Study of Hygrothermal Behavior of Bio-Sourced Material Treated Ecologically for Improving Thermal Performance of Buildings

Creating sustainable cities is the only way to live in a clean environment,and this problem can be solved by using bio-sourced and recycled materials.For this purpose,the authors contribute to the valuation of sheep wool waste as an eco-friendly material to be used in insulation.The paper investigates the thermal,hygrothermal,and biological aspects of sheep wool by testing a traditional treatment.The biological method of aerobic mesophilicflora has been applied.Fluorescence X was used to determine the chemical composition of the materials used.Also,thermal characterization has been conducted.The thermal conductivity is above 0.046(W·m^(-1)·K^(-1))and the thermal diffusivity is 1.56.10^(-6) m^(2)·s^(-1).Besides,the energy efficiency of using sheep wool in buildings was studied.Furthermore,its humidity behavior was evaluated in different aspects in both winter and summer.Results of biological analyses show the efficiency of the treatment by removing the majority of the microorgan-isms:the value of yeast and mildew was reduced from 38.10^(2) to 2.10^(2)(UFC·g^(-1)).In addition to that,sheep wool permits obtaining a low thermal transmittance on the scale of the walls and low cooling needs on the scale of the building with a gain of 45%and 52%,respectively.

The Thermal Comfort and Hygrothermal Performance of the First Certified Passive House in Estonia

This study presents the thermal comfort and hygrothermal performance of building envelope of the first certified passive single-family detached house in Estonia.Temperature and humidity conditions were measured from different rooms and building envelopes.This article presents analysis of measurement results during the first year after construction.Results showed high room temperature,achieved mainly due to large windows with southern exposure and the small heat loss of the building envelope.High indoor temperature decreased the indoor RH(relative humidity)to quite low levels.Even the RH was low,the moisture excess was high indicating that the design of PH(passive houses)indoor humidity loads cannot be decreased.Humidity in the externally insulated cross-laminated timber panels was observed to be high,caused by drying out of the constructional moisture and the high diffusion resistance of the wood fibre sheathing board.That caused water vapour condensation and risk for mould growth.In conclusion,while planning buildings with high-energy efficiency,more focused attention should be paid to the performance of the building service systems and moisture safety already in the preliminary stages of design.

BUCKLING AND POSTBUCKLING OF LAMINATED THIN CYLINDRICAL SHELLS UNDER HYGROTHERMAL ENVIRONMENTS

The influence of hygrothermal effects on the buckling and postbuckling of composite laminated cylindrical shells subjected to axial compression is investigated using a micro-to-macro-mechanical analytical model. The material properties of the composite are affected hy the variation of temperature and moisture, and are hosed on a micromechanical model of a laminate. The governing equations are based on the classical laminated shell theory, and including hygrothermal effects. The nonlinear prebuckling deformations and initial geometric imperfections of the shell were both taken into account. A boundary layer theory of shell buckling was extended to the case of laminated cylindrical shells under hygrothermal environments, and a singular peturbation technique was employed to determine buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling behavior of perfect and imperfect, cross-ply laminated cylindrical shells under different sets of environmental conditions. The influences played by temperature rise, the degree of moisture concentration, fiber volume fraction, shell geometric parameter, total number of plies, stacking sequences and initial geometric imperfections are studied.

Effect of Hygrothermal Cycle Aging on the Mechanical Behavior of Single-lap Adhesive Bonded Joints

The aging behavior of single lap joints(SLJ) in hygrothermal cycles was investigated and compared by using a shearing strength test, Fourier transform infrared spectroscopy(FTIR), thermogravimetric analysis(TG/DTG), energy dispersive spectrometry(EDS) and scanning electronic microscopy(SEM). The temperature/relative humidity was set at 80 ℃/95% and –40 ℃/30% for 20 cycles, 40 cycles, and 60 cycles(one cycle was 12 hours), respectively. The experimental results show that hygrothermal aging significantly decreases the failure strength of adhesive joints. However, the failure displacement increases as the number of aging cycles increases. In addition, hygrothermal aging changes the failure mode of the adhesive joints from a cohesive fracture in un-aged adhesive layers to an interfacial failure of aged adhesive joints.

Comparison of Decontamination Efficacy between the Rapid Hygrothermal Pasteurization and Sodium Hypochlorite Treatments

We developed a novel rapid hygrothermal pasteurization (RHP) method using saturated water vapor with a dew point of 100℃. The aim of this paper is to compare the effect of RHP treatment versus conventional sodium hypochlorite (NaClO) treatments on inactivation of natural mesophilic bacteria and quality attributes on fruits and vegetables. The RHP treatment was performed within a second by free-falling samples (cabbage, cucumber, carrot, bell pepper, pineapple and melon) through cylindrical processing chamber filled with steam. NaClO treatment was performed by washing samples with NaClO solution (100 mg/mL of free chlorine (pH 7), for 1 min). The RHP treatment showed a significantly higher inactivation effect than NaClO treatment on all tested samples. The RHP treatment had a slightly larger influence on color and vitamin C content than NaClO treatment in cabbage. Furthermore, the effects of treatment time and operated temperature were also determined using microbial model system. Elongation of treatment time did not significantly increase the microbial inactivation effect. Lowering of operated temperature by mixing air into steam tended to decrease the inactivation effect. From these results, RHP treatment could be used as an alternative method for decontaminating microorganisms on fruits and vegetables, except on leafy vegetable. In addition, it is suggested that microbial inactivation by RHP treatment was achieved through the initial condensation stage of water vapor on sample surface. By contrast, interfusion of air disturbed the effective condensation of water vapor.

The energy release rate for hygrothermal coupling elastic materials

In the fracture problems of hydrophilic elastic materials under coupling effects of heat conduction, moisture diffusion and mechanical deformation, the conventional J-integral is no longer path independent. The value of J is unequal to the energy release rate in hygrothermal coupling cases. In the present paper, we derived a general form of the energy release rate for hygrothermal fracture problems of the hydrophilic elastic materials on the basis of energy balance equation in cracked areas. By introducing the constitutive relations and the essential equations of irreversible thermodynamics, a specific expression of the energy release rate was obtained, and the expression can be reformmulated as path independent integrals, which is equivalent to the energy release rate of the fracture body. The path independence of the integrals is then verified numerically.

Effect Mechanisms of Hygrothermal Environments on Failure of Single-Lap and Double-Lap CFRP-Aluminum Bolted Joints

The high demands for load-carrying capability and structural efficiency of composite-metal bolted joints trigger in-depth investigations on failure mechanisms of the joints in hygrothermal environments.However,few studies have been presented to exhaustively reveal hygrothermal effects on the failure of CFRP-metal bolted joints,which differ from CFRP-CFRP or metal-metal bolted joints because of the remarkably different material properties of CFRPs and metals.In this paper,hygrothermal effects on tensile failures of single-lap and double-lap CFRP-aluminum bolted joints were experimentally and numerically investigated.A novel numerical model,in which a hygrothermal-included progressive damage model of composites was established and elastic-plastic models of metals were built,was proposed to predict the failures of the CFRP-metal bolted joints in hygrothermal environments and validated by corresponding experiments.Different failure mechanisms of single-lap and double-lap CFRP-aluminum bolted joints,under 23°C/Dry and 70°C/Wet conditions,were revealed,respectively.It follows that both the collapse failures of the single-lap and double-lap bolted joints were dominated by the bearing failure of the CFRP hole laminate in the two conditions,indicating that the hygrothermal environment did not change the macro failure modes of the joints.However,the hygrothermal environment considerably shortened the damage propagation processes and reduced the strength of the joints.Besides,the hygrothermal environment weakened the load-transfer capability of the single-lap joint more severely than the double-lap joint because it aggravated the secondary bending effects of the single-lap joint obviously.

Development and experimental validation of a one-dimensional dynamic hygrothermal modeling based on air humidity ratio

A modified one-dimensional transient hygrothermal model for multilayer wall was proposed using air humidity ratio and temperature as the driving potentials.The solution for the governing equations was obtained numerically by implementing the finite-difference scheme.To evaluate the accuracy of the model,a test system was built up to measure relative humidity and temperature within a porous wall and compare with the prediction of the model.The prediction results have good agreement with the experimental results.For the interface close to indoor side,the maximum deviation of temperature between calculated and test data is 1.87 K,and the average deviation is 0.95 K;the maximum deviation of relative humidity is 11.4%,and the average deviation is 5.7%.For the interface close to outdoor side,the maximum deviation of temperature between prediction and measurement is 1.78 K,and the average deviation is 1.1 K;the maximum deviation of relative humidity is 9.9%,and the average deviation is 4.2%.

Energy and long-term hygrothermal performance of building enclosures based on dynamic environmental simulation test

Dynamic environmental testing is an effective means to study the energy and long-term hygrothermal performance of building enclosures. Southeast University is designing and building a large-scale dynamic environment simulation testing facility. It can simuhaneously and dynamically simulate temperature, relative humidity, infrared solar radiation, UV radiation, and precipitation. A transformation is needed to predict the energy and long-term hygrothermal performance of building enclosures under real service conditions using data obtained from accelerated tests.

Out-of-Plane Compressive Behavior for UHMWPE/Polyurethane Composites after Hygrothermal Treatment

Quasi-static and high strain rate compressive behaviors and failure mechanisms of hygrothermal treated ultra-high molecular weight polyethylene/polyurethane(UHMWPE/PU)composites have been studied in this paper.Firstly,the UHMWPE composites were immersed in water at 70℃.The out-ofplane compression test was then performed on the dry/wet state specimens at quasi-static states(0.001-0.01 s^(-1))and high strain rate states(800-2 400 s^(-1)).The split Hopkinson pressure bar(SHPB)was adopted in the dynamic tests and waveform shapers were used to smooth and control the incident pulse.The results show that there are two platforms for the water absorption curve of UHMWPE composites.The absorption of moisture reduces the quasi-static compressive strength of the material while initially increasing,then decreasing the dynamic compressive strength.Matrix plasticization,fiber/matrix interface degradation and void expansion are the main factors affecting the irregular change of static/dynamic compressive strength of UHMWPE composites.

Hygrothermal effect on high-velocity impact resistance of woven composites

The woven glass fiber reinforced composites(GFRP)subjected to high-speed impact is investigated to identify the hygrothermal aging effect on the impact resistance.Both the hygrothermal aged and unaged glass/epoxy laminates are subjected to different impact velocities,which is confirmed as a sensitive factor for the failure modes and mechanisms.The results show the hygrothermal aging effect decreases the ballistic limit by 14.9%,but the influence on ballistic performance is limited within the impact velocity closed to the ballistic limit.The failure modes and energy dissipation mechanisms are confirmed to be slightly influenced by the hygrothermal aging effect.The hygrothermal aging effect induced localization of structural deformation and degradation of mechanical properties are the main reasons for the composite undergoing the same failure modes at smaller impact velocities.Based on the energy absorption mechanisms,analytical expressions predict the ballistic limit and energy absorption to reasonable accuracy,the underestimated total energy absorption results in a relatively poor agreement between the measured and predicted energy absorption efficiency.

The Influence of Two Natural Reinforcement Fibers on the Hygrothermal Properties of Earthen Plasters in Mogao Grottoes of China

Murals in Mogao Grottoes consist of three parts:support layer,earthen plasters and paint layer.The earthen plasters play a key role in the preservation of murals.It is a mixture of Dengban soil,sand,and plant fiber.Two different natural fibers,hemp fiber and cotton fiber,were reinforced to earthen plasters in the same percentage to evaluate the influence on hygrothermal performance.The two types of earthen plasters were studied:one containing hemp fiber in the fine plaster(HFP)and the other containing cotton fiber in the fine plaster(CFP).Specific heat capacity,dry thermal conductivity,water vapor permeability,and sorption isotherms were investigated.The results showed that the difference between two natural fibers has much more impact on the hygric properties(water vapor permeability and sorption isotherms)of earthen plasters than on their thermal performance(specific heat capacity and dry thermal conductivity).The CFP with higher density has higher thermal conductivity than the HFP with lower density.But no significant differences of specific heat capacity were observed.Compared with HFP,CFP used in murals can reduce the rate of water transfer and prevent salt from transferring water to the mural surface.The overall findings highlight that all these features of CFP are beneficial to the long-term preservation of murals.The study of the earthen plasters in Mogao Grottoes is of general significance,and the measured properties can be used to obtain coupled heat and moisture analysis of the earthen plasters and to dissect the degradation mechanism of murals.

Simulation of the Hygrothermal Behavior of a Building Envelope Based on Phase Change Materials and a Bio-Based Concrete

Phase Change Materials(PCMs)have high thermal inertia,and hemp concrete(HC),a bio-based concrete,has strong hygroscopic behavior.In previous studies,PCM has been extensively combined with many materials,however,most of these studies focused on thermal properties while neglecting hygroscopic aspects.In this study,the two materials have been combined into a building envelope and the related hygrothermal properties have been studied.In particular,numerical studies have been performed to investigate the temperature and relative humidity behavior inside the HC,and the effect of adding PCM on the hygrothermal behavior of the HC.The results show that there is a high coupling between temperature and relative humidity inside the HC,since the relative humidity changes on the second and third days are different,with values of 8%and 4%,respectively.Also,the variation of relative humidity with temperature indicates the dominant influence of temperature on relative humidity variation.With the presence of PCM,the temperature variation inside the HC is damped due to the high thermal inertia of the PCM,which also leads to suppression of moisture evaporation and thus damping of relative humidity variation.On the second and third days,the temperature changes at the central position are reduced by 4.6%and 5.1%,compared to the quarter position.For the relative humidity change,the reductions are 5.3%and 5.4%on the second and third days,respectively.Therefore,PCM,with high thermal inertia,acts as a temperature damper and has the potential to increase the moisture buffering capacity inside the HC.This makes it possible for such a combined envelope to have both thermal and hygric inertia.

湿热环境导致PCB腐蚀案例分析与优化

汽车电子接插件使用聚对苯二甲酸乙二醇酯(PET)与聚对苯二甲酸丁二醇酯(PBT)材料对端子进行了绝缘防护,但由于其与PCB形成狭窄空间结构,在潮湿环境下易结露形成液态水从而导致PIN脚腐蚀的问题。本文针对控制器接插件导致PCB腐蚀案例,结合控制器的工作环境,对控制器整车端接插件以及控制电路进行了分析,确定了引发PCB腐蚀的真因;之后从控制器端口防护、电源模块架构设计方向提出了改进措施,并通过整改方案的验证,证明了整改方案的有效性。并在最后从零部件环境负荷测试的角度也给出了验证建议。

湿热环境下复合材料含孔层合板静力拉伸性能及工程估算模型

湿热环境下的复合材料结构件力学性能预测对其工程应用具有重要意义。文中针对复合材料层合板静力拉伸性能和强度预测问题,开展6种湿热环境下复合材料含孔层合板的静力拉伸试验,分析其结构失效响应及损伤表征。基于应力场强法建立湿热环境下复合材料含孔层合板工程估算模型,与有限元渐进损伤模型和试验结果进行对比,分析了湿热环境对含孔层合板力学性能和拉伸失效的影响。结果表明,工程估算模型预测结果与有限元及试验结果误差范围较小,可用于预测温度和吸湿率对含孔层合板拉伸失效强度的影响;相比于室温干态,75℃吸湿饱和态下试件拉伸失效强度下降了6.1%;25℃干态和75℃吸湿饱和态下含孔层合板0°铺层出现最为严重的纤维拉伸失效,90°铺层出现最为严重的基体拉伸失效,纤维拉伸失效和基体拉伸失效为层合板主要破坏模式;通过扫描电镜对75℃吸湿饱和态下层合板厚度方向微观形貌进行分析,发现试件0°方向纤维与树脂的脱粘程度加重且出现明显的裂痕,90°方向纤维分布较为齐整,但黏附的树脂较少。

复合材料复杂环境效应加速试验设计及评估方法

目的指导复合材料在复杂湿热环境下环境适应性摸底与评价试验的开展,分析评估复合材料在复杂综合应力下的激活能参数。方法分析装备全寿命周期复杂自然环境剖面及各环境因素影响效应,确定复合材料各工作阶段敏感应力类型及条件,基于应力加速模型及累积损伤等原理,制定复合材料复杂环境效应综合加速试验剖面。构建复合材料复杂环境条件下的动力学模型,并提出相应参数估计方法。开展复合材料加速试验,并基于实测数据开展复合材料性能退化建模与评估。结果分析了复合材料全寿命周期环境影响因素及环境效应,明确了各工作阶段敏感应力主要有温度、湿度、太阳辐照、温度交变、振动以及冲击等。依据实际环境数据,设计并开展了3组不同湿热条件(80℃/75%RH、80℃/85%RH、80℃/95%RH)的综合试验,收集得到复合材料拉伸强度、拉剪强度、径向弯曲强度以及纬向弯曲强度等4种性能指标的试验数据。试验数据表明,拉剪强度(最大相对退化速率为0.1773/循环)、径向弯曲强度(最大相对退化速率为0.1292/循环)以及纬向弯曲强度(最大相对退化速率为0.2610/循环)等性能参数可用于产品退化建模与评估。通过参数估计,进一步确定了退化速率与湿热应力的关系,并针对当前试验提供了改进依据。结论复杂环境效应综合加速试验对装备复合材料产品经历复杂环境条件的模拟效果和加速效果较好,试验可实施性较强。提出的改进广义Eyring模型可涵盖温度应力与湿热应力的加速效应,并综合考虑多种应力的相互作用,通过少量组合试验便可量化评估激活能等参数。所建模型指出当前基于激活能参考值(Ea=0.7eV)试验方案可由不同温度应力的综合试验数据进一步修正与优化,且所提试验与分析方法主要针对大部分树脂基复合材料产品,并可依据需要推广至电子产品、机电产品等试验对象。

碳纤维层合板胶接接头在湿热环境下的性能演变

为了研究碳纤维复合材料(CFRP)胶接接头对汽车涂装过程中的高温高湿环境的适应性,对单搭接CFRP胶接接头进行了烘烤和加速吸湿实验,对经历不同湿热环境的胶接接头进行了剪切拉伸和正向拉伸试验,对连接强度改变及接头的失效模式演变进行了讨论,对环氧树脂与聚氨酯两种胶粘剂连接的接头对烘烤的适应性进行了比较,并研究了在搭接区域边缘增加胶瘤对提高连接强度的效果。研究结果表明:单搭接CFRP胶接接头的剪切拉伸强度远高于正向拉伸强度。烘烤处理后CFRP层合板及CFRP胶接接头的强度不但没有下降,反而有所提高。DP420环氧树脂胶比DP6330聚氨酯胶具有更好的耐烘烤性。吸湿后,CFRP胶接接头的强度、刚度以及最大断裂位移出现了减小。接头的失效模式从胶层内聚失效逐渐演变为与CFRP层合板的层间失效。在搭接区域边缘增加胶瘤能有效提高CFRP胶接接头的剪切拉伸强度。

铁锈锈斑污染对丝织品老化影响的研究

铁锈锈斑污染是纺织品文物的主要病害之一,严重影响文物的寿命及观赏价值。本文研究了不同老化条件下锈斑污染样和未污染样间老化程度的差异,旨在明晰锈斑污染及其在环境因素协同作用下丝织品的老化状态。结果表明:锈斑污染破坏了蚕丝纤维的外观形貌,拉伸性能和热稳定性的显著下降,加剧了蚕丝蛋白结构由β-折叠构象向α-螺旋构象和无序结构转变,使得未形成氢键—NH的数量下降,红外光谱中表现为酰胺Ⅰ带特征峰扁平化和I_(3280/1620 cm^(-1))峰高比下降;环境因素与锈斑污染起到了明显的协同作用,蚕丝的老化程度远大于环境条件、锈斑污染之和,其中土壤填埋老化的协同作用最强,湿热与紫外光老化次之。

湿热环境下端径比对复合材料螺栓连接结构静力拉伸失效的影响

为研究湿热环境下复合材料螺栓连接结构的静力拉伸性能,通过对七种不同端径比的T300碳纤维复合材料单钉单剪螺栓连接结构进行静力拉伸试验,得到不同端径比的连接结构在25℃干态(RTD)和70℃平衡吸湿(ETW)环境下极限失效载荷和破坏强度的变化规律,揭示了接头的破坏模式;建立复合材料单钉单剪螺栓连接有限元模型,对比不同端径比的连接结构试验的极限失效载荷,得到最优端径比为3;研究了湿热环境下最优端径比的连接结构不同铺层的损伤形式。结果表明,端径比从1增大到3时,RTD和ETW环境下连接结构的极限失效载荷分别增加了1.1倍和1倍,破坏强度均增加了1倍,当端径比从3增大到4时,RTD和ETW环境下极限失效载荷分别降低了6.56%和9.08%,破坏强度分别降低了6.83%和9.35%;在最优端径比下,与RTD环境下相比,ETW环境下连接结构的极限失效载荷和破坏强度分别下降了9.25%和9.52%,并且层合板孔周的压缩损伤更严重,存在更明显的纤维束拔起及纤维碎裂。

湿热环境下外贴CFRP加固RC梁抗弯性能有限元分析

本文研究了湿热环境下外贴CFRP加固RC梁抗弯性能。首先,基于已有的FRP-混凝土界面双参数黏结滑移模型,引入湿度和温度对断裂能G_(f)、界面刚度B的影响系数,建立了湿热环境下界面黏结滑移模型。然后,利用该界面模型对一组湿热条件作用下的试验梁进行有限元数值模拟,将模拟结果与试验结果进行对比分析,验证模型的正确性。最后,使用已验证的有限元模型深入分析不同湿热条件下CFRP与混凝土的宽度比和CFRP的加固量等因素对钢筋混凝土加固梁抗弯性能的影响。结果表明:本文建立的CFRP-混凝土黏结滑移模型,可以有效地模拟湿热环境下的界面性能;湿热条件下的加固梁主要发生剥离破坏,且随着湿热环境恶化,加固梁受弯承载力和对应的挠度明显下降;湿热环境下,可以通过适当增加CFRP与混凝土的宽度比和CFRP的加固量提高加固梁的受弯承载力。