Influence of Mechanical Behavior between the Grains on Stress Fluctuation of Aluminum Alloy Thick Plate

The research on fluctuation and inhomogeneity of internal stress of aluminum alloy thick plate is theoretical and technological base for stress control technology. By using X-ray diffraction technique and mechanical test method, aluminum alloy with typical fine sub-grains, coarse recrystallized grains, and second phase was analyzed; the interactive mechanical model between grains was built for analysis of variation of internal stress within the local micro structure by imitating the actual distribution of grains. The experimental result shows that the mechanical model can effectively explain the reason for fluctuation of microscopic stress, which also proves that the inhomogeneous distribution of metal organization is the cause for the complex distribution of microscopic stress. The model can well describe stress distribution of thick plate caused by thermal deformation. Besides, it well describes mechanism of stress fluctuation.

Determination of the Micro Stress Field in Composite by Homogenization Method

The objective of this study is to investigate the local stress fluctuation in two-phase composite by homogenization method. The composite was described by homogeneous macro structure and periodical micro structure sinudtaneously and the mechanical response of the composite can be described based on both macro and micro dimensional scales. Micro and mocro homogenization problems can be formulated. The effective material properties of the composite and the local stress field in the microstructure of the composite can be determined by solving these equntions.

A NEW METHOD IN GROUNDWATER FLOW MODELING

One of the challenges in groundwater modeling is the prediction of hydraulic head related to local stress fluctuations with a regional scale model. Typical applications of numerical models require extensive field information for input data and for calibration If we can model the change directly, we may not have to know all the modeling parameters because sometimes the changes only depend on fewer parameters. In this article, we present an improved methodology for groundwater modeling related to local stress fluctuations using a perturbation approach. Our results demonstrate that this approach is capable of matching an exact solution for drawdown in both confined and unconfined aquifers. The results suggest that this perturbation method can provide an accurate representation of head in a large-scale hydrogeological system.

Micro/nano-mechanical behaviors of individual FCC,BCC and FCC/BCC interphase in a high-entropy alloy

Here,a systematic investigation was made on the interphase strengthening effects induced superior me-chanical performances of multiphase high-entropy alloys(HEAs)at micro/nano-scale,compared with sin-gle phase HEAs.A pillar compression test under a scanning electron microscope(SEM)was performed on the individual face centered cubic(FCC),body centered cubic(BCC),and mixed-phases with different di-ameters in a Fe_(24)Co_(25)Ni_(24)Cr_(23)Al_(4)HEA using focused ion beam(FIB)milling and a nanoindenter equipped with a flat punch.The stress-strain response of pillar underneath the indenter was selected to explore the diameter/phase-dependent size effect,the periodically fluctuation of local stress,and strain hardening.It was revealed that the pillars at the interphase exhibited significantly higher strength,compared with the FCC and BCC pillars.An experiment also verified the coincident mechanical size effects independent with the type of phases.The stress responses in the mixed-phase pillars manifested as a distinct transition from the dramatic drop to the minor fluctuation during the post-yield stages with the increasing strain,indicating the propagation of Al-Ni enriched solid solution phase(BCC1)under compression.Except the BCC1 phase,numerous dislocations were observed in the post-deformed pillars,particularly serving as the major source to enhance the strain hardening of BCC pillars.

Study of methods for evaluating the probability of multiple site damage occurrences

Two methods currently available for evaluating the probability of Multiple Site Damage(MSD)occurrence were studied in this paper.One of the methods is a probabilistic analysis approach based on the statistical theory and fatigue characteristics of each structural detail,and the other is an approach which defines the initial damage scenario by means of Monte-Carlo simulation,and multiple initial crack scenarios are randomly generated.A modified method based on the Monte-Carlo simulation was proposed in this paper,in which the random fluctuation of the stress was considered to give more accurate evaluation results.In the presented method,the probability of MSD occurrence in a structural element containing multiple details was calculated based on the Monte-Carlo simulation and the p-S-N curve of a single structural detail.Fatigue tests were accomplished using specimens containing 21-similar-details to obtain the fatigue life corresponding to MSD occurrence.Tests on single-detail specimens and static calibration tests were also conducted to get the basic fatigue properties of the material and the degree of stress fluctuation.The aforementioned three methods were compared and validated via the test results.The influence of the stress random fluctuation degree on the probability of MSD occurrence and influence of the distribution types on evaluating the MSD occurrence probability were discussed.

A new method of LES verification and validation for attached turbulent cavitating flow

The large eddy simulation(LES)is used to resolve the flow structure in the cavitating turbulent flow around the Clark-Y hydrofoil coupled with a homogeneous cavitation model.A new method is proposed in this paper to calculate the LES error of the time-averaged streamwise velocity for the LES verification and validation(V&V).From the instantaneous cavity patterns,it is demonstrated that the predicted results agree fairly well with the experimental data.With this new proposed method,the LES errors can be easily and effectively calculated with a limited mesh number,and the method might be used in the other applications of the LES V&V.Results of the LES errors obtained by the new method show that the relatively steady flow can be simulated with small errors,while the complex flow structures at the cavity shedding region might lead to an increase of errors in the LES modeling.In addition,the distributions of the resolved Reynolds stresses are used to estimate the influences of the cavitation on the turbulent fluctuations.Results indicate that the turbulent fluctuations for the cavitating flow are much larger in magnitude as compared to the cases without cavitation.