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Fracture Mechanics for Structural Adhesive Bonds

Engineering Applications and Design
Strength and Mechanics of Materials

Fracture Mechanics for Structural Adhesive Bonds
Airforce Materials Laboratory
T. R. Brussat and S. T. Chiu, Lockheed-California Company,
S. Mostovoy, Materials Research Laboratory, Inc.,
107 Pages

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Open: Fracture Mechanics for Structural Adhesive Bonds

Fracture mechanics methodology was developed and experimentally demonstrated for the prediction of the growth of bondline flaws in an adhesively bonded structure. This work was considered to be an initial step toward providing the technology required to assess the influence of possible preexisting bondline flaws on the structural integrity of aluminum adhesively bonded fuselage structures.

TOC

Table Page
1 Finite Element Model Test Cases 17
2 Strain Energy Release Rates, CLS Specimen in Tension 17
3 WTB Compliance Data, Loading Holes at Taper Apex (X - 0) 23
4 WTB Compliance Data, Loading Holes at X - 0.37H 24
5 WTB Compliance Data From Two Test Machines 27
6 Accuracy of Equation (18) for Estimating Compliance of WTB Specimens 31
7 1 Measurements for FM-73m Adhesive 39 IC
8 Data for Sustained Loading in 333 0K (1400F) Water 40
9 Number of Crack Growth Data Points, FM-73m Adhesive 41
10 Engineering Values of da/dN Threshold, FM-73m 63
11 Assumed Crack Sizes for Nonlinear Finite Element Analysis of the SLJ Specimen 87

Illustrations

1 Cracked Lap Shear (CLS) Specimen 11
2 CLS Specimen and Its Deformed Shape 12
3 Crack Tip Region of the CLS Specimen 15
4 Symmetric Four-Point Bend Loading of a CLS Specimen 18
5 Width Tapered Beam (WTB) Specimen 20
6 Compliance of WTB Specimens with X = 0.37H 26
7 Deviations of Estimated from the Geometric Mean, 4 29
8 Comparison of Pure Mode I da/dN Data on AF-55S Adhesive From WTB and CDCB Specimens 33
9 Comparison of Data Reduction Methods for da/dN on UDCB Specimen UB-9 37
10 Pure Mode I da/dN in Laboratory Air for FM-73m 43
11 Verification of WTB Data Using UDCB Specimens 44
12 Pure Mode I da/dN in Laboratory Air at R = 0.6 45
13 Pure Mode I da/dN in Laboratory Air at R = 0.1 and f = 0.3 Hz 46
14 Mixed-Mode da/dN in Laboratory Air at R = 0.1 48
15 Use of &4 for Mixed-Mode Data Fitting for FM-73m 50
16 Correlation of FM-73m and AF-55S da/dN Data for Pure and Mixed Modes 51
17 Mixed-Mode da/dN in Laboratory Air at R - 0.6 52
18 Mixed-Mode da/dN in Laboratory Air at f = 15 Hz 53
19 Mode I da/dN in Hot Water 55
20 Effect of Fatigue Test Time on the Environmental da/dN Properties of FM-73m in Pure Mode I 56
21 Pure Mode I da/dN in 3330K (1400F) Water at R - 0.1 and f = 3 Hz 57
22 Pure Mode I da/dN in 3330K (1400F) Water at R - 0.6 and f 3 Hz 59
23 Mixed-Mode da/dN in 3330K (1400F) Water at R - 0i and f = 3 Hz 60
24 Mixed-Mode da/dN in Hot Water 62
25 Mating Fracture Surfaces of CLS Specimen C-102 at Transition from Fatigue to c Fracturing 64
26 Single Lap Joint (SLJ) Specimen with Thin Adherends 67
27 Gap-Opening Deflection of the SLJ Specimen for a Single Across-the-Width Bondline Crack 68
28 Crack Growth Data, Initial SLJ Specimens, FM-73m Adhesive 69
29 Fatigue Cracks on the Adhesive Surface of the Doubler on Specimen SLJ-101 71
30 Fatigue Cracks on the Adhesive Surface of the Doubler on Specimen SLJ-102 72
31 Fatigue Cracks on the Adhesive Surface of the Doubler on Specimen SLJ-105 73
32 Fatigue Cracks on the Adhesive Surface of the Doubler on Specimen SLJ-106 74
33 Displacement-Time Plots for SLJ Retests 76
34 Fatigue Cracks on the Adhesive Surface of the Doubler on Specimen SLJ-111 78
35 Fatigue Cracks on the Adhesive Surface of the Doubler on Specimen SLJ-112 79
36 Fatigue Cracks on the Adhesive Surface of the Doubler on Specimen SLJ-113 80
37 Fatigue Cracks on the Adhesive Surface of the Doubler on Specimen SLJ-115 81
38 Fatigue Cracks on the Adhesive Surface of the Doubler on Specimen SLJ-116 82
39 Final Crack Condition of Specimens SLJ-111 through 116 and Assumed Crack Length Relationships During Testing at 3 Hz 84
40 Deflection of the Thin-Adherend SLJ Specimen 85
41 Effective Strain Energy Release Rates for the SLJ Specimen 89
42 Crack Growth Data Comparison for Specimens SLJ-lll, -112 and -113 90