Multiobjective crashworthiness optimization of multi-cornered thin-walled sheet metal members

Plastic deformation of structures absorbs substantial kinetic energy when impact occurs. Therefore, energy-absorbing components have been extensively used in structural designs to intentionally absorb a large portion of crash energy. On the other hand, high peak crushing force, especially with regard to mean crushing force, may lead to a certain extent and indicate the risk of structural integrity. Thus, maximizing energy absorption and minimizing peak to mean force ratio by seeking for the optimal design of these components are of great significance. Along with this analysis, the collapse behavior of square, hexagonal, and octagonal cross-sections as the baseline for designing a newly introduced 12-edge section for stable collapse with high energy absorption capacity was characterized. Inherent dissipation of the energy from severe deformations at the corners of a section under axial collapse formed the basis of this study, in which multi-cornered thin-walled sections was focused on. Sampling designs of the sections using design of experiments (DOE) based on Taguchi method along with CAE simulations was performed to evaluate the responses over a range of steels grades starting from low end mild steels to high end strength. The optimization process with the target of maximizing both specific energy absorption (SEA) and crush force efficiency (CFE), as the ratio of mean crushing load to peak load, was carried out by nonlinear finite element analysis through LS-DYNA. Based on single-objective and multi-objective optimizations, it was found that octagonal and 12-edge sections had the best crashworthiness performance in terms of maximum SEA and CFE.     

Collapse behaviour of plastic tubes filled with wood sawdust

The influence of foam-like wood filler on the mode of collapse and energy absorption performance of polyvinylchloride (PVC) tubes has been investigated under quasi-static loading conditions. The mode of collapse of axially crushed PVC tubes has been found to revert from regular three-lobe diamond mode to axisymmetric concertina mode at a certain wood-filling density. The energy absorption capacity of the PVC tubes is enhanced by wood compression as well as by extra stretching in the tube circumference due to shifting from multi-lobe to axisymmetric mode. The collapse of the PVC tubes has been analyzed considering multi-lobe mode, concertina mode and mixed mode. In these models, the interaction of the wood sawdust filler on the final mode of collapse of the PVC tubes has been incorporated. The mean crushing load of the PVC tubes collapsing into the mixed mode is considered as the average mean of that of the concertina mode, the multi-lobe mode and that causing crushing of wood sawdust. Compression tests on wood sawdust were used to extract its mechanical properties and the results have been used in the validation of the analytical model. The analytical results obtained for the mean crushing load agree reasonably well with those from experimental observations.     

Structural behavior of multifunctional GFRP joints for concrete structures

A multifunctional all-FRP joint has been developed for the transfer of bending moments and shear forces in thermal insulation sections of concrete slab structures used in building construction. Tensile forces from moments are transferred by horizontal GFRP bars, while a pultruded cellular GFRP element transfers the compression forces. The shear forces are transferred by inclined GFRP bars and the webs of the GFRP element. The new joint considerably increases energy savings for buildings due to the low thermal conductivity of GFRP materials. The quasi-static behavior of the joint at the fixed support of cantilever beams was investigated. Two parameters were studied: shear- or moment-dominated loading mode and concrete strength. Results show that the all-FRP joint does not play a critical role at the ultimate limit state. Ductile failure occurs through concrete crushing. The GFRP bars lead to a significant improvement in joint performance compared with similar joints comprising steel bars. Higher concrete strength does not, however, significantly improve the ultimate load.     

混凝土骨料再生设备及工艺研究

先进破碎设备及经济合理的骨料再生工艺是生产和推广再生混凝土、实现建筑资源环境可持续发展和发展绿色混凝土的关键所在.以层压破碎理论为基础,通过对两级破碎设备出口粒径、挤压频率、转子偏心距等技术参数的改进设计和分析研究,提出实现这些参数改进的具体措施.在对国内外现有破碎工艺比较分析的基础上,拟订了废弃混凝土新的破碎工艺(挤压破碎、加热、碾磨、筛分),分析验证了所选参数及工艺安排的合理性.结果表明,改进设计后的破碎设备提高了再生骨料的品质,符合结构混凝土对骨料质量的要求;拟订的工艺经济合理可行,大幅度提高了废弃混凝土骨料的回收率.     

Relative merits of single-cell, multi-cell and foam-filled thin-walled structures in energy absorption

The axial crushing of hollow multi-cell columns were studied analytically and numerically. A theoretical solution for the mean crushing force of multi-cell sections were derived, and the solution was shown to compare very well with the numerical predictions. Numerical studies were also carried out on foam-filled double-cell and triple-cell columns. Based upon the numerical results, closed-form solutions were derived to calculate the mean crushing strength of these sections. It was found that the interaction effects between the foam core and the column wall contribute to the total crushing resistance by the amounts equal to 140% and 180% of the direct foam resistance for double cell and triple cell respectively. Finally, the relative merits of single-cell, multi-cell and foam-filled sections were discussed.     

基于全过程考核的混凝土结构基本原理课程评价模式探索

传统的课程考核方式是以期末考试成绩为主,平时成绩为辅,其弊端在于无法全面客观反映和评价学生的学习情况,尤其缺乏对学生在整个课程学习过程中知识掌握程度和学习效果的量化考核。以混凝土结构基本原理这一土木工程专业核心课程为例,提出了基于全过程考核的课程评价模式,增加平时成绩比例,通过随堂测验、课堂讨论、案例式作业、学生授课、科研小论文等丰富多样的评价方式,加强教学过程中的考核评价,督促调动学生的学习积极性和主动性,切实提高了课程学习效率,有力保障了教学质量。     

回收沥青路面材料(RAP)性能研究

为了评价回收沥青路面材料的路用性能,分别选取甘肃省境内高速公路6个就地热再生养护维修路段的RAP进行老化沥青及回收矿料性能研究,并与现行规范中相应技术指标进行对比.结果表明,老化沥青相比基质沥青针入度降低,软化点升高,延度降低.抽提后三档集料均比抽提前变细,尤其是5-10mm的变化最大,其次为0-5mm,对10-15m...     

破碎处理对陶粒及其混凝土性能的影响

采用对比试验的方法研究了破碎处理对页岩陶粒及陶粒混凝土性能的影响,结果表明:通过破碎处理的方式可有效地改善陶粒的级配、减小颗粒粒径、提高筒压强度和堆积密度;使用破碎陶粒配制混凝土可显著提高混凝土的抗压强度,增强抗离析能力,改善工作性能,但对混凝土的热工性能有一定程度的不利影响。     

刚性连接钢框架-内填剪力墙结构滞回性能试验研究

为研究钢框架-钢筋混凝土剪力墙结构（SRCW）的抗震性能,以一榀1：3比例的两层刚性连接钢框架-内填钢筋混凝土墙试件为研究对象,进行水平荷载下的滞回性能试验。根据试验结果分析了剪力墙的裂缝开展过程和破坏模式、结构抗侧刚度的变化、结构的延性等整体性能;钢框架柱的受力及变形、中梁受力及传力、剪力墙变形、剪力钉变形特性等局部性能。结果表明：结构具有较高的强度储备;良好的延性和耗能能力;试件的破坏模式为两柱脚形成塑性铰,一层剪力墙两底角部混凝土的压碎,一层剪力墙正好在暗梁上方形成水平裂缝,显示出明显的弯曲破坏模式。试验研究结果为研究SRCW结构的破坏机理、指导工程设计提供了合理的理论依据。     

空间格构腹板增强泡沫夹芯复合材料-试件准静态压缩吸能试验

采用聚氨酯泡沫作为填充材料,玻璃纤维增强复合材料作为面层和腹板,将双层正交格构腹板改变为双层错位格构腹板、多层错位格构腹板、六边形格构腹板和多层梯形格构腹板,制作空间格构腹板增强泡沫夹芯复合材料试件。对试件开展准静态压缩试验,记录试件的破坏过程,得到其荷载 位移曲线。分析试件产生不同破坏形式的原因,对比试件在压缩变形过程中承载力变化情况;引入能量吸收值、比吸能和平均压溃力3个指标比较试件的吸能性能。结果表明:改变竖直格构腹板的空间位置后,试件的准静态压缩破坏模式由竖直格构腹板突然屈曲失稳破坏改变为竖直格构腹板先产生倾斜再发生弯曲破坏,以及斜向格构与泡沫的剥离破坏和斜向格构与斜向格构的层间剥离破坏,有效减少了试件承载力的弹性突变,降低了试件的脆性;竖直格构腹板弯曲破坏比斜向格构的剥离破坏吸收更多能量,其能量吸收值波动幅度最大为16.6%;试件的能量吸收值随着压缩量增加呈线性增加,其耗能性能较为稳定。     

半刚接钢框架(柱弱轴)-内填剪力墙结构滞回性能试验研究

目前我国规范关于钢框架-内填RC剪力墙组合结构体系(SRCW)的有关内容基本空白,通过了解国际上在SRCW结构体系研究领域的发展状况,以尚未研究的半刚连接钢框架(柱弱轴)-RC剪力墙结构为研究对象,通过1∶3比例将原结构缩放为一两层单跨试件结构,进行了水平循环荷载下的滞回性能试验。根据试验结果分析了结构的抗侧刚度变化、裂缝开展过程与破坏模式、结构的耗能和抗震延性和安全性等整体性能;钢框架柱的变形、中梁受力与传力机理、PR连接性能、RC剪力墙和剪力钉的变形反映的结构变形模式局部性能。结果表明:试验结构具有较好的延性、耗能性能和安全储备;试件结构的破坏模式为RC墙角部混凝土压溃,钢框架柱脚和梁柱半刚性连接部位形成塑性铰,研究为SRCW规范的制订和工程应用提供了合理的理论依据。     

页岩烧结砖粉碎设备的比较和选择

在砖瓦行业,可以用于页岩粉碎的设备品种较多,也较繁杂.粉碎设备的正确选择和使用是页岩烧结砖厂节能降耗、降低成本、提高产量、保证质量的重要保证.选择粉碎设备时必须全面考虑原料的性质、状态、块度的大小、设备处理能力和设备的粉碎方式等因素.本文还对各种粉碎设备采取的原料粉碎工艺进行了比较,从中选出了比较经济的粉碎工艺.     

Theoretical prediction and numerical simulation of multi-cell square thin-walled structures

The axial crushing of square multi-cell columns were studied analytically and numerically. Based on the Super Folding Element theory, a theoretical solution for the mean crushing force of multi-cell sections were derived by dividing the profile into 3 parts: corner, crisscross, and T-shape. Numerical simulations of square multi-cell sections subjected to dynamic axial crushing were conducted and an enhancement coefficient was introduced to account for the inertia effects for aluminum alloy AA6060 T4. The analytical solutions show an excellent agreement with the numerical results. It was found that the crisscross part was the most efficient component for energy absorption and the energy absorption efficiency of a single-cell column can be increased by 50% when the section was divided into 3×3 cells. Finally, the proposed method was extended to analyze the plateau stress of square cell honeycomb subjected to out-plane axial crushing and to some extent validate the mechanical insensitivity of honeycomb to cell size.     

对钢管材料在液压膨胀试验中的应力—应变关系的测定

基于塑性膜理论和力平衡方程等,对试验数据进行曲线拟合,来确定在液压成形过程（THF）中薄壁管的应力一应变关系。由此提出一种简单实用的液压膨胀试验方法,并对不锈钢和低碳钢管进行自由膨胀试验,以得到所需的试验变形数据。而自由膨胀的有限元模拟同时也验证了该方法的有效性。结果表明：目前的做法是正确的,可用于对钢管材料的应力一应变性能进行界定,此外,由此法也可得到扩展的大应变流动应力曲线。     

六边薄壁构件在准静态径向压缩下的吸能特性

为增强巷道超前液压支架抵抗冲击地压能力,有效支护巷道防煤矿冲击地压灾害发生,设计一种六边薄壁吸能防冲构件安装在支架顶梁上方来提高支架抵抗冲击能力。对构件的吸能防冲特性进行理论和实验研究,结果表明:六角处为圆弧形的吸能防冲构件压缩过程中具有非常稳定的变形破坏模式、恒定的反作用力和较高的冲程效率。材料参数和几何尺寸对载荷波动系数和冲程效率影响较小。构件压溃峰值载荷、平均压溃载荷和总吸能均随长度增加而增大;构件压溃峰值载荷和平均压溃载荷随内边长增加而减小,内边长对总吸能影响较小。构件吸能防冲特性的理论解与实验结果有较好的吻合,为构件选取提供了理论依据。六边薄壁吸能防冲构件也可作为高速公路防护栏或汽车防撞前梁等。     

大跨度桥梁中央开槽颤振控制效果和机理研究

采用理论分析结合风洞试验的方法,对中央开槽这种已经在大跨度桥梁设计和建设中逐步得到应用的颤振控制措施的控制效果和控制机理进行研究。选取5种不同气动外形的基本断面,采取2种开槽宽度分别对其进行中央开槽处理。对全部5个系列15种断面开展节段模型风洞试验,并应用二维三自由度耦合颤振分析方法,对各断面开槽前后颤振性能、颤振驱动机理和颤振形态的变化规律进行分析。研究结果表明,中央开槽并不总是能提高结构的颤振稳定性能,其控制效果同基本断面的气动外形以及开槽宽度密切相关,当槽宽不恰当时中央开槽的控制效果会严重削弱,而对气动外形比较钝化的断面采用中央开槽后其颤振性能反而会恶化。对控制机理的理论分析表明,这种控制效果差异的原因在于各断面气动阻尼的形成和随风速发展规律存在明显差别,而颤振形态特别是竖向自由度的参与程度也影响到中央开槽的颤振控制效果。     

Frusta structure designing to improve quasi-static axial crushing performances of triangular tubes

To improve quasi-static axial crushing performances of thin-wallled triangular tubes, frusta structures were designed and fabricated. Quasi-static axial compression experiments were carried out to reveal the collapse mode and energy absorption characteristic of the triangular frusta tube. Peak loads and mean crushing forces (MCFs) of tubes with different taper angles were compared. In-extensible and extensible collapse modes were suggested to predict the MCF of the triangular frusta tube with small and great taper angles, respectively. A new collapse mode, inward folding, was observed in the experiments. An energy absorption stability factor was defined to evaluate the anti-crushing efficiency of the triangular frusta tube. With greater taper angles, the energy absorption stability factor is much closer to 1, denoting more stable deformation style. It is concluded that frusta structures with taper angles effectively enhance the anti-crushing efficiency and stability of thin-walled triangular tubes.     

Effects of hinges and deployment angle on the energy absorption characteristics of a single cell in a deployable energy absorber

Numerical simulation is carried out to investigate the crushing characteristics of a single cell in a fan-shaped deployable energy absorber (FDEA) under quasi-static axial loading. FDEA can effectively improve the crashworthiness behavior of aircrafts with the advantages of saving space and deploying actively. Hinges are added to the single cell to meet the need of fan-shaped deployment. The finite element model is established to study the effects of hinge׳s parameters, including material properties such as Young׳s modulus, yield strength and the tube thickness, on the single cell׳s energy absorption characteristics. The relationship between the deployment angle and the specific energy absorption (SEA) of the single cell is also studied. The numerical results indicate that the energy absorption increases rapidly as yield strength and the hinge׳s thickness increase, while it only has minor correlation with Young׳s modulus of the material. Three different modes of the cell appear during its axial crushing as the deployment angle increases. Besides, experiments were conducted to observe the crushing mode of the straight single cell, and the results are compared with the numerical simulation results. Finally, a theoretical model of a straight single cell with hinges is proposed to predict the mean crushing force, which is in good agreement with the numerical simulation.     

粗集料的技术指标对水泥混凝土性能的影响

通过大量的试验数据分析粗集料的级配、压碎值及含泥量等技术指标对混凝土的性能影响,并对桥梁施工中水泥混凝土用粗集料的质量控制提出了建议,以提高混凝土性能,达到预期目标。     

Prediction of bending collapse behaviours of thin-walled open section beams

Crushing behaviours of thin-walled open section beams are simulated using the simplified kinematic models. Systematic process of simulation is presented and applied to L-section and I-section beams. Basic processes can be conceptually divided into composition of mode shapes, location of deforming elements as a function of global process control parameter, calculation of plastic work done, estimation of mode parameters and calculation of crushing behaviours. A systematic numerical method is suggested to determine geometry and mode parameters according to the progress of collapse since it is generally very complicated to obtain closed form expressions for bending collapse problems. In the present method, mode parameters are determined by minimizing the plastic work done at very early stage of collapse, while it has been done conventionally by minimizing the mean crushing force. The results are in good agreement with those from finite element analyses and from the literature.