Project 2 - Failure modes and criteria
Objectives
- To determine the failure process of adhesive joint systems.
- To develop test methods for the measurement of key adhesive bond properties.
- To develop and prove failure criteria for the prediction of joint strength and lifetime of adhesively bonded joints.
Principal findings
- A wide variety of joint types was studied, including the thick adherend shear test (TAST); T-Peel; tapered double cantilever beam; contoured double cantilever beam; block shear; three point bend; wedge peel and cracked lap shear. The work concentrated on two adhesive types, a single part heat curing epoxy and a two part acrylic.
- To correctly predict the stresses and strains in a joint, requires accurate modelling of the materials (adhesive and adherend) and geometric non-linearity. Particular points of concern and analysis are pressure sensitive yield and failure in the adhesive and toughening mechanisms that induce non-linear local damage.
- Criteria based upon peak values need to accommodate geometric discontinuities and it is therefore necessary to apply the peak value over (or at) a distance. Although there is no physical basis for these criteria, reasonable strength prediction can be achieved within joint types of limited dimensions.
- Finite element analyses using displacement control are preferable for determining highly loaded joint behaviour.
- A non-linear material model, incorporating pressure sensitive yield and strain to failure has been written for DYNA 3D. Using this model, in conjunction with interface elements to stimulate interfacial failure, has provided reasonable calculation of ultimate failure load across joints of different types and dimensions.
- In the event that: the specimen is wide enough, the crack is sharp enough, and the adhesive layer thickness is representative, the tapered double cantilever beam is an effective means to measure the fracture toughness of adhesively bonded joints.
- Adhesively bonded joints are able to sustain a degree of damage before failure, generally close to an adherend. This failure is governed by a combination of peak strain in the adhesive and adhesive failure at the interface.
- The lifetime under cyclic fatigue loading of adhesively bonded joints is dominated by crack initiation. If, however, the cyclic stress in the adhesive is below the elastic limit, very long lifetimes can be expected. To assist in this, non-linear stress analysis has demonstrated a power-law relationship, between cycles to visible crack initiation and peak plastic strain in the adhesive.
- An adhesively bonded joint, when correctly designed, is resistant to creep loads, up to 70% of static failure.
- When subject to impact loading, the properties of the adhesively bonded joint become difficult to measure. The wedge peel test gives an indication of impact performance but little mechanical property data. The tapered double cantilever beam, however, allows reliable measurement of fracture toughness at varying test speeds.
- High resolution laser Moire inferometry has been successfully applied to TAST and T-peel joints to monitor the variations in strains along and across the bondlines up to the initiation of failure.
| REPORTS | |||||
| REPORT NO. | REPORT TITLE | ABSTRACT | NO. PAGES | SIZE (MB) | LINK |
| 1 | Review of Adhesive Bond Failure Criteria | Show | 80 | 6.617 |
|
| 2 | Experimental methodologies to determine the fracture properties of adhesive joints | Show | 58 | 4.564 |
|
| 3 | Summary Task 1: Detailed Study of Joint Failure Summary Report | Show | 40 | 2.815 |
|
| 3 a 1 | Theoretical Analyses of Stresses and Strains in Model Adhesive Joints | Show | 169 | 22.6 |
|
| 3 a 2 | The Effect of Short Term Static Loading on Adhesives F241 and AV119 | Show | 81 | 4.428 |
|
| 3 a 3 | A library of Images Obtained During Work on task 1.1, MTS Project 2, Short Term Static Loading | Show | 198 | 135.7 |
|
| 3 a 4 | The Effect of Long Term Static Loading on Adhesives AV119 and F241 | Show | 100 | 14.55 |
|
| 3 a 5 | Failure Modes in Adhesively Bonded Joints | Show | 23 | 1.296 |
|
| 3 a 6 | The Use of Laser Moire Interferometry to Assess Adhesive Bond Failure | Show | 64 | 6.017 |
|
| 3 a 7 | The Effect of Fatigue Loading on Adhesives AV119 and F241 | Show | 89 | 6.831 |
|
| 3 a 8 | The Experimental Measurement of Static, Creep and Fatigue Properties of Adhesive Peel and Shear Joints | Show | 71 | 5.1 |
|
| 3 a 9 | Impact Loading of Adhesive Joints | Show | 36 | 3.532 |
|
| 4 | Thin Lap Shear Joint Testing Summary Report | Show | 21 | 0.7 |
|
| 4 a 1 | Quasi-Static Tensile Testing of Adhesively Bonded Thin Lap Shear Joints | Show | 46 | 1.581 |
|
| 4 a 2 | Tensile Impact Testing of Adhesively Bonded Thin Lap Shear Joints | Show | 83 | 6.991 |
|
| 5 | Test Methods for Adhesive Fracture Properties Overall Summary | Show | 28 | 1.21 |
|
| 5 a 1 | Test Methods for Adhesive Fracture Properties | Show | 30 | 1.499 |
|
| 5 a 2 | Impact Testing of Adhesive Joints | Show | 70 | 6.312 |
|
| 6 | Failure Criteria for Adhesive Joints Summary Report | Show | 19 | 0.971 |
|
| 6 a 1 | Evaluation of the ALCAN Derived Quasi-Static Failure Criterion for Adhesively Bonded Joints | Show | 74 | 3.665 |
|
| 6 a 2 | Report on Quasi-Static Failure Criteria for Adhesive Joints at a Point or over a Distance Based on Detailed Analyses | Show | 48 | 5.14 |
|
| 6 a 3 | Prediction of Failure Criteria for Adhesive Joints Subjected to Short Term Static Loading | Show | 80 | 5.893 |
|
| 6 a 4 | Quasi-Static Failure Criteria for Adhesive Joints Based Upon Advanced Analyses | Show | 50 | 3.447 |
|
| 6 a 5 | Modelling the Response of Bonded Joints to Creep Loads | Show | 68 | 7.007 |
|
| 6 a 6 | Fatigue Failure of AV119 and F241 Strap Lap Shear Joints | Show | 50 | 11.82 |
|
| 7 | Overall Summary | Show | 23 | 1.039 |
|
