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Advances in the Bonded Composite Repair o f Metallic Aircraft Structure phần 4

Điều này tương đương sẽ được khai thác tại mục 7.4 để đánh giá phân bố lại căng thẳng do một tăng cường ngoại quan. Những căng thẳng tiềm năng trong đĩa trực tiếp bên dưới dải củng cố, 00 = op (x = 0), có thể dễ dàng xác định bằng cách tích hợp Eq. (7.4), (7,14) với S biểu thị các tỷ lệ độ cứng nhất định dưới đây, (7,15) mà là một chiều không quan trọng tham số đặc trưng cho một sửa chữa | 144 Advances in the bonded composite repair of metallic aircraft structure with a step change in stiffness from Eptp Vp to Eptp Vp Eptp v over a central potion _y B b as indicated in Figure 7.4 e with b given by ò tanh B 1 7.13 This equivalence will be exploited in Section 7.4 to assess the redistribution of stress due to a bonded reinforcement. The prospective stress in the plate directly underneath the reinforcing strip ƠQ ơp x 0 can be readily determined by integrating Eq. 7.4 -CO r O I -CO iur-iaj hfr ís sl 7I4 with 5 denoting the stiffness ratio given below 5 _ 1 - Vp Erír 1 - EPlP 7.15 which is an important non-dimensional parameter characterising a repair. As will be shown in the following section the actual prospective stress Ơ0 is somewhat higher than that given by Eq. 7.14 . This under-estimation is primarily due to the ignorance of the load attraction effect in a 2D plate associated with reinforcing. 7.4. Symmetric repairs We return to the solution of the problem formulated in Section 7.2 assuming that the repaired structure is supported against out-of-plane bending or the cracked plate is repaired with two patched bonded on the two sides. The analysis will be divided into two stages as indicated in Section 7.2. 7.4.1. Stage I Inclusion analogy Consider first the re-distribution of stress in an uncracked plate due to the local stiffening produced by the bonded reinforcement. As illustrated in Figure 7.2 a the reinforced region will attract more load due to the increased stiffness leading to a higher prospective stress than that given by Eq. 7.14 . The ID theory of bonded joints Section 7.3 provides an estimate of the load-transfer length T1 for load transfer from the plate to the reinforcement. If that transfer length is much less than the in-plane dimensions A B of the reinforcement we may view the reinforced region as an inclusion of higher stiffness than the surrounding plate and proceed in the following three steps. 1. Determine the elastic constants