果实亚临界损伤边界曲线

以洛川富士苹果为实验材料,研究了果实在临界损伤高度以下,跌落高度对其贮藏时间的影响,构建了洛川富士苹果的亚临界损伤边界曲线。结果表明,在临界高度以下,果实不会出现损伤,但其贮藏时间会缩短;跌落高度越高,贮藏时间缩短越明显;与传统损伤边界曲线相比,亚临界损伤边界曲线依赖于果实的贮藏时间。     

跌落冲击对苹果呼吸速率的影响

目的研究亚临界载荷对苹果呼吸速率变化的影响机制。方法首先通过在跌落临界高度以下设置不同高度的苹果跌落实验;然后测量跌落后的苹果在密封容器内CO2和O2浓度的变化;最后根据实验数据得到跌落高度与苹果呼吸速率的关系。结果在亚临界高度下,苹果受到损伤冲击后的呼吸速率发生了较大变化。在相同的时间内,跌落高度越高,密闭容器中O2的含量越少,CO2的含量越多,呼吸速率越大。随着跌落高度的增加,氧气的减少率越来越大,二氧化碳的增加率也越来越大。在同一跌落高度下,随着时间的增加,苹果的呼吸速率逐渐减小,当达到一定时间后,呼吸速率趋于平稳。根据实验数据建立了亚临界载荷下呼吸速率与跌落高度和时间的数学模型。结论研究结果有助于果品缓冲包装的改进。     

苹果临界跌落高度和损伤脆值的试验研究

目的研究苹果的损伤率与临界损伤脆值的关系。方法利用自制摆锤冲击试验机设计多个高度的苹果跌落试验,分析苹果跌落冲击过程的损伤特性,得到临界跌落高度;在临界跌落高度以上的高度进行跌落试验,得到苹果在跌落过程中的加速度-时间曲线。结果结合试样在不同高度跌落所得的峰值加速度幅值,得到了试样的损伤脆值;根据不同跌落高度下的苹果的损伤体积,得到了苹果在不同损伤率下的损伤脆值。结论研究得到的损伤脆值与损伤率的关系对苹果缓冲包装的改进具有参考意义。     

亚临界载荷对樱桃番茄呼吸强度的影响

目的分析单个樱桃番茄在亚临界载荷下受到跌落冲击而发生的延时损伤,以及这种损伤对果品呼吸强度的影响。方法以樱桃番茄为研究对象,设计多组跌落高度实验分析其损伤程度与跌落高度的关系,得出樱桃番茄的临界跌落高度。设计临界高度以下不同高度的对比实验,然后把跌落后的樱桃番茄放入密封的保鲜盒内,在相同的条件下间隔时间测量其CO2/O2浓度的变化。最后,绘制出跌落高度与呼吸速率的关系图,根据数据拟合出亚临界载荷强度与呼吸强度关系的数学模型。结果临界高度以下,樱桃番茄受到损伤冲击后的呼吸速率会发生变化;跌落高度越高,在贮藏初始阶段,樱桃番茄的呼吸速率下降越快,最后趋于平衡;跌落高度越高,呼吸速率越大。结论研究结果对果品包装上的改进具有重要价值。     

皇冠梨采后冲击损伤影响因素研究及模型预测

目的 考虑到皇冠梨在储运过程中损伤严重,探究跌落冲击及果实本身特性对水果的损伤的影响,为皇冠梨的减损提供理论依据。方法 以河北赵县皇冠梨为研究对象,研究跌落高度、接触材料、果实硬度、曲率半径以及环境温度对皇冠梨冲击损伤的影响,并利用多元线性回归分析方法,建立皇冠梨果实的损伤预测模型（P≤0.05）。结果 跌落高度与损伤面积呈线性相关,皇冠梨分别与钢板和橡胶板冲击时产生临界损伤的跌落高度为30 mm和50 mm,而与本实验选取的EPE板和瓦楞纸板冲击时产生临界损伤的跌落高度为220 mm和340 mm。皇冠梨与EPE板冲击时表现为当跌落高度小于400 mm时,果实曲率半径越小,损伤面积越大;当跌落高度大于400 mm时,较大的曲率半径导致更大的损伤面积,果实硬度越小,冲击时损伤面积越大,环境温度越高,损伤越严重。结论 接触材料种类和果实本身特性对水果冲击损伤有较大影响。依据试验结果建立了损伤预测模型,预测模型可为皇冠梨自动化采摘、分级装备以及贮存、运输包装提供一定的理论指导。     

一种马铃薯临界损伤跌落高度的测定方法

针对马铃薯这类不易观察跌落损伤的果蔬产品,提出了一种测定其临界损伤跌落高度的方法。首先对马铃薯进行准静态压缩,得到其产生损伤时的压缩变形量。同时,通过测量马铃薯在不同跌落高度下的跌落信号,分析得到反映不同跌落高度与跌落变形量之间关系的数学模型。对应压缩变形量在此数学模型中的值,即可得到马铃薯的临界损伤跌落高度,为38cm。     

跌落损伤脆值及损伤边界

提出了跌落损伤脆值与跌落损伤边界的新概念,并提出了测定获取跌落冲击损伤脆值与跌落损伤边界曲线的技术过程与方法.以嘎拉苹果为研究对象,设计多组高度对嘎拉苹果进行自由跌落刚性冲击试验.在测试获得冲击力-时间数据的基础上,通过理论分析计算,得到加速度-时间、变形量-时间等动态关系曲线,获得了嘎拉苹果跌落损伤脆值;构造了嘎拉苹果跌落损伤边界曲线.结果表明,跌落损伤边界曲线与传统产品跌落破损边界曲线存在较大差异.对应果品类产品,即使速度很小,只要产品瞬时加速度达到一定值,也将产生冲击损伤;对应不同的损伤率,可构造相应的多条损伤边界曲线.提出的概念及研究结果为控制果品类产品的跌落损伤、合理地进行缓冲包装设计提供了新的理论基础.     

单自由度模型苹果脆值的预测

目的 以苹果为研究对象,建立一种易操作的脆值测定方案对苹果进行缓冲包装设计和分析。 方法 通过静态压缩试验测得苹果的线刚度,通过跌落试验测出破损临界跌落高度,进而基于单自由度理论模型计算出苹果脆值。根据苹果的脆值和缓冲材料的静态缓冲系数设计出最优包装方案。最后,模拟公路随机振动和跌落试验评价上述缓冲方案的可行性。结果 无泡沫网苹果的破损临界跌落高度为 5 cm,线刚度为106.59 kN/m,固有频率为109.79 Hz;带泡沫网苹果破损临界跌落高度为10 cm,线刚度为104.48 kN/m,固有频率为106.58 Hz,临界脆值Gc约为96.28。据此,按照80 cm的搬运跌落高度设计时,缓冲材料EPE厚度需要达到1.98 cm。结论 建立的脆值测定方案具有精准度高,且较传统脆值测定方法对仪器依赖度低,具有操作简便易行、普适性强等优点,易于推广到其他类型包装件脆值的测定。     

单层与多层苹果跌落冲击损伤研究

跌落冲击是导致果品机械损伤的主要因素.利用MTS886跌落冲击试验机进行单个与多层苹果的跌落试验测定,分析跌落冲击试验机的冲击过程特性,提出了果品跌落吸收能量的计算公式,得到了苹果跌落损伤体积、速度变化量与其吸收能量之间的关系.结果表明:单个苹果的损伤体积与其吸收的能量之间成线性关系,苹果的速度变化量与损伤体积之间成二次项关系;多层苹果的总损伤体积与其吸收总能量存在线性关系,而其中的单个苹果与其吸收的能量之间不存在线性关系.     

多层苹果刚性跌落冲击模型与冲击响应研究

基于损伤条件下果实刚性跌落冲击变形特征,提出一表征其非线性黏弹性的动态流变模型,建立多层果实跌落冲击模型.以"富士"苹果为研究对象,实施多个高度下的跌落冲击试验,进行动态流变模型的参数识别、4层苹果跌落冲击响应的理论分析与试验结果比较.结果表明,试验结果与理论模型结果吻合性好,所提出苹果流变模型、多层果实跌落冲击模型能合理地表征苹果的非线性黏弹性流变特征、跌落中击动力学特征.研究结果为果实的合理运输包装设计提供了理论基础.     

葡萄贮运过程中跌落与振动损伤的试验分析

目的 以巨峰葡萄为试验对象,研究在贮运过程中跌落冲击机械损伤,以及振动疲劳累积对其生理品质产生的影响。方法 在现有贮运包装条件下对葡萄进行不同高度的跌落试验,得到跌落高度对葡萄力学特性的影响。在相同高度下,对葡萄进行不同包装的试验验证,得到新型减振包装对葡萄力学特性的影响,并使用模拟运输振动试验台和六度空间振动试验台进行试验,模拟实际运输路况下不同包装对葡萄生理品质的影响。结果 研究发现,新型减振包装在2种振动疲劳累积试验下,质量损失率比普通包装减少了27.07%和21.42%,表面损伤系数减少了20.11%与17.61%。结论 可为葡萄设计合理的包装方式和运输方式提供理论依据。     

Comparison of the Material Parameters of Polyethylene Grades with the Test Performance Behaviour of Packagings for the Transport of Dangerous Goods in Relation to the Pre‐Storage Time with 55% Nitric Acid

The material parameters melt flow rate (MFR), density (D), notched impact strength (NIS) at –30°C, stress crack resistance [determined with the Full Notch Creep Test (FNCT)] and resistance to oxidative degradation (Ox) have been selected for a comparison of polyethylene grades in the European standard EN 15507. These parameters have a relationship with design type tests of packagings for the transport of dangerous goods. This paper presents the results of additional investigations to determine the impact of the pre‐storage time of jerricans with 55% nitric acid at 40°C and 23°C on the marginal drop heights in drop tests at –18°C, on the MFR and on the tensile properties. Jerricans made of different polyethylene grades were pre‐stored with 55% nitric acid for 21, 42 and 84 days at 40°C and for six months at 23°C. The tests showed that the NIS values at –30°C of polyethylene grades were not comparable with marginal drop heights determined in drop tests at –18°C. Pre‐damage with 55% nitric acid for 21 days at 40°C led to an increase in the marginal drop heights of the jerricans. Altering the test regulations by increasing pre‐storage time with 55% nitric acid to 42 days would be an alternative. The test results demonstrated clearly that pre‐storage of the jerricans for six months at 23°C caused a higher increase in the MFR and lower marginal drop heights for the jerricans when compared with pre‐stored jerricans for 21 days at 40°C. Copyright © 2013 John Wiley & Sons, Ltd.     

海藻糖涂膜对鲜切苹果品质的影响

目的为了抑制鲜切苹果发生酶促褐变,改善其口感,延长其保质期。方法以富士苹果为实验材料,研究质量分数不同(0%,0.1%,0.5%,1%,5%)的海藻糖涂膜剂处理对鲜切苹果的保鲜效果,并测定褐变指数、Vc含量、SSC含量、可滴定酸含量、MDA含量等指标。结果采用海藻糖涂膜剂处理鲜切苹果的最佳质量分数为1%,可显著提高其品质。经质量分数为1%的海藻糖处理鲜切苹果后,其色泽口感俱佳,褐变抑制作用较强,明显降低了褐变指数和MDA的增长率,延缓了Vc、SSC和可滴定酸等含量的下降。结论海藻糖涂膜处理不仅可以抑制鲜切苹果在贮藏期间的褐变进程,而且还可以赋予其更好的风味,提高产品的品质,延长其保质期,对鲜切果蔬的保鲜研究具有重要意义。     

A performance study for two portable data recorders used to measure package drop heights

This study investigated the error in measuring package drop heights using the drop height recorder developed by Dallas Instruments and the environmental data recorder developed by Instrumented Sensor Technology. The shock measuring capabilities of the two recorders were also studied. Drops were made onto the bottom, edge and corner orientations from heights of 18, 24, 30 and 36 inches. The study concluded that the drop height recorder predicts the drop height most accurately and with the least variation using its 'zero-g' channel. Both recorders show much larger variations in predicted values (up to 30%) when using the recorded acceleration-time data. The edge and corner orientation drop heights are generally underestimated by both, owing to the inability of the accelerometers to differentiate between partial rotation on impact and vertical travel.     

Preventing failure in spent nuclear fuel canisters

A spent nuclear fuel canister has been developed with the goal of no containment failure even during accidental drop conditions. This canister was designed to be loaded with U.S. Department of Energy spent nuclear fuel and then used for interim storage, transportation to the nation’s repository, and final disposal at the repository. The design required a high degree of confidence against failure if the canister were subjected to loads (e.g., accidental drop events) resulting in large plastic deformations and high strains. Significant testing of the canister clearly demonstrates that it can safely achieve the intended design goals without failure. The canister skirt and its attachment to the containment boundary are the key engineered elements of the design that allow significant impact damage without failure of the containment. A combination of analytical techniques and physical testing was used to develop and demonstrate the viability of the design. Finite element modeling coupled with scaled drop tests established the design prototype. To validate the design concept, nine full-scale test canisters were fabricated and dropped from various heights and orientations. The nine test canisters experienced varying degrees of damage to their skirts, lifting rings, and containment boundary components. However, all of the tested canisters maintained the containment boundary as evidenced through the results of pressure and selective helium leak testing. Pre- and post-drop finite element analyses were also performed. The analytical results provide accurate predictions of canister responses to the drop tests. The results achieved for the canister can also be applicable to other well-designed containers (canisters, casks, cans, vessels, etc.) subjected to similar loads. Properly designed containers can maintain containment after experiencing dynamically induced high strains, and computer analyses can accurately predict the response of these containers to dynamic loads.     

Drop Test of Plastic Packagings – Correlation with Material Parameters and Change of Packaging Behaviour After Impact of Standard Liquids

A guided drop test was performed to achieve a defined and reproducible impact orientation of jerrycans. The drop heights where 50% of the jerrycans experienced a failure from a crack where fluid can escape (50% failure drop height) were compared among jerrycans made of four different materials, in their original state and preconditioned with standard liquids. To analyse the impact of only elevated temperatures, the packages were preconditioned for 21 days at 40°C without the use of chemicals. The 50% failure drop height was compared by using Young's modulus; the notched impact strength (NIS) of specimen cut from plates which were manufactured by compression moulding and the notched tensile impact strength of specimen cut‐outs of the jerrycans' side walls. The NIS depends highly on the thermal preconditioning of the plates being manufactured by compression moulding. A trend can be seen that a higher Young's modulus, a higher NIS and a higher notched tensile impact strength result in a higher 50% failure drop height, but the values are spread. The influence of the wall thickness cannot be neglected. The change of the 50% failure drop height in regard to the preconditioning at 40°C with and without nitric acid was compared in terms of their resistance to molecular degradation, density and degree of crystallinity. The conditioning at elevated temperature causes post‐crystallization. It was shown that the resistance to molecular degradation determined on pressed plates correlates with the change of the 50% failure drop height after pre‐storage with nitric acid. Copyright © 2013 John Wiley & Sons, Ltd.