A Review of Basic Mechanical Properties of Bamboo Scrimber Based on Small-Scale Specimens

This review summarizes the existing knowledge about the mechanical properties of bamboo scrimber(BS)in literature.According to literature reviews,the strength of BS under different load modes is affected by a series of factors,such as the type of original bamboo,growth position,resin content,treatment method and density.Therefore,different production processes can be adopted according to different requirements,and bamboo scrimbers can also be classified accordingly.In addition,this review summarizes the changes in different factors considered by scholars in the research on the mechanical properties of BS,so that readers can have an overall understanding of the existing research and make more innovative and valuable research on this basis.This review provides and discusses the conclusive observations,the current research gaps and future research directions on the mechanical properties of BS.

Experimental Study on the Axial Compression Performance of Bamboo Scrimber Columns Embedded with Steel Reinforcing Bars

In this paper,a new type of bamboo scrimber column embedded with steel bars(rebars)was proposed,and the compression performance was improved by pre-embedding rebars during the preparation of the columns.The effects of the slenderness ratio and the reinforcement ratio on the axial compression performance of reinforced bamboo scrimber columns were studied by axial compression tests on 28 specimens.The results showed that the increase in the slenderness ratio had a significant negative effect on the axial compression performance of the columns.When the slenderness ratio increased from 19.63 to 51.96,the failure mode changed from strength failure to buckling failure,and the maximum bearing capacity decreased by 43.03%.The axial compression performance of the reinforced bamboo scrimber columns did not significantly improve at a slenderness ratio of 19.63,but the opposite was true at slenderness ratios of 36.95 and 51.96.When the reinforcement ratio increased from 0%to 4.52%,the bearing capacity of those with a slenderness ratio of 51.96 increased by up to 16.99%,and the stiffness and ductility were also improved.Finally,based on existing specifications,two modification parameters,the overall elastic modulus Ec and the combined strength fcc,were introduced to establish a calculation method for the bearing capacity of the reinforced bamboo scrimber columns.The calculation results were compared with the test results,and the results showed that the proposed calculation models can more accurately predict the bearing capacity.

Dynamic Testing of Elastic Modulus,Shear Modulus,and Poisson’s Ratio of Bamboo Scrimber

The bamboo scrimber is an anisotropic material.The elastic constant values of the bamboo scrimber specimens measured by the dynamic and static methods are consistent,and the dynamic test method has the advantages of rapidity,simplicity,good repeatability,and high precision.Bamboo scrimber has strong potential as a building material,and its elastic constant is an important index to measure its mechanical properties.To quickly,simply,non-destructively,and accurately detect the elastic constant of the bamboo scrimber,they were dynamically tested by the free plate transient excitation method and cantilever plate torsional vibration method.The static four-point bending method was used to verify the accuracy and reliability of the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber.The mechanism analysis and evaluation of the quality grade,homogeneity,and size effect of the bamboo scrimber whole board were carried out.The main results show that the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber are 12 GPa,1500 MPa,and 0.31,respectively,which meet the requirements of GB/T 40247-2021 for structural bamboo scrimber.

Mechanical Properties and Stress Strain Relationship Models for Bamboo Scrimber

In order to investigate the basic mechanical properties and stress strain relationship model for bamboo scrimber manufactured based on a new technique,a large quantities of experiments have been carried out.Based on the analysis of the test results,the following conclusions can be drawn.Two main typical failure modes were classified for bamboo scrimber specimens both under tension parallel to grain and tension perpendicular to grain.Brittle failure happened for all tensile tests.The slope values for the elastic stages have bigger discreteness compared with those for the specimens under tensile parallel to grain.The failure modes for bamboo scrimber specimens under compression parallel to grain could be divided into four.Only one main failure mode happened both for the bending specimens and the shear specimens.With the COV values of 28.64 and 25.72 respectively,the values for the strength and elastic modulus under tensile perpendicular to grain have the largest discreteness for bamboo scrimber.From the point of CHV values,the relationship among the mechanical parameters for bamboo scrimber were proposed based on the test results.Compared with other green building materials,bamboo scrimber manufactured based on a new technique has better mechanical performance and could be used in construction area.Three stress strain relationship models which are four-linear model,quadratic function model,and cubic function model were proposed for bamboo scrimber specimens manufactured based on a new technique.The latter two models gives better prediction for stress strain relationship in elastic plastic stage.

Comparison and analysis of the main technological factors of influencing mechanical properties of scrimber and PSL

The main mechanical properties of scrimber and Parallel Strand Lumber (PSL) were researched through techno-logical test. Experimental materials of scrimber are small log of Aspen, Dahurian larch and Birch. Experimental materials of PSL come from fishtail veneer strips at plywood plant of Aspen and Birch. In the laboratory conditions low quality small log and wood residues can yield scrimber and PSL with high strength. After the technological conditions of scrimber were compared with that of PSL, the main factors of influencing their properties were separately pointed out and the reasons influencing proper-ties have been analyzed in this paper. The results showed that the hot-pressing pressure is an important technological factor for scrimber. The ratio of veneer-strand length to thickness is a key technological factor for PSL.

Flexural Performance of CFRP-Bamboo Scrimber Composite Beams

This study presents a new structure made up of bamboo scrimber and carbon fiber reinforced polymer(CFRP)to address the low stiffness and strength of bamboo scrimbers.Three-point bending test and finite element model were conducted to study the failure mode,strain-displacement relationship,load-displacement relationship and relationships between strain distribution,contact pressure and deflection,and adhesive debonding.The results indicated that the flexural modulus and static flexural strength of the composite beams were effectively increased thanks to the CFRP sheets.The flexural modulus of the composite specimens were 2.33-2.94 times that of bamboo scrimber beams,and the flexural strength were 1.49-1.58 times that of bamboo scrimber beams.Adhesive debonding had a great influence on the strain distribution and deflection of the composite specimens.It was an important factor for the failure of the CFRP-bamboo scrimber composite specimens.According to the finite element simulation,the strain distribution,contact pressure and deflection also greatly changed with the adhesive debonding.After complete peeling,the deflection of the specimen was 3.09 times that of the unpeeled because it was no longer an integral beam.

Experimental and Theoretical Study on Bonding Properties between Steel Bar and Bamboo Scrimber

To further verify the feasibility of newly designed reinforced bamboo scrimber composite(RBSC)beams used in building construction,the bonding properties between steel bar and bamboo scrimber were investigated by anti-pulling tests.Results indicated that the anti-pulling mechanical properties were significantly correlated to the diameter,thread form and buried depth of steel bar,forming density of bamboo scrimber as well as the heat treatment of bamboo bundle.There were two failure modes for anti-pulling tests:the tensile fracture and pulling out of steel bar.Both the ultimate load and average shear strength of anti-pulling specimen could be increased greatly with the ribbed bar,high forming density of bamboo scrimber and un-heated bamboo bundle.Furthermore,a theoretical calculation model of the bonding interface between steel bar and bamboo scrimber was developed.Based on the theoretical calculation model,the change laws of normal stress of bamboo scrimber,and shear stress of glue layer along the buried depth of steel bar were revealed.This study is beneficial for the safety application of RBSC beams in building construction.

我国木质重组材料研究现状与发展

木质重组材料是一种新型的高性能木质复合材料,在定向重组过程中,木、竹材在湿-热-力和树脂聚合反应作用下发生了一系列复杂的物理和化学变化,木、竹材原有构造特征发生了显著变化,形成了木质重组材料全新的多维构造,这种新构造特征的形成使得重组材料的物理力学性能与木材、竹材等原材料性能相比有了显著改善,并且重组过程中可通过添加不同添加剂赋予木质重组材料阻燃、防腐、防霉、耐候、防虫等新功能,克服了人工速生林木材材质软、强度低、材质不均、易开裂等缺陷,解决了竹材径级小、易劈裂、材质不均等问题,可用于替代优质木材、钢铁、水泥、塑料等建筑材料,具有广泛的应用前景,是实现人工林木材和竹材高效利用的有效途径之一。本文对木、竹材在重组过程中宏观、微观等构造演变,木质重组材料多尺度构造、多层次胶合界面等多维结构形成机制以及多维结构对木质重组材料物理力学性能影响进行了综合评述,提出了木质重组材料细胞选择性增强的观点,归纳了木质重组材料亟待解决的科学问题,建议加强在细胞和分子水平层面,对木质重组材料的理论基础、制造基础和应用基础等进行研究,构建木质重组材料理论体系,从而为人工速生林木材资源高效利用这一国家重大战略需求提供基础理论和技术支撑。

重组竹内置钢筋后受弯性能有限元分析

重组竹是通过将竹束热压胶合而成的新型工程材料,具有强度高、韧性好以及固碳能力强等优点,为提高重组竹的受弯性能,通过热压工艺在重组竹中内置钢筋形成增强重组竹受弯构件。在四点弯曲试验的基础上,通过ABAQUS有限元模拟研究配筋率及配筋形式对重组竹受弯性能的影响。分析结果表明,与纯重组竹相比,内置钢筋后重组竹的受弯力学性能得到明显提高;当配筋形式相同时,随配筋率的增加,重组竹的承载力及抗弯刚度逐渐提高,与纯重组竹相比,配筋率为1.0%~8.2%的单筋重组竹承载力和抗弯刚度分别提高5.6%~48.36%和10.57%~71.81%;当钢筋直径相同时,重组竹顶部和底部同时配筋的双筋重组竹与重组竹底部配筋的单筋重组竹相比,其承载力及抗弯刚度分别提高21.78%和95.98%。

Theoretical Analysis on Deflection and Bearing Capacity of Prestressed Bamboo-Steel Composite Beams

A theoretical analysis of upward deflection and midspan deflection of prestressed bamboo-steel composite beams is presented in this study.The deflection analysis considers the influences of interface slippage and shear deformation.Furthermore,the calculation model for flexural capacity is proposed considering the two stages of loading.The theoretical results are verified with 8 specimens considering different prestressed load levels,load schemes,and prestress schemes.The results indicate that the proposed theoretical analysis provides a feasible prediction of the deflection and bearing capacity of bamboo-steel composite beams.For deflection analysis,the method considering the slippage and shear deformation provides better accuracy.The theoretical method for bearing capacity matches well with the test results,and the relative errors in the serviceability limit state and ultimate limit state are 4.95%and 5.85%,respectively,which meet the accuracy requirements of the engineered application.

新型CFRP网格-重组竹复合板力学试验研究

为提高重组竹的力学性能并减轻其各向异性缺陷,设计了一种新型CFRP网格-重组竹复合板(CBCP).分别对8组CBCP拉伸试样和18组CBCP拉拔试样进行单轴拉伸试验和拉拔试验,以分析其力学行为并评估复合方法的影响.选择3个相似的构成模型对拉拔试样的黏结应力-滑移曲线进行拟合,根据试验结果确定CFRP网格和重组竹的临界锚固长度及计算方法,并分析讨论了CFRP层数、横向CFRP束特性和锚固长度对CFRP网格与重组竹黏结性能的影响.结果表明,复合CFRP网格可使重组竹的顺纹和横纹抗拉强度分别提高35.77%和135.20%,从而改善了重组竹的各向异性缺陷.增加网格层数和间距可提高CBCP的拉伸性能.随着锚固长度的增加,平均界面黏结强度呈幂函数递减,而峰值载荷滑移则线性递减.

单板厚度对杨木重组木性能的影响

以杨木单板为原料制备高性能特种重组木,重点探讨单板厚度对重组木性能的影响。结果表明,单板越薄,重组木及其内部单板表芯层密度差异越小,耐水性能也越好,但是垂直层向的抗压强度越低;0.7 mm单板制备重组木的静曲强度最高,为203.3 MPa,0.7 mm和1.0 mm单板制备重组木的弹性模量高于1.3 mm和1.8 mm单板制备重组木。

基于响应面法的菌草重组材制备工艺优化

菌草资源是目前世界上最丰富的农业资源之一,具有广阔的发展前景。以菌草绿洲一号为原料,制备菌草重组材,采用响应面Box-Behnken试验设计方法研究不同浸胶时间、热压时间、热压温度对菌草重组材主要物理力学性能的影响。在响应面试验结果基础上增加碱处理和帚化处理,探究改性对菌草表面结构及物理力学性能的影响。结果表明,菌草重组材的较佳制备工艺参数为浸胶时间33 min,热压时间1.12 min/mm,热压温度155℃。帚化制备的菌草重组材浸胶时间降低至15 min,其静曲强度(MOR)136.56 MPa和弹性模量(MOE)14.80 GPa比未帚化制备的菌草重组材分别提高154%和14%;吸水厚度膨胀率(TSR)5.84%和吸水宽度膨胀率(WSR)0.93%分别比未帚化制备的菌草重组材降低7和1.82个百分点,均达到GB/T 40247—2021《重组竹》的要求。碱处理试验结果显示,在NaOH质量分数为2%时MOR和MOE最佳,分别143.13 MPa和15.05 GPa;在NaOH质量分数1%时TSR和WSR最低,分别为1.85%和0.30%。通过扫描电镜分析可知,碱处理后菌草表面蜡质层出现降解,粗糙度增加;帚化处理产生的裂隙有利于酚醛树脂胶黏剂渗透到菌草内部,有利于菌草重组材的胶合,提高了力学性能和耐水性。本研究制备的菌草重组材为菌草新材料的开发提供新途径,对加快推进菌草重组材产业发展具有重要意义。

压缩率对杨木重组木表面硬度的影响

【目的】以速生人工林杨木为试验材料,利用定向重组技术制备高硬度重组木,揭示压缩率对杨木重组木表面硬度的影响规律,为杨木表面改性及其重组木制备工艺优化提供可靠的方法和科学依据。【方法】利用定向重组技术制备压缩率50%、55%和59%共3种杨木重组木,选取杨木、红榉和俄罗斯柞木为对照样,采用万能力学试验机测定3种木材和3种不同压缩率杨木重组木样品表面的金氏硬度;应用超景深三维显微镜(UDTM)、场发射扫描电镜(SEM)观察样品表面的宏观和微观形貌以及样品金氏硬度测试过程中破坏面的宏观和微观形貌;运用压汞法(MIP)测试样品孔隙率;使用激光共聚焦显微镜(LSCM)和透射电子显微镜(TEM)表征酚醛树脂在重组木中的分布情况。【结果】杨木重组木的金氏硬度随压缩率增大而增大,与杨木相比,压缩率59%杨木重组木的金氏硬度增加12.63倍,其硬度高于俄罗斯柞木和红榉。金氏硬度测试过程中的应力-应变曲线显示,压缩率越大,重组木的比例极限应力越大。场发射扫描电镜(SEM)和超景深三维显微镜(UDTM)观察可知,杨木原木的破坏面呈韧性断裂,制备的重组木随压缩率增大其破坏模式逐渐变为脆性断裂。压汞法(MIP)测试样品孔隙率可知,定向重组可显著降低杨木的孔隙率,压缩率越大,重组木的孔隙率越低。激光共聚焦显微镜(LSCM)和透射电子显微镜(TEM)观察可知,随压缩率增大,酚醛树脂沿胶层带分布的宽度和深度逐渐增加,且渗透到导管、木射线和纤维细胞的细胞腔中。通过纳米压痕测试重组木细胞壁力学性能,当重组木压缩率为55%、施胶量为15%时,其细胞壁硬度和弹性模量相较原木分别提高54.65%和20.14%。重组木表面硬度增大主要是因为杨木经定向重组后,其导管和木纤维细胞被压缩密实,孔隙率降低,单位体积内的细胞实质密度增加,细胞之间的结合面积增大,连接更紧密;同时,引入的酚醛树脂不仅将压缩的细胞结构固定,而且通过形成的胶钉可提高细胞之间的连接强度,浸入细胞壁的酚醛树脂还能够增强其硬度和弹性模量,从而赋予重组木表面较高的硬度。【结论】定向重组技术可有效解决速生人工林杨木木材材质软、表面硬度低的问题,且可通过控制压缩率调控重组木硬度,以满足不同应用场景对材料硬度的需求。

压缩率和施胶量对毛白杨重组木干状和湿状表面粗糙度的影响

表面粗糙度是评价木质材料表面质量和加工性能的重要指标之一。以毛白杨(Populus tomentosa)单板和酚醛树脂为原料,采用单因素试验制备重组木,探讨压缩率(50%、55%、59%)和施胶量(10%、15%、20%)对重组木干状和湿状表面粗糙度的影响。结果表明,压缩率对干状和湿状表面粗糙度影响显著,且对干状表面粗糙度的影响大于湿状;随着压缩率的增大,重组木的干状表面粗糙度逐渐降低,湿状表面粗糙度逐渐增大;施胶量对干状和湿状表面粗糙度影响显著,且对湿状表面粗糙度的影响大于干状;随着施胶量的增加,重组木干状和湿状表面粗糙度均逐渐降低。与毛白杨单板相比,在压缩率为59%和施胶量为15%时,重组木干状粗糙度参数Ra和Rz分别降低了79.64%和73.07%,湿状粗糙度参数Ra和Rz分别降低了62.85%和50.00%。在实际生产过程中,可通过控制压缩率和施胶量调控重组木干状和湿状表面粗糙度,以满足不同应用场景对重组木材料表面粗糙度的需求。

环保型家具用重组竹的制备及性能研究

本研究采用低温固化环保型酚醛树脂为胶黏剂制备重组竹板材,探索热压温度、施胶量和板材密度对重组竹物理力学性能的影响。结果表明:当热压温度为125℃时,板材芯层温度即能达到胶黏剂的固化温度范围,且此条件下的板材密度均匀性、理化力学性能以及各项性能的稳定性更优。然而,热压温度升高对性能的改善不明显。当施胶量达到8.6%以上时,重组竹的密度可达到1.00 g/cm^(3),物理力学性能较优。

高密度重组竹的物理力学性能研究

分析了高密度重组竹的孔隙率、微观结构、耐水性和力学性能,并通过构建性能参数与密度的关系,探究密度对物理力学性能的影响规律。结果表明:随着密度的增大,孔隙率逐渐降低。当密度为1.37 g/cm3时,孔隙率仅为5.52%,竹材细胞基本实现了密实化;薄壁细胞和导管细胞发生严重变形,但纤维细胞的形态几乎未受影响。经4 h水煮-20 h 60℃干燥-4 h水煮处理后,吸水率、厚度膨胀率和宽度膨胀率均随密度的增大而下降,分别低至9.67%、7.62%和1.47%。水平剪切强度、顺纹抗压强度、静曲强度(MOR)和弹性模量(MOE)则随密度的增大而增大,分别高达28.83、215.53、354.00 MPa和28.75 GPa。所有重组竹的性能参数均达到了户外用重组竹的性能要求,且部分参数远超国标中规定的最高等级要求。此研究结果可为重组竹性能的调控与应用提供理论依据和数据参考。

人工林柏木重组木的结构与性能

【目的】采用定向重组技术制备人工林柏木重组木,分析其结构与性能,揭示柏木制备成重组木后性能变化的内因,为人工林柏木高值化利用提供技术参考和理论依据。【方法】制备80%、100%和120%不同压缩率柏木重组木,探究压缩率对重组木耐水性能、力学性能(抗弯性能和水平剪切性能)的影响规律;应用超景深显微镜(UDM)、冷场发射扫描电子显微镜(SEM)、激光共聚焦显微镜(LSM)和透射电镜(TEM)观察重组木微观结构变化以及重组木中胶液分布情况;使用剖面密度测量仪测量垂直于板面表面方向的密度梯度,分析重组木剖面密度。【结果】随着压缩率增大,重组木表面纹理颜色加深,剖面密度逐渐均匀,吸水率(WAR)、吸水厚度膨胀率(TSR)和吸水宽度膨胀率(WSR)逐渐减小,静曲强度(MOR)和水平剪切强度(HSS⊥)逐渐增大。压缩率120%时重组木WAR最小,相比原木降低34.73%,同时重组木MOR和HSS⊥达到最大,分别为125.77和17.05 MPa,相比原木分别提升53.47%和84.32%。剖面密度测量仪、冷场发射扫描电子显微镜、激光共聚焦显微镜和透射电镜观测结果显示,重组木耐水性能和力学性能提升主要是因为随着压缩率增大,木材细胞压缩密实、胶液分布范围更广,在更多的细胞腔和胞间层形成胶合位点,减少吸水时水分进入通道,抑制细胞腔回弹,增强胞间层薄弱结构。【结论】采用定向重组技术将人工林柏木制备成高性能重组木后,其力学性能显著提升;随着压缩率增大,重组木的耐水性能显著增强,压缩率120%时重组木性能达到最优。

辊压树脂浸胶法对桉木重组木尺寸稳定性影响机理

【目的】为解决重组木制备过程中重组单元施胶不均匀导致的尺寸稳定性差的问题,通过辊压树脂浸胶工艺制备重组木,探究辊压树脂浸胶工艺对桉木重组木尺寸稳定性的影响机理。【方法】分别通过吊笼式浸胶法和辊压树脂浸胶法制备桉木重组木,采用超景深显微镜、扫描电子显微镜、微计算机断层扫描仪和激光共聚焦显微镜观察重组单元和重组木表面形貌、微观结构和胶液分布情况,并采用X射线光电子能谱仪、粗糙度仪、接触角测定仪以及63℃水泡24 h和28 h循环法(沸水煮4 h,63℃烘20 h,沸水煮4 h)研究重组木表面化学成分、表面粗糙度、表面润湿性和耐水性能。【结果】与吊笼式浸胶法制备的重组木(CWS)相比,辊压树脂浸胶法制备的重组木(RWS)表面裂隙减少,粗糙度降低,表面润湿性减弱,耐水性能显著增强。RWS表面粗糙度R_(a)和R_(z)相比CWS分别下降了34.38%和72.75%。接触角测试结果表明,第20 s时RWS的表面接触角相对于CWS增大幅度为283.95%。63℃水泡24 h测试结果显示:RWS的吸水厚度膨胀率和吸水宽度膨胀率分别为5.47%和1.11%,与CWS相比降低幅度分别达到52.16%和50.09%。28 h循环测试结果显示:RWS的吸水厚度膨胀率和吸水宽度膨胀率分别为6.24%和1.17%,与CWS相比降低幅度分别为51.45%和58.51%。辊压浸胶过程对重组单元产生了二次破坏,增加了胶液进入的通道;同时,辊压使细胞在被压缩到恢复原貌的过程中产生的负压,增加了胶液的渗透深度,形成网状胶合结构,加强了重组木的胶合性能,抑制了木材细胞在吸水后的回弹。【结论】辊压树脂浸胶法提高了重组木内部胶液分布的均匀性,降低了桉木重组木表面的粗糙度和润湿性,显著提高了重组木的耐水性能,改善了重组木的尺寸稳定性,对重组木的工艺优化和连续化生产具有重要的参考和指导意义。

施胶方式和单板厚度对重组木物理力学性能的影响

采用不同树种的不同厚度单板制备重组木,考察了单板施胶方式、厚度和树种对重组木耐水性能与抗弯性能的影响。结果表明:在0.7~2.2 mm范围内,树种和单板厚度相同时,采用单板表面喷胶制备重组木的吸水厚度膨胀率低于单板浸胶制备的重组木,静曲强度高于后者。树种相同时,单板越厚制备的重组木耐水性能越差。单板厚度和树种对重组木的静曲强度影响较大。单板厚度相同时,桉木重组木的耐水性能和弹性模量高于杨木重组木,但静曲强度低于后者。本研究可为薄单板制备重组木原料和施胶工艺的选择提供重要参考依据。