今日更新:International Journal of Solids and Structures 1 篇,Journal of the Mechanics and Physics of Solids 2 篇,Thin-Walled Structures 8 篇
Large deformation response of a novel triply periodic minimal surface skeletal-based lattice metamaterial with high stiffness and energy absorption
Lijun Xiao, Gaoquan Shi, Genzhu Feng, Shi Li, Song Liu, Weidong Song
doi:10.1016/j.ijsolstr.2024.112830
具有高刚度和吸能性能的新型三周期极小表面骨架晶格超材料的大变形响应
Triply periodic minimal surface (TPMS) lattice metamaterial presents superior mechanical performance over traditional strut-based lattice metamaterials due to their unique structural characteristics. However, the high stiffness–stable plastic response trade-off dilemma is still the major challenge for skeletal-based metamaterials. Herein, a novel TPMS skeletal lattice metamaterial is proposed. Finite element simulations are conducted to reveal its elastic properties and plastic response under compression. Afterwards, validation experiments are performed on the lattice specimens fabricated by the most common Fused Deposition Modeling (FDM) process. The nominal stress–strain curves and collapse mode of the lattice materials are obtained accordingly. Both the numerical simulations and experiments demonstrate that the proposed TPMS lattice metamaterial exhibits high specific modulus, strength and energy absorption, together with a smooth and elongated stress plateau, thereby overcoming the strength-efficiency trade-off. Different from the rigid nodal region in traditional strut-based lattices, the strut connection parts in the novel TPMS lattices experience shear and twisting, which avoids the catastrophic failure of the struts and enhances the loading efficiency of the structure under compression. Meanwhile, the numerical results indicate that the stable plastic response of the designed architecture is insensitive to the plastic flow behavior of the bulk material, which is also supported by the experimental results. It is also demonstrated that the novel TPMS lattice metamaterial presents several times higher stiffness as well as energy absorption simultaneously than the current strut-based lattice materials, which can be potentially applied as load-bearing components and impact energy absorbers.
三周期极小表面(TPMS)晶格超材料由于其独特的结构特性,比传统的基于结构的晶格超材料具有更优越的力学性能。然而,高刚度与稳定塑性响应之间的权衡仍然是骨基超材料面临的主要挑战。本文提出了一种新型的TPMS骨架晶格超材料。通过有限元模拟,揭示了其弹性性能和压缩下的塑性响应。然后,对最常用的熔融沉积建模(FDM)工艺制作的晶格试件进行了验证实验。得到了点阵材料的名义应力-应变曲线和崩溃模式。数值模拟和实验结果表明,所提出的TPMS晶格超材料具有较高的比模量、强度和能量吸收,并且具有光滑的细长应力平台,从而克服了强度-效率的权衡。与传统桁架的刚性节点区域不同,新型TPMS桁架中的桁架连接部分经历了剪切和扭转,避免了桁架的灾难性破坏,提高了结构在压缩下的加载效率。同时,数值计算结果表明,所设计结构的稳定塑性响应对块状材料的塑性流动行为不敏感,这也得到了实验结果的支持。研究结果还表明,新型TPMS晶格超材料的刚度和能量吸收能力均比现有的基于支柱的晶格材料高数倍,可以作为承载部件和冲击吸能材料。
Asymptotic, second-order homogenization of linear elastic beam networks
Yang Ye, B. Audoly, C. Lestringant
doi:10.1016/j.jmps.2024.105637
线性弹性梁网络的渐近二阶均匀化
We propose a general approach to the higher-order homogenization of discrete elastic networks made up of linear elastic beams or springs in dimension 2 or 3. The network may be nearly (rather than exactly) periodic: its elastic and geometric properties are allowed to vary slowly in space, in addition to being periodic at the scale of the unit cell. The reference configuration may be prestressed. A homogenized strain energy depending on both the macroscopic strain ɛ and its gradient ∇ ɛ is obtained by means of a two-scale expansion. The homogenized energy is asymptotically exact two orders beyond that obtained by classical homogenization. The homogenization method is implemented in a symbolic calculation language and applied to various types of networks, such as a 2D honeycomb, a 2D Kagome lattice, a 3D truss and a 1D pantograph. It is validated by comparing the predictions of the microscopic displacement to that obtained by full, discrete simulations. This second-order method remains highly accurate even when the strain gradient effects are significant, such as near the lips of a crack tip or in regions where a gradient of pre-strain is imposed.
我们提出了一种由2维或3维线性弹性梁或弹簧组成的离散弹性网络的高阶均匀化的一般方法。网络可能是接近(而不是完全)周期性的:除了在单位胞的尺度上具有周期性外,它的弹性和几何性质允许在空间中缓慢变化。参考结构可以是预应力的。通过双尺度展开,得到了由宏观应变和梯度∇ε决定的均匀应变能。均匀化后的能量比经典均匀化后的能量近近精确两个数量级。均匀化方法是用一种符号计算语言实现的,并应用于各种类型的网络,如二维蜂窝、二维Kagome晶格、三维桁架和一维受电弓。通过将微观位移的预测结果与完整的离散模拟结果进行比较,验证了该方法的有效性。这种二阶方法即使在应变梯度效应显著的情况下,如在裂纹尖端唇附近或施加预应变梯度的区域,也保持高度精确。
Scaling-law variance and invariance of cell plasticity
Jiu-Tao Hang, Huan Wang, Guang-Kui Xu
doi:10.1016/j.jmps.2024.105642
细胞塑性的尺度律变异与不变性
Scaling-laws are ubiquitous as universal physical principles in physics, biological systems, and human behavior. The scaling-law rheological responses of viscoelastic and plastic deformations and rate-dependent softening and stiffening during dynamic loading are remarkable characteristics of living cells and cell-like materials; however, the underlying mechanisms remain poorly understood. Here, we first propose a cellular structural model with 3-dimensional anisotropic discrete and plastic cytoskeletal networks to study the scaling-law rheological responses of cells. Besides the scaling-law invariance observed in cellular plastic deformation and viscoelastic deformation under large force ranges, there is evidence of scaling-law variance under relatively small force ranges. We develop a minimal mechanical model to elucidate the origins of scaling-law variance and invariance of cellular viscoelastic and plastic deformations. Interestingly, we find that cell materials can transition from fluid to solid over time and from elasticity to plasticity with increasing force. Furthermore, it is shown that the heterogeneity of three-dimensional cytoskeletal network dominates the anisotropic viscoplastic behavior of cells. We show that the stress-strain curves of cells with plastic cytoskeletons can be collapsed onto a single master curve of cells with elastic cytoskeletons. Moreover, we discover and derive a novel scaling-law ΔF∼v0α wherein the extent of force relaxation on cells during cyclical mechanical stimuli follows the same power-law dependence on the loading rate, as creep compliance on time. Our findings provide evidence that structure-based simulation and theoretical models can naturally capture the scaling-law invariance and variance of cellular deformations, in agreement with many experimental findings.
缩放定律是物理学、生物系统和人类行为中无处不在的普遍物理原理。动态加载过程中的粘弹性和塑性变形以及随速率变化的软化和僵化等缩放定律流变响应是活细胞和类细胞材料的显著特征;然而,人们对其内在机制仍然知之甚少。在此,我们首次提出了一种具有三维各向异性离散和塑性细胞骨架网络的细胞结构模型,用于研究细胞的比例律流变响应。除了观察到细胞塑性变形和粘弹性变形在大作用力范围下的比例律不变性外,还有证据表明在相对较小的作用力范围下存在比例律变异。我们建立了一个最小力学模型,以阐明细胞粘弹性和塑性变形的缩放规律方差和不变性的起源。有趣的是,我们发现细胞材料可以随着时间的推移从流体转变为固体,并随着力的增加从弹性转变为塑性。此外,研究还表明,三维细胞骨架网络的异质性主导着细胞各向异性的粘塑性行为。我们证明,具有塑性细胞骨架的细胞的应力-应变曲线可折叠为具有弹性细胞骨架的细胞的单一主曲线。此外,我们还发现并推导出一个新的缩放定律ΔF∼v0α,即在周期性机械刺 激下,细胞受力松弛的程度与蠕变顺应性随时间变化的幂律依赖关系相同。我们的研究结果证明,基于结构的模拟和理论模型可以自然地捕捉到细胞变形的尺度律不变性和变异性,这与许多实验结果是一致的。
Bearing–curling interaction of austenitic stainless steel thin sheet bolted connections
Ke Jiang, Shuai Li, Yukai Zhong, Ou Zhao
doi:10.1016/j.tws.2024.111912
奥氏体不锈钢薄板螺栓连接的轴承-卷曲相互作用
The bearing–curling interactive behaviour and capacities of austenitic stainless steel thin sheet bolted connections are studied in this paper, underpinned by testing and numerical modelling. Experiments were firstly conducted on 26 austenitic stainless steel thin sheet bolted connection specimens, including 19 specimens designed with curling and 7 specimens designed without curling. The test failure loads, failure modes, load–in-plane elongation curves and load–out-of-plane deformation curves were fully reported. The experimental programme was followed by a numerical modelling programme, where finite element models were firstly developed to repeat the experimental results and then used to carry out parametric studies to generate a numerical data pool. Based on the obtained numerical data, the influences of end distance, edge distance, longitudinal spacing, transverse spacing and sheet thickness on failure loads of austenitic stainless steel thin sheet bolted connections were discussed. The test and numerical data were used to assess the existing design provisions, as given in the European code and American specification. The assessment results revealed that the European code led to overall accurate but scattered failure load predictions, while the American specification was shown to result in overly unsafe and scattered failure load predictions.
在试验和数值模拟的基础上,研究了奥氏体不锈钢薄板螺栓连接的轴承-卷曲相互作用行为和能力。首先对26个奥氏体不锈钢薄板螺栓连接试件进行试验,其中卷边设计试件19个,不卷边设计试件7个。全面报道了试验破坏荷载、破坏模式、面内荷载延伸曲线和面外荷载变形曲线。实验程序之后是数值模拟程序,其中首先开发有限元模型以重复实验结果,然后用于进行参数研究以生成数值数据池。根据所获得的数值数据,讨论了端距、边距、纵向间距、横向间距和薄板厚度对奥氏体不锈钢薄板螺栓连接破坏载荷的影响。试验和数值数据被用来评估现有的设计规定,如欧洲规范和美国规范所给出的。评估结果表明,欧洲规范导致总体准确但分散的破坏荷载预测,而美国规范显示导致过度不安全和分散的破坏荷载预测。
Multi-objective shape-section optimization of free-form latticed shells using the RBF-NSGA-II algorithm
Ying Xu, Yufeng Gai, Hongtao Li, Qinghua Han
doi:10.1016/j.tws.2024.111918
基于RBF-NSGA-II算法的自由形式格壳形状截面多目标优化
In this study, a novel RBF-NSGA-II optimization framework based on the response surface methodology (RSM) and the constrained NSGA-II algorithm is proposed to simultaneously improve the static, nonlinear stability and economic performance of free-form latticed shells. The bending stiffness of joints is innovatively considered one of the design variables for shape-member section coupled optimization. The augmented radius basis functions (RBFs) are adopted to develop the metamodels of both the objectives and constraints. The improved minimum distance selection method (TMDSM) is used to select the optimal solution from the Pareto optimal solution set. Moreover, three alternative solutions are presented as supplements to meet various engineering requirements. The proposed RBF-NSGA-II algorithm is validated to have high accuracy for multi-objective optimization problems with high nonlinearity. Compared with those of the initial structures, the strain energy and steel consumption of the optimal structure decreased by 82.23% and 17.97%, respectively, while the buckling load considering both the geometric nonlinearity and material nonlinearity increased by 1.2 times. The involvement of the joint stiffness is demonstrated to have a great influence on the multi-objective optimization results. It is necessary to consider the joint stiffness as one of the design variables during shape-member section coupled optimization.
本文提出了一种基于响应面法(RSM)和约束NSGA-II算法的新型RBF-NSGA-II优化框架,以同时提高自由形式格壳的静力、非线性稳定性和经济性。创新性地将节点抗弯刚度作为形状-构件截面耦合优化的设计变量之一。采用增广半径基函数(rbf)建立目标元模型和约束元模型。采用改进的最小距离选择法(TMDSM)从Pareto最优解集中选择最优解。此外,还提出了三种替代方案作为补充,以满足各种工程要求。实验验证了所提出的RBF-NSGA-II算法对高非线性的多目标优化问题具有较高的精度。与初始结构相比,优化结构的应变能和钢材消耗分别降低了82.23%和17.97%,而考虑几何非线性和材料非线性的屈曲载荷增加了1.2倍。结果表明,关节刚度的参与对多目标优化结果有很大影响。在形杆截面耦合优化中,有必要将节点刚度作为设计变量之一加以考虑。
Direct Spot Joining of Thin Gauge Aluminum Alloy to Stainless Steel and Joint Performance in A Corrosion Environment
Abdul Sayeed Khan, Pingsha Dong, Kai Sun, Doug Larsen
doi:10.1016/j.tws.2024.111919
薄板铝合金与不锈钢的直接点焊及其在腐蚀环境下的接头性能
Direct joining of aluminum alloy and steel sheets offers a great potential for achieving effective structural lightweighting for transportation systems. The major challenge is how to avoid the formation of brittle intermetallic compounds (IMCs), which can be detrimental to joint load capacity and corrosion resistance. This paper presents a friction-based direct solid-state joining method for welding thin aluminum alloy (AA6061-T6) to stainless steel (316). Using a flat head friction stir tool, a strongly bonded interface was achieved under a steady-state dwell time of 20-sec and 1000 rpm by avoiding excessive heating via keeping the friction tool pin away from the steel surface, eliminating introducing detrimental IMCs. The effects of an automotive-relevant corrosion environment condition on joint strengths are considered. Mechanical test results show that aluminum and stainless-steel spot joints produced by the proposed method exhibit no corrosion-induced damage or cracking nor any noticeable reduction in strengths, resulting in dominantly ductile failure mode.
铝合金和钢板的直接连接为实现运输系统的有效结构轻量化提供了巨大的潜力。主要的挑战是如何避免脆性金属间化合物(IMCs)的形成,这可能对接头的承载能力和耐腐蚀性有害。提出了一种基于摩擦的薄铝合金(AA6061-T6)与不锈钢(316)直接固相连接焊接方法。使用平头摩擦搅拌工具,通过保持摩擦工具销远离钢表面,避免过度加热,避免引入有害的imc,在20秒和1000 rpm的稳态停留时间下实现了牢固的粘合界面。考虑了汽车腐蚀环境条件对接头强度的影响。力学试验结果表明,采用该方法制备的铝和不锈钢点接头没有腐蚀损伤或开裂,强度也没有明显降低,主要是延性破坏模式。
DYNAMIC RESPONSE OF CLAMPED METALLIC THIN-WALLED CYLINDRICAL SHELLS UNDER LATERAL SHOCK LOADING
Zhaoshuai Fan, Shuhong Ge, Zengshen Yue, Runpei Yu, Binchao Li, Jiankai Jiao, Jianhua Liu, Qiancheng Zhang
doi:10.1016/j.tws.2024.111922
横向冲击载荷下夹紧金属薄壁圆柱壳的动力响应
A combined experimental and numerical study was carried out to explore the dynamic response of Q235 thin-walled cylindrical shells under lateral shock loading. The machined Q235 specimens were clamped on both sides and subjected to centered lateral simulated shock loading via foam projectile impact tests, with their dynamic deformation evolution, mid-point deflections, and final deformation modes experimentally measured. The mid-point deflections of the impact side are all positive (the direction of deformation is the same as the impact direction) while those of the rear side all exhibit negative values (the direction of deformation is opposite to the impact direction). To further explore this phenomenon, the method of finite element (FE) was employed to simulate the foam projectile impact, with good agreement against experimental measurements achieved. Using the validated numerical model, the effects of impact velocity, length-to-diameter ratio, and thickness-to-diameter ratio on the dynamic response of the thin-walled cylindrical shell were further analyzed. The direction of both side deflections and deformation modes are significantly affected by the impact level and the shell geometries. For the rear side, within the given range of impact momentum, the numerically predicted deflection varies from -1.775 mm to 2.45 mm. Thereupon, the coupling of indentation and bulge deformation patterns are indicated, and their corresponding contribution changes are considered the main mechanism for determining the final deformation of the thin-walled cylindrical shell's rear side.
采用试验与数值相结合的方法,研究了Q235薄壁圆柱壳在侧向冲击载荷作用下的动力响应。通过泡沫弹丸冲击试验,对加工后的Q235试样进行双侧夹持,中心侧向模拟冲击加载,实验测量了Q235试样的动态变形演化、中点挠度和最终变形模式。撞击侧中点挠度均为正值(变形方向与撞击方向相同),后侧中点挠度均为负值(变形方向与撞击方向相反)。为了进一步探讨这一现象,采用有限元方法对泡沫弹丸的冲击进行了模拟,结果与实验测量结果吻合较好。利用验证的数值模型,进一步分析了冲击速度、长径比和厚径比对薄壁圆柱壳动力响应的影响。两侧挠度和变形模态的方向受冲击水平和壳体几何形状的显著影响。对于尾翼,在给定的冲击动量范围内,数值预测的偏转从-1.775 mm到2.45 mm不等。在此基础上,指出了压痕和凸起变形模式的耦合,并认为它们对应的贡献变化是决定薄壁圆柱壳后侧最终变形的主要机制。
Experimental and Numerical Investigation on Out-of-Plane Ultimate Strength of High-Strength Steel Arches
Zhenyu Pan, Hanwen Lu, Airong Liu, Jialin Wang, Mark A. Bradford
doi:10.1016/j.tws.2024.111898
高强钢拱面外极限强度的试验与数值研究
This study presents an experimental investigation on the out-of-plane ultimate strength of high-strength-steel (HSS) I-section arches, which has not been reported previously. Fourteen I-section HSS arches having different yield strengths, cross-sectional dimensions, slendernesses, and rise to span ratios were tested under three-point symmetrical vertical loading. The corresponding out-of-plane deformation modes and strengths are identified. Subsequently, in order to predict the out-of-plane capacities of HSS arches, a finite element analyses is carried out, which takes into consideration residual stresses and initial geometrical imperfections. This analysis demonstrates a strong alignment with the experimental results, confirming the accuracy of finite element model and experimental results. Furthermore, the study comprehensively analyzes the influence of yield strength of steel, rise-span ratio, and slenderness on the ultimate bearing capacity of HSS arches. Through a parametric analysis, design formulas for the out-of-plane bearing capacity of HSS arches subjected to arbitrary compression forces combined with arbitrary bending moments are formulated. It is found that the out-of-plane ultimate strength of HSS arches is significantly influenced by the yield strength of the steel. Compared to a low strength steel (LSS) arch, the out-of-plane ultimate bearing capacity of the HSS arch increases with an increase in yield strength in the plastic stage, and the ultimate lateral displacement of the HSS arch decreases with an increase in yield steel strength due to the lower ductility of HSS. In addition, after reaching the out-of-plane ultimate bearing load of arch, the load-displacement curve of the HSS arch drops faster than the LSS arch. It is also found that the proposed design formulas can effectively predict the out-of-plane bearing capacity of HSS arches.
本文对高强度钢(HSS)工字截面拱的面外极限强度进行了试验研究,这是以往未见报道的。对14个具有不同屈服强度、断面尺寸、细长度和升跨比的工字钢拱在三点对称垂直荷载作用下进行了试验研究。确定了相应的面外变形模式和强度。在此基础上,考虑残余应力和初始几何缺陷,对高钢拱进行了面外承载力的有限元分析。分析结果与实验结果吻合较好,证实了有限元模型和实验结果的准确性。综合分析了钢材屈服强度、升跨比、长细比对高钢拱极限承载力的影响。通过参数化分析,给出了任意压力和任意弯矩作用下高强钢拱面外承载力的设计公式。研究发现,钢的屈服强度对高钢拱的面外极限强度有显著影响。与低强度钢拱相比,塑性阶段高强度钢拱的面外极限承载力随着屈服强度的增加而增加,由于高强度钢的延性较低,高强度钢拱的极限侧向位移随着屈服钢强度的增加而减小。此外,在达到拱的面外极限承载荷载后,HSS拱的荷载-位移曲线下降速度快于LSS拱。提出的设计公式可以有效地预测高钢拱的面外承载力。
Analytical Modelling and Critical Temperature of Circular CFST Column Exposed to Standard Fire
Wei Li, Jie Hu
doi:10.1016/j.tws.2024.111900
CFST圆形柱在标准火灾下的解析模型和临界温度
This paper establishes a finite element (FE) model for the fire resistance analysis of concrete-filled steel tubular (CFST) columns with circular cross section with comparison of different modelling methods. This model is then validated by experimental results from a database consisted of 123 circular CFST columns fire tests. The critical temperature is clarified for the circular CFST column exposed to standard fire. The performance of circular CFST columns is discussed and extensive parametric study is performed by the FE model. The equation for the critical temperature of circular CFST columns to axial compression is proposed and compared with FE and test results. The results show that the established FE model well captures the CFST column behaviour exposed to standard fire, and the proposed critical temperature method can provide more accurate fire resistance predictions than current codes of practice.
本文建立了圆形截面钢管混凝土柱的耐火分析有限元模型,并对不同的建模方法进行了比较。然后通过123根CFST圆形柱的防火试验数据验证了该模型的有效性。阐明了CFST圆形柱在标准火下的临界温度。讨论了圆形钢管混凝土柱的性能,并通过有限元模型进行了广泛的参数化研究。提出了圆形钢管混凝土柱轴压临界温度方程,并与有限元和试验结果进行了比较。结果表明,所建立的有限元模型较好地反映了CFST柱在标准火灾下的行为,所提出的临界温度方法可以提供比现行规范更准确的耐火预测。
A new model for calculating the ultimate shear resistance of steel I-section girders
Luke Lapira, Leroy Gardner, M. Ahmer Wadee
doi:10.1016/j.tws.2024.111908
一种计算工字型钢梁极限抗剪承载力的新模型
The design resistance in shear of thin-walled I-sections has elicited numerous theories over the past decades. While there is a consensus on the post-buckling tension-field action that increases the ultimate resistance of thin webs in shear, the mechanism governing this tension-field action still remains debated. Presently, four constituent components for the shear resistance of I-sections are identified: (1) the resistance of the isolated web subject to a pure shear stress; (2) an increase in the web buckling stress due to flexural restraints provided by the flanges; (3) an increased web post-buckling resistance due to membrane restraint provided by the flanges; and (4) a direct contribution from the flanges to the shear resistance of the I-section. Each of these components is examined through parametric studies using finite element (FE) models analysed within Abaqus that are validated against published experimental results. A new design methodology for the resistance of I-sections in shear is presented, with closed-form expressions developed for each of the four component contributions. When compared with the current approach within EN 1993-1-5, the proposed formulae predict the shear resistance of the cross-section with greater accuracy and consistency.
在过去的几十年里,薄壁工字截面的抗剪设计引发了许多理论。虽然人们一致认为屈曲后的张力场作用会增加薄腹板在剪切中的极限阻力,但控制这种张力场作用的机制仍存在争议。目前,确定了工字截面抗剪能力的四个组成部分:(1)受纯剪应力作用的孤立腹板的抗剪能力;(2)由于法兰提供的弯曲约束,腹板屈曲应力增加;(3)由于法兰提供的膜约束,腹板屈曲后阻力增加;(4)法兰对工字截面抗剪能力的直接贡献。每个组件都通过参数研究进行检查,使用Abaqus中分析的有限元(FE)模型,并根据已发表的实验结果进行验证。提出了一种新的抗剪工字截面设计方法,为四个分量的贡献开发了封闭形式的表达式。与en1993 -1-5的现行方法相比,所提出的公式预测截面的抗剪能力具有更高的准确性和一致性。
Buckling analysis of a helical extension spring under combined loading
José González-Cabrero, Hugo Font, Francisco Cavas, Manuel Paredes
doi:10.1016/j.tws.2024.111914
螺旋伸缩弹簧在复合载荷作用下的屈曲分析
A new formula is introduced to analytically determine the critical torsional load or angle of rotation that confers instability in a tension spring under combined tension and torsion load using the theoretical framework of Greenhill's problem applied to an elastic bar as a starting point. The formula's effectiveness is evaluated with experimental torsion tests and finite element method simulations in Abaqus. The results demonstrate the formula's accuracy in predicting instability within specific stretched operating ranges, and achieving a relative error in correlation below 10% for most operating points. The study underscores the significance of preload and pre-stretching in enhancing the spring's resistance to buckling.
本文以弹性杆格林希尔问题的理论框架为出发点,提出了一种新的公式,用于解析确定张力弹簧在拉力和扭转载荷联合作用下引起失稳的临界扭转载荷或旋转角。在Abaqus中通过扭转试验和有限元模拟验证了该公式的有效性。结果表明,该公式在特定的拉伸工作范围内预测失稳是准确的,并且对大多数工作点的相关系数的相对误差在10%以下。研究强调了预加载和预拉伸对提高弹簧抗屈曲性能的重要意义。