tailieunhanh - Volume 17 - Nondestructive Evaluation and Quality Control Part 17

Tham khảo tài liệu 'volume 17 - nondestructive evaluation and quality control part 17', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Cut core X X Water in core X Cracks X Scratches X Blisters X Protrusions X Indentations dents dings X Wrinkles X Pits X Source Ref 1 Table 2 Frequency of rejectable flaws in adhesive-bonded assemblies Defect Number of defects Percentage of total Metal-to-metal voids and disbonds 378 74 Skin-to-core voids and disbonds 19 3 Gap in core-to-closure bond 9 2 Lack of foaming adhesive or voids in foaming adhesive 22 4 Difference in core density 6 2 Lack of fillets 1 1 Crushed or missing core 32 6 Short core 40 8 Total 507 100 Interface defects are the result of errors made during the pretreatment cycle of the adherends prior to the actual bonding process. In practice pretreatment flaws are reduced by careful process control and by adherence to specification requirements and inspection before proceeding with the bond cycle. Controls generally include the waterbreak test and measurement of the anodic layer and primer thickness. Interface defects can be caused by improper or inadequate degreasing deoxidizing anodizing drying damage to the anodizing layer or excessive primer thickness. Interface defects are generally not detectable by state-of-the-art NDT methods. Therefore test specimens are processed along with production parts and sent to the laboratory for evaluation. Applicable wedge crack specimens lap shear specimens or honeycomb flatwise tension specimens are fabricated and tested to determine if the process meets specification requirements before the bonding cycle starts. Considerable effort at Fokker in the Netherlands led to the important discovery that the ideal oxide configuration for adhesion on aluminum alloys can be detected by inspection with an electron microscope at suitable magnification Ref 2 3 4 . To inspect with the electron microscope a piece of the structure must be removed. As a consequence the electron microscope became a useful tool for adhesion quality control. Another physical parameter that was used as a basis for the NDT of surfaces for the .