Resilient modulus and cumulative plastic strain of frozen silty clay under dynamic aircraft loading

This paper describes an investigation into the factors influencing the resilient modulus and cumulative plastic strain of frozen silty clay. A series of dynamic triaxial tests are conducted to analyze the influence of the temperature, confining pressure, frequency, and compaction degree on the resilient modulus and cumulative plastic strain of frozen silty clay samples. The results show that when the temperature is below − 5 °C, the resilient modulus decreases linearly, whereas when the temperature is above − 5 °C, the resilient modulus decreases according to a power function. The resilient modulus increases logarithmically when the frequency is less than 2 Hz and increases linearly once the frequency exceeds 2 Hz. The resilient modulus increases as the confining pressure and compaction degree increase. The cumulative plastic strain decreases as the temperature decreases and as the confining pressure, frequency, and compaction degree increase. The research findings provide valuable information for the design, construction, operation, maintenance, safety, and management of airport engineering in frozen soil regions.

FCG Modelling Considering the Combined Effects of Cyclic Plastic Deformation and Growth of Micro-Voids

Fatigue is one of the most prevalent mechanisms of failure. Thus, the evaluation of the fatigue crack growth process is fundamental in engineering applications subjected to cyclic loads. The fatigue crack growth rate is usually accessed through the da/dN-ΔK curves, which have some well-known limitations. In this study a numerical model that uses the cyclic plastic strain at the crack tip to predict da/dN was coupled with the Gurson–Tvergaard–Needleman (GTN) damage model. The crack propagation process occurs, by node release, when the cumulative plastic strain reaches a critical value. The GTN model is used to account for the material degradation due to the growth of micro-voids process, which affects fatigue crack growth. Predictions with GTN are compared with the ones obtained without this ductile fracture model. Crack closure was studied in order to justify the lower values of da/dN obtained in the model with GTN, when compared with the results without GTN, for lower ΔK values. Finally, the accuracy of both variants of the numerical model is accessed through the comparison with experimental results.

Optimized design of wiring scheme for conductive layer in bending area of FOLED

In order to solve the problem of wiring breakage in conductive layer caused by fold in bend area of FOLED and improve the efficiency of conductive layer in bend area of FOLED, the wiring scheme of conductive layer in bend area of FOLED is optimized. First of all, the polymer substrate FOLED samples are prepared, and the bending area structure is formed by stacking resin, pin, metal wires and other layers. The equivalent working condition of bending process is analyzed, and the three-dimensional finite element modeling of the bending area of FOLED is completed. According to the simulation analysis results of bending area of FOLED, it is proposed that the optimal design of Resin ply thickness is: the limiting conditions of material damage in conductive layer should be fully considered, and the material damage mechanism should be studied to ensure that the cumulative plastic strain of A-A and B-B positions is smaller at the same time without damage; the optimal design of wiring scheme for conductive layer is: using the square of optimal stress distribution to reduce the fracture angle, and the routing scheme of crossing route type > full filling type> internal opening type should be adopted.

Comparison of 316LN Ratcheting Boundary at Room Temperature and 350 °C

The ratcheting boundaries of 316LN austenitic stainless steel under room temperature and 350 °C were determined by efficiency curve method. The iso-cumulative plastic strain curves of the material were obtained through numerical interpolation method. It is indicated that the primary stress and secondary stress range increase with the increase of cumulative plastic deformation. Under the same cumulative plastic strain, the iso-cumulative plastic strain curve at 350 °C is higher than that at room temperature. The effective primary stress was introduced to obtain ratcheting boundary curves. The results show that the material at 350 °C has a higher ratcheting boundary compared with that at room temperature. It is indicated that, under equivalent stress condition, the bearing capacity of 316LN at 350 °C is stronger than that at room temperature. This is due to the dynamic strain aging of the material at high temperature. At 350 °C, the solid solution atoms and dislocations are pinned together, which leads to a strengthening effect on the material. The ratcheting boundary curves determined in this study are compared with relevant standards. The test results suggest that the material served in different environments should be checked by different ratcheting boundary curves.

Optimum Strength Distribution for Structures with Metallic Dampers Subjected to Seismic Loading

A key aspect of the seismic design of structures is the distribution of the lateral strength, because it governs the distribution of the cumulative plastic strain energy (i.e., the damage) among the stories. The lateral shear strength of a story i is commonly normalized by the upward weight of the building and expressed by a shear force coefficient αi. The cumulative plastic strain energy in a given story i can be normalized by the product of its lateral strength and yield displacement, and expressed by a plastic deformation ratio ηi. The distribution αi/α1 that makes ηi equal in all stories is called the optimum yield-shear force distribution. It constitutes a major aim of design; a second aim is to achieve similar ductility demand in all stories. This paper proposes a new approach for deriving the optimum yield-shear force coefficient distribution of structures without underground stories and equipped with metallic dampers. It is shown, both numerically and experimentally, that structures designed with the proposed distribution fulfil the expected response in terms of both damage distribution and inter-story drift demand. Moreover, a comparison with other distributions described in the literature serves to underscore the advantages of the proposed approach.

Experimental Research on Deformation Characteristics of Using Silty Clay Modified Oil Shale Ash and Fly Ash as the Subgrade Material after Freeze-Thaw Cycles

To achieve the purposes of disposing industry solid wastes and enhancing the sustainability of subgrade life-cycle service performance in seasonally frozen regions compared to previous research of modified silty clay (MSC) composed of oil shale ash (OSA), fly ash (FA), and silty clay (SC), we identified for the first time the axial deformation characteristics of MSC with different levels of cycle load number, dynamic stress ratio, confining pressure, loading frequency, and F-T cycles; and corresponding to the above conditions, the normalized and logarithmic models on the plastic cumulative strain prediction of MSC are established. For the effect of cycle load number, results show that the cumulative plastic strain of MSC after 1, 10, and 100 cycle loads occupies for 28.72%~35.31%, 49.86%~55.59%, and 70.87%~78.39% of those after 8000 cycle loads, indicating that MSC possesses remarkable plastic stability after 100 cycles of cycle loads. For the effect of dynamic stress ratio, confining pressure, loading frequency, and F-T cycles, results show that dynamic stress ratio and F-T cycles are important factors affecting the axial deformation of MSC after repeated cycle loads; and under the low dynamic stress ratio, increasing confining pressure and loading frequency have insignificant effect on the axial strain of MSC after 8000 loads. In term of the normalized and logarithmic models on the plastic cumulative strain prediction of MSC, they have a high correlation coefficient with testing data, and according to the above models, the predicted result shows that the cumulative plastic strain of MSC ranges from 0.38 cm to 2.71 cm, and these predicted values are within the requirements in the related standards of highway subgrades and railway, indicating that the cumulative plastic strain of MSC is small and MSC is suitable to be used as the subgrade materials.

An An Analysis of Strain Rate Distribution Using Streamline Model and A Quick Stop Device in Metal Cutting

In this paper, a quick stop device technique and the streamline model were employed to study the chip formation in metal cutting. The behavior of chip deformation at the primary shear zone was described by this model. Orthogonal test of turning process over a workpiece of the 6061-T6 aluminum alloy at different cutting speeds was carried out. The results of the equivalent strain rate and cumulative plastic strain were used to describe the complexity of chip formation. Finite element analysis by ABAQUS/explicit package was also employed to verify the streamline model. Some behavior of formation and strain rate distribution differs from the experimental results, but the overall trend and maximum results are approximately close. In addition, the quick stop device technique is described in detail. Which could be used in other kinds of studies, such as the metallurgical observation.

Multidimensional Fragility Analysis for a NEES Frame Structure by Integrating a New Energy Damage Index: Cumulative Plastic Strain

Cumulative plastic strain (CPS) damage index is proposed in this study for seismic fragility analysis by integrating the force analogy method into the energy balance equation, and CPS can be defined as the ratio of the demand of plastic dissipation energy to its capacity. The cumulative plastic strain can indicate the structural damage cumulative effect under earthquakes, which makes it especially suitable to be selected as the damage index for the structural component. Threshold values of cumulative plastic strain for different performance limit state (PLS) levels are obtained through the degree of consistency of interstory drift-based fragility curves and CPS-based fragility curves. Regarding the multidimensional fragility evaluation, CPS and the floor acceleration will be selected as the quantification indices for performance limit state of the structural component and nonstructural component, respectively. The probabilistic seismic demand model (PSDM) following multivariate logarithmic normal distribution will be developed, and taking PLS uncertainty and correlation into consideration, multidimensional PLS function is constructed to identify the structural failure domain. A full-scale 2-bay 2-story frame structure for the Network for Earthquake Engineering Simulation (NEES) project is employed as the case study structure to demonstrate the proposed theory. Nonlinear dynamic time-history analysis is carried out for the structure to obtain its maximum responses under earthquakes. Consequently, the multidimensional fragility curves can be derived on the basis of CPS. Besides, the influence of PLS threshold value, engineering demand parameter (EDP) correlation, and PLS correlation on the multidimensional fragility is investigated. Results show that (1) CPS damage index can fully consider the cumulative effect of damage under earthquakes, which makes up for the deficiency of the interstory drift damage index in this aspect, (2) the multidimensional fragility framework can deal with the PLS correlation and EDP correlation simultaneously, which will generate a more precise seismic damage assessment result, and (3) multidimensional fragility is sensitive to PLS threshold values and PLS correlation parameters.