Relationship between Salt (NaCl) Stress and Yield Components in Three Varieties of African Yam Bean (Sphenostylis stenocarpa)

Salinity has threatened the existence of many useful and multipurpose legumes such as Sphenostylis stenocarpa. To revert this situation effort must be made towards its sustainable use by encouraging domestication of improved varieties that can thrive in salt stress region. This research study was aimed at establishing the effect of salt-stress on seed germination, morphological attributes and yield response of three ­varieties Sphenostylis stenocarpa. Data were collected from the third-weekly for a period of three months (12 weeks) on plant height and number of leaves. At 12 weeks, data were collected on the following traits: number of flowers per plant, number of pods per plant, length of pod and number of seeds per pod. The data on number of seed germinated was also taken. Data collected were subjected to analysis of variance (ANOVA) and mean were separated using Least Significant Difference (LSD) test. Results obtained revealed that sodium chloride (NaCl+) significantly affected some important morphological traits of Sphenostylis stenocarpa evaluated. All varieties treated at various levels (1 kg/l, 2 kg/l and 3 kg/l) with NaCl performed poorly than those without treatment (control). This study revealed that there was no significant difference amongst all varieties of African yam been treated at 1 kg/l levels of NaCl. There was no significant different (p<0.05) among varieties of African yam bean at 0 kg/l in different morphological parameters evaluated. Salt stress significantly reduced (p<0.05) the germination of African yam bean.

Process - Property Correlation of Friction Stir Welding of Marine Grade Aluminium Alloy 5083 Using Finite Element Analysis

In this article, a 3D finite element based thermo-mechanical model for friction stir welding (FSW) of a marine-grade aluminium alloy 5083 is proposed. The model demonstrates the thermal evaluation and the distribution of residual stresses and strains under the variation of process variables. The temperature profile of the weld joint during the FSW process and the mechanical properties of the joints are also experimentally evaluated. The necessary calibration of the model for the correct implementation of the thermal loading, mechanical loading, and boundary conditions was performed using the experimental results. The model simulation and experimental results are analyses in view of the process-property correlation study. The residual stress was evaluated along, and across the weld, centreline referred as longitudinal and transverse residual stresses, respectively. The magnitude of longitudinal residual stress is noted 60-80% higher than that of the transverse direction. The longitudinal residual stress generated a tensile oval shaped stress region around the tool shoulder confined to a maximum distance of about 25mm from the axis of the tool along the weld line. It encompasses the weld-nugget to thermo-mechanically affected zone (TMAZ), while the parent metal region is mostly experiences the compressive residual stresses. However, the transverse residual stress region appears like wing shaped region spread out in both the advancing and retreating side of the weld and occupying approximately double the area as compared to the longitudinal residual stresses. Overall, the study revealed a corelation between the FSW process variables such as welding speed and the tool rotational speed with the residual stress and the mechanical properties of the joint.

Diagnostic Fracture Injection Test Analysis Method Addresses Layered Rocks

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 199690, “Diagnostic Fracture Injection Test Analysis and Interpretation in Layered Rocks,” by Shuang Zheng, SPE, Ripudaman Manchanda, SPE, and HanYi Wang, The University of Texas at Austin, et al., prepared for the 2020 SPE Hydraulic Fracturing Technology Conference and Exhibition, The Woodlands, Texas, 4-6 February. The paper has not been peer reviewed. Formation-property estimations based on diagnostic fracture injection tests (DFITs) typically are based on analysis of pressure data assuming the closure of simple planar fractures in homogeneous reservoirs. These interpretations are incorrect when dealing with complex reservoir environments such as layered reservoirs with different properties and stresses. The complete paper investigates the effect of such complex environments on DFIT interpretation and presents a systematic method to analyze the data. Model Description A fully integrated hydraulic fracturing and reservoir simulator is used in this paper to simulate a DFIT. This simulator has been developed for designing and evaluating pad-scale fracturing treatments. It was then extended from a single-phase flow model to a multiphase black-oil-flow model and from a single-well fracturing simulator to an integrated fracturing and reservoir simulator. An energy-balance model was incorporated into the simulator to consider temperature changes. The fully implicit geomechanical hydraulic fracturing simulator was also extended to an integrated equation-of-state-based compositional fracturing and reservoir simulator in recent work. This simulator, which has been used in the literature and is discussed in detail in the complete paper, couples the reservoir fracture/wellbore system and has the capability to simulate the life cycle of wells: hydraulic fracturing, shut-in, flowback, primary production, and improved oil recovery. Base Case In the base case, a small amount of fluid is injected into the wellbore and the well is shut in for 10 days to mimic a DFIT job. The simulation domain is 400×400 m2 in the horizontal plane and 200 m in the height direction. The perforation clusters are placed in the middle of the domain. The bottomhole pressure vs. time is computed and plotted in this simulation. The simulation involves propagation of a single vertical fracture from a horizontal wellbore drilled in a formation with layered stress heterogeneity. The fracture maintains the largest width in the middle low-stress region, and the two low-stress regions below and above the middle low-stress region also have a large width compared with the fracture-tip regions and the high-stress regions. During fracture closure, fracture width decreases; however, the fracture width in the low-stress region is always higher than in the high-stress region. Results and Discussion The authors applied the numerical DFIT model to study the effect of different layer properties on DFIT signature and its interpretation. The simulation results indicate that most of the layer proper-ties have a major effect on DFIT signature and interpretation.

A non-local continuum poro-damage mechanics model for hydrofracturing of surface crevasses in grounded glaciers

Hydrofracturing can enhance the depth to which crevasses propagate and, in some cases, allow full depth crevasse penetration and iceberg detachment. However, many existing crevasse models either do not fully account for the stress field driving the hydrofracture process and/or treat glacier ice as elastic, neglecting the non-linear viscous rheology. Here, we present a non-local continuum poro-damage mechanics (CPDM) model for hydrofracturing and implement it within a full Stokes finite element formulation. We use the CPDM model to simulate the propagation of water-filled crevasses in idealized grounded glaciers, and compare crevasse depths predicted by this model with those from linear elastic fracture mechanics (LEFM) and zero stress models. We find that the CPDM model is in good agreement with the LEFM model for isolated crevasses and with the zero stress model for closely-spaced crevasses, until the glacier approaches buoyancy. When the glacier approaches buoyancy, we find that the CPDM model does not allow the propagation of water-filled crevasses due to the much smaller size of the tensile stress region concentrated near the crevasse tip. Our study suggests that the combination of non-linear viscous and damage processes in ice near the tip of a water-filled crevasse can alter calving outcomes.

Stress and Mesh Stiffness Evaluation of Bimaterial Spur Gears

Lightweight spur gears have been a trending topic in aerospace and automotive applications recently. Traditionally, weight reduction could be ensured by using gear body with holes or thin rim design which result in to fluctuate mesh stiffness or it may increase stress and deformation levels. Indeed, high stresses occur in only contact and root region of gear tooth during the meshing process, so other regions are subjected to low stress. Based upon this point; various materials with low density and adequate strength could be used in low stress region while gear steel remains for high stress region. In this study, two different lightweight materials (Aluminum alloy and Carbon fiber reinforced polymer) were used for low stress region. The effect of these materials was investigated in view of stiffness and root stress for the same gear design parameters. Unidirectional CFRP laminas were used in a symmetric lay up to ensure quasi-isotropic laminate properties. Finite element analyses were conducted to obtain root stress and then total deformation of the tooth for stiffness calculation. Interface properties of ring and core regions were assumed as pure bonded. Meshing load was applied on the highest point single tooth contact (HPSTC) line. Weight reduction ratios were also compared. According to results, the steel/composite design is superior to steel/aluminum hybrid design in view of stress, stiffness and weight.

Quantification of slip planes in the stem wood of Eucalyptus grandis

The objective of this work was to analyze the natural occurrence of slip planes (SPs) inEucalyptus grandiswood fibers in terms of their characterization, distribution in the stem and associations with other wood characteristics. A 28-year-oldE. grandiswas studied, whose stems were sampled in the base-top direction. The longitudinal compressive stress regions (LCompSR, in the inner part of the stem) and longitudinal tensile stress region (LTensSR, in the outer parts of the stem) were separately considered. The following parameters were measured: microfibril angle (MFA), slip plane angle (SPA), number of SPs per millimeter (SP mm−1), slip plane index (SPI) and the relative abundance of SP in the fiber. The SPAs differ only slightly between LCompSR (76°) and LTensSR (77°). The base of the stem, which supports a larger mass, contains the most SPs and the number of SPs decreases from the base to the top. In the LCompSR, the SPI reduction was from 21 to 8%, and in the LTensSR, from 18 to 7%.

Controlling residual stress and distortion of friction stir welding joint by external stationary shoulder

Friction stir welding (FSW) can achieve a sound welding joint, but its residual stress and distortion cannot be avoided due to the non-uniformity of temperature distribution during welding. Stationary shoulder friction stir welding (SSFSW) was employed to butt weld 6005A-T6 aluminum alloy plates. The effects of welding speeds ranging from 200 mm/min to 600 mm/min on residual stress and distortion were investigated in detail. A thermo-mechanical model was utilized to compare the residual stress distribution between conventional FSW and SSFSW. SSFSW was beneficial to decreasing the peak temperature of stir zone (SZ) and then obtaining a narrower SZ. The peak residual stress produced by SSFSW was 50% lower than that by conventional FSW and a narrower tensile stress region was attained by SSFSW. Moreover, the stationary shoulder applied a function of synchronous rolling during the welding, which controlled the distortion effectively.

Intermediate-Temperature Creep Deformation and Microstructural Evolution of an Equiatomic FCC-Structured CoCrFeNiMn High-Entropy Alloy

The tensile creep behavior of an equiatomic CoCrFeNiMn high-entropy alloy was systematically investigated over an intermediate temperature range (500–600 °C) and applied stress (140–400 MPa). The alloy exhibited a stress-dependent transition from a low-stress region (LSR-region I) to a high-stress region (HSR-region II). The LSR was characterized by a stress exponent of 5 to 6 and an average activation energy of 268 kJ mol−1, whereas the HSR showed much higher corresponding values of 8.9–14 and 380 kJ mol−1. Microstructural examinations on the deformed samples revealed remarkable dynamic recrystallization at higher stress levels. Dislocation jogging and tangling configurations were frequently observed in LSR and HSR at 550 and 600 °C, respectively. Moreover, dynamic precipitates identified as M23C6 or a Cr-rich σ phase were formed along grain boundaries in HSR. The diffusion-compensated strain rate versus modulus-compensated stress data analysis implied that the creep deformation in both stress regions was dominated by stress-assisted dislocation climb controlled by lattice diffusion. Nevertheless, the abnormally high stress exponents in HSR were ascribed to the coordinative contributions of dynamic recrystallization and dynamic precipitation. Simultaneously, the barriers imposed by these precipitates and severe initial deformation were referred to so as to increase the activation energy for creep deformation.

Creep Features of Ti-600 Alloy at the Temperature of 650°C

Creep tests were carried out on one kind of near alpha titanium alloy named after Ti-600 alloy at the temperature of 650°C, and with the stresses of 150MPa, 200MPa, 250 MPa, 300 MPa and 350 MPa, respectively. The alloy ingot was conventionally forged and rolled to diameter 18mm bars. The creep samples were cut from the rolling bars and were solutioned at 1020°C for 1 h, air cooling, then aged at 650°C for 8 h, air cooling (STA). Steady state creep rate and the stress exponent n at different stresses were calculated for the alloy. Threshold stress σ0 was introduced to get the true stress exponent p. Creep deformation mechanism was also investigated. The results indicated that the steady state creep rate will increase with the rise of stress, and the creep time will also be shortened at the same time. At 650°C, the threshold stress is 83.8MPa. The value of n and p is 7.7 and 3.3 respectively for the alloy crept at lower stress region (150-200MPa); and which is 2.1 and 4.7 respectively for the alloy crept at relatively higher stress region (200-350MPa). Constitutive equations of steady state creep rate were also established for the alloy crept at 650°C. The creep deformation for the alloy is controlled by dislocation slipping at lower stress region, and which is mainly controlled by dislocation climbing and subordinately controlled by dislocation slipping at higher stress region.