纤维-金属层板粘接质量的非线性超声评价研究

传统超声检测利用超声波传播中遇到缺陷时波的反射、散射等特征进行缺陷检测和评价,实际上表征的是缺陷和周围介质的声阻抗差别。当超声波在材料中传播时,位错等微小缺陷会与其发生非线性相互作用,非线性超声检测就是利用这些非线性响应信号进行材料性能的评估和微小缺陷的检测,本质上反映的是微小缺陷对材料非线性的影响。文中从非线性超声理论出发,提出运用2阶和3阶非线性系数进行纤维-金属粘接层的评价,实验结果表明非线性系数可以表征粘接缺陷。

Fatigue crack growth in fiber-metal laminates

Fiber-metal laminates(FMLs)consist of three layers of aluminum alloy 2024-T3 and two layers of glass/epoxy prepreg,and it(it means FMLs)is laminated by Al alloy and fiber alternatively.Fatigue crack growth rates in notched fiber-metal laminates under constant amplitude fatigue loading were studied experimentally and numerically and were compared with them in monolithic 2024-T3 Al alloy plates.It is shown that the fatigue life of FMLs is about 17 times longer than monolithic 2024-T3 Al alloy plate;and crack growth rates in FMLs panels remain constant mostly even when the crack is long,unlike in the monolithic 2024-T3 Al alloy plates.The formula to calculate bridge stress profiles of FMLs was derived based on the fracture theory.A program by Matlab was developed to calculate the distribution of bridge stress in FMLs,and then fatigue growth lives were obtained.Finite element models of FMLs were built and meshed finely to analyze the stress distributions.Both results were compared with the experimental results.They agree well with each other.

Structural behaviour of fibre metal laminates subjected to a low velocity impact

Structural impact tests were first presented to cover typical fibre metal laminates (FMLs) subjected a low velocity projectile impact,which produced the corresponding load-displacement traces and deformation/failure modes for the validation of numerical models.Finite element (FE) models were then developed to simulate the impact behaviour of FMLs tested.The aluminium (alloy grade 2024-0) layer was modelled as an isotropic elasto-plastic material up to the on-set of post failure stage,followed by shear failure and tensile failure to simulate its failure mechanisms.The glass fibre laminate (woven glass-fibre reinforced composite) layer was modelled as an orthotropic material up to its on-set of damage,followed by damage initiation and evolution using the Hashin criterion.The damage initiation was controlled by failure tensile and compressive stresses within the lamina plane which were primarily determined by tests.The damage evolution was controlled by tensile/compressive fracture energies combined with both fibre and matrix.The FE models developed for the 2/1,3/2 and 4/3 FMLs plates made with 4-ply and 8-ply glass fibre laminate cores were validated against the corresponding experimental results.Good correlation was obtained in terms of load-displacement traces,deformation and failure modes.The validated models were ready to be used to undertake parametric studies to cover FMLs plates made with various stack sequences and composite cores.

Recycling of Aluminum from Fibre Metal Laminates

Recycling of aluminum alloy scrap obtained from delaminated fibre metal laminates （FMLs） was studied through high temperature refining in the presence of a salt flux. The aluminum alloy scrap contains approximately mass fraction w（Cu） = 4.4%, w（Mg） = 1.1% and w（Mn） = 0.6% （2024 aluminum alloy）. The main objective of this research is to obtain a high metal yield, while maintaining its original alloy compositions. The work focuses on the metal yield and quality of recycled A1 alloy under different refining conditions. The NaCI-KC1 salt system was selected as the major components of flux in the A1 alloy recycling. Two different flux compositions were employed at NaC1 to KC1 mass ratios of 44：56 and 70：30 respectively, based on either the euteetic composition, or the European preference. Different additives were introduced into the NaCI-KC1 system to study the effect of flux component on recycling result. Although burning and oxidation loss of the alloying elements during re-melting and refining take place as the drawbacks of conventional refining process, the problems can be solved to a large extent by using an appropriate salt flux. Experimental results indicate that Mg in the alloy gets lost when adding cryolite in the NaCI-KC1 salt system, though the metal yield can reach as high as 98%. However, by adding w（MgF2） = 5% into the NaCI-KC1 salt system （instead of using cryolite） all alloying elements were well controlled to its original composition with a metal yield of almost 98%.

Degradation Behavior of Epoxy Resins in Fibre Metal Laminates Under Thermal Conditions

GLARE （glass fibre/epoxy reinforced aluminum laminate） is a member of the fiber metal laminate （FML） family, and is built up of alternating metal and fiber layers. About 500 m2 GLARE is employed in each Airbus A380 because of the superior mechanical properties over the monolithic Muminum alloys, such as weight reduction, improved damage tolerance and higher ultimate tensile strength. Many tons of new GLARE scraps have been accumulated during the Airbus A380 manufacturing. Moreover, with the increasing plane orders of Airbus A380, more and more end-of-life （EOL） GLARE scrap will be generated after retire of planes within forty years. Thermal processing is a potential method for the material recycling and re-use from GLARE with the aim of environmental protection and economic benefits. The current study indicatdes that thermal delamination is a crucial pre-treatment step for the GLARE recycling. The decomposition behavior of the epoxy resins at elevated temperatures was investigated by using the simultaneous thermal analysis, thermogravimetry analysis （TGA） and differential scanning calorimetry （DSC）. Based on the thermal analysis results, GLARE thermal delamination experiments at refined temperatures were carried out to optimize the treatment temperature and holding time.