摘要
基于扫描电镜和共振柱系统,研究了动剪应变、围压和密度对高聚物喷涂材料动力特性的耦合影响规律和机理.结果表明:随着动剪应变的增大,高聚物喷涂材料的动剪切模量呈线性减小,阻尼比增速先快后慢;相同密度条件下,围压越大,高聚物喷涂材料的动剪切模量越大,阻尼比越小;动剪应变、围压和密度对高聚物喷涂材料动剪切模量的耦合影响效应显著,围压和密度对其阻尼比的耦合影响效应显著;泡孔间的错动摩擦和对波动的传播衰减构成高聚物耗能机制,较高围压下,密度为0.250 g/c
随着中国“交通强国”战略的实施,穿越强震区及环境敏感区(学校、文物建筑、精密科研所等)的交通隧道大量涌现.如何保证强震区隧道的震时安全性及环境敏感区列车振时稳谧性是当前亟待解决的关键技术难
目前,针对高聚物喷涂材料的动力特性尚不清晰,探究该材料的动力学特性将有利于其在隧道工程减震隔振领域的应用.本文基于高聚物注浆材料优良特
试验所用高聚物喷涂材料(下文简称高聚物)为一种非水反应类双组分喷涂型聚氨酯类材料. 该高聚物由A、B双组分反应而成,A组分由组合多元醇及发泡剂(改性HFO‑1233zd体系)等添加剂组成的组合料,B组分是主要成分为异氰酸酯的原材料,双组分按质量比1∶1混合反应后生成高聚物. 在适宜的条件下,使用喷涂设备将A组分和B组分充分混合后直接喷涂在隧道初期支护表面,迅速发泡与隧道初衬形成一体,对隧道衬砌适应能力强,且无拼缝,从根本上消除了热桥影响.
为尽可能还原现场施工中不同密度喷涂层自由膨胀的效果,本试验设计了双向开口的圆柱模具,并在常温(20 ℃)条件下,通过喷涂设备直接向涂有凡士林的模具喷涂混合浆液,材料膨胀固化后使用切割和打磨设备削掉因膨胀超出模具的部分材料,最终制成尺寸为50×100 mm的标准圆柱体试样.
基于扫描电镜(SEM)测试了不同密度高聚物试样的形貌与结构,并借助共振柱试验系统(GDS‑RCA)对高聚物进行动力特性试验.用动剪切模量Gd和阻尼比D表征高聚物的动力特性,并研究动剪应变γd、围压p和密度ρ对高聚物动力学特性的影响规律. 结合设备量程和隧道工程实际,设置激励电压UE为0.002、0.005、0.010、0.020、0.050、0.100、0.200 V,ρ为0.122、0.250、0.307、0.352、0.396 g/c
对试样施加逐渐增大的激励电压,由系统自动记录试样出现最大振幅时对应的扭转共振频率fnt,用于测定其动剪切模量Gd;阻尼比D通过自由振动法测得,当试样发生共振时切断动力,使其在无干扰力条件下自由振动,并测其衰减曲线,得到振次N与相对振幅A的关系曲线. 动剪切模量Gd与阻尼比D的计算
(1) |
(2) |
式中:hc为试样固结后的高度,cm;βs为扭转无量纲频率因数;δ为对数递减率;AN 、AN+m分别为第N、N+m次振幅.
不同密度高聚物的SEM照片见

图1 不同密度高聚物的SEM照片
Fig.1 SEM images of polymers with different densities
不同围压及不同密度下激励电压对高聚物动剪应变的影响规律相似.限于篇幅,本文仅给出围压p=400 kPa时高聚物的动剪应变与激励电压的关系,结果见

图2 高聚物动剪应变与激励电压的关系
Fig.2 Relationship between γd and UE of polymers (p=400 kPa)
不同密度下,围压对高聚物动剪切模量与动剪应变关系的影响规律相似,故本文仅以ρ=0.352 g/c

图3 不同围压下高聚物动剪切模量与动剪应变的关系
Fig.3 Relationship between Gd and γd of polymers at different confining pressures(ρ=0.352 g/c
不同围压下密度对高聚物动剪切模量-动剪应变关系的影响见

图4 不同围压下密度对高聚物动剪切模量-动剪应变关系的影响
Fig.4 Effect of density on the relationship between Gd and d of polymers at different confining pressures
动剪应变为0.01%时,不同围压下高聚物动剪切模量与密度的函数关系见
,p100 kPa | (3) |
,p200 kPa | (4) |
式中:a、A为动剪切模量常数,MPa;b、c、B为动剪切模量系数,MPa·c

图5 不同围压下高聚物动剪切模量与密度的函数关系
Fig.5 Relationship between Gd and ρ of polymers at different confining pressures(d=0.01%)
拟合得到的Gd‑ρ关系式也列于
阻尼比是阻尼系数与临界阻尼系数之比.一方面反馈了地震(振动)能量在材料内部因错动摩擦而耗能的情况;另一方面反映了波动在材料内部传播的衰减大小.错动量越大、传播途径越多,阻尼比越大.不同密度下,围压对高聚物动剪应变-阻尼比关系的影响规律相似,本节仅以密度ρ为0.122、0.250、0.396 g/c
不同密度下围压对高聚物阻尼比-动剪应变关系的影响见

图6 不同密度下围压对高聚物阻尼比-动剪应变关系的影响
Fig.6 Effect of confining pressure on the relationship between D and d of polymers at different densities
不同围压下密度对高聚物阻尼比-动剪应变关系的影响见

图7 不同围压下密度对高聚物阻尼比-动剪应变关系的影响
Fig.7 Effect of density on the relationship between D and d of polymers at different confining pressures
(1)随着动剪应变的增大,高聚物喷涂材料的动剪切模量呈线性减小,阻尼比先迅速增大后缓慢增加;相同密度条件下,当围压由300 kPa增加到400 kPa、400 kPa增加到500 kPa时,高聚物喷涂材料动剪切模量的增速先快后慢;当围压由100 kPa增加到300 kPa、300 kPa增加到400 kPa时,高聚物喷涂材料阻尼比的降速先快后慢.
(2)在低围压50、100 kPa下,较小动剪应变时,高聚物喷涂材料的动剪切模量随着密度的增大而增大,但当其动剪应变超过某一“应变阈值”时,高密度高聚物喷涂材料的动剪切模量随着密度的增大而减小;动剪应变、围压和密度三者对高聚物喷涂材料动剪切模量存在“耦合影响效应”;围压和密度对高聚物喷涂材料阻尼比存在显著的耦合影响效应;不同围压下高聚物喷涂材料密度与动剪切模量函数关系式可用于工程实际中快速计算不同围压条件下由不同密度高聚物喷涂材料构成的减震隔振层的动剪切模量.
(3)高聚物耗能依靠泡孔间的错动摩擦和对波动传播的衰减两者共同作用,较高围压下,密度为0.250 g/c
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