Joint Stress Research Articles

Residual Stress Testing and Simulation Analysis of Crystal Structures of Electronic Device Materials

In this paper, we analyze the residual stress of different components of the crystal structures of electronic device materials following exposure to elevated temperatures using a combination of experimental tests and finite element simulations. X-ray diffraction (XRD) and LXRD micro-area residual stress analyzer were employed to determine the residual strain and stress of the CBGA sample encapsulation cover and solder joints. Subsequently, the experimental data were utilized to verify the accuracy of the simulation. The discrepancy between experimental measurements and simulation outcomes of the residual stress following reflow soldering of CBGA-assembled micro-solder joints is below 14%. The analysis also included thermal warping deformation of the CBGA encapsulation cover and how the residual stress was influenced by the diameter, spacing, and height of the solder joints. The study reveals that the residual stress following reflow soldering of BGA solder joints is non-uniformly distributed within the array. Within a single solder joint, residual stress gradually increases in distribution from its middle to the point where it make contact with the PCB and chip, with the highest level of residual stress observed where the solder joint contacts the chip. The variation in material parameters, such as the coefficient of thermal expansion, is the primary cause of thermal warping deformation on the surface of CBGA encapsulation covers. Three primary factors significantly impact the residual stress on BGA solder joints: solder joint diameter, spacing, and height. The maximum value is inversely proportional to the height of the solder joints and the residual stress. Conversely, the diameter and spacing of the joints are positively proportional to the highest value. When the diameter of the solder joint is increased from 0.55 mm to 0.75 mm, the maximum residual stress in the BGA solder joint increases from 37.243 MPa to 36.835 MPa. Conversely, increasing the height of the solder joint from 0.36 mm to 0.44 mm reduces the stress from 39.776 MPa to 36.835 MPa.

Controlling deformation and residual stresses in a TIG joint for Invar steel molds

Invar steel is used to produce molds for composite materials for its thermal expansion coefficient similarity to those materials. These molds show wear resistance, provide good dimensional accuracy of produced parts, and they are produced with tungsten inert gas (TIG) welding. In this study, welding deformation and residual stress optimization of an Invar steel TIG welded butt joint were studied experimentally and numerically. Results show that deformation can be controlled effectively with the appropriate welding sequence from both sides to the middle of the joint when compared to sequential welding. When double welding guns are used to weld concurrently from both ends along the same welding path in segmental welding, deformation developed is minimum, while deformation increases significantly at the weld segmental area. When segmental bidirectional welding is used, deformation is slightly increased, but the highest deformation area can be avoided compared to segmental unidirectional welding, and residual stresses can be improved. The equivalent stresses were reduced following heat treatment, and especially stress concentration in the weld, with optimal values reached for heat treatment at 420 °C.

Statistical Shape Modeling Enables Identification of Subtalar Contact Stress Differences Following Tibiotalar Arthrodesis and Total Ankle Replacement

Category: Hindfoot; Ankle Arthritis Introduction/Purpose: Clinical studies have shown 32% of patients with a TAR progress to subtalar OA within 5 years, whereas 78% of patients with a tibiotalar arthrodesis presented with subtalar OA by 7.5 years. Higher rates of subtalar OA after arthrodesis may be explained by a transfer of ankle forces and stress through the adjacent subtalar joint while TAR may mitigate these changes. The objective of this study was to compare subtalar joint contact stresses between patients treated with tibiotalar arthrodesis and total ankle replacement (TAR) during an overground walking activity using correspondence particles to enable regional analysis. Methods: With IRB approval, ten individuals with unilateral tibiotalar arthrodesis and six individuals with unilateral TAR were imaged with biplane fluoroscopy during overground walking. Discrete element analysis (DEA) was performed to estimate subtalar joint contact stress using the tracked bone models. Cartilage was modeled using linear-elastic material properties (E=12 MPa, v=0.42) and uniformly extruded compressible surfaces from rigid subchondral bone (0.98 mm talar side, 0.75 mm calcaneal side1). A calcaneal statistical shape model (SSM) was created and resulting correspondence particles served as registered locations for comparison of cumulative stress across three phases of normalized stance (loading-response 0-24%, mid 25-54%, and terminal 55- 87%). Two-sample t-tests or Wilcoxon rank-sum tests were used to evaluate differences (p < 0.05) in cumulative contact stresses at each correspondence particle within the 3 phases based upon Shapiro-Wilk findings of normality. Results: There were significant differences in contact stress exposure across all three phases of gait. Differences were identified along the superior-medial aspect of the posterior facet and within the anterior facet (Figure 1). Higher cumulative stresses were observed along the border of the posterior facet and in the medial facet. This model is limited by a lack of validation, uniform cartilage thickness assumptions applied across groups, and that DEA only estimates contact stress without consideration of shear. Conclusion: This study was the first to localize regional differences in subtalar joint stress for patients having undergone TAR and tibiotalar arthrodesis. Interestingly, TAR patients experienced higher stress in this study compared to those with arthrodeses. These ostensibly counterintuitive findings of higher TAR stress may relate to the pre-existence of subtalar OA which is a common indication of TAR versus fusion.

Salicylic Acid- and Potassium-Enhanced Resilience of Quinoa (Chenopodium quinoa Willd.) against Salinity and Cadmium Stress through Mitigating Ionic and Oxidative Stress.

Salinity and cadmium (Cd) contamination of soil are serious environmental issues threatening food security. This study investigated the role of salicylic acid (SA) and potassium (K) in enhancing the resilience of quinoa against the combined stress of salinity and Cd. Quinoa plants were grown under NaCl (0, 200 mM) and Cd (0, 100 µM) stress, with the addition of 0.1 mM SA and 10 mM K, separately or in combination. The joint stress of Cd and NaCl caused >50% decrease in plant growth, chlorophyll contents, and stomatal conductance compared to the control plants. The higher accumulation of Na and Cd reduced the uptake of K in quinoa tissues. The joint stress of salinity and Cd caused an 11-fold increase in hydrogen peroxide and 13-fold increase in thiobarbituric acid reactive substances contents, and caused a 61% decrease in membrane stability. An external supply of 0.1 mM SA and 10 mM K helped plants to better adapt to salinity and Cd stress with less of a reduction in plant biomass (shoot 19% and root 24%) and less accumulation of Na and Cd in plant tissues. The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) were enhanced by 11-fold, 10-fold, 7.7-fold, and 7-fold, respectively, when SA and K were applied together to the plants subjected to the joint stress of Cd and salinity. Based on the values of the bioconcentration factor (>1), the translocation factor (<1), and the higher tolerance index, it was clear that Cd-contaminated, salty soils could be stabilized with quinoa under the combined supply of SA and K.

Fatigue behavior of single-lap adhesive joints with similar and dissimilar adherends under cyclic loading: A combined experimental and simulation study

This study aims to research the fatigue behavior and reveal the failure mechanism of the adhesive joints with similar and dissimilar adherends, which made of the aluminum alloys (Al) and carbon fiber reinforced plastics (CFRP). Firstly, the electronic universal testing machine and fatigue testing machine were used to obtained the failure strength and fatigue life of the joints. Secondly, the joints were modeled by cyclic cohesive zone model (CCZM) to obtained the damage evolution process of the joint. Finally, the fatigue failure mechanism of the joint was analyzed based on the experimental failure mode and microscopic morphology. The results showed that in the fatigue process, the damage in CFRP-Al joints extends from the CFRP end to the Al end and eventually fractures near the Al end, while the damage in CFRP-CFRP and Al-Al joints are symmetrically distributed along the central axis of the lap area. In addition, the failure characteristics of the joints are mainly affected by the peel stress, and compared to differences in substrate stiffness (the cause of peel stress in joints with dissimilar adherends), the differences in the strength of the substrate-adhesive connection (the cause of peel stress in joints with similar adherends) plays a greater role in the generation of peel stress.

Analytical method for deformation and stress calculation of bell-and-spigot joints in PVC-U pipes

The stable operation of water supply pipelines relies significantly on the structural safety of pipe joints. A novel analytical pipe joint structural calculation method based on the Novozhilov thin shell theory was proposed to calculate the deformation and stress of bell-and-spigot joints in unplasticized polyvinyl chloride (PVC-U) pipes under internal pressure. An equivalent stress index was established to investigate and evaluate the safety performance of pipe joints. The effects of various factors, including spigot insertion depth, the clearance between the bell and spigot, internal pressure, and different pipe nominal outside diameter (DN) and nominal pressure (PN) series, on the maximum equivalent stress of pipe joints, were thoroughly analyzed. The results indicate that the maximum equivalent stress under nominal pressure is located on the inner surface of the bell and consistently exceeds the design stress. The influence of spigot insertion depth on the maximum equivalent stress is minimal. However, as the clearance value between the bell and spigot decreases and the internal pressure increases, the maximum equivalent stress increases significantly. Pipes with smaller DN and PN series result in a higher maximum equivalent stress at the joint. The analytical method indicates that increasing pipe thickness and reinforcing the bell with continuous carbon fiber filament winding are two potentially effective methods to enhance the mechanical performance of the joint and reduce the maximum equivalent stress. This study's findings offer valuable theoretical support for designing and selecting joints in PVC-U pipelines.

Maternal steroids during pregnancy and their associations with exposure to lifetime stressful life events, prenatal stress appraisal and psychological functioning

BackgroundDuring pregnancy, steroids enable physiological adaptations in response to many factors, including maternal stress or psychological functioning. While stress and psychological dysfunction can have endocrine-disrupting effects beyond cortisol disruption, associations between prenatal maternal stress or related psychological dysfunction and the broader steroid milieu remain understudied. AimTo assess associations between independent and joint maternal stress and psychological functioning measures and steroid profiles in pregnancy (22–40 gestational weeks) in the Programming of Intergenerational Stress Mechanisms (PRISM) birth cohort (n = 334). MethodsSerum metabolomics detected 42 steroids and their metabolites, which were grouped into five classes (pregnenolone, androgens, estrogens, progestin, and corticosteroids). The Perceived Stress Scale, Life Stressor Checklist-Revised, and Edinburgh Postnatal Depression Scale indexed lifetime traumatic/non-traumatic stressors, global prenatal stress appraisal, and depressive symptoms during pregnancy, respectively. Exposures were categorized as high-low using the corresponding 3rd quartiles. We assessed associations between both individual and joint stress exposures with steroid classes using linear mixed effect models and with individual steroids using linear regressions. We also examined fetal sex-specific effects. ResultsHigh prenatal perceived stress was independently associated with lower levels of androgens and estrogens in the overall sample [β (95%CI): androgens: −0.13 (−0.25;−0.01); estrogens: −0.16 (−0.31;−0.01)], particularly among women carrying males [androgens: −0.22 (−0.39;−0.05); estrogens: −0.28 (−0.50;−0.07)]. Results on estrogens were consistent when considering joint exposure to both greater lifetime stressors and higher prenatal perceived stress. We also found a single testosterone metabolite—5alpha-androstan-3alpha,17alpha-diol disulfate—negatively associated with both individual high perceived stress and joint exposure to high lifetime stressors and high perceived stress among women carrying males. ConclusionsIncreased maternal perceived stress experienced in pregnancy was independently associated with lower maternal androgen and estrogen levels during pregnancy in the overall sample, particularly among women carrying males. Results on estrogens were consistent when we considered the joint exposure of increased lifetime stressors and higher prenatal perceived stress.

The Association between Hip Joint Morphology and Posterior Wall Fracture: Analysis of Radiologic Parameters in Computed Tomography.

Although numerous radiologic parameters of abnormal hip joint morphology are utilized in practice, studies on the relation of these parameters to acetabular fractures are limited. This study hypothesized that certain morphological features of hip joints are associated with acetabular posterior wall (PW) fracture patterns and aimed to identify morphological characteristics predictive of acetabular PW fracture. The records of 107 consecutive patients, who were diagnosed with acetabular fractures in a level I trauma center from August 2017 to April 2021, were initially reviewed. After excluding patients who lacked proper radiographic evaluation and had previous surgery or concomitant injury on the ipsilateral lower limb, a total of 99 patients were analyzed to investigate the morphological characteristics of the hip joint, measured in computed tomography, associated with acetabular posterior wall fracture. We included patient demographics, acetabular index (AI), sharp angle, acetabular depth-to-width ratio (AD/WR), center-edge angle (CEA), head-neck offset ratio (HNOR), acetabular head index (AHI), anterior acetabular sector angle (AASA), posterior acetabular sector angle (PASA), and acetabular version angle (AVA) in the univariate and multivariate analyses. The injury mechanism (p = 0.001) and AD/WR (p = 0.021) were predictors of PW fracture in the univariate analysis. In the multivariable analysis, injury mechanism (p = 0.011), AI (coefficient B = 0.320; Exp (B) = 1.377; p = 0.017), and AD/WR (coefficient B = 33.047; Exp (B) = 2.250 × 1014; p = 0.028) were significant predictors of PW fracture. This study highlights the importance of morphological factors, such as a larger AI and AD/WR, that may influence joint stress distribution, resulting in acetabular PW fracture. Understanding these pathomechanisms may protect the hip joint and prevent future injuries through the early identification and treatment of pathological conditions.

Strength Analysis in Bonded, Bolted and Bolted-Bonded Joints, Single Lap Joints, Metal/Composite Plates

Today, especially in many fields that require structural durability, such as the aerospace and automotive industries, there has been a need to use different bonding techniques separately or together in order to use materials together with different mechanical properties. In this study, stress and damage analysis of single lap joints, bonding and bolt-bonding metal/composite joints under tensile loads were performed. The nine kinds of single lap joint models in different combinations (bonded, bolted and bolt-bonded) were prepared by using acrylic adhesive (Acrytron 1E1) and 100-25-3 mm in size; AZ91/AZ91, AZ91-carbon fiber and carbon fiber-carbon fiber plates. Some comparisons were carried out by examining the stresses and deformations that occur in joint models exposed to tensile and 4-point bending tests. As a result of the tensile test, it was determined that the highest maximum tensile stress occurred in AZ91-CF bolt-bonded samples. In the four-point bending test, the maximum shear force value was determined in the CF-CF bolted-bonded samples.

Finite element analysis of the knee joint stress after partial meniscectomy for meniscus horizontal cleavage tears

ObjectiveTo establish a finite element model of meniscus horizontal cleavage and partial resection, to simulate the mechanical changes of knee joint under 4 flexion angles, and to explore what is the optimal surgical plan. MethodsWe used Mimics Research, Geomagic Wrap, and SolidWorks computer software to reconstruct the 3D model of the knee joint, and then produced the horizontal cleavage tears model of the internal and lateral meniscus, the suture model, and the partial meniscectomy model. These models were assembled into a complete knee joint in SolidWorks software, and corresponding loads and boundary constraints were added to these models in ANSYS software to simulate the changing trend of pressure and shear force on femoral condylar cartilage, meniscus, and tibial cartilage under the flexion angles of 0°, 10°, 20°, 30° and 40° of the knee joint. At the same time, the difference of force area between medial interventricular and lateral interventricular of knee joint under four states of bending the knee was compared, to explore the different effects of different surgical methods on knee joint after horizontal meniscus tear. ResultsWithin the four medial meniscus injury models, the lowest peak internal pressure and shear force of the knee joint was observed in the meniscal suture model; the highest values were found in the bilateral leaflet resection model and the inferior leaflet resection model; the changes of pressure, shear force and stress area in the superior leaflet resection model were the most similar to the changes of the knee model with the meniscal suture model. ConclusionSuture repair is the best way to maintain the force relationship in the knee joint. However, resection of the superior leaflet of the meniscus is also a reliable choice when suture repair is difficult.

Energy flow in men's javelin throw and its relationship to joint load and performance.

Performance in javelin throwing is dependent on the release speed and therefore the energy transferred to the javelin. Little is known about the flow of mechanical energy in javelin throwing and whether there is a connection to joint loading and throwing performance. The purpose of the study was therefore to investigate (1) the energy flow within the kinetic chain of the throwing arm, (2) how it is related to performance and joint loads and (3) how joint forces and torques are used to transfer, generate and absorb mechanical energy. The kinematics of 10 experienced javelin throwers were recorded using a 12-camera infrared system. 16 markers were placed on the athlete's body, five on the javelin to track the movement of each segment. A segmental power analysis was carried out to calculate energy flow between upper body, upper arm, forearm and hand. Stepwise regression analysis was used to calculate the variable that best predicts release speed and joint loads. The results indicate that the higher the peak rate of energy transfer from the thorax to the humerus, the higher the release speed and the joint loads. While there were no differences between the peak rate of energy transfer in the different joints, the energy transferred differed depending on whether joint forces or torques were used. It can be further shown that higher joint torques and thus higher rotational kinetics at the shoulder are linked to higher release speeds. Thus, the movements of the upper body can be of great influence on the result in javelin throwing. Furthermore, the data show that athletes who are able to transfer more energy through the shoulder, rather than generate it, experience a smaller joint loading. An effective technique for improved energy transfer can thus help perform at the same level while lowering joint stress or have higher performance at the same joint loading.

Prediction of contact stress in bolted joints using the Polynomial Chaos-Kriging model

Bolted joints are one of the most widely used forms of connection. As the weak link, its contact stress directly influences the mechanical properties of a structure. In this work, Polynomial Chaos-Kriging (PCK) surrogate model is adopted to predict the contact stress in bolted joints. Firstly, a Finite Element (FE) model of the bolted joint is established using a parametric modeling method. On this basis, the stress datasets for the contact area of the plate are obtained. Subsequently, the generated stress datasets are imported into the PCK surrogate model for training and validation. Maximum axial stress and influence coefficient are used to conduct the characterization analysis of the contact stress. Results show that the PCK surrogate model is suitable to predict these two parameters. In the case that compressive stress does not exist in all contact areas, quantitative analysis of the contact stress can be further carried out by using this model. The main influencing parameters of contact stress are extracted according to the correlation analysis results. The trained PCK surrogate model can be used as an alternative to finite element analysis for the prediction of contact stress. Design of bolted joints can also be achieved by the parametric control using this model.

Enhancing Patient Autonomy in Home Hemodialysis: Innovations in 3D Printed Aids for Independent Tubing Connection

Home Hemodialysis(HD) is an advantageous alternative to in-center treatments, offering greater convenience, flexibility, and improved quality of life [1]. The rising prevalence of end-stage renal disease (ESRD) globally has increased the demand for accessible renal replacement therapies [2]. Factors such as an aging population, higher rates of chronic conditions, improved survival rates for chronic kidney disease patients, and increased healthcare access contribute to the growing burden on healthcare systems [3]. Home HD has gained prominence by enabling patients to receive treatment at home, providing control over their healthcare management [1]. It offers flexibility in scheduling, reduces travel time and costs, and creates a relaxed environment that positively impacts the patient experience [4]. Improved clinical outcomes, including better blood pressure control and enhanced quality of life, have been associated with home HD. However, challenges persist during the inlet/ outlet preparation and tubing connection phase, involving awkward elbow and wrist maneuvers, which can cause joint stress and discomfort [5]. Limited mobility or dexterity can further complicate the task, leading to potential complications. Addressing these challenges and promoting patient autonomy in tubing connection are crucial for improved treatment experiences and outcomes. Innovative solutions are being developed to facilitate independent tubing connection in home HD, empowering patients and reducing complications. Evaluations of the aids have shown promising results, enhancing patient outcomes and satisfaction [6].

Joining of graphite to Mo using Ti/Cu and Ti/Cu/Nb/Ti/Cu foils

Graphite/Mo joining has been carried out using Ti/Cu or Ti/Cu/Nb/Ti/Cu foils. The joining region in the joint using Ti/Cu foils is mainly composed of Ti3Cu4 and TiCu. The joining region using Ti/Cu/Nb/Ti/Cu foils contains a joining zone I, an Nb interlayer and a joining zone II. Both the joining zones I and II are made up of Ti3Cu4 and TiCu. The Nb foil diffuses and dissolves into the liquid fillers during the bonding. The joint using Ti/Cu/Nb/Ti/Cu foils shows higher shear strength than that using Ti/Cu foils, implying the contribution of Nb foil to the joint stress relief and to the joint strength promotion.

Effects of different friction stir welding processes on residual stress and deformation of Ti62A alloy joints

Residual stress induced by welding easily causes deformation and even fracture failure in welded structures. In this paper, a three-dimensional thermal-mechanical coupling finite element model of friction stir welding (FSW) was developed. The effects of different welding processes, namely conventional friction stir welding (C-FSW), stationary shoulder friction stir welding (SS-FSW), and bobbin tool friction stir welding (BT-FSW), on the temperature, residual stress, and deformation of welded joints were investigated by employing a heat source model and a force model to the welding analysis. The results reveal that a discernible disparity in temperature gradient is observed in the region ahead of the tool and behind it among various welding processes. The peak values of longitudinal residual stress along the surface and bottom paths of SS-FSW are reduced by 35.7% and 34.1%, respectively. In addition, the deformation at the initial end of the weld is slightly larger than that at the final end along the welding direction in three welding processes. Compared with other FSW processes, SS-FSW exhibits the smallest deformation, which is advantageous for improving assembly accuracy and enhancing the load-bearing capacity of weldments. The above results provide an important theoretical reference for the FSW process optimization of Ti62A alloy.

Effect of hydraulic retention time on the performance of sequencing batch reactor under combined stress of ibuprofen and ciprofloxacin

The impacts of changes in hydraulic retention time (HRT) on nitrogen elimination, the activity of sludge and the structure of microbial communities in a sequencing batch reactor under the joint stress of ibuprofen (IBP) and ciprofloxacin (CIP) were investigated. Under the combined stress of IBP (belonged to nonsteroidal anti-inflammatory drugs) and CIP (belonged to antibiotics), the elimination level of ammonia nitrogen, chemical oxygen demand, and the rate of specific ammonia oxidation, specific nitrite oxidation, specific nitrate reduction in activated sludge declined with the shortening of HRT. Under the joint stress of IBP and CIP, the content of polysaccharide (PS) and protein (PN) together with the ratio of PN to PS in the extracellular polymeric substances grew with the shortening of HRT, and the content of aromatic proteins increased significantly, which indicated that aromatic proteins were the major protective response substances to the shortening of HRT. Under the joint stress of IBP and CIP, with the reduction of HRT, and the reduction rate of relative abundance of nitrifying bacteria was more evident than that of denitrifying bacteria. This exploration gives novel thoughts for understanding the impacts of HRT on biological nitrogen removal of wastewater under combined stress of IBP and CIP.

Design of a lightweight universal talus implant using topology optimization.

Total talus replacement is a promising alternative treatment for talus fractures complicated by avascular necrosis and collapse. This surgical option replaces the human talus bone with a customized talus implant and can maintain ankle joint functionality compared to traditional treatment (e.g., ankle fusion). However, the customized implant is costly and time-consuming due to its customized nature. To circumvent these drawbacks, universal talus implants were proposed. While they showed clinically satisfactory results, existing talus implants are heavier than biological talus bones as they are solid inside. This can lead to unequal weight between the implant and biological talus bone, and therefore leading to other complications. The reduction of the implants' weight without compromising its performance and congruency with surrounding bones is a potential solution. Therefore, this study aims to design a lightweight universal talus implant using topology optimization. This is done through establishing the loading and boundary conditions for three common foot postures: neutral, dorsi- and plantar-flexion. The optimized implant performance in terms of mass, contact characteristics with surrounding joint cartilage and stress distributions is studied using a 3D Finite Element (FE) model of the ankle joint. The mass of the optimized implant is reduced by approximately 66.6% and its maximum stresses do not exceed 70MPa, resulting in a safety factor of 15.7. Moreover, the optimized and solid implants show similar contact characteristics. Both implants produced peak contact pressures that were approximately 19.0%-196% higher than those produced by the biological talus. While further mechanical testing under in-vivo loading conditions is required to determine clinical feasibility, preliminarily, the use of a lightweight universal implant is expected to provide the patient with a more natural feel, and a reduced waiting period until surgery.

The Effect of Clamping Force and Friction Coefficient on The Clamping Clamp

In order to study the influence of clamping force and friction coefficient on the stress distribution of drill pipe joint during the buckling process, the nonlinear contact problem and elastoplastic mechanical properties of Φ139.7mm × 9.17mm drill pipe were simulated by finite element analysis method in this paper, and the stress distribution and size of drill pipe joint during the buckling process were obtained. And the effect of clamping force and friction coefficient on the joint of drill pipe. It is found that the stress of drill pipe joint is mainly concentrated in the contact position of drill pipe and the stress value of drill pipe joint shows a trend of increasing. When the friction coefficient is 0.15 and the clamping force is 600KN, although there is stress concentration in the contact position between the clamp teeth and the drill pipe joint, it does not exceed the yield limit of the drill pipe joint, and no plastic deformation occurs. Through the simulation calculation, it is found that the maximum clamping force and the maximum torque are 1200KN and 81.9KN.m respectively. When the torque is fixed, the change of friction coefficient has a great influence on the maximum clamping force of drill pipe joint. With the increase of friction coefficient, the maximum clamping force of drill pipe joint decreases continuously, and the friction coefficient is inversely proportional to the maximum clamping force. The research in this paper enriches the understanding of the buckling process of punching pliers and provides a reference for the rational buckling of pipe string.

Structural optimization of thermal stresses in BGA solder joints based on improved BP neural network-genetic algorithm

Structural optimization of thermal stresses in BGA solder joints based on improved BP neural network-genetic algorithm

The regulatory effects of biochar on PSII photochemistry, antioxidant system and nitrogen assimilation in Lemna minor exposed to inorganic pollutants, arsenic and fluoride

The excessive accumulation of inorganic pollutants such as arsenic (As) and fluoride (F) are destructive contaminants for plants. There are some reports about the toxicity mechanisms of individual exposure of As or F. Biochar (BC), carbon-rich organic material, can sequester pollutants and help in increasing growth, nutrient uptake and water holding capacity in soils. However, the defense responses of plants to a combination of two stresses and the interactions between BC and combined exposure of As and F are not explicit. In order to fill this gap, different BC concentrations (BC1; 1 g L−1 and BC2; 5 g L−1) were hydroponically applied to Lemna minor subjected to sodium fluoride (F, 15 mM NaF) and sodium arsenate (As, 100 μM Na2HAsO4). As or F pollutants caused a reduction in the chlorophyll fluorescence (Fv/Fm and Fv/Fo) but BC application under stress conditions improved the fluorescence levels. The photochemical reactions of photosystems and fluorescence kinetics impaired by stress were re-regulated through all BC concentrations. The relative expressions of genes belonging to proteins in PSI-PSII (psaA, psaB, psbA and psbD) were up-regulated in both BCs and As/F treatments. As-treated L. minor had only induction in superoxide dismutase-SOD- and ascorbate peroxidase-APX-, the enhancement in SOD, catalase-CAT-, glutathione reductase-GR- and glutathione S-transferase-GST- was observed under F toxicity. Also, the joint stress (As+F) caused declines in all antioxidant capacities except with SOD activity. Due to the sufficient antioxidant activation, hydrogen peroxide (H2O2) and thiobarbituric acid reactive substances (TBARS) increased in L. minor. While, 1 mg L-1 BC induced the regeneration of ascorbate (AsA) under individual application of As or F, 5 mg L-1 BC increased APX, MDHAR, DHAR, total ascorbate (tAsA), and DHA against F stress. As- and NaF-mediated stress suppressed the nitrogen assimilation of L. minor. Interestingly, the induced accumulation of NH4+ was prevented in BC plus stress-applied plants through glutamate dehydrogenase (GDH) activity rather than glutamine synthetase-glutamate synthase (GS-GOGAT) pathways. All findings indicated that BCs reduced lipid peroxidation and ROS accumulation by modulating electron fluxes and photochemistry in PSI and PSII, gene expression, nitrogen metabolism as well as the antioxidant system under stress conditions (As, F, and As+F).