Flexural creep test and prediction of GFRP-balsa sandwich beams
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摘要: 以玻璃纤维增强复合材料(GFRP)为面层,轻木(Balsa)为芯材的GFRP-balsa夹芯结构在基础设施领域的应用范围不断扩大,但GFRP-balsa夹芯结构具有粘弹性,易于发生蠕变变形。为此,在温度为(25±1)℃,相对湿度为55%±5%的环境下,利用自主设计的弯曲蠕变加载装置对GFRP-balsa夹芯梁在20%、25%和30%荷载等级下的三点弯曲蠕变性能进行了3000~8760 h的测试,并利用多种模型对GFRP-balsa夹芯梁的蠕变响应进行了模拟和预测。结果表明:在试验荷载等级下,GFRP-balsa夹芯梁表现出线性粘弹性;弯曲蠕变对GFRP-balsa夹芯梁的跨中挠度具有重要影响,所有试件在3000 h的蠕变系数均不小于0.35;Findley模型适用于单一荷载等级下GFRP-balsa夹芯梁时变总挠度的拟合,在3000 h的拟合值与试验值之间的最大相对误差仅为0.7%;Bailey-Norton模型和通用幂次律模型分别适用于荷载等级不超过30%的GFRP-balsa夹芯梁蠕变挠度和时变总挠度的预测,在一年时,Bailey-Norton模型和通用幂次律模型预测值与试验值之间的最大相对误差分别为8.3%和5.9%。
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关键词:
- 玻璃纤维增强复合材料 /
- 轻木 /
- 夹芯梁 /
- 弯曲蠕变 /
- 预测模型
Abstract: The application scope of the glass fiber reinforced plastic (GFRP)-balsa sandwich structure composed of GFRP facings and a balsa wood core is constantly expanding in the field of infrastructure. However, GFRP-balsa sandwich structures are susceptible to creep deformation due to their viscoelasticity. Under the controlled temperature of (25±1)℃ and relative humidity of 55%±5%, the three-point flexural creep performance of the GFRP-balsa sandwich beams at 20%, 25% and 30% load levels were tested for a period of 3000-8760 h using the self-designed flexural creep loading devices. Various models were used to simulate and predict the creep response of the GFRP-balsa sandwich beams. The results show that the GFRP-balsa sandwich beams exhibit linear viscoelasticity at the test load levels. Flexural creep has an important impact on the mid-span deflection of the GFRP-balsa sandwich beams, and the creep coefficients at 3000 h of all the specimens are not less than 0.35. The Findley model is applicable for fitting the time-dependent total deflection of the GFRP-balsa sandwich beams at a single load level, and the maximum relative error between the fitting value and the test value at 3000 h is only 0.7%. The Bailey-Norton model and the general power law model are applicable for predicting the creep deflection and the time-dependent total deflection of the GFRP-balsa sandwich beams when the load level does not exceed 30%, respectively. At one year, the maximum relative error between the predicted value of the Bailey-Norton model and the test value is 8.3%, and the maximum relative error between the predicted value of the general power law model and the test value is 5.9%.-
Key words:
- glass fiber reinforced plastic /
- balsa /
- sandwich beam /
- flexural creep /
- prediction model
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表 1 蠕变测试试件尺寸及加载情况汇总
Table 1. Summary of the dimensions and the loading conditions of the creep test specimens
Specimen Length/
mmWidth/
mmDepth/
mmF/N 20%-1 380.3 69.82 28.80 1196 20%-2 379.8 69.88 28.76 20%-3 380.5 70.02 28.74 25%-1 380.0 69.90 28.82 1495 25%-2 380.2 69.96 28.78 25%-3 379.4 69.96 28.70 30%-1 380.0 69.78 28.74 1794 30%-2 380.2 69.98 28.72 30%-3 380.1 70.00 28.78 Notes: "20%", "25%" and "30%" refer to the load level; "1", "2" and "3" refer to the serial number in a repeated test; F—Required force to be applied at the loading point. 表 2 GFRP-balsa夹芯梁三点弯曲蠕变测试结果汇总
Table 2. Summary of the three-point flexural creep test results of the GFRP-balsa sandwich beams
Specimen d/mm da/mm D/mm Da/mm Dc/mm Dca/mm $\phi $ 20%-1 1.11 1.03±0.075 1.52 1.43±0.085 0.41 0.40±0.012 0.37 20%-2 0.96 1.35 0.39 0.41 20%-3 1.03 1.42 0.39 0.38 25%-1 1.30 1.32±0.082 1.80 1.81±0.091 0.50 0.49±0.012 0.38 25%-2 1.25 1.73 0.48 0.38 25%-3 1.41 1.91 0.50 0.35 30%-1 1.55 1.60±0.050 2.15 2.19±0.040 0.60 0.59±0.021 0.39 30%-2 1.65 2.23 0.57 0.35 30%-3 1.60 2.20 0.61 0.38 Notes: d—Initial static deflection; da—Mean initial static deflection; D—Total deflection at 3000 h; Da—Mean total deflection at 3000 h; Dc—Creep deflection at 3000 h; Dca—Mean creep deflection at 3000 h; $\phi $—Creep coefficient at 3000 h. 表 3 不同荷载等级下GFRP-balsa夹芯梁测试跨中挠度与容许挠度的对比
Table 3. Comparison of the test mid-span deflections and the allowable deflections of the GFRP-balsa sandwich beams at the different load levels
Load level Deflection type Comparison [l/150] [l/200] [l/250] 20% da < < < Da < < > 25% da < < > Da < > > 30% da < > > Da > > > Note: l—Span length. 表 4 Findley模型中各参数拟合结果汇总
Table 4. Summary of the fitting results of various parameters in the Findley model
Load level d a N R2 20% 0.9798 0.1481 0.1410 0.9953 25% 1.2752 0.1767 0.1410 0.9978 30% 1.5454 0.2299 0.1320 0.9971 Notes: a—Amplitude of creep; N—Time exponent. 表 5 GFRP-balsa夹芯梁一年时的蠕变测试值与模型预测值对比
Table 5. Comparison of the creep test values and the model prediction values at one year for the GFRP-balsa sandwich beams
Load level Dce/
mmDcB/
mmδ1/
%De/
mmDG/
mmδ2/
%20% 0.44 0.47 6.4 1.47 1.48 0.7 25% 0.55 0.60 8.3 1.85 1.91 3.1 30% 0.67 0.73 8.2 2.22 2.36 5.9 Notes: Dce—Creep deflection test value at one year; DcB—Bailey-Norton model extrapolated value at one year; δ1—Relative error between Dce and DcB; De—Total deflection test value at one year; DG—General power law model prediction value at one year; δ2—Relative error between De and DG. -
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