-iteration process. Grain shape is seen to influence the sensitivity of the effective stress–strain curves to the applied stress state (i.e., to the orientation of the principal stress directions) relative to (i) the material principal directions and (ii) the geometric principal directions of grains with high aspect ratio. Limitations of the current results and opportunities for future improvements are discussed.

Modeling the viscoelastic-viscoplastic behavior of glassy polymer membrane with consideration of non-uniform sub-chains in entangled networks

Glassy polymers are common engineering materials and usually work in a linear elastic stage. However, some functional glassy polymers, such as perfluorinated sulfonic acid (PFSA) membranes, face more complicated working conditions: varied temperature, humidity, and long-term loading, where the viscoelastic behavior has a huge impact on their durability. The early studies on the constitutive model of glassy polymers focus on the elastic–plastic behavior, especially yielding and strain hardening, while showing limitations in predicting the time-dependent viscoelastic response of the PFSA membrane at complex conditions. This paper establishes a viscoelastic-viscoplastic (VE-VP) constitutive model of glassy polymers based on the non-uniform length distribution of entangled molecular chains. During loading, heating and hydration, the prior activation of short entangled chains is the precondition of the viscoelastic response of the material in the small deformation stage. To distinguish activated molecular chains from others, a calculation method of chain activation is established based on the energy conservation criterion and applied to monitor the activation state of the entangled chain network. For the verification of the model, uniaxial tensile, stress relaxation, and dynamic thermomechanical tests are conducted. The present model shows great accuracy in predicting the VE-VP behavior of the PFSA membrane, with the error less than 8% in the stress relaxation tests, providing a new perspective of constitutive modeling for glassy polymers.

Characterization of crack-tip fields for elastoplastic fatigue crack growth Part II: Effects of crack closure and in-plane constraint

The crack-tip fields of elastoplastic fatigue crack growth with crack closure are studied and correlated to the ΔJ-integral. Computational results confirmed that the singularity of the effective stress ranges of the opening process reduces with increasing crack closure, whereas the effective stress ranges from the closing process possess the known HRR solution form. The far-field ΔJeff-integral can be used to characterize the crack-tip field stress in the closing process, which is not affected by the loading ratio and by the path dependence of the ΔJ-integral. Based on extensive FEM computations, an estimation formula for the effective ΔJeff-integral was proposed for various loading ratios and plastic hardening materials. The in-plane constraint effects in fatigue crack growth can be quantified based on the J−Q concept of elastoplastic fracture mechanics, within the frame of ΔJeff-Q characterization. The relationship between Q and the transverse stress defined in the closing processes was established for a quantitative description of the crack tip constraint.

A modified K&C model for concrete subjected to coupled effect of high temperature and high strain rate

The K&C model is a commonly used constitutive model for concrete that simulates its dynamic response to blasts and impacts. However, this model is calibrated using data obtained at room temperature and is therefore not suitable for high-temperature conditions. To address this limitation, we propose a new constitutive model, named the KC-HT model, which is based on extensive modifications to the commercially available K&C model. The new model incorporates a failure surface that takes into account the temperature effect, which was established through triaxial compressive tests performed at high temperatures. The plastic hardening and softening behaviors of heated concrete are also considered by a new damage determination algorithm. The KC-HT model was integrated into the ABAQUS software using the VUMAT interface for simulation purposes, and its accuracy was confirmed through both single-element simulation and numerical SHPB tests. Finally, the KC-HT model was further validated by predicting the dynamic behavior of fire-damaged RC beams. The results reveal that the KC-HT model can replicate the dynamic behavior and crack morphology of concrete with different fire durations, while the K&C model is unable to take into account the temperature effect or the combined effect of high temperature and high strain rate.

Fatigue crack initiation life prediction using different plasticity models in cold expanded AL-alloy plates utilized in double shear lap joints

Cold expansion of fastener holes is a recognized technique for enhancing the fatigue life of holed plates utilized in detachable joints. This method involves introducing compressive residual stress around the holes, which has proven to be effective in improving the structural integrity and longevity of such components. In this research, the role of using different plasticity models in finite-element simulations of cold expansion (CE) in determining residual stress distribution and predicting the fatigue life of lap joints was investigated. Finite-element simulations were conducted to analyze the distribution of residual stress in cold-expanded Al-alloy 2024-T3 plates utilized in double-shear lap joints. Three time-independent plasticity models, specifically multilinear kinematic hardening, multilinear isotropic hardening (M.L.I.H) based on monotonic tensile tests, and nonlinear combined hardening models derived from saturated hysteresis stress and strain loops, were employed in the simulations. These models allowed for an accurate determination of the residual stress distribution in the plates. In finite-element simulations, two CE sizes of 1.5% and 4.7% were employed to create residual stresses. In the simulations, after creating residual stress by CE, remote sinusoidal loads are applied to the joints corresponding to the previously conducted fatigue tests in order to obtain stress and mechanical strain distributions. In order to predict the fatigue life, four different multiaxial fatigue criteria (Smith–Watson–Topper, Glinka, Kandil–Brown–Miller, and Fatemi–Socie) were employed, using the stress and strain distributions obtained from the finite element simulations with the different plasticity models. The simulations yielded varying stress and strain distribution results for the multilinear kinematic and M.L.I.H models, while the results of the nonlinear combined hardening model fell between the other two models. Notably, the fatigue life prediction based on the nonlinear combined hardening plasticity model closely matched the experimentally observed fatigue lives, with an absolute percentage deviation of 24.8%.

Theory of Plasticity and Strain Hardening of Glassy Polymers

Theory of Plasticity and Strain Hardening of Glassy Polymers

Effect of Si on the evolution of plasticity mechanisms, grain refinement and hardness during high-pressure torsion of a non-equiatomic CoCrMnNi multi-principal element alloy

The present study unraveled the defining role of small silicon (Si) addition (5 atomic %) in dramatically altering the plasticity mechanisms, grain refinement and hardening response of a non-equiatomic CoCrMnNi multi-principal element alloy (MPEA) during high-pressure torsion (HPT) processing. Both the Si-free and the Si-added MPEAs had a face-centered cubic (FCC) structure and were subjected to a quasi-constrained HPT processing at 6 GPa pressure to different number of turns (0.5 and 5). Microstructure evolution was studied at the center and edge of the HPT-processed discs using X-ray diffraction line profile analysis (XLPA) and transmission electron microscopy (TEM). Si addition altered the predominant plasticity mechanism from micro-band formation to extensive occurrence of nano-twinning at the early stage of HPT processing. At later stages of HPT processing, both alloys exhibited deformation twinning but its propensity was considerably higher for the Si-added MPEA, as revealed by ∼50% higher twin fault probability. Additionally, the Si-added MPEA showed ∼30% higher dislocation density at any given stage of HPT processing compared to the Si-free MPEA. A significantly accelerated nano-structuring coupled with a finer saturation grain size was observed in the Si-added MPEA (34 nm for Si-free versus 23 nm for Si-added). These effects can be explained by the influence of Si addition on lowering the stacking fault energy (SFE) (from ∼40 mJ/m2 in Si-free to ∼20 mJ/m2 in Si-added MPEA) and increasing the solute pinning effect of Si on lattice defects. The plasticity mechanisms at nano-scale were also influenced by the presence of Si as confirmed by the formation of nano-twins and stacking faults inside the nano-grains for the Si-added and Si-free MPEAs, respectively. The differences in plasticity mechanisms and microstructure evolution resulted in enhanced hardness in the early stages of HPT processing for the Si-added MPEA, but the difference in hardness between the two alloys tended to be reduced at higher strains.

Achieving strength-ductility synergy in metallic glasses via electric current-enhanced structural fluctuations

Structural applications of metallic glasses are limited by their room-temperature brittleness and strain-softening, associated with the extreme localization of plastic flow in shear bands. Herein, we alleviate this dilemma by the structural fluctuation induced by electric currents, achieving simultaneous improvement of strengths, compression plasticity, and strain hardening capacity. The electric current enhances the structural fluctuations at the atomic scale, introducing more soft zones while densifying their surroundings, which differs from previously reported rejuvenation strategies. This unique structural pattern featuring soft zones surrounded by hard zones leads to extensive sprouts and interactions of shear bands, capturing substantial atoms to participate in the deformation. The plausible mechanism behind the electric current-influenced dynamic evolution of amorphous clusters is proposed. Electric current introduces interatomic electrostatic forces between shell atoms of amorphous clusters through charge transfer. This force decreases the coordination of Zr- and Cu-centered clusters and increases the Al-centered icosahedra in the glassy matrix. Differential evolution of clusters under electric currents enhances atomic structural fluctuations and originates from the cohesion mechanism determined by electron distribution. These findings are suggestive of vanishing room-temperature brittleness and shed atomic-scale light on modulations of the structure and properties of metallic glasses by electric currents.

Enhanced cavitation erosion resistance of GX40CrNiSi25-20 cast stainless steels by surface TIG re-melting

This study aimed to reduce cavitation erosion effects by improving the surface properties of high-alloyed steel cast parts using the tungsten inert gas (TIG) surface physical modification technique. Local surface melting was performed at different linear energies (El = 4080–8880 J/cm) by varying the current between 100 and 200 A at a constant voltage of 10.2–11.1 V. Hardness increased from 210 to 390 HV5 when a TIG current of 150 A with a linear energy of El = 6630 J/cm was implemented.Using this technique, a surface layer with increased resistance to cavitation erosion was formed. This new surface absorbed large amounts of impact energy owing to a favourable combination of microstructural changes, leading to improved elastic and plastic properties, work hardening, cracking, and failure response. The cavitation erosion performance of the re-melted surface layer was analysed using a piezoceramic vibrating device according to the ASTM G32–2016 standard. Following TIG surface re-melting, the average penetration depth of erosion and the cavitation erosion rate increased by approxmately 6.8 times. Based on optical and electronic metallographic analyses, hardness measurements, and X-ray diffraction, it was shown that the morphology of the surface layer following cavitation erosion tests was affected. Microcraters tended to develop at locations where carbide particles from the alloying elements were previously present. At a current of 150 A, the depth of the microcraters reached values of approximately 15 μm; however, microcrater depth reached 10 μm in the austenite matrix. Based on these investigations, an understanding of the mechanisms that result in the improvement of the resistance to erosion by cavitation of cast high-alloy steels whose surfaces were re-melted using the TIG technique is developed.

Analysis of the treatment of comminuted fractures of tubular bones of the extremities in cats and dogs

Surgical resolution of comminuted fractures of tubular bones is an urgent issue for practicing veterinarians. Comminuted fractures account for 52%, transverse fractures for 8.7%, oblique fractures for 26.1%, and compression fractures for 13.0% of total canine fractures. Thus, comminuted fractures of the tubular bones of the extremities are the most frequent. There are several types of bone fixation in comminuted fractures. Many authors do not recommend using of intramedullary osteosynthesis in the treatment of this type of fracture since it is not possible to connect all bone fractures. The aim of this study was to compare the methods of surgical treatment of comminuted fractures in dogs and cats admitted to the clinics and to choose the most optimal ways of treatment. In total, 4,396 cats and dogs were admitted to the clinic, excluding those admitted for vaccination. The surgical department received 35% of the total number of animals. Patients with bone and joint pathology accounted for 19% of all surgical causes and to 7% of all animals admitted to the clinic. In the group of 9 cats and 9 dogs three main types of fracture were diagnosed: transverse fracture in 6 animals (4 dogs and 2 cats), oblique fracture in 4 animals (3 dogs and 1 cat) and comminuted fracture in 8 animals (2 dogs and 6 cats). The article is illustrated with X-rays images of the clinical cases presented. In order to perform osteosynthesis using a single-plane bilateral external fixator, the authors injected 2-3 Kirchner spokes each into the proximal and distal bone fragments by drilling through the bone while perforating soft tissue on both sides. The ends of the spokes on both sides were bent towards the opposite fragment, parallel to the bone axis, at a distance of 1.0 to 3.0 cm from the skin surface. The ends of the spokes form the rods of a bilateral single-plane fixator. The rod-forming spokes are tightened with wire serrations on 3-4 levels and additionally fixed with fast hardening plastic (turbocast) or bone cement (Palacos, GMW, Osteobond) while controlling the fracture reposition. Combination with wire serclages, sutures, compression screw or intramedullary Kirschner wire osteosynthesis is possible.

Interaction of Segmental Tunnel Linings and Dip-Slip Faults—Tabriz Subway Tunnels

In some subsurface urban development projects, bedrock faults intersecting with the tunnel path are inevitable. Due to the high costs of urban tunnel projects, it is necessary to study the behavior of such concrete structures under fault movement risks. Using an advanced 3D numerical finite difference code and a plastic hardening constitutive model for the soil, this paper examined the performance of the straight and oblique segmented structures of Tabriz Subway Line 2 under large deformations. The Tabriz Line 2 tunnel passes through a reverse fault called the Baghmisheh Fault. The fault–tunnel simulations were validated by centrifuge tests on the segmental tunnel for normal faulting. In the centrifuge tests and validation models, there was a maximum difference of 15%. According to the results of the Tabriz Line 2 tunnel under reverse faulting, segmental structures outperform no-joint linings when it comes to fault movement. During reverse fault movement, line 2 segments did not collapse but showed slight deformations. However, continuous structures collapsed under faulting, i.e., the structural forces created exceeded the section strength capacity. Among the segmental structures, the lining with oblique joints showed better behavior against faulting than the lining with straight joints. For better tunnel performance under fault movement, oblique joints should be used in segmental structures in faulting areas.

Development of glow-in-the-dark and color-tunable poly(methyl methacrylate) plastic concrete immobilized with rare-earth aluminate

A simple method is reported for the prospective industrial production of lightweight poly(methyl methacrylate) (PMMA) plastic concrete with persistent afterglow. Nanoparticles (NPs) of lanthanide activated aluminate (LAA) pigment were molded into a plastic bar. With the uniform dispersion of LAA NPs in the plastic fluid, the produced plastic bar can be made transparent. was A simple polymerization of methyl methacrylate (MMA; bulk material) blended with silica nanoparticles (filler), and LAA nanoparticles (luminous agent) was applied in the presence of 2,2-azobisisobutyronitrile (AIBN) catalyst to provide photoluminescent PMMA plastic concrete. In studies, LAA NPs were found to have sizes between 9 and 95 nm. When excited at 369 nm, the luminescent PMMA concrete displayed an emission peak at 518 nm. For pigment concentrations over 1%, persistent photoluminescence was observed, whereas fluorescence was tracked for the LAA contents equal to or below 1%. The manufactured plastic concrete was shown to exhibit photochromism from colorless under daytime light to green below UV, and greenish-yellow in the dark. By measuring the static contact angle, we were able to confirm the excellent superhydrophobic activity. Indications of enhanced UV protection and photostability were monitored upon increasing LAA ratio in the concrete bulk. Strong durability, reversibility and continuous afterglow emission were hallmarks of the photoluminescent hard composite concrete. The created plastic concrete morphology, elemental content and hardness properties were studied.

Simulation of 2D ground movement due to tunnel excavation using Finite Element Method (FEM)

Sustainability in construction of tunnel is very important to reduce environmental impact and also minimal use of earth resources. Therefore, numerical modelling is proposing at design stage to achieved this objective. To evaluate the changes in soil settlements during tunnel excavation, empirical, analytical, and numerical methods have been frequently applied movement research and the numerical method is effective in anticipating possible underground excavation scenarios. This paper describes the project on prediction of 2D ground movement due to the tunnel excavation by using Finite Element Method via ADONIS with the soil properties data from certain soil section of Goose Creek Tunnel project. The tunnel is in horse-shoe shape and typically be 1.8 m wide by 2.2 m tall. However, in this paper, the tunnel is assumed as a circular tunnel with diameter 2.2 m. This paper is focus on the effects of the constitutive soil models. The influence of type of soil model to the ground settlement is investigated and discussed. The simulation is confirmed by comparing the output of the settlement with manual calculation. The findings prove the Plastic Hardening (PH) model is more suitable in modelling ground movement due to tunnel excavation. By designing a tunnelling structure with a low prediction error, the engineers can build the most efficient tunnel.

A novel elastoplastic model for Yunnan sandstone under poly-axial loading

The lack of understanding of plastic hardening (softening) laws, especially under anisotropic stress conditions, results in inappropriate geotechnical management. Most of the yielding envelopes do not consider the effect of intermediate principal stress and the influence of Lode’s angle. In addition, the application of plastic flow rules regarding yielding surfaces compromises the softening of rock internal friction as well as the influence of Lode’s angle on the plastic potential. Moreover, the ductility to brittleness transition in the intermediate principal stress direction still requires a theoretical foundation. In this study, based on poly-axial testing results of Yunnan sandstone, we adopted a failure criterion with the intermediate principal stress proposed by Menétrey and Willam. The proposed new failure envelope was applied to capture the plastic evolution of rock samples. A plastic hardening-softening model is constructed, based on the framework of the plastic theory. The softening envelope is modified to better present the stress drop and considers the deterioration of rock internal friction in the post-peak stage of poly-axial loading. The differential of plastic potential according to the principal stresses is also modified, considering the rotation of Lode’s angle in the poly-axial loading tests. The model results were compared with laboratory testing results, which showed great consistency across 9 different loading tests (5 under triaxial stress and 4 under poly-axial stress with 22 stress-strain curves in total). The induced brittleness by the intermediate principal stress is also well captured by the proposed model.