Joints destructive testing

Munns, G.A. Georgiou, Non-destructive testing methods for adhesively bonded joint nspection - a review, INSIGHT, Vol 37, No 12, Dec 1995, pp 941-952... 

The first stage in any inspection is to generate a proeedure which is specific to the component being examined in many instances, such a procedure will be based on a standard such as CEN J5I/-EN1714 Non-Destructive Testing of Welds - Ultrasonic Examination of Welded Joints . CamuS incorporates a tool ProcGen to provide assistance with this task. 

Furthermore, a cell header with its 70-100 connections is not easy to replace, and considerable numbers of safety features have to be incorporated into its design. Composite materials do not lend themselves to effective non-destructive testing and a leaking joint may lead to delamination of the chemical-resistant liner from its mechanical support. Since any leaks cannot be detected easily in such circumstances, the entire header must be replaced with a corresponding electrolyser downtime. 

The best approach to achieving good performance in bonded joints is to select the proper adhesive, design the joint properly for the specific application, and maintain rigid process control. One disadvantage in the use of adhesives is the absence of good non-destructive tests to determine the strength of adhesive-bonded joints in a wide variety of ord applications... 

So-called white glues are particularly important. The chemical basis is polyvinyl acetate (PVA), the bonded joints - or traditionally adhesive gluings - are characterized by very high adhesive strengths, which usually result in adherend fractions after destructive testing. In order to avoid possible tensions, it is recommended to let the bonded joint set under even pressure (clamp) for more than the indicated... 

Thus, independent of the dimensions of the test pieces, the strength values obtained are always comparable. These relationships refer also to bonded joints for which the term adhesive strength has become established for destructive testing of overlapped test pieces (Figure 10.2). It is abbreviated by the Greek letter r (pronounced tau) referenced with the index B ... 

The most important methods, however, are the destructive test methods by means of special test pieces which allow for the determination of the strength of bonded joints. 

Collagenase production and release are partly responsible for the joint destruction that characterises human rheumatoid arthritis. Triterpenes from the lupane and a-amyrin groups have been studied in vitro to examine their effects on the release of the arthritic joint degradative enzyme collagenase using the rat osteosarcoma. This test and the rat synovial granuloma of adjuvant arthritis are similar both models are based on connective tissue tumours with bone-invasive properties. The pentacyclic triterpenes assayed have been shown to possess general antiproteolytic effects that can explain the anti-arthritic effects in adjuvant arthritis in rats [71,103]. 

On that basis, the book intends to bridge current issues, aspects and interests from fundamental research to technical apphcations. In seven chapters, the reader will find an arrangement of latest results on fundamental aspects of adhesion, on adhesion in biology, on chemistry for adhesive formulation, on surface chemistry and pretreatment of adherends, on mechanical issues, non-destructive testing and durability of adhesive joints, and on advanced technical applications of adhesive joints. Prominent scientists review the current state of knowledge about the role of chemical bonds in adhesion, about new resins and nanocomposites for adhesives, and about the role of macromolecular architecture for the properties of hot melt and pressure sensitive adhesives. Thus, insight into detailed results and broader overviews as well can be gained from the book. 

Munns. 1. J.. and Georgiou. G. A. (1995). Non-destructive testing methods for adhesively bonded joint in.spection--A review. Insight. Dec. 1995. 12. 941 9.S2. 

Adams RD, Cawley P. A review of defect types and non-destructive testing techniques for composites and bonded joints. NDT Int 1988 21 208-22. 

In summary, bonded repairs are the preferred approach for manufacturing repairs to both honeycomb sandwich and monolithic secondary stmcture. However, for the FAA and European Airworthiness and Safety Administration, the main reason for withholding certification of bonded repairs for primary structure is the lack of certainty over bond quality as it is not possible to assess strength and durability of bonded joints without destructive testing. 

Stainless steel type 321 with addition of titanium has been used to enhance the mechanical performance of the structural material at high temperature (520-550 C). The intensive French programme of non-destructive tests since 1989 has shown that 321 stainless steel has not performed satisfactorily over time, with cracks in welded joints occurring under load and high temperature. The sections of Phenix secondary pipework made in this steel have been replaced by 316SPH steel. 

Appropriate test methods for the control of fabrication procedures and non-destructive testing (NDT) are basic requirements for the formation of structural adhesive joints. Such methods should be based upon relatively easily measurable parameters that have a close identity with the properties of the bonded assembly that need to be controlled. However the quality of bonded joints depends upon many factors, requiring a range of very different procedures. 

Non-destructive testing. NDT represents a large and diverse field in which a number of review papers have been published in recent years(6,10-13). Brief mention only of the most important techniques is given below because few are currently readily applicable to adhesive joints in civil engineering. The techniques in general are void detectors. 

Intensive programmes of non destructive tests since 1989 have shown that the 321 stainless steel has not performed satisfactorily over the time, with fissures in welded joints kept under load and high temperature. 

After the adhesive is cured, the joint area can be inspected to detect gross flaws or defects. This inspection procedure can be either destructive or non-destructive, as discussed in Section 12.1. Destructive testing generally involves placing samples of the production run in simulated or accelerated service and determining if it has properties similar to a specimen that is known to have a good bond and adequate service performance. The causes and remedies for a number of faults revealed by such mechanical tests are described in Table 12.1. Most of the destructive (mechanical) tests that can be carried out on adhesive bonds are listed in Section 12.2.1.1 (ASTM methods for mechanical properties). Non-destructive tests are far more economical, and every assembly can be tested, if desirable. ... 

Adams, R.D. and B.W. Drinkwater, Non-destructive testing of adhesively-bonded joints. International Journal of Materials and Product Technology, 14(5/6), 1999. 

Practical adhesion Destructive Tests of adhesion are also said to measure the adhesion of a joint or coating. Adhesion here refers to the number that results from Shear test. 

We have now come to a position where most recognize that both joint rheology and fundamental interfacial forces contribute to the measures given by destructive tests, and both determine the loads under which the joint will fail in service. The relation between the three - fundamental forces, rheology and test results - is understood in broad principle, and in a few cases has been elucidated in quantitative detail. This will now be discussed. 

Fig. 1. Comparison of destructive shear strength tests on laminates with the predicted strengths using a Fokker bond tester. A series of laminates is represented where the adherend thickness t varies as follows ( ), t = 0.6 mm (O), t = 0.8 mm (x), f = 1.0 mm (-h), f = 1.2 mm (A), t = 1.5 mm. To construct this standard plot, 120 specimens of Dural 2024-T3 were used 95% of all results are within the range 0.36 kg mm . (From R J Schliekelmann, Non-destructive testing of adhesively bonded joints, in Adhesion, Fundamentals and Practice, McClaren, London, 1966)...

The safety of the system is analytically determined from the joint contributions of all components. Modeling of thermal and mechanical properties of batteries remains a useful method to approximate their systemic behavior. However, the experimental verification and the (expensive) destructive testing still provide the most valuable data on the actual event progress and propagation. Improvements in the accuracy of thermal models as well as the ever-increasing wealth of data from the past and ongoing testing are expected to improve the reliability of the cell performance predictions. 

BS 470 1984 Specification for inspection, access and entry openings for pressure vessels BS 709 1983 Methods of destructive testing fusion welded joints and weld metal in steel. 

BS EN 1435 1997 Non-destructive testing of welds. Radiographic examination of welded joints. 

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