不同预拉力和冲击能量下BFRP筋的横向抗冲击性能

为研究玄武岩纤维增强树脂基复合材料(Basalt fiber reinforced polymer,BFRP)筋的低速冲击性能,通过落锤冲击试验测试了不同预拉力比值(2％、10％、20％和30％)和不同能量(12.76-31.90J)作用下BFRP筋的低速冲击响应,同时测试了未完全断裂试件的残余拉伸承载力.结果 表明:...     

温度老化对GFRP/BFRP筋残余弯曲性能的影响

对玻璃/玄武岩纤维增强复合材料(GFRP/BFRP)筋材在温度老化作用后的弯曲性能进行了试验研究,重点探讨了不同作用温度及恒温时间对不同直径的两类FRP筋材的弯曲性能影响特性,同时采用扫描电子显微镜(SEM)对温度老化作用后部分GFRP/BFRP筋的微观结构变化及损伤机理进行了分析.试验与分析结果表明:(1)温度老化作用后GFRP/BFRP筋材弯曲强度与最大应变随作用温度升高均呈阶段性下降的趋势,而弯曲弹性模量无明显退化,其保留率均在90％以上;(2)温度老化作用后直径较大的GFRP筋材的弯曲性能退化更为明显;且G12筋的弯曲性能保留率退化曲线均高于B12筋,说明BFRP筋的弯曲性能对温度作用更为敏感;(3)在270℃高温环境下,GFRP/BFRP筋弯曲性能随着恒温时间的延长均呈现线性下降趋势;(4)结合试验结果和SEM微观结构分析,可认为造成温度老化作用后两类FRP筋弯曲强度退化的主要原因是纤维与树脂基体间协同工作效果和纤维-树脂基体界面性能的显著降低.最后,结合本试验结果,给出了500℃以内温度老化作用后GFRP/BFRP筋材弯曲强度退化的计算模型以及线性插值预测方法,便于实际工程应用.     

BFRP筋钢-混组合梁高温后力学性能试验

设计了常温(25℃)、200℃、400℃和600℃四个工况，通过模型试验方法探究了玄武岩纤维增强树脂复合材料(Basalt fiber reinforced polymer,BFRP)筋钢-混组合梁高温后的破坏形态和力学性能。通过分析试验梁裂缝开展、挠度变形、温度场和破坏过程规律，研究BFRP筋和普通钢筋钢-混组合梁的破坏模式和承载能力。结果表明：经历400℃高温后，BFRP筋劣化导致力学性能大幅降低；筋体膨胀导致混凝土板开裂，其裂缝开展与普通钢筋钢-混组合梁显著不同，主裂缝沿横向筋材规律开展，且裂缝较宽。温度低于400℃时，由于混凝土的包裹，BFRP筋未达到劣化温度，两种钢-混组合梁承载能力和外观差别较小；600℃后，BFRP筋劣化，削弱了混凝土板刚度和强度，导致BFRP筋钢-混组合梁承载能力比普通钢筋钢-混组合梁降低更多；BFRP筋钢-混组合梁因整体刚度较小，加载后变形更大。高温后两种钢-混组合梁破坏模式相似，均为剪切破坏，有明显弹性、弹塑性和破坏阶段；600℃时，两种钢-混组合梁延性大幅降低，塑性变形减少，破坏较为突然。研究成果可为BFRP筋在钢-混组合梁中的应用提供参考。     

中低加载速率下BFRP筋-混凝土粘结性能研究

BFRP(basalt fiber reinforced polymer)筋是一种取代钢筋用于土木工程领域的新型纤维复合材料,中低加载速率下BFRP筋-混凝土粘结性能是保证其协同作用承受动荷载的重要前提.该文根据正交试验方法设计了16组粘结试件,利用MTS试验系统对不同加载速率(0.005 mm/s～5 mm/s)下的...     

CFRP筋的疲劳性能

进行了不同循环应力下CFRP筋的常温疲劳试验,选取CFRP筋70％的极限拉伸应力作为最大循环应力,在R=0．5（最小循环应力与最大循环应力的比）和R=0的应力率下,测量了CFRP筋的疲劳寿命曲线,研究了CFRP筋的疲劳性能．结果表明：CFRP筋的最大循环应力应控制在70％极限拉伸应力以下;在R=0．5应力率下,最大循环应力下降5％的极限拉伸应力时,CFRP筋的疲劳寿命增长10倍左右;最大循环应力分别为60％和50％极限拉伸应力时,R=0应力率下CFRP筋的疲劳寿命分别为R=0．5应力率下疲劳寿命的百分之一和十分之一．这说明CFRP筋具有很大的脆性,需要有足够的强度安全系数,才能发挥作用;根据试验拟合的疲劳寿命曲线,CFRP筋的疲劳性能远高于Q235光圆钢筋．     

BFRP筋与低碱度硫铝酸盐水泥混凝土粘结性能试验

为研究玄武岩纤维增强聚合物复合材料(Basalt fiber reinforced polymer,BFRP)筋与低碱度硫铝酸盐水泥混凝土的粘结性能，对共90个粘结试件进行中心拉拔试验，研究了筋材表面形貌、混凝土强度等级等因素对粘结性能的影响。试验结果表明：对筋材表面进行喷砂、缠绕纤维和螺纹处理能显著提高粘结性能，深螺纹环氧树脂BFRP筋与65 MPa低碱度硫铝酸盐水泥混凝土的粘结强度高达39.09 MPa，远大于光滑BFRP筋的13.32 MPa。强度等级对BFRP筋-低碱度硫铝酸盐水泥混凝土粘结试件的粘结强度的影响更明显，此外BFRP筋与低碱度硫铝酸盐水泥混凝土粘结性能高于普通硅酸盐混凝土。最后，通过Cosenza-ManfrediRealfonzo(CMR)模型和修正后的Bertero-Popov-Eligehausen(mBPE)模型)对BFRP筋-混凝土粘结试件的粘结滑移(τ-s)曲线进行拟合，发现CMR模型对粘结滑移曲线的上升段拟合效果较好，清晰准确地反映了其粘结-滑移本构关系，为研究BFRP筋增强硫铝酸盐水泥混凝土结构的力学性能提供了关键理论依据。     

疲劳损伤件中温热等静压后的疲劳性能试验研究

对40Cr调质试样先进行了0.6N(N为全寿命）拉-拉疲劳试验，再中温热等静压，在随后的继续拉-拉疲劳试验中，发现其数据分散度降低，疲劳寿命大幅度提高，经分析，认为其主要原因是，中温热等静压使试样表面硬度增加，残余压应力提高，约束并减缓了随后继续疲劳试验时损伤区微裂纹的发展。     

氯盐侵蚀作用下BFRP筋增强海砂ECC的拉伸及弯曲性能试验

为推广使用海洋资源,采用海砂代替硅砂制备工程水泥基复合材料(Engineering cementitious composites,ECC).将海砂ECC与玄武岩纤维增强树脂复合材料(Basalt fiber reinforced polymer,BFRP)筋结合,充分发挥两种材料的优点,以获得更强的耐腐蚀性能及更为优...     

一种疲劳破坏的损伤模型

对数种典型疲劳损伤模型进行了研究,以局部范围材料的力学行为作研究对象,用应变信号分析的方法,依据疲劳断裂理论,为疲劳损伤的估算提出一个能够实际的计算模型。     

刚柔复合式路面沥青层温度疲劳损伤及开裂研究

运用损伤力学、传热学、断裂力学理论和有限元法,分析了沥青层的温度疲劳损伤特性、疲劳寿命、裂缝扩展等。研究结果表明：温度疲劳损伤主要集中在沥青层表面,随着温变次数的增加,沥青层表面的损伤度线性增加;随着沥青层模量与温变幅值的增加,沥青层表面的损伤度不断增加;随着温变次数的增加,沥青层表面的水平拉应力线性减小;随温变幅值的增大,沥青层的疲劳寿命不断减小;基于高温效应的沥青层最小临界厚度为4cm;增加沥青层厚度和减小沥青层模量可以起到延缓沥青层温度裂缝扩展的作用。研究结果对刚柔复合式路面的合理设计和推广应用有重大意义。     

循环荷载作用下钢桥面铺装疲劳损伤失效行为研究

针对钢桥面铺装工程中普遍采用的改性沥青(Stone Matrix Asphalt,SMA)、浇筑式沥青(Guss asphalt,GA)、环氧沥青(Epoxy asphalt,EP)混合料双层铺装结构,进行了循环车载作用下钢桥面与沥青混凝土铺装疲劳损伤特性理论分析与试验研究。基于疲劳损伤度,研究了钢桥面铺装疲劳损伤失效行为和疲劳开裂过程中损伤场、应力和应变场动态演变机制,推导出疲劳失效时的损伤场、应力和应变场计算表达式,并给出钢桥面铺装疲劳寿命理论公式。以三座钢箱梁桥桥面铺装(润扬长江大桥2005,南京长江三桥2005,苏通大桥2008)为例,对不同铺装结构组合方案下的复合梁进行疲劳试验分析和使用寿命理论预测。实例研究结果表明,钢桥面铺装疲劳损伤失效行为预估模型合理可行;相较于改性沥青、浇筑式沥青,环氧沥青混合料具有较强高的强度低变形能力,更适合于大跨径钢桥面铺装抗疲劳的设计要求;由环氧沥青混合料组合而成的“双层环氧沥青混凝土”和“浇注式沥青混凝土(下层)+环氧沥青混凝土(上层)”的抗疲劳性能优于其它沥青混合料铺装结构组合方案,同等厚度组合情况下疲劳使用寿命可延长1倍~2倍以上;“双层环氧沥青混凝土”已应用于润扬长江大桥、南京长江三桥和苏通长江大桥钢桥面工程,并已成功运行10年以上,其跟踪观测结果良好。     

Fatigue damage discrepancies,the intrinsic fatigue damage map locus and the multiple stages of the similitude concept

The work demonstrates how the theory of the fatigue damage map (FDM) can be used in order to define a closed form locus where fatigue crack growth can be sought. The Intrinsic FDM Locus depending only on readily material properties represents a tool able to accurately predict crack growth of polycrystals. If the Locus is expressed in terms of a surface plot after triangulation of the data, it concludes into visualization of the potential for multiple similitude stages. The stages are defined as a function of the maximum far field stress and ΔK. Multiple similitude stages are found to dominate the short and near threshold area (Stage I growth) and represent direct result of the effect of polycrystalline behaviour to flow resistance. The work concludes that interrogation of the points defining the Intrinsic FDM Locus and related to the three thresholds can provide potential characteristics in the quest for an ideal damage tolerance material.     

Fatigue and damage accumulation in open cell aluminium foams

Open‐cell aluminium foams are a relatively new material with interesting uses in different engineering applications. This study investigates the fatigue behaviour and damage accumulation of metal foams via a fatigue analysis (Weibull E‐N model), a failure criterion (the relation among the prepeak compressive and tensile slopes, the reduction in the tensile stress, or the reduction in the compressive stress), and a mathematical approach (linear, quadratic, or exponential). As a result of combining the 3 mathematical approaches and 3 failure criteria, different approaches are obtained, analysed, and validated by using experimental data. Finally, the proposed approaches can be used to directly obtain the damage accumulation level for open‐cell metal foams under fully reversed cyclic loading as a function of the number of cycles applied, the total strain amplitude, and the initial damage accumulation condition.     

BFRP筋钢纤维高强混凝土梁受弯承载力试验与理论

通过11根玄武岩纤维增强聚合物复合材料（BFRP）筋钢纤维高强混凝土梁的受弯性能试验,研究了钢纤维混凝土层厚度、钢纤维体积分数和BFRP筋配筋率对BFRP筋钢纤维高强混凝土梁受弯破坏形态及其承载力的影响。结果表明,BFRP筋钢纤维高强混凝土梁的破坏模式可分为受压破坏、受拉破坏和平衡破坏3种;钢纤维混凝土层厚度和钢纤维体积分数的变化对于BFRP筋钢纤维高强混凝土梁受弯承载力具有一定程度的影响,当BFRP筋配筋率为0.77%时,掺加体积分数为1.0%钢纤维的梁受弯承载力较无钢纤维梁提高了22.7%,在受拉区0.57倍截面高度内掺加1.0vol%钢纤维的梁受弯承载力达到全截面钢纤维混凝土梁受弯承载力的86.7%;增大BFRP筋配筋量可显著提高BFRP筋钢纤维高强混凝土梁的受弯承载力,BFRP筋配筋率为1.65%的试验梁受弯承载力较配筋率为0.56%的试验梁提高了39.4%。针对不同的破坏模式,提出了BFRP筋钢纤维高强混凝土梁受弯承载力和平衡配筋率的计算方法,并结合安全配筋率的概念对试验梁的破坏模式进行了预测,试验结果与分析结果吻合良好。     

单向帘线/橡胶复合材料的疲劳损伤模型与疲劳寿命预报

将不可逆热力学和损伤力学应用于橡胶复合材料的疲劳研究，在大量试验工作的基础上，选择适当的热力学势函数，建立了橡胶复合材料的损伤演变方程和橡胶复合材料的疲劳寿命预报方程。应用本模型对单向橡胶复合材料的疲劳寿命进行了预报，发现理论预测值与试验结果比较符合。     

Fatigue damage of medium carbon steel under sequential application of axial and torsional loading

Fatigue tests were conducted on S45C steel under fully reversed strain control conditions with axial/torsional ( at ) and torsional/axial ( ta ) loading sequences. The linear damage value (n₁/N₁+n₂/N₂) was found to depend on the sequence of loading mode ( at or ta ), sequence of strain amplitude (low/high or high/low) and life fraction spent in the first loading. In general, at loading yields larger damage values than ta loading and the low–high sequence of equivalent strain leads to larger damage values than the high–low sequence. The material exhibits cyclic softening under axial cyclic strain. Cyclic hardening occurs in the torsion part of ta loading, which elevates the axial stress in the subsequent loading, causing more damage than in pure axial fatigue at the same strain amplitude. Fatigue life is predicted based on the linear damage rule, the double linear damage rule, the damage curve approach and the plastic work model of Morrow. Results show that overly conservative lives are obtained by these models for at loading while overestimation of life is more likely for ta loading. A modified damage curve method is proposed to account for the load sequence effect, for which predicted lives are found to lie in the factor‐2 scatter band from experimental lives.     

结构风振的概率疲劳累积损伤

本文通过考虑脉动风压的随机过程性,利用风荷载的规范标定方法和结构疲劳试验结果,从结构风振随机反应分析着手,提出了基于疲劳累积损伤机制的抗风结构疲劳可靠性和寿命估计的分析方法,并通过一典型单自由度结构说明了此方法的应用。     

Fatigue issues in aircraft maintenance and repairs

Many design considerations are involved in ensuring structural integrity of Boeing jet transports, which have common design features validated by extensive analyses, tests, and service performance. Designing for continued structural integrity in the presence of damage such as fatigue or corrosion is an evolutionary process. Performance demands, increasing structural complexity, and aging fleet reassessments have required development of standards suitable for application by large teams of engineers. This presentation is focused on such methods with special emphasis on practical fatigue reliability considerations. Durability evaluations are based on quantitative structural fatigue ratings which incorporate reliability considerations for test data reduction and fleet performance predictions. Fatigue damage detection assessments are based on detection reliability estimates coupled to damage growth and residual strength evaluations. Data are presented to airline operators on detection check forms which permit efficient maintenance planning to achieve required fatigue damage detection reliability levels.     

Fatigue damage analysis based on energy parameters in reinforced polyamide

This article proposes an analysis method for the identification of the damage caused in a reinforced polyamide fatigue process through the evolution of the generated energy per cycle. Monotonous fatigue tests have been carried out at different stress levels using Polyamide 6 reinforced with short fibre glass tensile specimens. The loss of mechanical properties is measured using a damage parameter, defined as the variation in energy per cycle with respect to the initial conditions. Three clearly differentiated zones can be distinguished in the evolution of damage as a function of the energy per cycle. The first zone is one of deaccelerated rapid growth; in the second, the damage grows linearly, so that the damage growth speed can be determined as a function of the potential of variation of the stress applied; and finally, the third is a zone of accelerated growth of the damage until fracture.     

Fatigue and ratcheting assessment of AISI H11 at 500°C using constitutive theory coupled with damage rule

Hot extrusion is one of the most commonly used manufacturing methods for metal plastic deformation, and the consumption of extrusion tooling is considerably high due to its fatigue damage under cyclic serving condition. Hot‐work tool steel AISI H11 is one of these typical materials employed in extrusion tooling. This work is dedicated to calculating the stress/strain state of AISI H11 and predicting its lifetime at high temperature 500°C by building a unified constitutive model coupled with Lemaitre's damage law. Tensile tests and strain/stress reversed cycling tests have been conducted at 500°C to investigate mechanical properties and damage evolution. A unified constitutive model with Armstrong‐Fredrick/Ohno‐Wang kinematic hardening rule and a new proposed isotropic hardening rule is built; Lemaitre's damage law is employed as well. Parameters are determined based on tests and are temperature dependent. Finite element simulation of the deformation behaviour and fatigue lifetime is implemented into commercial software ABAQUS Standard v6.14‐2 with user material subroutine to validate the proposed method. The comparison shows good agreement with experimental results, and this part of work is essential and crucial to subsequent structure analysis.