挤压对灵武长枣应力应变影响的有限元分析

为了分析灵武长枣在采摘过程中内部应力应变对挤压的响应规律,为采摘机器人的设计提供理论依据,本文利用万能力学试验机在15、20、25、30、35 mm/min五种不同挤压速率下对灵武长枣整果进行了横向和纵向压缩,对力-变形曲线进行拟合,求得长枣在压缩破裂时的刚度及破裂力,并对15和35 mm/min两种横向挤压速率进行了有限元模拟,建立了有限元模型。结果表明:灵武长枣在受到挤压时,其力学性能具有各向异性,横向的抗压能力更强。横向压缩时,整果破裂负载为214.34~266.53 N,弹性模量为14.90~17.05 MPa,相对变形量为20.70%~22.67%;纵向压缩时,整果破裂负载为132.52~185.40 N,弹性模量为4.59~6.07 MPa,相对变形量为13.72%~17.25%。受力点的应力应变在果肉中是最大的,并沿赤道向果核周围延伸,且逐渐减小。压缩速率为15 mm/min的有限元模型的模拟值与其实验值的偏差为14.98%,35 mm/min的偏差为11.06%。运用有限元法对灵武长枣挤压模拟是可行的。     

Deformation behaviour simulation of an apple under drop case by finite element method

This study focuses on the deformation behaviour of organic materials under a drop case. A Golden Delicious apple was chosen as the sample organic material. A three-dimensional (3D) scanner, high speed camera and finite element method (FEM) simulations were utilised to investigate drop case deformation events of the organic material. In total, 22 steps after impact were set up in the simulation by comparing high speed camera screen steps. Maximum equivalent stress of 0.416 MPa and maximum contact force (resultant normal force from rigid plane at impact) of 250.980 N were obtained from simulation results. Visual investigations and simulation results relating to deformations observed under the drop case, agreed well. This study contributes to further our understanding of fruit and vegetable damage/deformation by using computer aided engineering applications.     

Predicting Cantaloupe Bruising Using Non-Linear Finite Element Method

In this study, the mechanical properties of the skin and flesh of cantaloupe were determined by individual experiments and then finite element simulation was developed for cantaloupe fruit under compression loading. The applied deformations were equal to 10, 20 and 30% of rupture deformation or 4.5, 9 and 13.5 mm, respectively. The results showed that the internal tissue of fruit reached to yield point in 20% of whole deformation or in force 90 N and the internal failure occurred with no visibility. The statistical comparison of finite element method results with experimental data was performed. The results showed finite element method was able to determine the force threshold of internal bruising for cantaloupe.     

Drop test simulation of a sample tomato with finite element method

BACKGROUND: The aim of this study was to investigate deformation behaviour of a biological material upon crashing. The 50 samples for the study were randomly selected from harvested tomatoes. RESULT: Mechanical parameters were obtained by a compression test of the chosen cherry tomato samples. The behaviour of the drop characteristics of cherry tomato was investigated using finite element simulation, and deformation characteristics were determined by a combination of the finite element results and measured data. A comparison between experimental data and finite element simulation shows that the two sets of results agree well. CONCLUSION: The results of this study provide the foundation for further investigations of the mechanical parameters of fruits and vegetables by using finite element simulations. Copyright © 2008 Society of Chemical Industry     

鲜枣整果力学特性研究及其有限元分析

为预测鲜枣在收获、贮运过程中的机械损伤,对甘肃靖远产小口大枣进行整果压缩特性研究及仿真分析。通过压缩实验,获得了不同加载速率条件下（10～30 mm/min）整果在横向和纵向上的弹性模量、破裂负载和破裂相对变形量：横向分别为：8.23～9.70 MPa、227.52～305.97 N、16.07%～17.46%;纵向分别为：10.05～11.44 MPa、288.50～383.17 N、16.33%～20.12%。通过观察鲜枣破裂特征,建立鲜枣压缩力学有限元模型,比较鲜枣在横向和纵向受压的模拟值和实验值,最大差异为11.4%。结果表明：鲜枣的抗挤压能力具有各向异性（相同压力下,鲜枣横向放置时的变形量大于纵向放置;相同压缩位移下,纵向承载压力大于横向）。在验证了仿真数值可行的基础上,利用有限元法可分析鲜枣内部应力应变的分布情况。研究结果可为鲜枣的作业装备设计以及减少其机械损伤提供理论依据。     

Determination of Drop-Test Behavior of a Sample Peach Using Finite Element Method

It is very important to determine mechanical damage quantity of fruit and vegetables during harvesting, handling, transportation, and storage. Specifically, determining damage quantity of agricultural products is very difficult on existing external forces. However, one of the useful methods is the finite elements method that can be used in different engineering disciplines to simulate the behavior of materials under the defined boundary conditions. In this study, a drop-test simulation was performed for peach samples by means of finite elements method. Some mechanical properties of the sample were measured by an experimental study (compressive test) and the obtained data were used in the finite elements method simulation. The stress-strain and force-deformation curve of peaches were determined as maximum force, Poisson’s ratio, specific deformation, modulus of elasticity, stress, and deformation energy were found to be: 59.6 N, 0.29, 10.9%, 0.89 Nmm^–2, 1.19 Nmm^–2, and 162.2 Nmm, respectively. At the end, the distribution of stress and shape of deformation of sample peaches at impact was obtained. When the stress magnitudes were evaluated, simulation outputs showed that simulation stress values are quite a bit compatible with experimental data.     

Finite element analysis of monofilament woven fabrics under uniaxial tension

Mechanical behavior of woven fabrics under tensile load is complex because their deformation could result from the combined effects of tension, compression, bending, and shear. In this study, the tensile behavior of woven fabrics is simulated using finite element method. The input parameters are the mechanical properties of constituent yarns obtained from tensile and friction coefficient tests and the geometry of woven fabric repeating unit. First, a 3D geometric model of the repeating unit based on Pierce’s model was built using computer-aided design tools. Then, finite element analysis which incorporates material properties, frictional contact, and periodic boundary conditions was implemented using ANSYS. A non-linear mechanical behavior was defined. Frictional contact algorithm for the cross-sectional zone of the repeating unit and periodic boundary conditions to the contour of the repeating unit was implemented. Numerical simulation data and experimental data were compared, which showed good agreement.     

响应面法结合模糊数学优化南瓜籽酸奶发酵工艺

为了探究南瓜籽酸奶最优发酵工艺及参数,以南瓜籽和牛奶为主要原料,在单因素试验的基础上,应用响应面法结合模糊数学综合评价南瓜籽酸奶发酵工艺及参数。结果表明,南瓜籽酸奶发酵工艺最佳参数为：质量分数为17%的南瓜籽浆与牛奶的体积比为1∶1,蔗糖添加量为质量分数的9%,发酵剂为12种酸奶菌,菌种添加量为5 g/L,发酵时间为6 h,此条件下南瓜籽酸奶的感官评分为8.27,颜色微绿,质地丝滑,入口柔顺,有南瓜籽的香味,凝固性好。     

对数应变幂次强化本构模型研究

就有限压缩变形规律 ,对阿尔曼西应变和对数应变的适用性作了比较 .以铅的实验数据为例 ,采用对数应变—真应力描述给出了幂次强化本构方程 ,并在此基础上进行了有限元计算分析 .定出最佳回归参数 :强化系数B =10 0 0 ,强化指数n =0 0 6 2 5 2 .使用该方法得到的变形量与理论值非常接近 ,且叠代收敛次数少 ,计算效率高 ,计算过程适用于其他金属材料有限变形的研究     

橡胶果破壳力学特性试验与分析

为研究橡胶果在不同条件下静态压缩破壳力的变化规律,对橡胶果分别进行X、Y、Z 3个加载方向的剪切力、锥刺力、挤压力的静态压缩试验;运用有限元法建立橡胶果的力学模型,研究橡胶果在压缩载荷作用下应力应变情况及损伤规律。试验结果表明:橡胶果在剪切力、锥刺力、挤压力下的破壳力大小关系为F_(挤压力)F_(剪切力)F_(锥刺力);橡胶果较佳的加载方向为Y方向;试验中Ⅰ类、Ⅱ类、Ⅲ类橡胶果的挤压破壳力分别为0.548 0,0.564 5,0.715 1 kN,破壳力随着橡胶果尺寸的增加而增加;有限元分析出最佳加载方向为Y方向,与试验结果一致。     

基于分形的棉条建模及其牵伸过程的仿真

为分析计算棉条牵伸力的变化，以提高棉纤维牵伸的质量，依据分形理论的建模思想，将具有相同圆形截面的棉纤维按照分形理论进行排列，构建了新的棉须条模型。基于动态牵伸和静态牵伸的相似性，将该模型进行静态拉伸仿真，得出不同定量的棉条静态牵伸力。结果显示须条静态拉伸力与动态牵伸力的平均误差为5.66%,最大相对误差在12%以内。利用线性拟合求出动态牵伸力与静态牵伸力的关系式，成功预测了不同定量下的牵伸力。此外，得出了在定量为25.60 g/m时，静态牵伸力随牵伸倍数的变化曲线。结果表明仿真牵伸力与动态牵伸力的变化趋势基本一致。建立的分形须条模型有效，也为动态牵伸力的近似预测提供参考。     

Experimental investigation and numerical simulation of three-point bending fatigue of 3D orthogonal woven composite

This paper reports the three-point bending fatigue behavior of three-dimensional (3D) orthogonal woven composite (3DOWC) in experimental and finite element analysis (FEA) approach. In experimental, the S–N curve was obtained to illustrate the relationship between applied stress levels and number of cycles to failure. The stiffness variation was recorded to present the degradation of mechanical properties of the 3DOWC during the process of fatigue loading. Furthermore, the fatigue damage morphologies of the tested 3DOWC coupons were given to indicate the damage modes of different parts (resin, yarns, and their interface) of the composite under the range of stress levels. In FEA approach, a user-defined material subroutine UMAT which characterizes the stiffness matrix and fatigue damage evolution of the 3DOWC was developed and incorporated with a finite element code ABAQUS/Standard to calculate the maximum deflection of the 3DOWC during each loading cycle. The bending deformation at different loading cycles was also calculated. From the comparisons between FEA and experimental approaches, it is indicated that the proposed model is reasonable for calculating the fatigue bending deformation.     

Computational modeling of dough sheeting and physical interpretation of the non-linear rheological behavior of wheat flour dough

Controlling the dough sheeting processes has been a long standing challenge in the food industry. This paper presents the results of a study aimed at developing a validated finite element model for simulating dough sheeting processes. An instrumented, two-roll dough sheeter was constructed to measure roll forces and dough thickness during sheeting. To develop a rheological model, true rheological properties of dough were measured in compression and extension. A filament stretching device was constructed to obtain consistent data for dough extension. Results showed dough to be a non-linear, rate-dependent material that was capable of undergoing large deformations with only moderate elastic recovery. Freshly mixed dough had additional complexities of anisotropy and Mullins softening. The Bergstrom–Boyce model, which has been known to capture large deformation behaviors of lightly cross-linked elastomers, was modified to include anisotropy and Mullins softening and applied to dough. The sheeting process was modeled in finite element simulations as a plane-strain rolling operation using the commercially available software, Abaqus. The simulation predictions were in good agreement with experimental data for both roll forces and dough thickness. Techniques for controlling dough flow rates utilizing on-line, roll force measurements have been projected. Future studies for delineating sheeting effects on dough structure have been identified.     

Identification of the geographical origin of pumpkin seed oil by the use of rare earth elements and discriminant analysis

The aim of this work was to develop an analytical method to assure the geographical origin of Styrian pumpkin seed oil, a high priced local product which is protected by the European Union. The development of such a method is not only of interest for scientists but also of importance for producer that want to guarantee the purity and quality of their products as well as the consumer wanting to know the origin of the food products.Since the rare earth elements (REE) concentrations are extremely low in pumpkin seed oil a fast and sensitive analytical method with ICP-MS had to be developed and validated. In the current project, pumpkin seeds from different regions in Austria were sampled. The REE patterns in the extracted oil of these seeds were determined and a preliminary classification with discriminant analysis was successfully done on a statistical basis.The study demonstrates that pumpkin seed oils from different geographical origin show variable rare earth element patterns making it possible to trace the origin of these oils.     

Hen’s eggshell strength under impact loading

An experimental method for evaluation of an eggshell’s mechanical characteristics under impact loading is discussed. Proposed experimental set up enables recording of time history of the force at the contact area between the rod and eggshell, as well as the vibration response of the tested egg. By the gradual increasing of the rod impact velocity, a rupture force of the eggshell was determined. The value of this force depends on the position of the rod impact. This dependence is more significant than that of static loading of the eggs. The preliminary results also show the non-negligible dependence of rupture force on the loading rate. An introductory numerical simulation of the given test was also performed. The LS DYNA finite element code was used. Numerical results exhibit reasonable agreement with experimental results.     

X型方钢管节点平面内受弯性能研究

为考察X型方钢管节点在平面内弯矩作用下的静力性能,通过ABAQUS进行建模及非线性有限元计算,结合验证性试验,对节点的破坏模式、应变强度发展过程、极限承载力进行研究,并讨论轴力和平面内弯矩联合作用对节点极限承载力的影响．结果表明：节点在平面内弯矩作用下,发生弦杆受拉侧鼓凸,受压侧凹陷,腹杆受拉侧焊缝被拉开;节点弦杆最先进入塑性,最终由于塑性变形过大而导致试件破坏;试件极限承载力随着届值的增大而增大;在轴力和平面内弯矩联合作用下,节点的受弯极限承载下降．     

Finite element analysis of penetration force for needle during tufting process

Tufted carpet is one of the most used carpets. The penetration force of needle is an important factor in tufting process. Few know how to calculate the penetration force during the tufting, although the principle is one of the least understood processes. This paper presents our research on using finite element method (FEM) to study the penetration force of needle during tufting. In this study, the model is developed using ABAQUS software, and the material properties of nonwoven fabric are approximately modeled by linear elastic orthogonal anisotropic continuum. The required engineering constants were obtained from experimental test. A user-defined subroutine VUMAT for characterizing the constitutive relationship of the orthogonal anisotropy nonwoven fabric and the damage evolution was compiled and connected with a commercial software package ABAQUS/Explicit to calculate the penetration force. At the same time, needle penetration force was tested by sensor mounted on needle bar of tufting machine. It was found that there is an approximate agreement of the penetration force between FEM calculations and experimental results. The reasonable agreement proves the validity of finite element analysis model, which could be used to calculate the impact response of the needle penetration stress precisely. The finite element model has been verified experimentally and can be used to study the influence of the key tufting parameters such as the backing material properties and the needle geometry on penetration force, which is vital for designing needle and driving mechanism.     

电动钉枪性能试验台植入组件移动板设计

根据电动钉枪性能试验台的工作原理,植入组件移动板的设计要求是：在有足够刚度的前提下,质量尽可能小。文章在对移动板进行受力分析的基础上。针对方形移动板和蝴蝶型移动板2种方案。用有限元分析了其在外载荷作用下的变形。对蝴蝶型移动板设计方案给予了肯定。然后,研究了在外载荷作用下,蝴蝶型移动板的厚度对其变形量的影响,最终得出较为合理的移动板设计方案。图6表2参6     

南瓜子粉加工工艺中乳化稳定性的研究

对南瓜子粉加工工艺中的乳化稳定性进行了研究。采用包埋剂包裹瓜子仁中的油脂,乳化剂、稳定剂解决瓜子浆中蛋白质和脂肪的分层问题,获得了理想的成粉效果。试验结果表明,添加配料(占瓜子浆总固形物)的最佳配方为:麦芽糊精40%、黄原胶1%、复配乳化剂2%。其中复配乳化剂由32∶1∶的单甘酯、蔗糖酯和吐温-80组成,HLB为9.4。     

A composite model for wheat flour dough under large deformation

The mechanical behaviour of dough, gluten and starch were studied in an effort to investigate whether bread dough can be treated as a two phase (starch and gluten) composite material. Mechanical loading tests revealed rate dependent behaviour for both the starch and gluten constituents of dough. There is evidence from cryo-Scanning Electron Microscopy (SEM) that damage in the form of debonding between starch and gluten occurs when the sample is stretched. In addition, a reasonable agreement is seen between the Lodge material model and the compression test data only, indicating again that possibly ‘damage’ is essentially debonding which does not occur under compression, unlike tension and shear loading. A composite finite element model was developed using starch as filler and gluten as matrix. The interface between the starch and gluten was modelled as a cohesive contact interaction. When the interaction of starch and gluten is strong, as indicated for the dough with no damage, the stress-strain curve is always higher than the gluten stress-strain curve under both tension and shear loading. In contrast, when damage is activated in the form of debonding, the dough stress-strain curves under tension are seen to cross over the curves for gluten and therefore leading to lower stress values than in gluten. No damage/debonding occurs under compression when a damage function is used which is in good agreement with the experimental data.