Influence of geometric parameters on stress concentration factors of undermatched butt joint with single V-groove under three-point bending load

In order to improve the bending load-carrying capacity （BLCC） of undermatched butt joint under three-point bending load, the influence of joint geometric parameters on stress concentration factors （SCF） at the weld bottom center and the weld toe of uudermatched butt joint with single V-groove are studied respectively based on the finite element method in this paper. Results show that the reinforcement height and the cover pass width play decisive role in the BLCC for undermatched butt joint. BLCC of undermatched butt joint can be improved by choosing the appropriate joint geometric parameters.

Effect of a Nerve Graft Substitute Single-walled Carbon Nanotubes on Rat Pheochromocytoma Cells

Carbon nanotubes （CNTs） were extensively explored for their beneficial use in nervous system tissue engineering. However, an important concern regarding the use of CNTs is their toxicity during the interaction between cells and the nano particles. The rat pheochromocytoma cell line （PC12） was co-cultured with three types of single-walled carbon nanotubes （SWNTs）, purified raw SWNTs （C）, hydroxyl purified SWNTs （C-OH） and carboxyl purified SWNTs （C-COOH） at 25 μg/mL and 100 μg/ml. The experimental results revealed that SWNTs at the concentration below 100 μg/mL did not affect the cell viability. Notably, powerful antioxidant system in nerous system tissue is able to counteract with the toxicity of CNTs, which is characterized by the prominently enhanced expression of main antioxidant enzymes （catalase （CAT）, superoxide dismutase （SOD）, glutathione peroxidase （GPx） and glutathione-S-transferase （GST））. Therefore, we believe that CNTs can be good candidates for the fabrication of biomedical scaffolds for the nerve tissue repair.

Methods for obtaining two way memory effect and stressed two way memory effect of CuAlNi single crystals

Various training methods for two way memory effect (TWME) and stressed two way memory effect (STWME) were tried on Cu 13.4Al 4.0Ni (mass fraction, %) single crystals by applying tensile stress along 〈001〉 direction of β phase. The training method of cooling with load can induce a lot of martensite prone to stabilize, thus cause large residual deformation, wide hysteresis and small TWME. Training with constant load can produce STWME larger than 8% with the least residual deformation. By training procedure of martensite reorientation below M f followed by thermal cycling, the TWME is relatively large with very small residual deformation and with comparatively narrow hysteresis of two way memory. The obtained two way memory curve after such training is not a closed loop, and the obtained TWME is not stable. However, these can be improved by thermal cycling. Training with martensite reorientation below M f and thermal cycling under relatively low constant stress throughout the whole training procedure is the optimum way of obtaining TWME, and more than 1.7% TWME can be obtained. The thermomechanical history of the sample has a pronounced effect on the training result. Thermomechanical cycling has a softening effect on martensite. [

Effects of loading rate and peak load on nanoindentation creep behavior of DD407 Ni-base single crystal superalloy

Nanoindentation experiments were conducted under loading rates of 500–6000μN/s and applied peak loads of 4000-12000μN to measure the creep behavior of DD407 Ni-base single crystal superalloy at room temperature.Experimental results demonstrated that DD407 Ni-base single crystal superalloy had a good creep resistance,but its creep properties were sensitive to the loading rate and peak load.The fitting creep parameters significantly increased with increasing loading rate and peak load based on the Findley’s model,and the corresponding creep mechanism was governed by dislocation based on the calculation of creep stress exponent.During nanoindentation creep tests,it was found that the hardness and reduced modulus decreased with increasing the loading rate and peak load,and through a dimensionless analysis,it was also noted that the effect of the dimensionless loading rate was stronger than that of dimensionless peak load on the creep properties.

Experimental study of seepage characteristics of single rock fracture based on stress states and stress history

Through seepage tests under different loading and unloading confining pressures and different hydraulic gradients,the authors studied the effects of stress states and stress history on fracture permeability evolution for single granite fracture and sandstone fracture. The results show that there exists a linear relationship between the seepage discharge and osmotic pressure in sandstone fissure under each level of confining pressure. With the increasing in the confining pressure,the permeability of the fracture decreases,but the decreasing rate is changeing. During the unloading process,the fracture seepage velocity cannot be fully recovered to the size of the loading process. Therefore,in the unloading process of the confining pressure,the recovery of fracture permeability shows obvious hysteresis effects. The flow rate of the fracture remains unchanged during five cycles of loading and unloading processes of the confining pressure. In each cycle,the evolution character of the flow rate with the confining pressure remains unchanged. These experiments show that the seepage characteristics of sandstone and granite fractures are not the same under the same stress state.

Reflection and transmission of elastic waves through a couple-stress elastic slab sandwiched between two half-spaces

The reflection and transmission of elastic waves through a couple-stress elastic slab that is sandwiched between two couple-stress elastic half-spaces are studied in this paper. Because of the couple-stress effects, there are three types of elastic waves in the couple-stress elastic solid, two of which are dispersive. The interface conditions between two couple-stress solids involve the surface couple and rotation apart from the surface traction and displacement. The nontraditional interface conditions between the slab and two solid half-spaces are used to obtain the linear algebraic equation sets from which the amplitude ratios of reflection and transmission waves to the incident wave can be determined. Then,the energy fluxes carried by the various reflection and transmission waves are calculated numerically and the normal energy flux conservation is used to validate the numerical results. The special case, couple-stress elastic slab sandwiched by the classical elastic half-spaces, is also studied and compared with the situation that the classical elastic slab sandwiched by the classical elastic half-spaces. Incident longitudinal wave(P wave) and incident transverse wave(SV wave) are both considered. The influences of the couplestress are mainly discussed based on the numerical results.It is found that the couple-stress mainly influences the transverse modes of elastic waves.

High-cycle fatigue behavior of nickel-base single crystal superalloy

High-cycle rotating bending fatigue behavior of SRR99 nickel-base single crystal alloy at 700 and 900℃ was investigated. The fatigue strengths for 107 cycles are 350 and 335MPa at 700 and 900℃, respectively. The total fatigue life becomes shorter when the temperature increases regardless of the loading stress and frequency. With the number of cycles decreasing, the difference in fatigue strength at the two temperatures becomes smaller. Typical fatigue rupture process including crack initiation site, crack propagation region and final rupture region exhibits at 700℃. The fracture surface is basically characterized by cleavage rupture at 900℃.

Superelastic behavior and stabilization of stress-induced martensite in Cu-13.4Al-4.0Ni single crystals

By applying tensile stress along 〈100〉 of β phase, the superelastic behavior and stabilization of stress induced martensite (SIM) of Cu 13.4Al 4.0Ni(mass fraction, %) single crystals were studied. The results show that the pseudo yield stress decreases with the increase of cycling number, and keeping load isothermally has an effect on stabilization of SIM. Previous thermal cycling between ( M s-20 ℃) and ( A f+20 ℃) promotes the superelasticity and the stabilization of SIM as well; the pre thermal cycling also reduces the pseudo yield stress. However, once the stabilization of SIM is produced, it can be destabilized by either the afterwards thermal cooling heating cycling or load and immediately unload cycling in ( A f～ M d). Isothermal treatment in ( A f～ M d) brings restabilization of SIM. The maximum superelastic value from β → β ′ 1(18 R ) is 9% for the studied single crystal. When test temperature is in A f～( A f+50 ℃) and stress is in 0～350 MPa, the superelastic behavior exist. [

Web Shear Strengthening Technique of Deep Precast Prestressed Hollow Core Slabs under Truck Loads

Precast prestressed Hollow Core Slabs (HCS), are one of the famous and widely used slabs for concrete structures all over the world and widely implemented in the Middle East. HCS are used in industrial, commercial, residential buildings, as well as, in the parking structures. This paper succeeded to present new special details for deep HCS to enhance and strengthen the web shear strength capacity of HCS 400 and 500 mm depths respectively at the open parking area. This is subjected to heavy truck wheel loads so as to achieve the LRFD Code’s requirements. However, it is noticed many web shear cracks of HCS are used at parking area at many projects in Gulf Region. On the other hand, ACI318-14 permits no shear reinforcement in prestressed HCS thickness of less than 12.5 in (320 mm). The paper presents experimental tests program, to verify the numerical finite element of deep HCS under maximum design uniform loads, in addition to the new strengthening techniques. New strengthening techniques succeed to enhance the web shear capacity by significant percentage, due to the new details for HCS 400 by 68% up to 256% increasing of the web shear capacity compared to the ordinary HCS section. Also, HCS 500 shear capacity is enhanced with different percentages of strengthening techniques by 55%, up to 197% based on the different cases of strengthening. Furthermore enhancing deep HCS shear performance;the new techniques have an advantage of an easy execution at the site;casting with structural topping, otherwise the preparation can be done in precast factory before site handover, which saves time and cost compared to the others traditional strengthening techniques.

Stress-induced deformation at A_p～M_p and thermal cycling behavior of Cu-Al-Ni single crystals

Stress induced deformation in A p～ M p and concomitant shape recovery behavior of Cu 13.4Al 4.0Ni single crystals were studied. Abnormal high stress induced deformation exists in A p～ M p under the conditions of either heating with load or cooling with load. The recovered deformation is successively composed of four parts, the recoveries from superelasticity, normal reverse transformation, thermally activated reverse transformation of partially stabilized martensite and reverse transformation of stabilized martensite by over heating. With increasing cycling number, the recovery part from normal reverse transformation decreases, while that from reverse transformation of stabilized martensite by over heating increases, which shows a typical stabilization of martensite.

RESEARCH ON TRANSVERSE STRESS CHARACTER OF SINGLE MODE OPTICAL FIBER

This paperdetails experimental work done to quantify stress measurements made optically utilizing ordinary single mode optical fibers. Strain-induced changes of birefringence for ordinary single mode optical fiber responses are characterized against standard stress measurements in a well understand configuration. The experimental scheme for this work and the results are presented in detaial. In this paper, POssible applications for this transverse stress character of single mode fibers are also proposed.

Unanticipated Bond Failure over Supporting Band Beams in Grouted Post-Tensioned Slab Tendons with Little or No Initial Prestress

After grouting the ducts in a large band beam and one-way slab post-tensioned floor system in a large shopping mall （in excess of 1.5 km2 in plan）, doubts arose concerning the level of initial prestress and the strength and serviceability of the slabs was questioned. To assess the strength of the slabs, it was assumed, as a worst case scenario, that some spans may have been constructed with zero initial prestress. Load tests on prototype specimens, with similar dimensions and reinforcement quantities as the floor slabs, were performed to assess the stress development in initially unstressed, but fully grouted, tendons. Unexpected bond failures occurred at the junctions of slab and band beam where the abrupt change in section depth caused a sudden change in tendon stress. The maximum stress that was developed in the initially unstressed tendons at these locations was about 60% of the strength of the tendons.

TWO COPLANAR CRACKS IN A TRANSVERSELY ISOTROPIC ELASTIC SLAB SUBJECTED TO ANTIPLANE SHEAR STRESSES

The problem of a transversely isotropic elastic slab containing two coplanar cracks subjected to an antiplane deformation is considered. With the aid of an integral transform technique, we formulate the problem in terms of a finite-part singular integral equation which can be solved numerically, Once the integral equation is solved, relevant quantities such as the crack energy can be readily computed.

Role of Interatomic Force to Critical Resolved Shear Stress of Single Crystals

Experimental results of the temperature dependence of critical resolved. shear stresses (CRSS)of Mo, Fe, Al and Mg single crystals are shown. Associating reports in recent years, we point out that the approximate exponential relationship between CRSS and the absolute temperatureat least in the region of the steep temperature dependence range of many materials is more common, even for bcc, fcc, and hcp single crystals. polycrystals and other covalent crystals,provided that the slip plane and slip direction are kept the same. Successful explanation with atomic force law shows that the interatomic forces (electronic structure) play a decisive role in determining the temperature dependence of yield stresses for a large number of materials.

Size-dependent sinusoidal beam model for dynamic instability of single-walled carbon nanotubes

In this study, a model for dynamic instability of embedded single-walled car- bon nanotubes （SWCNTs） is presented. SWCNTs are modeled by the sinusoidal shear deformation beam theory （SSDBT）. The modified couple stress theory （MCST） is con- sidered in order to capture the size effects. The surrounding elastic medium is described by a visco-Pasternak foundation model, which accounts for normal, transverse shear, and damping loads. The motion equations are derived based on Hamilton＇s principle. The differential quadrature method （DQM） in conjunction with the Bolotin method is used in order to calculate the dynamic instability region （DIR） of SWCNTs. The effects of differ- ent parameters, such as nonlocal parameter, visco-Pasternak foundation, mode numbers, and geometrical parameters, are shown on the dynamic instability of SWCNTs. The re- sults depict that increasing the nonlocal parameter shifts the DIR to right. The results presented in this paper would be helpful in design and manufacturing of nano-electromechanical system （NEMS） and micro-electro-mechanical system （MEMS）.

单孔电视胸腔镜手术与常规胸腔镜手术在非小细胞肺癌根治术中的应用价值

目的 探讨单孔电视胸腔镜手术在非小细胞肺癌根治术中的效果。方法 选取河南科技大学附属黄河三门峡医院2021年1月至2023年1月收治的100例非小细胞肺癌患者,分为对照组50例(常规胸腔镜手术),观察组50例(单孔电视胸腔镜手术),分组方法为随机数字表法。比较两组临床指标。结果 观察组引流管留置时间、住院时间短于对照组(P<0.05);观察组术后1d、2d、3d的疼痛评分均低于对照组(P<0.05);观察手术后组血清生长激素、PGE2、Cor水平低于对照组(P<0.05),各项临床症状评分均高于对照组(P<0.05),并发症发生率低于对照组(P<0.05)。结论 非小细胞肺癌根治术患者应用单孔电视胸腔镜手术对缩短住院时间、缓解临床症状、降低疼痛水平、减轻应激反应方面具有积极作用,更利于患者康复。

Effect of Ru on stress rupture properties of nickel-based single crystal superalloy at high temperature

Two experimental single crystal superalloys, Ru-free alloy and Ru-containing alloy with [001] orientation, other alloying element contents being basically kept same, were cast in the directionally solidified furnace. The effect of Ru on the stress rupture properties of the single crystal superalloy was investigated at （980 ℃, 250 MPa）, （1100 ℃, 140 MPa） and （1120 ℃, 140 MPa）. The results show that Ru can enhance high temperature stress rupture properties of single crystal superalloy. The improvement effect of Ru addition on stress rupture properties decreases with increasing test temperature. The γ′ coarsening and rafting directionally are observed in Ru-free alloy and Ru-containing alloy after stress rupture test. Needle shaped TCP phases precipitated in both of alloys after stress rupture test at （1100 ℃, 140 MPa） and （1120 ℃, 140 MPa） and no TCP phase was observed in both of alloys after stress rupture test （980 ℃, 250 MPa）. The precipitate volume fraction of TCP phases is significantly decreased by the addition of Ru. At last, the relationship between the microstructure change with Ru addition and improvement of stress rupture properties was discussed.

Microstructure and property of stress aged Al-Cu single crystal under various applied stresses

The stress aging behavior of Al-Cu alloy under various applied stresses, i.e., elastic stress, yield stress and plasticdeformation stress, was investigated using single crystals. The resulting microstructures and the yield strength were examined bytransmission electron microscopy （TEM） and compression tests, respectively. The results indicate that an elastic stress of 15 MPa ishigh enough to influence the precipitation distribution of θ′ during aging at 180℃. The applied stress loading along [116]Aldirection results in increased number density of θ′ on （001）Al habit planes. This result becomes more significant with increasingapplied stress and leads to lower yield strength of Al-Cu single crystals during aging. Moreover, the generation of the preferentialorientation of θ′ was discussed by the effect of the dislocation induced by applied stress as well as the role of the misfit between theθ′-precipitate and Al matrix. The results are in agreement with the effect of the latter one.

基于Switch-Capacitor网络的单开关升压变换器

在新能源并网发电系统中,传统Boost变换器存在升压能力有限、纹波大和效率低等问题,为此,提出了一种基于Switch-Capacitor网络的单开关升压变换器,并推演出了相应的多级单开关升压变换器。详细分析了该变换器在CCM和DCM模式下的工作原理和工作性能,并搭建了实验模型,实验结果表明:①在不增加开关器件电压应力的情况下,随着串联的Switch-Capacitor网络个数的增加,这类变换器的升压能力逐渐增强;②输入电流纹波和输出电压纹波小;③变换器中只有一个开关管,控制电路简单;④可以根据串联网络个数的奇偶性改变输出电压的极性,扩大了该变换器的适用范围。

七氟醚预处理对PTSD大鼠行为学及海马Akt-mTOR信号通路的影响

目的探讨七氟醚预处理对创伤后应激障碍(PTSD)大鼠行为学及海马Akt-mTOR信号通路的影响。方法将雄性SD大鼠108只,随机分为:正常对照组(C组,n=10),侧脑室置管组(T组,n=10),PTSD模型组(P组,n=22),七氟醚组(S组,n=22),胰岛素生长因子-1组(I组,n=22)和胰岛素生长因子-1联合七氟醚组(IS组,n=22)。采用单一连续应激(SPS)方案建立PTSD大鼠模型。T组侧脑室注射生理盐水5μl;P组侧脑室注射生理盐水5μl后,SPS造模;S组侧脑室注射生理盐水5μl后,吸入七氟醚2h,然后SPS造模;I组侧脑室注射胰岛素生长因子-15μl(0.4μg/μl)后,SPS造模;IS组侧脑室注射胰岛素生长因子-15μl(0.4μg/μl)后,吸入2%七氟醚2h,然后SPS造模。在造模成功后30min、1、2和4h,每组取4只大鼠处死提取海马组织,WesternBlot检测海马Akt、p-Akt、mTOR、p-mTOR表达量;造模后第7天,每组6只,分别行旷场实验和木僵率测试。结果与C组和T组比较,P组、S组、I组和IS组中央格停留时间明显缩短、直立次数明显减少、木僵率、造模后1hp-Akt/Akt和p-mTOR/mTOR表达量明显升高(P<0.05)。与P组和I组比较,S组和IS组中央格停留时间明显延长、直立次数明显增加、木僵率明显降低(P<0.05)。与P组比较,S组造模后1hp-Akt/Akt和p-mTOR/mTOR表达量明显降低(P<0.05);而I组和IS组p-Akt/Akt和p-mTOR/mTOR表达量明显升高(P<0.05)。与I组比较,IS组木僵率、造模后1hS组、IS组p-Akt/Akt和p-mTOR/mTOR表达量明显降低(P<0.05)。与造模后30min比较,造模后1hP组的p-Akt/Akt和p-mTOR/mTOR表达量明显升高(P<0.05)。结论七氟醚可以改善PTSD模型大鼠术后7d的焦虑水平和木僵行为,其效应可能与其抑制PTSD大鼠海马Akt和mTOR的磷酸化有关。