层合瓦楞纸板三向静态平压性能研究

通过静态压缩试验,对B楞和C楞层合瓦楞纸板X,Y,Z3个方向的平压性能进行了研究,并绘制了其载荷-变形曲线和应力-应变曲线。纸板的载荷-变形曲线表明：压缩时各纸板3个方向的曲线走势类似,都有一段线性变形部分,当载荷达到最大值后,X向和Z向的曲线呈波浪状下降,而Y向的曲线近似于水平波动。纸板的应力-应变曲线表明：3个方向的压缩中,Z向的压缩强度值最大,X向次之,Y向最低,Z向值为X向的3～6倍,为Y向的12～14倍。此外还对瓦楞纸板平压强度与Y向压缩强度的关系和瓦楞纸板边压强度与Z向压缩强度的关系进行了分析。     

瓦楞纸板托盘结构及性能研究

目的探讨瓦楞纸板托盘结构与性能的关系。方法托盘由铺板和垫块或纵梁粘合而成,铺板为1块3A楞瓦楞纸板或2块AB楞瓦楞纸板粘合而成,垫块或纵梁通过瓦楞纸板层叠粘合或卷绕成型,利用抗弯和抗压试验测试托盘抗弯强度和抗压强度,并分析托盘力学性能。结果托盘抗弯性能主要与铺板瓦楞纸板层数有关,1块3A楞瓦楞纸板铺板的抗弯性能优于2块AB楞瓦楞纸板粘合铺板;托盘抗压性能与垫块或纵梁结构有关,层叠粘合成型的垫块或纵梁的抗压性能优于回字卷绕成型的,抗压强度可达到33.48 k N;B楞瓦楞纸板层叠粘合成型的垫块或纵梁的抗压强度优于AB楞的;垫块的抗压强度优于纵梁。结论通过对瓦楞纸板托盘结构、抗弯性能、抗压性能的研究与测试,可为实际应用提供参考和依据。     

Stress Plateau of Multilayered Corrugated Paperboard in Various Ambient Humidities

This paper presents a mathematical model to predict the stress plateau of multilayered corrugated paperboard under flatwise compression in various humidity environments. The model relates the stress plateau to the thickness‐to‐flute pitch ratio of corrugated core cell, the yield stress of corrugated medium and the relative humidity in surrounding air. Multilayered corrugated paperboards with a wide range of thickness‐to‐flute pitch ratios are investigated under several levels of ambient humidities to explore the effect of relative humidity on the stress plateau of multilayered corrugated paperboard. Comparison of the predictions and experiments is made, and a good correlation is achieved corroborating the feasibility and accuracy of the model. The proposed method can be used for practical application of the optimum design and material selection of multilayered corrugated paperboard. Copyright © 2011 John Wiley & Sons, Ltd.     

基于屈曲准则的瓦楞纸板强度仿真分析

分别建立了典型的A、C、B楞型单瓦楞纸板的有限元模型,计算了3种瓦楞纸板的临界屈曲载荷。以临界屈曲载荷为纸板抗压能力的判定准则,定量分析了3种瓦楞纸板的抗压能力,同时研究了材料与结构对瓦楞纸板抗压能力的影响及每种瓦楞纸板的材料抗压效率。分析结果表明,大瓦楞有更好的抗压能力,其抗压能力的提高主要是依靠其结构实现的,约束条件能够极大地改变瓦楞纸板的抗压效率。     

Theoretical framework for estimating a product's reliability using a variable‐amplitude loading spectrum and a stress‐based approach

An innovative approach for predicting the reliability of a structure that is subject to a variable‐amplitude dynamic load is presented. In this approach, a Gassner durability curve with its scatter is modelled using a 2‐parametric Weibull's probability density function (PDF). The trend of the Gassner durability curve is modelled with a general hyperbola equation in a log‐log scale. The hyperbola equation is applied to represent the durability curve for the 63.2% probability of fatigue failure that describes the dependency of the Weibull's scale parameter on the loading spectrum's maximum stress. Equations are derived to link the parameters of the hyperbola curve to the material's S‐N curve and the loading spectrum. The Weibull's shape parameter is estimated from the scatter of the material's S‐N curve. The proposed Gassner‐curve model is applied to calculate the fatigue reliability from the PDF of the loading spectrum's maximum stress and the PDF of the durability‐curve's amplitude stress for the selected number of loading‐cycles‐to‐failure.     

Energy method of calculating longevity under an irregular loading. Report 1. Consideration of loading sequence

A method of predicting longevity under a programmed loading to the formation of a fatigue crack, which is based on an energy criterion of fatigue failure, is proposed. Kinetic diagrams and a model of the cyclic deformation of the material were used to calculate energy dissipation during the loading cycles. A differential equation of the accumulation of relative energy, which enables us to derive the equation of the fatigue curve from single positions, and relationships for calculating longevity under irregular symmetric and axisymmetric loadings are formulated. The computed results are compared with experimental data for 40Kh steel with stepwise variation in loading.Translated from Problemy Prochnosti, No. 7, pp. 3–12, July, 1995.     

瓦楞结构纸蜂窝夹层的动态性能研究

比较了瓦楞结构蜂窝夹层和普通蜂窝夹层用纸量的差别,用聚醋酸乙烯酯乳液作为黏合剂,使用不同楞型和定量的瓦楞纸板制得瓦楞结构蜂窝夹层,利用冲击实验机研究其动态性能。结果表明:瓦楞结构纸蜂窝夹层受到冲击时会产生规则的褶皱变形,从而吸收冲击能量;瓦楞结构纸蜂窝夹层所用瓦楞纸板定量越大,用纸质量越好,试样受到冲击时产生的冲击加速度值就越大;在冲击高度确定的条件下,随着冲击重锤重量的增加,不同纸板所制试样其最大冲击加速度值都会有一个极小值,该极小值与材料本身有关。     

Quantification of banding on printed corrugated board using spatial frequency analysis

The human visual system has an exceptional ability to detect systematic print mottle. One type of systematic print mottle is banding on printed corrugated board, resulting in a disturbing print defect. A new method that quantifies banding on printed corrugated board is proposed. The method is based on spatial frequency analysis, and the degree of banding is determined using a band‐pass filter range adapted to fit the flute wavelength and orientation of the acquired image of the printed board. The results for B‐flute corrugated board gave a correlation coefficient of 0.98 between the technical measurements and the subjective ratings. Methods of quantifying the banding on the different types of corrugated board available on the market are discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Bond behaviour of high‐strength concrete flexural member under low cyclic fatigue loading

Use of high‐strength concrete can lead to more economical design reducing the material requirements, weight of structure and extended service life of structure. The effect of fatigue loading is more prominent on the structures using high‐strength concrete. Bond between concrete and reinforcing bars is a major factor affecting the performance and sustainability of reinforced concrete structures. Less research is available on the effect of low cyclic fatigue loading on the bond strength of high‐strength concrete. In this research, reinforced concrete beams (1165 × 150 × 225 mm) were tested under low cyclic loading with different stress range levels. It can be concluded that the bond strength of high‐strength concrete is more than for normal‐strength concrete. Low‐cyclic fatigue loading decreased the bond strength under monotonic loading by about 43–45%. Energy dissipation during cycling is found to be good. At higher cycles, energy dissipation decreased because of local damages in front of bar ribs. With the increase in number of cycles, change in slip behaviour was found.     

A theoretical and experimental study on corrugated paperboard crushing under quasi‐static loadings

This paper presents 2 mathematical models to predict the initial peak stress and the plateau stress of corrugated paperboard which is simplified and regarded as the orthotropic plate under longitudinal compression. The resultant stress‐strain curve exhibits initial stiffening stage and a long plateau stage, where the initial peak stress determining the edgewise crush resistance of the board and most impact energy will be absorbed by the long plateau stage. By analyzing the elastic buckling of the board wall, a model of predicting the initial peak stress was obtained, while the plateau stress model was developed based on the gradual process of compression for corrugated board and energy conservation principle. Moreover, experiments were carried out to corroborate the presented model by comparing the predicted value with that by experiments, showing overall good agreement. It can be concluded that the proposed models can be applied for design of corrugated containers and cushioning packaging by corrugated paperboard.     

立式瓦楞复合纸板静态压缩试验与有限元分析

目的对立式瓦楞复合纸板的静态压缩过程进行试验研究和有限元分析,研究不同楞型立式瓦楞复合纸板的力学性能。方法制作A楞、AB楞、B楞等3种不同立式瓦楞复合纸板试样,进行静态压缩实验,得到其压缩应力-应变曲线;建立3种楞型的立式瓦楞复合纸板有限元模型,进行静力学分析,得到其压缩应力-应变曲线,并与实验结果进行对比分析。结果试验和有限元分析均显示立式瓦楞复合纸板的静态压缩过程与蜂窝纸板的静态压缩过程类似,包括弹性阶段、屈服阶段、平台阶段、密实化阶段,试验和有限元分析所得到的压缩应力-应变曲线相吻合。纸板的峰值应力和平台应力与楞型有关,且随着楞高的增大而减小。结论通过试验研究和有限元分析方法得到了不同楞型立式瓦楞复合纸板的静态压缩性能,对该新型材料的应用有重要参考价值。     

Material damping in 6061-T6511 aluminium to assess fatigue damage

Studies in fatigue can be summarized into two stages, fatigue crack initiation and crack propagation. Fatigue damage may increase the risk of failure under cyclic load. Energy dissipation, termed damping, occurs in engineering metals and is a function of the cyclic loading history. Damping behaviour of materials has been estimated using many different experimental techniques, and parameters i.e. the loss factor vs. strain amplitude, frequency range, etc. However, micro‐structural changes in the form of fatigue damage are also contributors to damping in engineering materials. In order to measure energy dissipation, a damping monitoring method has been used. Under a constant cyclic load up to the point of fatigue crack initiation, the effects of fatigue on damping factor were studied for 6061‐T6511 aluminium alloy. In the experiments, the stress levels were below yield point, 50% and 70% of ultimate strength. Experimental results showed that the damping factor changes with the number of fatigue cycles. Percentage increase in damping energy was calculated using experimental data.     

The Influence of Package Size and Flute Type of Corrugated Boxes on Load Bridging in Unit Loads

Shipping pallets often are designed with the assumption that the payload carried is flexible and uniformly distributed on the pallet surface. However, packages on the pallet can act as a series of discrete loads, and the physical interactions among the packages can add stiffness to the pallet/load combination. The term ‘load bridging’ has been used to describe this phenomenon. The study reported in this paper investigated the relationships of package size, corrugated flute type and pallet stiffness to load bridging and the resulting unit‐load deflection. The experimental results indicated that an increase in box size changed the unit‐load deflection by as much as 75%. Flute type was found to impact load bridging and the resulting unit‐load deflection. Changing the corrugated box flute type from B‐flute or BC‐flute to E‐flute reduces the unit‐load deflection by as much as 40%. Also, experimental data indicates that the effect of package size and corrugated board flute type on pallet deflection is the greatest for low stiffness pallets. The results provide information that can be used to design unit loads that use material more efficiently. Copyright © 2017 John Wiley & Sons, Ltd.     

Modelling the impact of crushing on the strength performance of corrugated fibreboard

This paper presents different ways of modelling the strength of corrugated fibreboard (CFB) subjected to different levels of pre-crushing. The strength performance was measured through four-point bending loading and edge crush test (ECT). The models used in this study were an analytical solution, an equivalent flute model, and detailed flute geometry models that consisted of idealized sine geometry and real geometry. The study found that the bending performance was dependent on the calliper of CFB rather than the flute geometry. All models showed a similar trend in predicting the drop in bending stiffness as the level of pre-crushing increased, albeit with different absolute value. It was found that the real geometry model of the board predicted ECT performance better than the other models. However, at severe pre-crushing levels (>50%), there was a significant drop in the experimental ECT force not predicted by the models. For these cases, there was evidence of delamination of the flute, a failure mechanism that was not included in any of the models. The analytical solution model provides the quickest prediction but could not predict the crushed ECT performance due to not considering the calliper variable in the equation. The equivalent model showed faster solving time compared with both real and idealized geometry models, although these microgeometry models predicted ECT the most accurately.     

Quasi‐static and Impact Responses of Multi‐layered Corrugated Paperboard Cushion by Virtual Mass Method

Quasi‐static compressive and impact behaviours of multi‐layered corrugated paperboard (MLCP) cushioning structure were analysed by a recently proposed virtual mass method. First, virtual mass method was applied and verified analytically to solve quasi‐static compressive responses for representative two‐layer corrugated paperboard cushioning structure. The results show that the two layers in the cushioning structure reach the buckling state in chronological order because of the existence of the small perturbations triggered by inertial force related to virtual mass, which leads to the two typical stress peaks in stress–strain curves. Second, the quasi‐static compressive behaviours of MLCP cushioning structure were further studied numerically, showing that the buckling order of multi‐layer cushioning structure depends on virtual mass, but the stress–strain curves remain unchanged when the virtual mass is smaller than some certain value. Finally, quasi‐static and dynamic impact tests of MLCP cushioning structure composed of C‐flute corrugated paperboard were carried out to further validate the capacity of the virtual mass method to describe layer‐wise collapse mechanism given the constitutive relationship of the monolayer corrugated paperboard. Copyright © 2014 John Wiley & Sons, Ltd.     

Fatigue analysis of unidirectional GFRP composites under combined bending and torsional loads

Fatigue behavior of unidirectional glass fiber reinforced polyester (GFRP) composites at room temperature under in-phase combined torsion/bending loading was investigated. All fatigue tests were carried out on constant-deflection fatigue machine with frequency of 25 Hz. A 30% reduction from the initial applied moments was taken as a failure criterion in the combined torsion/bending fatigue tests of the composite materials. A series of pure torsional fatigue tests were conducted to construct the failure contour of GFRP composites using different failure theories. The obtained S–N curves from combined torsion/bending tests were compared with both, pure torsion fatigue test results and published results of pure bending fatigue tests of GFRP rods. Pictures by scanning electron microscope were used to closely examine the failure mode of the tested specimens under combined torsion/bending loading.

The results showed that, the unidirectional glass fiber reinforced polyester composites have poor torsional fatigue strength compared with the published results of pure bending fatigue strength. Endurance limit value (calculated from S–N equation at N = 10⁷ cycles) of GFRP specimens tested under combined torsion/bending loading equals 8.5 times the endurance limit of pure torsion fatigue. On the other hand the endurance limit of combined torsion/bending fatigue strength approximately half the fatigue limit of pure bending fatigue strength. The predicted values of combined torsion/bending fatigue strength at different number of cycles, using the published failure theory are in good agreement with the experimental data. For the investigated range of fiber volume fractions (V_f) it was found that higher stress levels are needed to produce fatigue failure after the same number of cycles as V_f increases.     

Development of a new device to perform torsional ultrasonic fatigue testing

The interest in gaining experimental knowledge on fatigue strength of materials over 10⁹ cycles is rapidly increasing as evidenced for the large amount of investigations on this subject presented at the last very high cycle fatigue meeting (VHCF-3), held on September 2004. Most of the fatigue results presented at this conference were obtained under tension-compression, rotating bending, flexion and bending cyclic loading (some attaining 10¹⁰ cycles), using ultrasonic devices whose design was based on the natural frequency principles. In general, very little literature concerning the metallic alloys behavior under torsion cyclic loading using ultrasonic is available; however, in order to perform an accurate component design under multi-axial loading and VHCF, the material behavior under torsion cyclic loading is required. This investigation presents the development of a new mechanical device for testing and characterizing metallic alloys in the range of 10⁹–10¹⁰ cycles in torsional cyclic loading and the first experimental results for medium carbon steel (38MnSV5S). The new device was designed to excite the components under testing with pure torsional vibration mode at a frequency of 20 kHz.     

Application of an energy model for fatigue life prediction of construction steels under bending, torsion and synchronous bending and torsion

The paper contains a mathematical model of the material’s behaviour under cyclic loading taking into account the dynamics of the fatigue process, including the number of cycles to failure, induced by the mean stress value. The coefficients in the proposed model have been obtained from experimental tests under symmetrical and nonsymmetrical loading (with the stress ratio R=0). The proposed model has been used in order to modify an energy criterion with the aim of accounting for the influence of the mean stress on the fatigue life. The fatigue tests have been performed for structural steels 10HNAP and 18G2A subjected to cyclic bending, torsion and synchronous bending with torsion, by considering different values of the mean stress. A good agreement between the calculated and experimental results has been obtained.     

层合瓦楞纸板结构沿瓦楞方向的准静态压缩性能研究

试验研究了层合瓦楞纸板结构沿瓦楞方向的准静态压缩性能。研究结果表明:该结构准静态压缩载荷-变形曲线可分为2段——线弹性段和褶皱化变形段;楞型不同、厚度相同的样品,其准静态压缩最大值与瓦楞纸板的边压强度完全相关;楞型相同、厚度不同的样品,随着厚度的增加静态压缩最大值逐渐降低,厚度对载荷最大值所对应的变形值的影响不大。     

Schwingfestigkeitsbewertung von Nahtenden unter kombinierter Beanspruchung

In the present study, a local stress based concept for the fatigue assessment of weld ends in thin sheet structures under combined normal and shear loading is introduced. The notch stresses were calculated using the finite element method and submodel technique. An idealised weld end model was used in order to determine the stress state for such loading situations. Moreover, a numerical method was used to consider size effects, which combines both the geometrical and statistical size effects, to an integrated approach. Therewith and in connection with the cycles‐to‐failure from fatigue test results, a standardised S‐N curve was derived.