Kinematic and Static Solutions for Beam Column with Nonlinear Springs Using the Extended Linear Matching Method

In this paper, the kinematic and static solutions for solving the static response of the beam column with nonlinear springs are presented by adopting the extended linear matching method (LMM). The extended LMM can be used to predict the displacement response of the beam-column system consisting of perfectly plastic and strain-softening materials. It is found that the kinematic solution generated by the extended LMM demonstrates a monotonic decrease for perfect plastic materials with certain restrictions on the yield surface. The potential energy of the system is proved to decrease with iterations for both perfect plastic and strain-softening materials if the loading multiplier remains constant. The extended LMM method is then applied to analyse the response of the pile system in a 3-leg offshore platform. An incremental procedure is recommended to determine the peak load for the soil exhibiting strain-softening. A displacement-control approach is used with the loading multiplier obtained from the variation of the potential energy. Good convergence of the method is obtained.

A Perfect Plastic Material for Studies on Self-Propelled Motion on the Water Surface

We describe a novel plastic material composed of camphene, camphor, and polypropylene that seems perfectly suited for studies on self-propelled objects on the water surface. Self-motion is one of the attributes of life, and chemically propelled objects show numerous similarities with animated motion. One of important questions is the relationship between the object shape and its motility. In our previous paper, {R. Löffler et al. PCCP, 2019, 21, 24852–24856}, we presented a novel hybrid material, obtained from the solution of camphor in camphene, that allowed making objects of various shapes. This hybrid material has wax-like mechanical properties, but it has a very high tackiness. Here, we report that a small amount of polypropylene removed this undesirable feature. We investigated the properties of camphor–camphene–polypropylene plastic by performing the statistical analysis of a pill trajectory inside a Petri dish and compared them with those of camphor-camphene wax. The plastic showed the stable character of motion for over an hour-long experiment. The surface activity of objects made of plastic did not significantly depend on the weight ratios of the compounds. Such a significant increase in usefulness came from the polypropylene, which controlled the dissipation of camphor and camphene molecules.

Analytical Solutions of Model Problems for Large-Deformation Micromorphic Approach to Gradient Plasticity

The objective of this work is to present analytical solutions for several 2D model problems to demonstrate the unique plastic fields generated by the implementation of micromorphic approach for gradient plasticity. The approach is presented for finite deformations and several macroscopic and nonstandard microscopic boundary conditions are applied to a gliding plate to illustrate the capability to predict the size effects and inhomogeneous plastic fields promoted by the gradient terms. The constitutive behavior of the material undergoing plastic deformation is analyzed for softening, hardening and perfect plastic response and corresponding solutions are provided. The analytical solutions are also shown to match with the numerical results obtained by implementing a user element subroutine (UEL) to the commercial finite element software Abaqus/Standard.

Leakage of a High Temperature and High Pressure Flange Metal Gasket due to its Ratcheting in Alternating Pours of Rain

In the high pressure ethylene polymerization process, pipes transmitting reaction product are often bolt-flange connected with metal gaskets which demands high tightness. However ethylene and polyethylene was found leaking from a flange connection in the pipe out of a polymerization kettle after several pours of rain, which leads to an emergency shutdown. A finite element model was worked out to simulate the ratcheting of the metal gasket during the on and off rains by keeping the temperature of the pipe, flange, and gasket as 270°C, but changing the temperature of bolts from higher temperature 270°C to a lower temperature cyclically. Elastic and perfect plastic model was conservatively employed in the ratcheting analysis. It is found that gasket plastic strains accumulate with the bolt temperature drop cycles. The higher the bolt temperature drop, the more plastic strain accumulation. Consequently, the contact pressure between the flange and the gasket reduces with the bolt temperature cycles. The higher the temperature drop, the less the flange connection tightness. It reveals that bolt temperature drop below 155°C does not destroy the flange connection tightness with a gasket parameter 3.0. When temperature drops are above 155°C, temperature cycles to destroy the flange connection tightness decrease with temperature drops, namely the higher the temperature drop, the less temperature cycles needed to destroy the flange connection tightness. A margin line has been worked out to correlate the bolt temperature drops and cycles to the gasket leakage.

Mechanical behaviour of a creased thin strip

In this study the mechanical behaviour of a creased thin strip under opposite-sense bending was investigated. It was found that a simple crease, which led to the increase of the second moment of area, could significantly alter the overall mechanical behaviour of a thin strip, for example the peak moment could be increased by 100 times. The crease was treated as a cylindrical segment of a small radius. Parametric studies demonstrated that the geometry of the strip could strongly influence its flexural behaviour. We showed that the uniform thickness and the radius of the creased segment had the greatest and the least influence on the mechanical behaviour, respectively. We further revealed that material properties could dramatically affect the overall mechanical behaviour of the creased strip by gradually changing the material from being linear elastic to elastic-perfect plastic. After the formation of the fold, the moment of the two ends of the strip differed considerably when the elasto-plastic materials were used, especially for materials with smaller tangent modulus in the plastic range. The deformation patterns of the thin strips from the finite element simulations were verified by physical models made of thin metal strips. The findings from this study provide useful information for designing origami structures for engineering applications using creased thin strips.

A Pore-Scale Simulation on Thermal-Hydromechanical Coupling Mechanism of Rock

Thermal-hydromechanical (THM) coupling process is a key issue in geotechnical engineering emphasized by many scholars. Most existing studies are conducted at macroscale or mesoscale. This paper presents a pore-scale THM coupling study of the immiscible two-phase flow in the perfect-plastic rock. Assembled rock matrix and pore space models are reconstructed using micro-CT image. The rock deformation and fluid flow are simulated using ANSYS and CFX software, respectively, in which process the coupled physical parameters will be exchanged by ANSYS multiphysics platform at the end of each iteration. Effects of stress and temperature on the rock porosity, permeability, microstructure, and the displacing mechanism of water flooding process are analyzed and revealed.