Lingzhen Li

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Li

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Lingzhen

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0000-0001-8887-4498

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Publications 1 - 10 of 26

Strengthening of steel beams with adhesively bonded memory-steel strips
Wang, Sizhe; Li, Lingzhen; Su, Qingtian; et al. (2023)
Thin-Walled Structures
This study entails the development of a non-destructive prestressed strengthening solution for steel beams using adhesively bonded memory-steel (also known as iron-based shape memory alloy, Fe-SMA) strips. The Fe-SMA strip is activated via heating and subsequent cooling to generate prestress, while the two ends of the Fe-SMA strip are adhesively bonded as anchorages. The behavior of the Fe-SMA-to-steel bonded joints was investigated through lap-shear tests, from which an effective bond length of approximately 120 mm was determined. Subsequently, a strengthening solution for a 5.3 m span steel I-beam was designed based on finite element analysis. A 4200 mm × 100 mm × 1.5 mm Fe-SMA strip was bonded to the bottom of the steel beam with a bond length of three times the effective bond length, and a two-step activation strategy using torches was proposed. Furthermore, the designed strengthening solution was experimentally tested. With activation to the target temperature of 240 °C, the Fe-SMA developed a prestress level of approximately 280 MPa. A series of static and fatigue four-point bending tests were conducted. After 3 million cycles of fatigue loading, no debonding or degradation was observed for the adhesively bonded Fe-SMA-strengthened specimen; this demonstrated the reliable performance of the strengthening solution under service loads.
Arresting fatigue cracks in steel plates using prestressed bonded Fe-SMA strips: Analytical prediction and experimental validation
Li, Lingzhen; Wang, Sizhe; Chen, Tao; et al. (2025)
Thin-Walled Structures
Bonded iron-based shape memory alloy (Fe-SMA) strengthening has shown great potential in fatigue strengthening for steel structures. However, there is a lack of a comprehensive model for analysing the fatigue behaviour of systems strengthened with prestressed bonded Fe-SMA. This study proposes the first analytical model, integrating a prestress analysis and fatigue analysis, to predict fatigue crack arrest in steel plates strengthened with prestressed bonded Fe-SMA strips. Four steel plates, each featuring a central through-thickness crack, were strengthened using bonded Fe-SMA strips, and subsequently, tested under fatigue loading after generating prestress via heating and cooling. The proposed model succeeded in predicting (i) the fatigue crack arrest at certain load levels and (ii) onset of crack propagation at increased load levels.
Analysis and design recommendations for structures strengthened by prestressed bonded Fe-SMA
Li, Lingzhen; Wang, Sizhe; Chatzi, Eleni; et al. (2024)
Engineering Structures
Previous studies have demonstrated a great potential of prestressed strengthening of structures employing iron-based shape memory alloys (Fe-SMAs). A bonded Fe-SMA strengthening solution with partial activation has been proposed. However, an analytical model for assessing the strengthening efficiency was lacking, due to the unique nature of the employed prestressing mechanism involving heating. In this study, a symmetric strengthening model and an asymmetric strengthening model are developed to analyze the prestress level in steel and glass beams and plates strengthened by bonded Fe-SMA strips. The asymmetric strengthening model is then modified to analyze reinforced concrete (RC) beams strengthened by embedded Fe-SMA rebars. Recovery stress at different activation temperatures, the influence of the activation temperature on the adhesive bond, as well as the prestress loss resulting from the deformation of substrate elements and adhesive joints are taken into account. The predicted strains and deflections in the parent structure closely approximate the experimental measurements that appear in current literature. A parametric study and a sensitivity analysis are then conducted to assess the impact of the four influential features on the final prestress level, and their impact is ranked in the following order: recovery stress ≈ Fe-SMA width > activation length > bonded anchorage length. Based on these findings, a design strategy, in line with Eurocode 0, for the bonded/embedded Fe-SMA strengthening system is proposed. Finally, some perspectives on potential areas for future research are offered.
Bond behavior and debonding failure in Fe-SMA strengthened steel members
Li, Lingzhen (2023)
The porous cantilever beam as a model for spinal implants: Experimental, analytical and finite element analysis of dynamic properties
Du, Xiaoyu; Zhou, Yijun; Li, Lingzhen; et al. (2023)
Mathematical Biosciences and Engineering
Investigation of the dynamic properties of implants is essential to ensure safety and compatibility with the host's natural spinal tissue. This paper presents a simplified model of a cantilever beam to investigate the effects of holes/pores on the structures. Free vibration test is one of the most effective methods to measure the dynamic response of a cantilever beam, such as natural frequency and damping ratio. In this study, the natural frequencies of cantilever beams made of polycarbonate (PC) containing various circular open holes were investigated numerically, analytically, and experimentally. The experimental data confirmed the accuracy of the natural frequencies of the cantilever beam with open holes calculated by finite element and analytical models. In addition, two finite element simulation methods, the dynamic explicit and modal dynamic methods, were applied to determine the damping ratios of cantilever beams with open holes. Finite element analysis accurately simulated the damped vibration behavior of cantilever beams with open holes when known material damping properties were applied. The damping behavior of cantilever beams with random pores was simulated, highlighting a completely different relationship between porosity, natural frequency and damping response. The latter highlights the potential of finite element methods to analyze the dynamic response of arbitrary and complex structures, towards improved implant design.
Fatigue strengthening of cracked steel plates with bonded Fe‐SMA strips
Li, Lingzhen; Wang, Sizhe; Chen, Tao; et al. (2023)
ce/papers ~ EUROSTEEL 2023
Prestressed fatigue strengthening of steel structures has been proven effective by numerous investigations. Bonded iron-based shape memory alloy (Fe-SMA) strengthening has shown a great potential in this regard, however, with limited corroborating studies. Moreover, a proper model for fatigue analysis of systems that are retrofitted with bonded Fe-SMA strengthening is missing. In this study, an analytical model, coupling prestress analysis and fatigue analysis, is proposed. Four steel plates with central through-thickness cracks were strengthened with use of bonded Fe-SMA strips, and subsequently tested under fatigue loading after generating prestress via heating and cooling. The fatigue behavior predicted by the proposed model lies in excellent agreement with the fatigue testing results.
Influence of post-processing methods on bond-slip behavior of nonlinear Fe-SMA lap-shear joints
Li, Lingzhen; Martinelli, Enzo; Wang, Wandong; et al. (2024)
Case Studies in Construction Materials
Prestressed bonded strengthening for structures employing iron-based shape memory alloy (Fe-SMA) has been proven promising. Analyzing adhesively bonded joints necessitates a thorough understanding of the bond-slip behavior. However, when examining the bond-slip behavior of Fe-SMA-to-steel joints comprising nonlinear adhesives, the “forward” and “backward” post-processing methods, representing the current state-of-the-art, produce a trilinear and a trapezoidal bond-slip pattern, respectively, which is inconsistent. To address this inconsistency, the current study investigates the bond behavior of Fe-SMA-to-steel joints, with a particular focus on the bond-slip behavior. Two finite element (FE) joints, one featuring a linear adhesive and the other comprising a nonlinear adhesive, are modeled and compared against physical tests from literature. The “forward” and “backward” processing methods are used to analyze the bond behavior of the two FE joints. Eventually, the aforementioned inconsistency is resolved; a triangular and a trapezoidal bond-slip pattern are characterized for Fe-SMA-to-steel lap-shear joints with linear and nonlinear adhesives, respectively. The trilinear bond-slip behavior is concluded as a result of error accumulation and propagation during the “forward” processing. A hybrid post-processing method, which takes the advantages of both the “forward” and “backward” processing methods, is further proposed for inferring the full-range behavior; the resulting experimental behaviors closely align with simulations using a trapezoidal bond-slip model as input. A comparison against carbon fiber reinforced polymer (CFRP) lap-shear joints demonstrates similar bond-slip characteristics between Fe-SMA and CFRP lap-shear joints.
A Graphical Solution to Bond Capacity
Li, Lingzhen; Chatzi, Eleni; Czaderski, Christoph; et al. (2024)
Procedia Structural Integrity ~ SMAR 2024 – 7th International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures
This study proposes an analytical model, referred to as the "Wine Glass model", offering an elegant graphical solution to the bond capacity. It is built on the basis of two key assumptions: (i) the bond length is sufficiently long (longer than an effective bond length) and (ii) the stress-strain behavior of the adherent monotonically increases, which is typically met by the majority of engineering materials. The tensile stress-strain (σ - ϵ) curve of the adherent can be visualized as a wine glass when plotted against the vertical axis (σ-axis). In this analogy, the fracture energy of the adhesive bond divided by the thickness of the adherent strip (Gf/t) represents the wine poured into the glass. The height of the wine within the glass corresponds to the level of adherent tensile stress, with respect to the bond capacity (Fb). This Wine Glass model, which suits lap-shear joints with both linear and nonlinear adherents, is validated on experimentally measured bond capacities of various types of lap-shear joints, including carbon fiber reinforced polymer (CFRP)-to-steel joints and iron-based shape memory alloy (Fe-SMA)-to-steel joints. It unveils the mechanism of bond capacity.
Fatigue strengthening of damaged steel members using wire arc additive manufacturing
Ghafoori, Elyas; Dahaghin, Hamid; Diao, Chenglei; et al. (2023)
Engineering Structures
In this study, a directed energy deposition (DED) process called wire arc additive manufacturing (WAAM) is employed for the fatigue strengthening of damaged steel members. Three steel specimens with central cracks were tested under a high-cycle fatigue loading (HCF) regime: (1) the reference specimen; (2) the WAAM-repaired specimen with an as-deposited profile, and (3) the WAAM-repaired specimen machined to reduce stress concentration factors (SCF). The corresponding finite element (FE) simulation of the WAAM process was calibrated using static experimental results, which revealed the main mechanism. The process was found to introduce compressive residual stresses at the crack tip owing to the thermal contraction of the repair. The FE results also revealed that stress concentration exists at the root of the as-deposited WAAM; this stress concentration can be mitigated by machining the WAAM to a pyramid-like shape. The fractography analysis indicated that the cracks were initiated at the WAAM-steel interface, and microscopic observations revealed that the microcracks were arrested by the porosities in the melted interface. The results of this pioneering study suggest that WAAM repair is a promising technique for combating fatigue damage in steel structures.
Debonding model for nonlinear Fe-SMA strips bonded with nonlinear adhesives
Li, Lingzhen; Chatzi, Eleni; Ghafoori, Elyas (2023)
Engineering Fracture Mechanics
The application of adhesively-bonded joints for strengthening of structures using iron-based shape memory alloys (Fe-SMAs) has recently emerged in construction. Fe-SMAs and the majority of structural adhesives exhibit a pronounced nonlinear material behavior, which may result in a favorable ductile failure mechanism. The development, however, of a mechanical model to predict the structural behavior of the joint is non-trivial due to the presence of nonlinearity in the adherent and adhesive. This study aims to propose a semi-analytical and semi-numerical model for describing the mechanical behavior of Fe-SMA-to-steel adhesively bonded joints. The developed model serves three main functions: (i) estimating the bond capacity for a given interfacial fracture energy, and vice versa; (ii) processing the bond–slip (τ−s) behavior directly from the load–displacement (F−Δ) curve, and vice versa; and (iii) delivering a numerical method to simulate the full-range mechanical behavior of the bonded joints, namely the behavior at different loading stages. The model is validated using the experimental testing of 26 Fe-SMA-to-steel lap-shear joints, as well as 24 further bonded joints subject to shear with different adherents (e.g., stainless steel strips and Nickel–Titanium SMA wires) and base materials (e.g., concrete and composite polymer). An experimental data processing protocol, on the basis of the experimentally measured force–displacement (F−Δ) behavior and the distributed displacement along the bond line (s−x) via the Digital Image Correlation (DIC) technique, is further proposed to assess the full-range behavior of bonded joints.

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