Study on the mechanism and law of temperature,humidity and moisture content on the mechanical properties of molded fiber products

The change of temperature, humidity and moisture content (MC) will lead to the change of mechanical properties of molded fiber products (MFP). However, it is difficult to decouple the effects of temperature, humidity and MC on the mechanical properties of MFP, and predict the mechanical properties of MFP during the use. In this study, the laws and mechanism of mechanical properties of MFP with ambient temperature, humidity and MC were studied. The results showed that the direct effect of temperature (20−70 °C) on mechanical properties of MFP was insignificant, and the mechanical properties of MFP were mainly changed by MC. The MC was related to ambient temperature and humidity, and the relationship between the three could be described by the modified Guggenheim-Anderson-de Boer (GAB) model (20−70 °C and 30 %–90 % relative humidity). With the increase of MC, the elastic modulus and fracture strain was increased and decreased linearly, the yield strength and failure strength were presented GaussAmp laws, and the failure strain was presented asymptotic regressed distribution law. Two fracture modes of MFP, brittle fracture and ductile fracture, were revealed by the scanning electron microscopy of the mesoscopic fiber structure of sugarcane bagasse molded fiber products. The mathematical models and the changes of fiber structure were verified by wheat straw molded fiber products and waste paper molded fiber products. This study was contributed to understand the effects and mechanism of the change of temperature, humidity and MC on the mechanical properties of MFP.

Effects of soil mechanical properties on the height and tractive performance of rubber grouser at different moisture contents

Rubber tracked vehicles are commonly used on agricultural machinery that perform agricultural operations such as rice harvesting in soft paddy fields with low bearing capacity.Research was carried out to assess the influence of soil moisture content and mechanical properties on the tractive performance of a rubber grouser with three heights(45 mm,55 mm,60 mm).The direct shear test and penetration test were used in this study,which was based on a semi-empirical approach of determining tractive parameters.Direct shear tests were used to measure soil shear strength parameters such as cohesion,adhesion,internal and exterior friction angles.The results of the penetration test were used to determine tractive parameters such as soil thrust,running resistance,and traction,for the penetration test,a device was designed and developed.The experimental results revealed that soil cohesion and adhesion increased linearly with increasing soil moisture content,however adhesion dropped after 30.7%.Similarly,the soil thrust initially increased till 21.5%then decreased.Furthermore,running resistance had a decreasing trend over soil moisture content whereas maximum traction achieved for 45 mm grouser height at 21.5%moisture content.It was concluded that a rubber grouser with 45 mm height had better traction rather than 55 mm and 60 mm,it can be suitably used for designing a track system for a crawler vehicle(e.g.,harvester)leading to its greater adoption among the farmers.

Influences of moisture content and compressive loading speed on the mechanical properties of maize grain orientations

Determination of the mechanical properties(rupture force,deformation,hardness,and toughness)of maize grain could be a significant concern for designing the harvester,thresher,and handling,processing,and storage equipment.Thus,the present research was conducted to assess the vertical and lateral rupture force,deformation,hardness,and toughness of maize grain(Beijing Denong,Lianchuang,Suyu 20,Liyu 88 and Suyu 29)influenced by different moisture contents(11.2%,17.5%,and 21.3%)and compressive loading speeds(5,10,15,20,and 25 mm/min,respectively).Besides,the mean length,width,thickness,geometric mean diameter,equivalent diameter,arithmetic diameter,sphericity,grain volume,surface area,and aspect ratio of the selected varieties were measured.The results showed that the highest length,width,thickness and sphericity,grain volume,surface area,and aspect ratio were obtained at moisture of 21.3%,whereas the lowest was at 11.2%.Moreover,it was observed that as increasing the loading speed from 5 to 25 mm/min,the vertical and lateral rupture forces decreased.However,as increasing moisture contents from 11.2%to 21.3%,the vertical and lateral rupture forces,hardness,and toughness decreased noticeably.Furthermore,the maximum correlation(R2=0.9957)between rupture force and loading speed was found for Liyu 88 at moisture of 17.5%and minimum correlation(R2=0.7002)was found for Suyu 29 at moisture of 11.2%.Moreover,the highest lateral and vertical rupture force was noticed(p<0.05)at a loading speed of 5 mm/min.Based on the experimentally obtained results,it was concluded that the properties of maize grain evaluated were relevant to the design of planter,harvesters,thrashers,and processing machine.

Study of the Mechanical Properties of 3D-printed Onyx Parts: Investigation on Printing Parameters and Effect of Humidity

Recently,an increasing number of parts have been produced using additive manufacturing technology.They are no longer simply prototypes but structural parts whose mechanical characteristics must be known before printing.One of the weaknesses of 3D printing is the significant variability in the dimensions and geometrical and mechanical properties of the printed parts.These properties depend on specific printing parameters and environmental conditions.This study aims to determine the influence of two printing parameters,namely,the orientation and positioning of the parts on the printing platform and the influence of humidity on the mechanical properties of the parts.The studied samples were fabricated with onyx using a Markforged X7 printer.The results showed that onyx could be considered an isotropic material to a certain extent because its mechanical properties do not vary sufficiently according to the orientation angle on the printing platform;a maximum deviation of 10%was observed between the different orientations.In contrast to the orientation,the positioning(flat or XY,on-edge or XZ,and upright or ZX)of the workpieces significantly influenced the mechanical properties.Positioning on the edge allowed the Young’s modulus to be up to 50% greater than that of flat and upright positioning.The study of the sensitivity to humidity revealed that a specimen absorbs approximately 2%of the humidity and loses up to 65%of its Young’s modulus after 165 days of exposure,significantly influencing the mechanical properties of the parts.Consideration should be given to this aging of onyx when using printed parts as structural parts.

Influence of moisture content and time on the mechanical behavior of polymer material

The effects of moisture content and time on mechanical behavior of polymer materials are investigated both theoretically and experimentally in this paper. An equivalence relationship between time intervals and the moisture content for polymer nylon-6 has been established by way of experimental observation and measured results. The relationship shows that there exists equivalence between moisture and service time in affecting mechanical properties. In other words, an increase in moisture can be replaced by prolonging acting time in producing the same effect on material properties. Consequently, a moisture-time superposition principle is presented based on the experimental results and the analogy of temperature-time superposition principle. Numerical results such as stress-strain curves with different moisture contents are presented to verify the applicability and correctness. The proposed method appears very promising in study on the effect of moisture content on mechanical behavior of polymer materials.

Mechanical Properties of Sunflower Seed and Its Kernel, Azargol Variety as a Case Study, under Compressive Loading

The objective of this study was to investigate the effect of moisture content, size and loading orientation on mechanical properties such as force, deformation and energy absorbed per unit volume for fracturing Iranian sunflower seed and its kernel （Azargol as a case study） under quasi-static loading. Sunflower seeds and their kernels were quasi-statically loaded in horizontal and vertical orientations with moisture content in three levels： 3%, 7% and 14%, and size category in three levels： small, medium and large. The obtained results showed that rupture force for both sunflower seed and its kernel decreased with increasing moisture content while the absorbed energy and deformation at rupture point increased for all size categories in both horizontal and vertical loading orientations. Also, seeds in the vertical orientation developed hull cracks at a higher level of force than those loaded in the horizontal orientation. However, for the kernels it was the opposite. In addition, the average forces required to cause kernel rupture were lower （11.64-39.9 N） than those required to rupture the seed （30.06-117.46 N） in both orientations. Seeds loaded in a vertical orientation absorbed more energy （87.67 mJ） prior to rupture than those loaded in the horizontal （46.60 mJ） orientation. However, for the kernels it was the opposite.

冻融循环作用下不同含水率灰土的细微观结构与宏观力学性能

为了探明素土和灰土在不同含水率时细微观结构与宏观力学性能受冻融循环的影响规律,开展了素土和灰土在不同含水率时的冻融循环试验、抗压强度试验和核磁共振试验。结果表明,素土和灰土抗压强度均随含水率的提高而降低;素土和灰土抗压强度在同一含水率时均随着冻融循环次数的增加而降低,冻融循环六次时降低率可达到12次时的80%左右;灰土T_(2)谱信号峰值大于素土,T_(2)谱信号峰值随着灰土比例的提高而增大;不同含水率时素土和灰土T_(2)谱面积在冻融循环次数由3次增大至6次的增长率均明显大于6次至12次。

不同含水率下煤岩组合体力学特性损伤规律研究

浅埋富水煤层长期受覆岩导水裂隙中地下水渗流侵蚀影响,矿井留设隔水煤岩柱及阶段间柱在水岩作用下产生力学损伤劣化。开采活动进一步加快损伤进程,并直接关系到工作面的稳定及安全生产。以陕西榆林锦界煤矿煤岩体为研究对象,制成砂岩-煤-砂岩(S-M-S)组合体,开展不同含水率条件下单轴压缩试验,揭示水岩作用下煤岩组合体的含水率变化规律、力学行为演化特征和声发射损伤规律,基于电镜微观扫描图像,分析水岩作用下组合体内部结构损伤劣化机理。研究结果表明:煤岩组合体吸水速率随着浸水时间的增加不断降低;水岩作用对煤岩组合体抗压强度和弹性模量有明显的劣化效应,组合体弱余强度随含水率增加不断降低,强度损伤速率随着含水率的提高不断加快;组合体的声发射计数和累计计数在水岩作用下衰减明显,并伴随组合体损伤破坏整个过程;水岩作用致使组合体内部结构原生链钝化,裂隙扩展,破裂形式发生明显改变。研究结果可为采动影响下煤岩矿柱水害预测评价提供指导。

土石混合填料工程力学性能试验研究

土石混合填料力学性能是影响路堤设计和施工的重要参数,相关研究一直是热点问题。为分析不同含水率、土石混合比例、击实功、土料厚度条件下土石混合体工程力学性能,开展了不同组合下土石混合体击实试验和大型直剪试验,揭示了上述因素对混合料最优含水率和力学指标的影响,并建立了土石混合填料力学指标计算方法。研究表明:总击实功、含水率和含石量对试样干密度影响较大,且随着含石量的增大,土石混合料最大干密度逐渐增大但最优含水率逐渐降低;干密度随着每层击实次数的增加而增加;随着法向应力的增大,土石混合料应力-应变曲线由应变硬化型逐渐变为应变软化型;随着含石量的增大,其内摩擦角随之减小但黏聚力随之增大,但增大幅度较小。成果可为土石混合填料路堤施工和设计提供理论参考。

深圳西部地区海积软土指标及相关性研究

以深圳西部地区滨海建设的实地勘察资料为基础,收集了该区20余项重大工程的软土原状土样试验数据,并进行统计学回归分析,得出了a_(1-2)-w曲线和E_(s)-w曲线、c-w曲线和c-I_(L)曲线、φ_(q)-w曲线和φ_(q)-r曲线,确定了深圳西部海积软土天然含水率与压缩指标关系方程、天然含水率、液性指数与黏聚力关系方程、天然含水率、天然密度与摩擦角的关系方程。通过回归曲线归一化整理,结合工程经验,提出了不同天然含水率区段的深圳西部海积软土对应的压缩指标和抗剪指标建议值。持续性地研究了深圳西部软土的工程特性,对该区软土研究具有借鉴意义。

冲击作用下含水煤样能量吸收和耗散规律及本构关系研究

煤层注水是综放开采回采巷道预防冲击地压的主要措施之一。为了研究含水煤样动态力学性质和力学参数,利用霍普金森压杆(SHPB)试验系统,对不同含水率的圆柱形煤样进行单轴冲击压缩试验,研究含水率和冲击速度对煤样动态应力-应变曲线、动态力学参数以及耗散能变化规律的影响。研究结果表明:①煤样动态力学参数与冲击速度和含水率有关。当煤样含水率一定时煤样动态抗压强度、动态弹性模量与冲击速度成正相关;而冲击速度一定时煤样动态抗压强度、动态弹性模量与含水率成负相关;②在冲击过程中煤样的损伤耗散能直接反映煤样中微裂隙发育程度,随着冲击时间的增加,煤样损伤耗散能增大,煤样坍塌破坏时损伤耗散能达到最大值。当含水率一定时煤样破坏耗散能与冲击速度成正相关;而冲击速度一定时煤样破坏耗散能与含水率成负相关;③损伤因子定义为煤样损伤耗散能与破坏耗散能的比率。基于煤样单轴冲击压缩试验结果,建立了煤样损伤体-黏弹性本构模型和本构关系,对不同含水率煤样动态应力-应变试验曲线进行理论拟合,理论拟合曲线与试验曲线拟合度高,因此理论曲线可用来表示单轴冲击压缩煤样的应力-应变关系。研究结论为冲击地压矿井深孔煤层注水预防冲击地压提供了理论基础。

不同含水率煤样单轴冲击力学性质试验研究

目前,巷道煤层注水是预防综放开采煤岩体冲击地压的有效技术措施之一。利用义马矿区耿村煤矿综放工作面煤样,在室内进行煤样吸水性试验后,制作成不同含水率的圆柱形煤样,进行霍普金森(SHPB)单轴冲击试验,研究冲击速度和含水率对煤样动态力学性质的影响。结果表明:(1)煤样含水率与浸水时间呈正相关。按照含水率-浸水时间曲线拐点,将煤样浸水过程划分为2个阶段即前期浸水和后期浸水阶段。(2)煤样动态力学参数均与煤样冲击速度和含水率有关。当煤样含水率一定时,随着冲击速度增大,煤样动态抗压强度和动态弹性模量均与冲击速度呈正相关;当煤样冲击速度一定时,随着含水率升高,煤样动态抗压强度和动态弹性模量均与含水率呈负相关。(3)根据屈服强度和峰值强度,将煤样单轴动态应力-应变全过程划分为3个变形阶段即弹性阶段、屈服阶段和应变软化阶段,回归出煤样各阶段应力-应变拟合方程。研究结果可为冲击地压矿井深孔煤层注水防冲措施的实施和应用提供参考。

陶粒加气混凝土砌块的力学性能试验研究

为研究陶粒加气混凝土砌块(CACB)强度与养护环境、含水率、龄期的关系,分别测试了六种不同龄期(0、3、7、14、28、56 d)CACB试件在自然养护、恒温恒湿环境养护和标准养护下的强度和含水率,分析了含水率、龄期和强度变化相关性。结果表明:CACB的抗压强度、劈裂抗拉强度、抗折强度前期增长较快,28 d后增长率趋于平缓;CACB的强度对含水率的变化不太敏感;在标准养护条件下,CACB的28 d和56 d抗压强度、抗拉强度均比其他养护条件略高;恒温恒湿环境养护条件下,CACB的28 d、56 d抗折强度比其他养护条件略高;根据试验结果,同时考虑生产的经济性和施工条件,CACB推荐的施工养护环境为自然养护,最佳养护龄期为28 d。

竹纤维增强磷石膏板性能试验研究

文章设计了3组添加不同纤维增强材料的磷石膏板,旨在研究其对磷石膏板抗弯、抗压等性能的影响。研究结果显示:竹纤维的掺入能够提高磷石膏板的弹性模量,但不能改变其受弯脆性破坏模式。加入竹纤维后,试件的抗压强度显著提高。对照组磷石膏板的抗压强度更容易受到水浸泡的不利影响,其强度降低超过60%。加入竹纤维后(第二、三组),虽然其含水率较高,但是其强度降低明显减弱(约35%)。

水分添加量对高水分挤压大豆粕植物蛋白肉品质及结构特性的影响

豆粕作为优质植物蛋白质资源,探究利用大豆粕替代大豆分离蛋白作为高水分挤压植物蛋白肉加工原料的可能性,对生产企业控制生产成本及提高大豆粕经济价值都具有重要意义。本文以大豆粕为原料,通过测定硬度、弹性、咀嚼度、色泽、持水性、持油性、化学交联作用力等指标,以及利用傅里叶红外光谱和扫描电子显微镜等技术,系统地探究水分添加量(10.5、11、11.5、12、12.5 kg/h)对高水分挤压植物蛋白肉的品质及结构特性的影响。结果表明,随着挤压过程中水分添加量的增加,植物蛋白肉的硬度、弹性、咀嚼性均显著(P<0.05)下降,而亮度值、持水性和持油性均呈先升高后降低的趋势,并在水分添加量为11.5 kg/h时,植物蛋白肉具有较好的品质特性和外观色泽,内部形成了更加致密的纤维细丝,组织蛋白层状结构变得清晰整齐,呈现出精细的定向结构。傅里叶红外光谱与化学交联结果表明水分添加量对植物蛋白肉的结构具有影响显著,并且其结构由共价键和非共价键的交互作用共同维持。

长江荆江段二元结构河岸土体力学性能及崩塌试验

通过连续3 a对荆江崩岸情况进行现场调查、室内土工试验和概化模型试验,分析荆江崩岸特点及规律、河岸上部黏性土的物理及力学性能以及二元结构河岸崩塌过程的特点和影响因素。结果表明:荆江段崩岸分布规律主要表现为下荆江多于上荆江,左岸多于右岸;二元结构河岸崩塌过程可概括为坡脚受冲刷变陡,岸顶裂缝形成发育,岸坡渐进侵蚀,河岸失稳导致崩塌,岸坡形态趋于稳定,进入下一次河岸崩塌循环;黏性土含水率对水位变化的响应速度快于对浸泡时长的响应速度;黏性土的起动切应力为0.531 N/m^(2),影响黏聚力值的临界含水率约为16%,受纵向水流及土体含水率的影响,岸坡在枯水期稳定性较高,在涨水期会产生局部崩岸,洪水期和退水期时坡脚冲刷和崩岸强烈。

含水率波动状态下公明公路路基土劣化微观机理与本构模型

通过固结排水三轴剪切试验、压汞试验和电镜扫描试验探究含水率波动对公明公路路基土力学特性的影响与其劣化微观机理,基于邓肯-张模型提出了一个能够考虑含水率波动影响的路基土经验本构模型。结果表明:含水率波动使得路基土中、大孔隙增多,同时微裂隙得到发展引起试样结构被分割,导致试样剪切应力-应变关系从应变软化向应变硬化型转变,试样剪缩特性提升、剪切强度降低;含水率波动程度越大,试样剪缩特性越明显,剪切强度则越弱;提出的路基土本构模型的计算结果与试验结果吻合较好,证明了模型的有效性和适用性。

含水率与倾角对复合岩体软弱夹层力学性质影响

为了研究软弱夹层倾角和含水率对含软弱夹层复合岩体的力学性质和破坏特征的影响,通过室内制样,制作了含5种不同倾角和3种不同含水率软弱夹层的复合岩体,并进行室内单轴试验。研究表明:随着倾角的增大,软弱夹层的峰值强度和变形模量减小,峰值点应变增大;实验中,无论软弱夹层倾角为多少时,软弱夹层两侧最先破坏,当软弱夹层倾角θ=15°、20°和25°时,软弱夹层不仅发育有两侧破坏,还发育始于左侧顶面止于右侧底面的贯通斜裂纹,并且也通过理论部分研究推测出对应的破坏模式;当软弱夹层倾角不变,随着软弱夹层含水率的增大,软弱夹层的峰值强度和变形模量先增大再减小,峰值强度点应变先减小后增大,含水率ω=8%试样的承载能力最强,此时软弱夹层的峰值强度和变形模量最大。

低温环境下重塑性煤体抗压性能研究

为研究低温重塑性煤体抗压性能,实现安全快速石门揭煤,防治煤与瓦斯突出,将煤样进行破碎、筛选、压制得到重塑煤样试件,在一定温度(−40、−30、−20、−10、0、20℃),一定含水率(0%、4%、8%、12%、16%)相互耦合下进行单轴压缩实验研究,分析重塑性煤体的破坏特征和力学性能。实验结果表明:重塑性煤体在常温(20℃)和0℃条件下,抗压强度随含水率升高逐渐降低;在冻结温度下,煤样试件内部产生的冻胀力随着温度的降低而逐渐减小,重塑性煤抗压强度得到明显的增强;低温(−40℃)和高含水率(16%)耦合作用下重塑性煤体抗压强度、峰值应力、峰值应变均达到最大,最大依次提高164.24%、165.71%、685.72%。

黄金百香果藤蔓力学性能参数的测定

为获取黄金百香果藤蔓力学性能参数,以其藤蔓为试验材料,对其进行了径向压缩、轴向压缩、三点抗弯和抗剪试验。结果表明:黄金百香果的大主藤、小主藤、支藤的径向平均压缩弹性模量分别为36.48、30.84、20.83MPa,轴向平均压缩弹性模量分别为19.44、10.35、4.31MPa;大主藤、小主藤、支藤的平均抗弯强度分别为13.37、11.23、7.46MPa,平均抗剪切强度分别为4.82、4.88、5.16MPa;抗压强度、弯曲强度、剪切强度均与含水率呈负相关,与密度呈正相关。研究结果可为黄金百香果藤蔓加工处理设备关键部件设计与开发提供一定的理论依据。