Weidong Li

The Effect of a Hot–Wet Environment on Adhesively Bonded Joints Under a Sustained Load

The aim of this research was to develop numerical modelling techniques for simulating the simultaneous effects of moisture, elevated temperature, and applied load on the performance of adhesively bonded joints. Associated experimental data are also reported. The degradation process of the joints was modelled using a fully-coupled approach, with the moisture concentration affecting the stress distribution and the stress state affecting the moisture diffusion analyses simultaneously. Further, the stress analysis contains a moisture-dependent creep model to accommodate viscous effects, and both swelling and thermal strains were included in the simulation. The governing parameters adopted in the modelling procedure were determined from experimental work based on the bulk adhesive. The joint response was monitored throughout the ageing process and good correlation was found between the experimental and numerical results.

Fatigue Analysis of Adhesive Joints Under Vibration Loading

Adhesively bonded joints have been used extensively for many structural applications. However, one disadvantage usually limiting the service life of adhesive joints is the relatively low strength for peel loading, especially under dynamic cyclic loading such as impulsive or vibrational forces. Moreover, accurately predicting the fatigue life of bonded joints is still quite challenging. In this study, a combined experimental–numerical approach was developed to characterize the effect of the cyclic-vibration-peel (CVP) loading on adhesively bonded joints. A damage factor is introduced into the traction-separation response of the cohesive zone model (CZM) and a finite element damage model is developed to evaluate the degradation process in the adhesive layer. With this model, the adhesive layer stress states before and after being exposed to various CVP loading cycles are investigated, which reveals that the fatigue effect of the CVP loading starts first in the regions close to the edges of the adhesive layer. A good correlation is achieved when comparing the simulation results to the experimental data, which verifies the feasibility of using the proposed model to predict the fatigue life of adhesively bonded joints under the CVP type of loading.

Research on Multi-Motor Synchronization Control Based on the Ring Coupling Strategy for Cutterhead Driving System of Shield Machines

With the research object of cutterhead rotation electric drive system, influencing factors of the system synchronous coordination and the multi-motor torque synchronization control strategy is studied. The paper analyzes the dynamics of the cutterhead rotary motors-driving system, discusses the interaction mechanism between motors and gear nonlinear transmission unit, and then the mathematical model of the cutterhead rotary driving system with consideration of gear frequency cycle error and backlash is presented. Based on that, the multi-drive synchronization control based on the ring coupling strategy is given. Simulation results using Matlab platform show the effectiveness of the proposed strategy.

Predicting the Strength of Adhesively Bonded T-joints Under Cyclic Temperature using a Cohesive Zone Model

The objective of this study is to analyze the effect of cyclic-temperature environment on adhesively bonded T-joints. Experiments on steel and aluminum T-peel joints were conducted to illustrate the influence of cyclic temperature on the ultimate load of T-joints. An environmental degradation factor Deg was utilized in conjunction with a cohesive zone model (CZM) to simulate the strength of T-joints caused by temperature variation. The experimental results showed that long-term cyclic-temperature exposure caused significant degradation on the ultimate load of the T-joints. And with the increase of the temperature cycles experienced, the ultimate load of the T-joints gradually decreased. In order to model the adhesive layer between joint components and simulate the damage propagation in the interface, a CZM implemented in the finite element code ABAQUS was used. Comparison between the experimental and numerical results proved the adopted modeling procedure be successful and effective.

Strength Prediction of Adhesively Bonded Single Lap Joints Under Salt Spray Environment Using a Cohesive Zone Model

The aim of this research was to develop an experimental–numerical approach to characterize the effect of salt spray environment on adhesively bonded joints and predict the degradation in joint strength. Experiments were conducted on bulk adhesive specimens and single lap joints (SLJs) under salt spray condition and the corresponding experimental results were reported. The environment degradation factor, Deg, was incorporated into a bilinear cohesive zone model (CZM) to simulate the degradation process of the joints. The degraded CZM parameters, determined from static tests on bulk adhesive, were imported into the CZM using an approximate moisture concentration gradient approach. The reduction in residual strength of SLJ under salt spray environment was successfully predicted through comparing the experimental and numerical results.

Strength Degradation of Adhesively Bonded Single-Lap Joints in a Cyclic-Temperature Environment Using a Cohesive Zone Model

Adhesively bonded joints are widely used in automotive industry. Adhesively bonded joints permit to have more uniform stress distributions, join complex shapes, and reduce the weight of the structures. The requirement to reduce the weight of automobiles is also increasing the application of composites. In this article, CFRP (carbon fiber-reinforced plastics) composite was used in experimental tests. In many cases, adverse environments cause non-negligible degradation in joints mechanical performance. So a combined experimental–numerical approach was developed to characterize the effect of cyclic-temperature environment on adhesively bonded joints. Experimental tests were carried out on single-lap joints with CFRP and steel adherend in a cyclic-temperature environment. A cohesive zone model was taken into consideration to predict the results observed during the experimental tests and an environmental degradation model was developed. Scanning electron microscopy was utilized to investigate the fracture surfaces.

Experimental and numerical analysis on fatigue durability of single-lap joints under vibration loads

ABSTRACT Fatigue is one of the most common yet complicated failures that can cause damage to mechanical structures. Structural adhesively bonded joints are not exempt from this deleterious phenomenon and have to be assessed under vibration loads. In this work, fatigue characteristics of single-lap joints (SLJ) made of steel and carbon fibre reinforced plastic (CFRP) laminates under vibration loads are primarily investigated by experiments. The aim of this work is to analyze the changes in the ultimate load of the SLJ under vibration loads. The experimental results showed that SLJ will face cohesive failure after the uniaxial tensile loading test. In addition to the increase of vibration cycles, the ultimate load and failure displacement gradually decrease. In order to model the adhesive between joint components and simulate the damage propagation, a new traction–separation law called the embedded process zone (EPZ) and a damage factor are introduced and developed within the framework of cohesive zone Modeling (CZM) techniques. Meanwhile, the stress variations in the adhesive layer of SLJ in different vibration cycles are researched using the finite element method in ABAQUS.

Research on Adaptive Load Sharing Control for Multi-Motor Synchronous Driving System of Shield Machine

This paper presents an adaptable controlling approach on account of the mathematic modeling and the quantitative analysis of experimental data on a ring-coupling controlling structure. It is based on the research of transmission characteristics of non-linear coupling gear rotation in main electric-driving system of cutterhead, and it is aimed at reducing the deviation of system synchronization caused by the mutation load, and improving the compliance capability of multi-motor synchronization system.

Fatigue Analysis of Adhesively Bonded Single Lap Joints Under Vibration Loads

Many structural applications of adhesive joints experience vibration loads. The dynamic loads due to vibration motions are therefore one of the primary causes for structural damage, especially when the outside cyclic stir vibration frequency is adjacent to the natural frequencies of the adhesive joint frame. This is so called the vibration fatigue. In this paper, the fatigue behavior of adhesively bonded single lap joint (SLP) subject mainly to normal stresses induced by vibration excitations is investigated. Combining with static tests, the NI PXI-1045 vibration measurement and analysis system are used to analyze the effect of vibration loading on the fundamental modal frequency with long-term fatigue cycle. Furthermore, a virtual fatigue analysis approach for the fatigue damage prediction of adhesive joints subject to vibration loads is performed in this study. It is found that the joint stiffness decreases with the cyclic durations under which the vibration loads are applied. As a result, a stable decrease of the fundamental resonance frequency of the joint structure is observed during the tests. The experimental data demonstrate a significant correlation between the shear strength of adhesive joints and the vibration cycling time. A gradual decrease in the shear strength with increasing load cycles is seen in vibration fatigue, the maximum shear strength of adhesively bonded joints drops about 12% after 1.35e8 cycles. Based on the test data, a new approach called virtual fatigue analysis modeling (VFAM) is proposed for the fatigue damage of the adhesive joints under vibration loads. The VFAM shows that the fatigue damage occurs first at the end of the overlap area of the adhesive layer.Copyright

Effect of Temperature on Shear Strength of Adhesively Bonded Joints for Automobile Industry

Due to the significant effect on vehicle lightweight, adhesively bonded joint in structural components is widely adopted in automobile industry in recent years, which leads to the benefits in fuel economy, reduced emissions and driving safety. In this paper, the performances of adhesively bonded joints with three different adhesive types after different temperature treatments are investigated through joint shear strength test. Visual inspection is performed on fracture surfaces after joint failure. Results showed that both low and high temperatures have impact on joint strength and lead to different fracture modes. Stiff and flexible adhesives also result in different fracture surfaces in the overlap zone as the temperature varies.