Stretch rate and deformation for pre-stretching aluminum alloy sheet

Numerical simulation combined with experimental test was carried out to analyze the pre-stretching process of the 7075 aluminum alloy sheet,from which the stress variation curves and residual stress of aluminum alloy sheet in different stretch rates were obtained.The results show that the residual stress in length direction is released after unloading the stretch force,while the residual stress in width direction is released during the stretching process.The study of residual stress elimination is beneficial for optimizing stretch rate on the basis of residual stress distribution law.By comparing the variation principle of residual stress in length direction,the size range of three deformation areas and elimination percentage of residual stress were obtained.The residual stresses of clamping area and transition area are not eliminated effectively,so sawing quantity should be the sum of both the areas.The elimination rate of residual stress in even deformation area could reach 90% after choosing a proper stretch rate,which is verified by both simulation and experiment.

Static Stretching Combined with Conscious Slower Breathing May Increase Parasympathetic Activity and Reduce Stress in Adult Women

Background: Women are thought to be more susceptible to stress than men in a stressful society, and reducing stress is crucial for women to maintain their health. Static stretching (SST) is applied in various fields to not only increase muscle flexibility but also reduce stress. Additionally, conscious slower breathing (CSB) predominates parasympathetic activity, causing a relaxing effect. These results indicate that combining SST and CSB may be more useful in reducing stress. However, to the best of our knowledge, the effect of this combination remains unclear. Objective: This study aimed to elucidate the effects of the combination of SST and CSB on autonomic activity and stress in adult women. Methods: Eleven healthy Japanese adult female participants performed SST with nonconscious natural breathing for 20 min. The same participants performed SST in combination with CSB (2 s inspiratory and 4 s expiratory) for 20 min on another day. Salivary cortisol and chromogranin A levels were measured before and after stretching as stress markers of the hypothalamic-pituitary-adrenal axis and sympathetic nervous system. The coefficient of variation of the R-R interval (CVR-R) and high-frequency component (HF), which reflect parasympathetic nerve activity, and heart rate and low-frequency component (LF)/HF ratio, which reflect sympathetic nerve activity, were measured before, during, and after stretching. Results: SST decreased cortisol levels but with no significant changes in chromogranin A, heart rate, CVR-R, HF, or LF/HF ratio. The combination of SST and CSB increased CVR-R and HF levels in addition to decreasing cortisol levels but with no significant changes in chromogranin A, heart rate, or LF/HF levels. Conclusion: These results indicate that the combination of SST and CSB may increase parasympathetic activity and reduce stress. However, future randomized controlled trials with larger sample sizes should support this conclusion.

Impact of stretching-segment on saturated flow rate of signalized intersection using cellular automation

In order to analyze the impact of stretching-segment on the saturated flow rate of signalized intersection approach, an improved cellular automation model was proposed to estimate its saturated flow rate. The NaSch model was improved by adding different slow probabilities, turning deceleration rules and modified lane changing rules. The relationship between the saturated flow rate of stretching-segments and adjacent lanes was tested in numerical simulation. The length of stretching-segment, cycle length and green time were selected as impact factors of the cellular automation model. The simulation result indicates that the geometrics design of stretching-segment and the traffic signal timing scenario have major effects on the saturated flow rate of the intersection approach. The saturated flow rate will continually increase with increasing stretching-segment length until it reaches a threshold. After reaching the threshold, the stretching-segment can be treated as a separate lane. The green time is approximately linearly related to the threshold length of the stretching-segment. An optimum cycle length exists when the length of the stretching-segment is not long enough, and it is approximately linearly related to the length of stretching-segment.

基于链路关联度模型的绿色节能路由框架

随着信息技术的高速发展,互联网的规模逐渐增大,与此同时,网络的能耗也随之攀升。业界普遍采用关闭利用率较低的链路来降低网络能耗。然而,目前的网络节能方案并不能有效平衡能量节约率、计算开销和路径拉伸度三者之间此消彼长的关系。为了应对上述问题,文中提出了一种基于链路关联度模型的绿色节能路由框架。该框架支持不同的链路关联度模型,仅需要网络拓扑结构,而不需要网路中的实时流量矩阵,更易于在实际网络中部署。基于提出的链路关联度模型的绿色节能路由算法的框架,文中实现了链路行关联度算法LRC(Link Row Correlation)、链路列关联度算法LCC(Link Column Correlation)、链路行-列关联度算法LRCC(Link Row Column Correlation)和链路介数关联度LBC(Link Betweenness Correlation)4种不同的绿色节能路由算法。实验结果表明,在The Internet Topology Zoo公布的真实拓扑和由Brite模拟生成的拓扑中,LRC,LCC,LRCC和LBC的平均能量节约率比DLF算法的平均能量节约率高12.65%和7.17%,且它们的平均路径拉伸度比DLF算法的平均路径拉伸度低3.00%和13.75%。

无缝钢管张力减径工艺减径率分配修正模型理论研究

无缝钢管张力减径工艺减径率分配是孔型分配合理与否的关键步骤,但其分配仍依赖于经验公式。从金属流动的角度分析了减径率的分配规律,在经验的基础上提出了“三点两段统合式”减径率分配修正模型。将修正模型得到的结果与传统模型计算结果以及企业生产数据相比,发现变化趋势相近,减径率和减径量变化曲线更加光滑,应用于生产有利于金属流动。

聚脲材料动态力学性能试验研究

应用低阻抗分离式霍普金森压杆和拉杆试验装置开展了聚脲材料动态力学性能的试验研究。分别开展了聚脲8380材料常温条件(T=18℃)下的动态压缩和动态拉伸试验,以及高温(50、80℃)和低温(-40、-20℃)条件下的动态压缩试验,研究了该种材料的动态压缩和动态拉伸性能,并研究了应变率和温度对材料动态力学性能的影响规律。研究结果表明:在不同温度下,聚脲8380材料的动态力学性能均呈现出显著的应变率效应;随着加载应变率的增大,材料的强度、变形能力和耗能能力均有不同程度的提升;聚脲8380材料的动态力学性能具有明显的温度相关性,高温和低温条件下材料的动态压缩性能呈现出不同的变化规律;高温条件下聚脲8380材料的动态压缩性能发生劣化,其动态抗压强度较常温条件下有较大幅度的降低,随着温度的升高,材料的动态抗压强度降低;低温条件下聚脲8380材料的动态压缩性能有显著的改善与提升,其动态抗压强度和耗能能力较常温条件下有大幅度的提高,随着温度的降低,材料的动态抗压强度提高。

拉伸速率对天然橡胶/有机黏土复合材料力学性能的影响

采用I.44P有机黏土填充天然橡胶(NR)制备天然橡胶/有机黏土复合材料(NRCNs),考察拉伸速率对NRCNs力学性能的影响。结果表明,单轴拉伸测试下,拉伸速率为50 mm/min时,NRCNs的力学性能最优,拉伸强度达到19.50 MPa,较拉伸速率为500 mm/min时的拉伸强度提高了22.64%;随着拉伸速率的提高,NRCNs的结晶度逐渐减小,表明NRCNs在较慢的拉伸速率下降温结晶性能更好。多轴拉伸测试下,当应变为120%、拉伸速率为50 mm/min时,NRCNs的力学性能最优,拉伸强度达到0.38 MPa,较拉伸速率为10 mm/min时的拉伸强度提高了8.57%;在相同的拉伸速率下,经过单轴拉伸的NRCNs的拉伸强度为0.8 MPa,较多轴拉伸的NRCNs的拉伸强度提高了128.57%。

掺氢天然气输送用X52管线钢的氢脆行为研究

将氢气以一定比例掺入现有天然气管网进行大规模长距离输送是氢能储运较为高效和经济的方式之一,但是在氢气环境中管线钢会发生氢脆现象,导致管线钢的力学性能发生退化,给管道的安全运行带来隐患。针对不同氢气含量环境条件下管线钢的氢脆行为进行研究,对X52管线钢进行慢应变速率拉伸试验和准静态断裂韧性试验,并结合断口形貌分析掺氢比对管线钢力学性能的影响。结果表明:在管道压力为7.5 MPa,掺氢比为3%、5%、10%的条件下,X52管线钢与无氢环境相比断后总伸长率下降程度小于8%;断口形貌表明在掺氢比小于10%的条件下,以韧性断裂为主,没有典型脆性断口形貌;随着氢气含量的增加X52管线钢的劣化程度增加。

骨膜牵张技术配合中药治疗糖尿病足患者的效果

目的:分析骨膜牵张技术配合中药治疗糖尿病足患者的效果。方法:选取2021年1月—2023年10月建瓯市立医院收治的97例糖尿病足患者作为研究对象,依据治疗方法不同将患者分为对照组(常规疮疡贴湿化再生治疗,n=49)和观察组(骨膜牵张技术配合中药治疗,n=48),比较两组溃疡面愈合情况、溃疡大小、溃疡深度、经皮氧分压、踝肱指数、足部皮温、疼痛程度、神经病变情况、生活质量。结果:治疗后,观察组溃疡面愈合率、经皮氧分压、踝肱指数、足部皮温、生活质量评分高于对照组,溃疡大小、溃疡深度、视觉模拟评分法(visual analogue scale,VAS)评分、密歇根神经病变筛查表(Michigan neuropathy screening instrument,MNSI)评分、10 g尼龙丝试验评分低于对照组,差异有统计学意义(P<0.05)。结论:与常规疮疡贴湿化再生治疗相比,骨膜牵张技术配合中药治疗糖尿病足患者效果更好,可提高溃疡面愈合率,缩小溃疡面积,促进局部微循环,减轻疼痛,改善神经病变,提高生活质量。

A combination therapy of massage and stretching increases parasympathetic nervous activity and improves joint mobility in patients affected by fibromyalgia

Objective: to investigate how therapeutic mas-sage, combined with stretching, can really con-tribute to the treatment of fibromyalgia (FM) symptoms. Design: Feasibility study. Setting: A single center. Participants: Twenty women having a preexisting diagnosis of FM based on American College of Rheumatology criteria were recruited. Intervention: Subjects received a total of 18 sessions of light massage administered by a physical therapist twice a week and then performed passive stretching exercises. Main out-come measures: heart rate (HR) and Heart Rate variability (HRV), the assessment of joint flexi-bility through elettrogoniometer, the Fibromyal-gia Impact Questionnaire (FIQ), the Pittsburgh Sleep Quality Index (PSQI), and the Borg scale or Rating of Perceived exertion (RPE). Evalua-tions were conducted at the screening visit (T0), immediately at the end of the session of mas-sage (T1) and after completion of 18 sessions (T2). Results: HRV showed an improvement in terms of decreased sympathetic tone and in-crease of parasympathetic tone at the end of treatment. Also joint flexibility showed a sig-nificant improvement at T2 compared with the screening. FIQ, PSQI, RPE did not change. Conclusions: the findings highlight the excellent compliance of FM patients to the combined therapy of massage and stretching, showing an amelioration of muscle stiffness and an improvement of autonomic nervous system with a decrease of sympathetic tone and an increase of parasympathetic tone. The questionnaires did not show any ameliorations, probably because in these patients the perception of quality of life is distorted compared with more objective pa-rameters, such as muscle rigidity, the articular mobility and the autonomic nervous system.

The Effects of Cyclic Stretching on the Proliferation of Lung Adenocarcinoma Cells in Vitro

Using FX-4000 strain unit, the prolieration in human lung adenocarcinoma A549 cells that underwent mechanical strain of different waveform、frequency and duration were studied. Image analysis revealed that cellular proliferation rate(PR) reduced significantly after cells were subjected to square wave with 0～20% elongation at frequency 30,40,50 and 60 cycles/min for 2h. The PR had no distinct difference at heart wave , triangle wave and sine wave group compared with control. It is concluded that square wave and higher frequency play an important role in inhibiting A549 cells proliferation.

AlNi_(3)单轴拉伸的分子动力学模拟

采用分子动力学方法研究AlNi_(3)的拉伸力学性能。模拟300 K、恒定工程应变速率对AlNi_(3)拉伸性能的影响,以及探究不同温度和应变速率对AlNi_(3)拉伸性能的影响;模拟300 K条件下含预制孔洞AlNi_(3)的拉伸过程,研究不同孔洞半径和孔洞个数对其拉伸性能的影响。结果表明:在300 K条件下,当应变为0.1342时,AlNi_(3)应力达到峰值23.397 GPa;含孔洞的AlNi_(3)在应变为0.1096时,应力达到峰值21.047 GPa。升高温度会使AlNi_(3)的弹性模量和抗拉强度减小;增加应变速率会提高其抗拉强度,但对弹性模量没有影响;增大孔洞半径、增加孔洞个数会使抗拉强度明显降低。

肛提肌应变率评估初产妇盆底肌收缩及拉伸功能的研究

目的应用四维盆底超声技术检测初产妇产后6~8周的肛提肌应变率,以评估盆底肌的收缩和拉伸功能,并对不同分娩方式的结果进行对比研究。方法选取103例初产妇(顺产组63例、剖宫产组40例)和30例健康未育妇女(对照组)作为研究对象。采集静息状态、最大缩肛状态及最大Valsalva状态下盆底轴平面肛提肌裂孔图像,并测量裂孔面积(A)、周长(C)。统计肛提肌静息状态与收缩状态的A、C差值(ΔA1、ΔC1),计算收缩应变率(ε1);统计肛提肌最大Valsalva状态与静息状态的A、C差值(ΔA2、ΔC2),计算拉伸应变率(ε2),比较不同组别间差异。结果缩肛状态下,对照组ΔA1、ε1高于顺产组及剖宫产组,ΔC1高于顺产组(P<0.05);剖宫产组ΔA1、ε1、ΔC1均高于顺产组(P<0.05)。Valsalva状态下,对照组ΔA2、ε2、ΔC2均低于顺产组及剖宫产组(P<0.05);剖宫产组与顺产组ΔA2、ΔC2、ε2比较差异无统计学意义(P>0.05)。结论经阴道分娩和选择性剖宫产在产后早期均对肛提肌的收缩和拉伸功能造成影响,选择性剖宫产对肛提肌收缩功能的影响较小,两者对肛提肌拉伸功能的影响无差异。盆底超声能量化评估肌提肌收缩与拉伸功能。

西藏嵩草根系抗拉特性试验研究

为研究黄河源区曲流河岸优势植物种在单调荷载和循环荷载拉伸下的受力特性,以滨河优势植物种西藏嵩草(Kobresia tibetica)为研究对象,开展不同拉伸标距和不同拉伸速率的轴向单调荷载拉伸试验及不同循环次数条件下的疲劳拉伸试验。结果表明:西藏嵩草根系单根抗拉强度随着拉伸标距和拉伸速率的增大均呈减小的趋势,其减小幅度最大达到31.67%,在5 mm/min拉伸速率下能充分发挥西藏嵩草的抗拉作用。对西藏嵩草根系分别进行50次和100次循环荷载后,单根抗疲劳拉伸强度与根径呈指数函数负相关关系,较单调荷载其单根平均抗拉强度增大幅度为7.21%和17.13%;随着循环次数的增加,西藏嵩草根系拉伸应力—应变曲线滞回环间距越来越密集,最后滞回环几乎在同一个滞回环上不断重复直至断裂或达到循环次数。西藏嵩草根系具有较强的抗疲劳拉伸特性,对减缓河岸崩塌速率有一定作用。

建筑钢筋材料的高应变率下拉伸力学性能研究

文中在设定好的5个等级应变率条件下,通过引入拉伸试验系统,对建筑钢筋材料的拉伸力学性能开展试验分析,研究应变率和屈服强度的关系,并且修正本构模型,以获取拉伸应力-应变关系的模型和材料参数。结果表明,钢筋的屈服应力伴随应变率提高而提高,越小的钢筋规格,在高速率下对屈服强度影响较大,完成修正之后的本构模型可以更好地描述拉伸应力-应变关系。

拉伸速率对聚氯乙烯绝缘材料机械性能的影响

采用分拉法对聚氯乙烯绝缘材料进行了拉伸试验,研究了聚氯乙烯绝缘材料在同一设备、同一操作人员、同一环境和不同拉伸速率下机械性能的变化。结果表明,选择不同的拉伸速率对材料的抗张强度的影响不明显,但对断裂伸长率的影响较大。

深大断裂对松辽断陷盆地群南部的控制作用

通过野外地质调查及对各断陷典型地震剖面和构造发育史剖面的综合研究,系统探讨了研究区深大断裂对断陷盆地群的控制作用。以西拉木伦河-长春-延吉板块拼接带、赤峰-开原超岩石圈断裂为边界,将研究区自南向北分为辽西盆地区、辽北盆地区和吉西盆地区等3个一级构造分区;根据控盆断裂及其断陷盆地群的时空分布、断陷构造样式、不同时期伸展量等特征将辽北盆地区分为西部、中西部、中东部等3个二级断陷区。西拉木伦河断裂控制了西部区断陷的形成和分布;嫩江—八里罕断裂和孙吴—大庆—阜新断裂对中西部断陷区的控盆效应大体相近;孙吴—大庆—阜新断裂与佳木斯—伊通断裂共同对中东部断陷区起着重要的控制作用;昌图断陷主要受佳木斯—伊通断裂所控制。辽北盆地区主要表现为双断式地堑,断陷群的形成和分布不仅受北北东向断裂控制,也受到近东西向的西拉木伦河断裂和赤峰—开原断裂重新活动的控制。中西部断陷区伸展率具有从九佛堂组沉积期—沙海组沉积期—阜新组沉积期依次减小的变化规律。中东部断陷区与中西部断陷区存在明显差异,NNE向与近EW向深大断裂对两区构造分区控制程度不同。

7075铝合金拉伸残余应力数值模拟及实验测试

对7075铝合金板材淬火过程进行温度场和应力场的直接热力耦合数值模拟,获得淬火残余应力分布规律,在此基础上开展基于等向强化Mises屈服准则和Prandtl-Reuss塑性流动增量理论的铝合金拉伸过程数值模拟,仿真不同拉伸率对内部残余应力的消除效果,采用盲孔法对铝合金淬火及不同拉伸量拉伸后残余应力进行实验测量,结果表明对于厚12mm的7075铝合金试件最优拉伸率为1.0%。同时根据不同拉伸率拉伸后铝合金板材残余应力分布规律的变化趋势可以看出,以不同拉伸率拉伸后铝合金板材表面和内部残余应力的消除效果具有相同的变化趋势。

松散回潮工序工艺参数对片烟加工物理性能的影响

为研究松散回潮设备不同加工条件对滚筒内部片烟加工质量的影响,采用无线温湿度监控技术和Imagepro plus图像处理工具分析了不同工艺参数、控制模式以及能量给予方式条件下片烟的舒展率以及加工性能。结果表明:(1)回风温度的提升增加了松散回潮滚筒对物料的加工强度,有利于提升片烟的舒展率。(2)工艺蒸汽系数为2.1时最有利于提升片烟加工的物理质量。(3)新鲜风低温控制模式加工后的片烟舒展率最高,表现出较好的片烟物理加工效果。(4)增加热风管道内蒸汽比例、减少直喷蒸汽比例有利于片烟温度的快速升高,并有利于提升片烟舒展率和感官质量。

剪切流场中液滴形变的三维力学模型初探

分析了油水乳化液中分散相液滴的受力及形变,从理论上提出了剪切流场中液滴形变的三维力学模型。通过实验观测了液滴在由两个同心圆筒形成的旋转剪切流场中的变形情况,并对建立的三维力学模型进行了验证。测量结果表明:实验观测值和理论值有较好的一致性。未加乳化剂时,在z方向上,随着液滴拉伸率的增加,液滴的变形收缩系数也随之增加;与未加乳化剂时相比,加入乳化剂时液滴的变形收缩系数偏离理论值更大;对于有表面活性剂的自由液滴来说,液滴破裂所需要的临界剪切率比没有表面活性剂时要低。