Lik-ho Tam

Beihang University (BUAA) | BUAA · Department of Civil Engineering

This paper presents a numerical investigation of the flexural behavior of timber beams externally strengthened with carbon-fiber-reinforced polymer (CFRP) sheets. At first, the accuracy of linear elastic and elastic-plastic models in predicting the behavior of bare timber beams was compared. Then, two modeling approaches (i.e., the perfect bond met...

The exceptional mechanical properties of carbon nanotubes (CNTs) have encouraged the development of high-performance synthetic fibers in composite materials. To understand the effect of twisting on the mechanical and slipping performances of CNT bundles, molecular dynamics simulation is applied to investigate the tensile performances, failure mode,...

In recent years, with the fast development of the technology and the economy associated with the growth of the global population, the construction of economical, sustainable, and eco-friendly infrastructures with improved ductility, resistance to external elements, and durability has increased the need for the development of high-performance constr...

Carbon fiber-reinforced polymer (CFRP) composite has been increasingly used in constructions, which is subjected to external loads that cause severe nonlinear vibrations and final structural failure. In this work, a machine learning approach is adopted to investigate nonlinear vibrations of CFRP composite. A dataset about nonlinear frequency ratios...

Normally, raw and non-vulcanized polymer matrix is sticky, soft, and exhibits poor mechanical, electrical, and thermal properties. In order to improve the properties of polymer matrix, different nanofillers have been used as the reinforcements, such as carbon nanotube, graphene, clay minerals, and silica, and different processing techniques have be...

Fiber-reinforced polymer composites have been increasingly applied as reinforcing and load-bearing components in building constructions and civil infrastructures. Long-term exposure to changing environmental and loading conditions leads to composite degradation, which is highly related to degraded structure and properties of fiber/ matrix interface...

Epoxy thin films have been widely used in microelectromechanical systems, aerospace and civil engineering, which are exposed to external excitations in wet environment that lead to severe nonlinear vibration. In this paper, a multiscale simulation consisting of molecular simulation and meshless simulation is adopted to study moisture effect on nonl...

Web crippling is a critical premature failure of pultruded glass fiber reinforced polymer (GFRP) composites. One solution is to combine several sections to form a built-up section to carry the web crippling load. However, there is no existing study on the web crippling behavior of built-up sections under transverse loading. This paper presents an e...

This paper reports an investigation on the damage tolerance of adhesively bonded pultruded glass fiber–reinforced polymer (GFRP) joints under fatigue loading. Double-strap joints with and without bondline defects were subjected to constant amplitude fatigue loading. The study investigated the effects of the defect location, size, and number on the...

The shear response of ultra-high performance fiber reinforced concrete (UHPFRC)-encased H-shaped steel section composite beams is simulated using a three-dimensional (3D) non-linear finite element model (FEM) in the present study. The proposed FEM's accuracy is validated against experimental data from previously tested steel and UHPFRC beams availa...

Mechanical performance of polyvinyl alcohol (PVA) gel features temperature dependence, which is closely related to the behaviors of water molecules at the microscale. In this study, we use molecular dynamics simulation to study the effect of temperature on hydrogen bonding and tensile properties of PVA gel. By analyzing the states of water molecule...

恰逢我国“十四五”规划系统布局新型基础设施与现代综合交通运输体系建设，以及国家重点研发计划启动实施“先进结构与复合材料”重点专项之际，受《复合材料学报》编委会的邀请，组织出版了本期“高性能纤维增强复合材料结构与性能的多尺度研究”专栏，邀请了来自北京科技大学、同济大学、哈尔滨工业大学、浙江大学、东南大学、大连理工大学、湖南大学、上海交通大学、长沙理工大学、合肥工业大学、南京林业大学等数十家单位的优秀团队与科研工作者，报道了纤维增强复合材料与结构相关的研究进展。按照学报审稿流程和审稿要求对投稿论文进行多轮评审和修改，最后录用了1篇综述论文和50篇研究论文，内容涵盖了新型高性能纤维增强树脂基和水泥基复合材料以及混凝土材料等研究方向，涉及相关材料与结构的多尺度结构设计、制备工艺、性能表征和应用技术。

本文从价值认知、政策驱动和自然架构的角度，对传统聚落空间的地理位置和生态环境进行了理论研究，结合传统文化保护的国家方针政策，因地制宜提出了“以点成线，以线带面，面面相连”的聚落数字连片保护方案。通过科技手段对传统民居进行了数字化的建模和创新性应用，实现聚落空间文化在传承中发展、在保护中活化。研究成果为河北省乃至全国传统聚落的连片保护起到了参考借鉴的作用，为推动中华优秀传统文化创造性转化和创新性发展提供了思路和方法。

Steel structures strengthened with CFRP (carbon fiber-reinforced polymer) composite may encounter extreme load such as earthquake or impact which may cause steel yielding and plasticity. But very limited investigations exist on the effect of steel yielding on the bond behaviour between CFRP and steel. This paper presents a comprehensive study on th...

Steel plate connection is popular in modern timber structures. However, the steel plate may be subjected to corrosion issue due to the presence of moisture in timbers. This paper proposes to replace steel plate with glass fiber reinforced polymer (GFRP) plate for connecting timber elements, so that the durability of the timber structure is expected...

Adhesive bonding has gained increasing acceptance in joining pultruded glass fiber reinforced polymer (GFRP) sections. However, one of the major issues hindering the widespread application of adhesive bonding in building and construction industries is the difficulty in predicting the mechanical behavior of the joints in the presence of adhesion def...

Polymer resins have yellowing issue when subjected to elevated temperatures or UV exposure, which limit their applications in color-sensitive fields. This paper presents an experimental study on the yellowing mechanisms of epoxy and vinyl ester resins under thermal, UV and natural aging conditions. Anti-yellowing methods including air isolation, an...

This work focuses on molecular creep behavior of carbon fiber/epoxy interface under sustained loads at different levels. Threshold stress and energy barrier for the onset of interfacial creep failure under peeling loads are found greater than those under shearing. Microstructural changes during creep show that the epoxy has a large and irreversible...

Owing to the excellent mechanical properties, polymethyl methacrylate (PMMA)/carbon nanotube (CNT) composite has been increasingly adopted in the aerospace field, which is usually subjected to various temperature conditions and supersonic aerodynamic loads. Using a molecular dynamics (MD)-based multiscale simulation, the nonlinear forced vibration...

With rapid development of society and economics, frequent population flow and transportation activities have increased the demand for improving load capacity and resilience of building construction and civil infrastructures. Compared with traditional building materials, fiber-reinforced composite (FRC) materials possess outstanding properties inclu...

Polypropylene (PP) is vulnerable to creep under constant loads, which is a serious problem for PP-based applications. By incorporating carbon nanotubes (CNTs), the CNT/PP composite exhibits improved creep resistance, while the CNT aggregation with high contents could limit the improvement. In order to ensure the long-term durability, the creep resp...

The volume fraction of the carbon nanotube (CNT) plays a key role in ensuring the performance of the CNT reinforced polymer composite, especially under the severe vibration, which leads to the resonance and failure of the composite structure. In this paper, a bottom-up multiscale method is adopted to study the effect of the CNT volume fractions on...

With promising mechanical properties, fiber reinforced polymer (FRP) composite has increasing applications in civil engineering, such as external strengthening material for building structures, and load-bearing component and internal reinforcement for new constructions. During intended service-life, the composite is inevitably exposed to changing e...

为研究钢板屈服对碳纤维增强树脂基复合材料（CFRP）-钢粘接界面的性能影响，开展了一系列CFRP-钢双搭接粘接节点拉伸试验和有限元模拟。以钢板厚度和CFRP粘接长度为变量，通过拉伸试验，得到了钢板屈服条件下的节点拉伸荷载-位移曲线、有效粘接长度和失效模式。试验结果表明，15mm厚钢板的粘接节点在破坏之前表现为弹性状态，而8mm厚钢板的粘接节点破坏前已经屈服并进入塑性状态。钢板屈服使得节点的荷载-位移曲线由线性变为非线性，且钢板屈服时节点的失效位移增加；随着钢板屈服，节点的失效模式由CFRP层离破坏变为CFRP层离和钢板-胶层界面脱粘混合模式，且随着钢板屈服程度的增大，钢板-胶层脱粘面积也在增大。根据本文所采用的节点试件及所选取的材料属性，当8mm厚钢板节点在出现钢板屈服后，其失效位移约为15...

尺寸效应是土木工程领域研究的重要课题。随着3D打印技术的广泛应用，了解3D打印试件的尺寸效应十分重要。本文通过五种尺寸的3D打印石膏立方体试件的单轴抗压试验研究了3D打印石膏试件的尺寸效应，研究发现3D打印石膏试件抗压强度随尺寸增大而降低，不同尺寸试件具有相似的破坏模式，但由于粘结点个数和位置具有一定的随机性导致小尺寸试件抗压强度离散性较大。

With the incorporation of carbon nanotubes (CNTs), the CNT/Polypropylene (PP) composites are found to possess enhanced mechanical properties, but the reinforcing effect of CNT weakens at high-percentage addition due to the CNT aggregation. To optimize the properties of nanocomposite, it requires a fundamental understanding of the effect of CNT disp...

Due to the high load-bearing capacity and light weight, composite leaf spring with variable width and variable thickness has been increasingly used in the automobile industry to replace the conventional steel leaf spring with a heavy weight. The optimum structural design of composite leaf spring is particularly favorable for the weight reduction. I...

The strong interfacial integrity of FRP/concrete bonded system is shown to be significantly weakened in wet environment, with the interfacial debonding between concrete and epoxy adhesive as a major failure mode. However, the fundamental mechanism is still largely unknown. Here a molecular model of calcium silicate hydrate (C-S-H)/epoxy interface i...

Steel plate bolted connections are frequently used in timber structures. However, these connections may incur durability problem due to the corrosion of the steel plates. This paper proposes using GFRP plate to replace steel plate in timber connections to mitigate the corrosion issue. The group effect of the proposed GFRP-timber bolted connection i...

Poly (methyl methacrylate) (PMMA)/carbon nanotube (CNT) composite plates have been extensively used in aviation and aerospace fields. During intended service life, the PMMA/CNT composite structure is prone to severe vibration, which leads to the formation of cracks and the fracture of structures. In order to achieve vibration attenuation, it requir...

木结构中多采用钢板-木螺栓连接节点，由于木材本身含水率及环境影响，会导致钢板发生腐蚀，从而给结构带来耐久性问题。文章提出采用拉挤成型玻璃纤维增强复合材料(GFRP) 板替代钢板作为木结构的连接板，以提高结构耐久性，并且研究了 GFRP 板-木螺栓连接节点的群组效应。文章通过 GFRP 板-木螺栓连接节点拉伸试验，研究螺栓直径、螺栓间距、螺栓个数、螺栓列数等关键参数对螺栓连接群组效应的影响，分析节点失效模式和荷载-位移曲线。研究结果表明，GFRP 板-木螺栓连接节点的抗拉承载力与螺栓直径和螺栓数量正相关，与螺栓间距无关。最后文章根据试验结果提出 GFRP 板-木螺栓连接节点考虑群组效应的抗拉承载力计算公式。

Steel structures strengthened with CFRP composite may have potential galvanic corrosion issue. It was recommended that a layer of glass fiber sheet (GFS) be embedded in the adhesive layer to protect the CFRP-steel bonded system against galvanic corrosion. But the inclusion of GFS in the adhesive may negatively affect the bond behaviour between stee...

Carbon fiber-reinforced polymer (CFRP) composite is subject to external loads during service life, suffering the interfacial creep between the fiber and the matrix and eventually the interfacial slippage. CFRP composite loses the interfacial integrity due to the interfacial creep and the long-term durability is weakened. In order to understand the...

Seawater sea sand concrete (SWSSC) is a promising alternative to ordinary concrete in terms of saving valuable natural resources of freshwater and river sand. Basalt fiber reinforced polymer (BFRP) rebars can be a good solution to corrosion of steel rebars in SWSSC. This paper presents an experimental study on the bond behavior between SWSSC and BF...

With a network structure formed by cross-linking process, epoxy resins possess excellent mechanical properties. Among them, SU-8 photoresist (bisphenol-A epoxy resin) is widely used as coatings in mi-croelectronic applications. This paper reports molecular dynamics simulations of the cross-linking process of SU-8 photoresist with detailed scripts a...

Interfacial bonding between fiber and matrix plays an essential role in composites, especially in fiber reinforced cementitious composites that are superior forms for bearing flexural and tension load in construction applications. Yet, despite the importance, effective and economical approaches to improve the interfacial bonding between steel fiber...

在土木工程领域， 碳纤维增强复合材料 (CFRP) 由于有着优异的力学性能而被越来越多地用在建筑结构中。 碳纤维与环氧树脂之间粘结界面的性能对于 CFRP 内部应力的有效传递极为关键， 并很大程度上决定了复合材料的长期耐久性能。 然而， 纤维/树脂粘结界面易受到湿热、 盐雾及海水等恶劣环境的侵蚀， 导致界面脱粘及最终的复材破坏。 为了确保复材的长期耐久性能， 需要全面认识界面在环境侵蚀下的退化行为。分子动力学模拟可以“自底向上” 地描述界面在环境侵蚀下的行为， 有利于探究界面的退化和失效机制。 本文综述了不同环境因素影响下碳纤维/环氧树脂界面退化的分子模拟研究进展， 包括界面模型的建立， 界面在潮湿、 盐雾等环境中结构、 性能的退化及其背后的机制。 最后， 提出了未来界面退化的研究方向， 例...

Pultrude glass fiber reinforced polymer (GFRP) sections have gained increasing acceptance in building and construction industries considering their promising physical and mechanical properties. However, they are prone to premature web crippling failure due to their orthotropic nature and relatively low interlaminar shear strength and modulus when s...

Stability has been an important subject in the design of a portal frame structure. Conventional stability analysis of the portal frame is normally conducted assuming that all the joints are rigid. However, the joints of a portal frame in real applications are not always rigid and semirigid connections often exist. AISC design code requires that the...

Carbon fibre reinforced polymer (CFRP) composite has an increasing usage in civil engineering, including the external reinforcements and internal rebars in civil infrastructures, and the load-bearing materials in composite structures, in which the CFRP composite is inevitably subject to constant loads. The external loads on the CFRP composite cause...

Understanding the deformational and failure behaviors of thermoplastic semicrystalline polymers is crucial due to the practical usages in various engineering applications. Taking isotactic polypropylene (iPP) as a semicrystalline polymer model system, atomistically informed coarse‐grained (CG) molecular dynamics (MD) simulations are employed to inv...

Carbon fiber reinforced polymer (CFRP) composite has been increasingly used in civil engineering field. The durability of CFRP composite is highly dependent on the interfacial integrity between carbon fiber and epoxy matrix. During the long-term service-life, the composite is inevitably subject to external loading, which causes the creep between fi...

The strong interfacial interaction between carbon fiber and epoxy matrix plays a key role in ensuring the performance of carbon fiber reinforced polymer (CFRP). During a prolonged service-life, CFRP is inevitably exposed to the hygrothermal environment and the integrity of fiber/matrix interface is most vulnerable, but the microscopic behavior of t...

In this work, molecular dynamics simulation is used to study the effect of hygrothermal conditioning on carbon fiber/epoxy interface. By simulating the debonding process, it is measured that the interface possesses lowest adhesion in high-temperature saltwater, which is related with the epoxy mechanical degradation, as demonstrated by the depressed...

Defects between fiber reinforced polymer (FRP) and repaired concrete components may easily come out due to misoperation during manufacturing, environmental deterioration, or impact from external load during service life. The defects may cause a degraded structure performance and even the unexpected structural failure. Different non-destructive tech...

The robust structural integrity of the epoxy plays an important role in ensuring the long-term service life of its applications, which is affected by the absorbed moisture. In order to understand the mechanism of the moisture effect, the knowledge of the interaction and dynamics of the water molecules inside the epoxy is of great interest. Molecula...

由于其优异的力学性能，碳纤维增强复合材料（ CFRP）近年来被越来越多地应用在海洋、水工结构中，例如作为海水-海砂混凝土的加强筋。在 CFRP 复材中，碳纤维/环氧树脂粘结界面起着均衡应力、传递应力等作用，此界面的粘结性能直接影响复合材料的宏观力学性能。在潮湿、海水等服役环境下， CFRP 复材的性能会发生退化，以纤维/树脂粘结界面为关键退化部位。然而，目前对环境侵蚀下碳纤维/环氧树脂粘结界面退化的机理所知甚少。本研究目的是探索高温盐水环境下碳纤维/环氧树脂粘结界面的退化机理。通过建立粘结界面的全原子分子动力学模型，在干燥、水以及盐水环境下对其进行模拟，确定粘结界面在高温盐水环境下粘接性能的退化程度，并与已有的实验结果进行对比，对模拟方法进行验证。同时，比较不同环境下纤维表层环氧树脂的玻璃化...

Epoxy resins are widely used as matrices for bonding carbon fiber tightly together in fabricating carbon fiber reinforced polymer (CFRP), which has been increasingly used in marine and offshore applications. To analyze CFRP performance in salt environment, it requires a fundamental understanding of the behavior of carbon fiber/epoxy interface under...

The fiber reinforced polymer (FRP) has been increasingly used for strengthening concrete infrastructure through external bonding by using epoxy adhesive. The long-term durability of FRP-concrete structure is seriously degraded under hygrothermal environment at high level of temperature and humidity, which is mainly caused by interfacial debonding b...

Polymeric materials have received tremendous attention in both industrial and scientific communities, and can be readily found in applications across a large range of length scales, ranging from the nanoscale structures, such as the photoresist lithography in the micro-electro-mechanical systems, to the macroscale components, such as the adhesive b...

The epoxy-bonded system has been widely used in various applications across different length scales. Prior investigations have indicated that the moisture-affected interfacial debonding is the major failure mode of such system, but the fundamental mechanism remains unknown, such as the basis for the invasion of the water molecule in the cross-linke...

The strong structural integrity of polymer nanocomposite is influenced in the moist environment; but the fundamental mechanism is unclear, including the basis for the interactions between the absorbed water molecules and the structure, which prevents us from predicting the durability of its applications across multiple scales. In this research, a m...

Changes in chemical structure have profound effects on the physical properties of epoxy-based materials, and eventually affect the durability of the entire system. Microscopic structural voids generally existing in the epoxy cross-linked networks have a detrimental influence on the epoxy mechanical properties, but the relation remains elusive, whic...

Graphene is one of the most promising materials in nanotechnology. It is crucial to establish reliable structure–property relationships in the important two-dimensional crystals—graphene—to fully use their remarkable properties. With the success in synthesizing large-area polycrystalline graphene, understanding how grain boundary loops in graphene...

The damage evolution and structural failure in trees and other plants are mainly originated from the plastic yielding in the wood cell wall at the microstructural level, which consists of cellulose fibrils embedded in a polymer matrix of hemicellulose and either lignin or pectin. Understanding the mechanical behavior of wood cell wall at the plasti...

Cellulose is one of the most abundant substances in the world, and the major constituent in the wood structure. Phenolic adhesive is largely used in the wood manufacture for gluing the wood panels together. The cellulose/phenolic adhesive interface is a representative of the interface between the wood panels and adhesives in the wood products. As t...

Adhesive bonding of fiber-reinforced polymers (FRP) to wood has been proven as a general way to achieve reinforcement and rehabilitation for wood structures. Although a significant mechanical enhancement can be acquired by using such approach, there exists a big concern about the long-term performance of the FRP–wood composite, especially under the...

Epoxy-based materials are extensively used in industry due to their excellent mechanical and thermal stability. As the epoxy products are getting smaller and smaller nowadays, there are difficulties arising from the material processing and measurement, which need to be carefully considered in the design stage. SU-8 photoresist, which is commonly us...

Organic composite materials can be readily found in our daily life, such as plywood used in construction industry and bamboo composites as indoor and outdoor flooring materials. These organic composite material systems consist of cellulose fibers bonded with each other through adhesives, leading to a bonded system with a gradient structure that pos...

We pioneered a study about how the geometric relationship of single-walled carbon nanotubes (SWCNT) is influenced by curvature factor and non-planar geometry factor in cylindrical coordinate system based on the assumption of complete symmetry. The bond length and angle of every carbon-carbon bonds are determined by using the principle of the minimu...