ASM Metals HandBook Vol. 8 - Mechanical Testing and Evaluation
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predicting the strength of a bond from tests on other, quite different, joints by using linear elastic fracture
mechanics.
As noted, in principle, fracture mechanics lends itself to using test results from one test in the design of other
joints that have significantly different geometries. A number of adhesive geometries have been proposed to
measure fracture toughness in addition to the split-cantilever beam, but to date, it is the only one formalized by
ASTM (Ref 3, 4, 6, 12, 36, 47, and 48). A recent paper by the authors (Ref 61) has demonstrated how such
factors as end rotation (at the cantilever point assumed rigidly fixed in the original ASTM analysis) shear, and
presence of the adhesive and its thickness (also neglected in the original analysis) affect the energy release rate.
It is shown that inclusion of these effects can dramatically affect the results and greatly reduce test scatter.
Furthermore, this paper demonstrates how fracture mechanics may be used to predict the locus of adhesive
crack growth. To accomplish this, various crack paths were assumed, and using finite element methods, the
energy release rate calculated for each path.
References cited in this section
3. G.P. Anderson, S.J. Bennett, and K.L. DeVries, Analysis and Testing of Adhesive Bonds, Academic
Press, 1977
4. A.J. Kinlock, Adhesion and Adhesives, Chapman and Hall, 1987
6. K.L. Mittal, Adhesive Joints, Plenum Press, 1984
12. A.N. Gent and G.R. Hamed, Peel Mechanics, J. Adhes., Vol 7, 1975, p 91
13. A.N. Gent and G.R. Hamed, J. Appl. Polym. Sci., Vol 21, 1977, p 2817
25. J.A. Marceau, Y. Moji, and J.C. McMillan, A Wedge Test for Evaluating Adhesive Bonded Surface
Durability, 21st SAMPE Symposium, Vol 21, 6–8 April 1976
26. D. Broek, The Practical Use of Fracture Mechanics, Kluver Acad. Press, Dordrect, NL, 1989
27. S. Mostovoy and E.J. Ripling, J. Appl. Polym. Sci., Vol 15, 1971, p 661
28. S. Mostovoy and E.J. Ripling, J. Adhes. Sci. Technol., Vol 9B, 1975, p 513
29. E.F. Rybicki and M.F. Kanninen, Eng.Fract. Mech., Vol 9, 1974, p 921
30. G.P. Anderson and K.L. DeVries, J. Adhes., Vol 23, 1987, p 289
31. E.H. Andrews, T.A. Khan, and H.A. Majid, J. Mater. Sci., Vol 20, 1985, p 3621
32. E.H. Andrews, H.A. Majid, and N.A. Lockington, J. Mater. Sci., Vol 19, 1984, p 73
33. D.W. Aubrey and M. Sherriff, J. Polym. Sci. Polym. Chem. Ed., Vol 18, 1980, p 2597
34. W.D. Bascom and J. Oroshnik, J. Mater. Sci., Vol 10, 1978, p 1411
35. W.D. Bascom and D.L. Hunston, Fracture of Epoxy and Elastomer-Modified Epoxy Polymers, Treatise
on Adhesion and Adhesives, Vol 6, R. L. Patrick, K.L. DeVries, and G.P. Anderson, Ed., Marcel
Dekker, 1988, p 123
36. H.F. Brinson, J.P. Wightman, and T.C. Ward, Adhesives Science Review 1, VPI Press, 1987
37. J.D. Burton, W.B. Jones, and M.L. Williams, Trans. Soc. Rheol, Vol 15, 1971, p 39
38. G. Danneberg, J. Appl. Polym. Sci., Vol 5, 1961, p 125
39. F. Erdogan, Eng. Fract. Mech., Vol 4, 1972, p 811
40. T.R. Guess, R.E. Allred, and F.P. Gerstle, J. Test. Eval., Vol 5 (No. 2), 1977, p 84
41. G.R. Hamed, Energy Conservation During Peel Testing, Treatise on Adhesion and Adhesives, Vol 6, R.
L. Patrick, K. L. DeVries, and G. P. Anderson, Eds., Marcel Dekker, 1988, p 233
42. R.W. Hertzberg and J.A. Manson, Fatigue of Engineering Plastics, Academy, 1980
43. G.R. Irwin, Fracture Mechanics Applied to Adhesive Systems, Treatise on Adhesion and Adhesives, Vol
1, R. L. Patrick, Ed., Marcel Dekker, 1966, p 233
44. W.S. Johnson, J. Test. Eval., Vol 15 (No. 6), 1987, p 303
45. D.H. Kaelble, Physical Chemistry of Adhesion, Wiley-Interscience, 1971
46. H.H. Kaush, Polymer Fracture, Springer-Verlag, Berlin, 1978
47. W.G. Knauss and K.M. Liechti, Interfacial Crack Growth and Its Relation to Crack Front Profiles, ACS
Organic Coatings and Applied Polymer Science Proceedings, Vol 47, American Chemical Society,
Washington, DC, 1982, p 481
48. K.M. Liechti and C. Lin, Structural Adhesives in Engineering, Institute of Mechanical Engineering,
London, 1986, p 83
49. J.C. McMillan, Developments in Adhesives in Engineering, 2nd ed., Applied Science, London, 1981, p
243
50. D.R. Mulville, D.L. Hunston, and P.W. Mast, J. Eng. Mater. Technol., Vol 100, 1978, p 25
51. J.R. Rice and G.C. Sih, J. Appl. Mech., Vol 32, 1965, p 418
52. E.F. Rybicki and M.F. Kanninen, Eng. Fract. Mech., Vol 9, 1974, p 921
53. G.B. Sinclair, Int. J. Fract., Vol 16, 1980, p 111
54. J.D. Venables, D.K. McNamara, J.M. Chen, T.S. Sun, and R.L. Hopping, Appl. Surf. Sci., Vol 3, 1979, p
88
55. S.S. Wang, J.F. Mandell, and F.J. McGarry, Int. J. Fract., Vol 14, 1978, p 39
56. J.G. Williams, Fracture Mechanics of Polymers, Ellis Horwood, Chichester, 1984
57. M.L. Williams, J. Adhes., Vol 5, 1973, p 81
58. R.J. Young, in Structural Adhesives: Developments in Resins and Primers, A.J. Kinlock, Ed., Applied
Science, London, 1986, p 163
59. J.R. Rice, A Path Independent Integral and the Approximate Analysis of Strain Concentration by
Notches and Cracks, J. Appl. Mach., 1979, p 379–386h
60. J.W. Hutchinson and P.C. Paris, Stability of J-Controlled Crack Growth, STP 668, ASTM, 1979, p 37–
64
61. K.L. DeVries and P.R. Borgmeier, Fracture Mechanics Analyses of the Behavior of Adhesion Test
Specimens, Mittal Festschrift, W.J. Van Ooij and H.R. Anderson, Jr., Ed., 1998, p 615–640
Testing of Adhesive Joints
K.L. DeVries and Paul Borgmeier, University of Utah
Conclusions
The adhesive researcher or technologist has many standard test methods from which to choose. These
techniques are designed with various goals and objectives in mind. Many of these methods are useful for the
purposes of comparing different adhesives and substrates, investigating the effects of different loading,
investigating chemical or physical attacks on adhesives, exploring aging phenomena, determining the effects of
radiation and moisture combined with sustained loading on adhesive properties, and so on. On the other hand,
care should always be exercised not to use the test results for purposes for which they are not well suited.
Results from many of the adhesive strength tests are conventionally reported as the failure force divided by the
bond area. Such average stress at failure results cannot, in general, be consistently and reliably used to predict
failure of other joints that differ even slightly from the test geometry. Fracture mechanics approaches, on the
other hand, show promise and have been used to predict the strength of joints that differ considerably from the
reference joint. ASTM D 3433 and Ref 27 and 28 describe a standard adhesive fracture mechanics joint in the
form of a tapered double-cantilever beam. The specimen dimensions are shown in Fig. 9. It is important to note,
however, that fracture mechanics is not limited to this or any other specific testing geometry. In principle, any
geometry for which the described energy balance (or alternatively, calculation of the stress intensity factor, J-
integral, and so on) can be accomplished might be used as an adhesive test.
Sometimes, circumstances dictate the use of a nonstandard test geometry. For example, a few years ago, the
authors were given the problem of measuring the quality of natural barnacle adhesive. The barnacle dictated the
exact form of the joint between the barnacle's shell and the plastic sheets that were placed in the ocean. This
form did not lend itself to tensile, lap shear, or split-cantilever testing. It was, however, possible to predrill
holes in the plate and to fill these holes with dental waxes that were solid and hard at the ocean temperatures
near San Francisco, CA, where the barnacle growth experiments were conducted. The wax was later easily
removed at a moderately elevated temperature. The base of the barnacle covering this hole was thereby exposed
and could be tested by application of fluid pressure, thus forming a blister. Measurement of the pressurization at
failure allowed the determination of the adhesive fracture energy (Ref 3, 62).
Once the adhesive fracture energy is determined by testing, fracture mechanics points the way that it, along
with a knowledge of the flaw size and a stress-strain analysis of the joint, can be used to predict the
performance of other joints. Modern computational techniques greatly facilitate the application of these
methods.
Finally, it is noted that the stresses, strains, fracture energy, and other such parameters used in the adhesive
analysis depend on loading rate, mode of stress at the crack tip, temperature, environment, and other factors.
Development of means for incorporating these parameters into joint design has been, and continues to be, an
area of active research. Such concepts and methodology can be found in the references cited previously in this
section.
References cited in this section
3. G.P. Anderson, S.J. Bennett, and K.L. DeVries, Analysis and Testing of Adhesive Bonds, Academic
Press, 1977
27. S. Mostovoy and E.J. Ripling, J. Appl. Polym. Sci., Vol 15, 1971, p 661
28. S. Mostovoy and E.J. Ripling, J. Adhes. Sci. Technol., Vol 9B, 1975, p 513
62. R.R. Despain, R.D. Luntz, K.L. DeVries, and M.L. Williams, J. Dental Res., Vol 52, 1973, p 742
Testing of Adhesive Joints
K.L. DeVries and Paul Borgmeier, University of Utah
Acknowledgments
Major portions of the authors' research has been supported by The National Science Foundation, most recently
under grant No. CMS-9522743.
Testing of Adhesive Joints
K.L. DeVries and Paul Borgmeier, University of Utah
References
1. Adhesives, Edition 6, D.A.T.A. Digest International Plastics Selector, 1991
2. R.L. Patrick, Ed., Treatise on Adhesion and Adhesives, Vol 1–6, Marcel Dekker, 1966–1988
3. G.P. Anderson, S.J. Bennett, and K.L. DeVries, Analysis and Testing of Adhesive Bonds, Academic
Press, 1977
4. A.J. Kinlock, Adhesion and Adhesives, Chapman and Hall, 1987
5. A. Pizzi and K.L. Mittal, Ed., Handbook of Adhesive Technology, Marcel Dekker, 1994
6. K.L. Mittal, Adhesive Joints, Plenum Press, 1984
7. Adhesives, Annual Book of ASTM Standards, Vol 15.06, ASTM (updated annually)
8. E.P. Plueddemann, Silane Coupling Agents, Plenum Press, 1982
9. G.P. Anderson and K.L. DeVries, Predicting Strength of Adhesive Joints from Test Results, Int. J.
Fract., Vol 39, 1989, p191–200
10. J.L. Gardon, Peel Adhesion, I. Some Phenomenological Aspects of the Test, J. Appl. Polym. Sci., Vol 7,
1963, p 654
11. D.H. Kaelble, Theory and Analysis of Peel Adhesion: Mechanisms and Mechanics, Trans. Soc. Rheol.,
Vol 3, 1959, p 161
12. A.N. Gent and G.R. Hamed, Peel Mechanics, J. Adhes., Vol 7, 1975, p 91
13. A.N. Gent and G.R. Hamed, J. Appl. Polym. Sci., Vol 21, 1977, p 2817
14. R.D. Adams and A. Crocombe, J. Adhes., Vol 12, 1981, p 127
15. O. Volkersen, Die Nietraftverteilung in Zugbeanspruchten Nietverblendugen mit Knastaten
Laschenquerschntlen, Luftfahrt forsch., Vol 15, 1938, p 41
16. M. Goland and E. Reissner, The Stresses in Cemented Joints, J. Appl. Mech., Vol 11, 1944, p 17
17. J.J. Plantema, “De Schuifspanning in eme Limjnaad,” Rep. M1181, Nat. Luchtvaart-laboratorium,
Amsterdam, 1949
18. G.R. Wooley and D.R. Carver, J. Aircr., Vol 8 (No. 19), 1971, p 817
19. R.D. Adams and N.A. Peppiatt, Stress Analysis of Adhesive-Bonded Lap Joints, J. Strain Anal., Vol 9
(No. 3), 1974, p 185
20. P.S. Cooper and J.W. Sawyer, “A Critical Examination of Stresses in an Elastic Single Lap Joint,”
NASA Tech. Rep. 1507, NASA Scientific and Technical Information Branch, 1979
21. G.P. Anderson and K.L. DeVries, Analysis of Standard Bond-Strength Tests, Treatise on Adhesion and
Adhesives, Vol 6, R.L. Patrick, K.L. DeVries, and G.P. Andersen, Ed., Marcel Dekker, 1989
22. J.K. Strozier, K.J. Ninow, K.L. DeVries, and G.P. Anderson, Adhes. Sci. Rev., Vol 1, 1987, p 121
23. G.P. Anderson, D.H. Brinton, K.J. Ninow, and K.L. DeVries, A Fracture Mechanics Approach to
Predicting Bond Strength, Advances in Adhesively Bonded Joints, Proceedings of a Conference at the
Winter Annual Meeting of ASME, 27 Nov-2 Dec 1988 (Chicago), S. Mall, K.M. Liechti, and J.K.
Vinson, Eds., ASME, 1988, p 98–101
24. V.L. Hein and F. Erodogan, Stress Singularities in a Two-Material Wedge, Int. J. Fract.,Vol 7, 1971, p
317
25. J.A. Marceau, Y. Moji, and J.C. McMillan, A Wedge Test for Evaluating Adhesive Bonded Surface
Durability, 21st SAMPE Symposium, Vol 21, 6–8 April 1976
26. D. Broek, The Practical Use of Fracture Mechanics, Kluver Acad. Press, Dordrect, NL, 1989
27. S. Mostovoy and E.J. Ripling, J. Appl. Polym. Sci., Vol 15, 1971, p 661
28. S. Mostovoy and E.J. Ripling, J. Adhes. Sci. Technol., Vol 9B, 1975, p 513
29. E.F. Rybicki and M.F. Kanninen, Eng.Fract. Mech., Vol 9, 1974, p 921
30. G.P. Anderson and K.L. DeVries, J. Adhes., Vol 23, 1987, p 289
31. E.H. Andrews, T.A. Khan, and H.A. Majid, J. Mater. Sci., Vol 20, 1985, p 3621
32. E.H. Andrews, H.A. Majid, and N.A. Lockington, J. Mater. Sci., Vol 19, 1984, p 73
33. D.W. Aubrey and M. Sherriff, J. Polym. Sci. Polym. Chem. Ed., Vol 18, 1980, p 2597
34. W.D. Bascom and J. Oroshnik, J. Mater. Sci., Vol 10, 1978, p 1411
35. W.D. Bascom and D.L. Hunston, Fracture of Epoxy and Elastomer-Modified Epoxy Polymers, Treatise
on Adhesion and Adhesives, Vol 6, R. L. Patrick, K.L. DeVries, and G.P. Anderson, Ed., Marcel
Dekker, 1988, p 123
36. H.F. Brinson, J.P. Wightman, and T.C. Ward, Adhesives Science Review 1, VPI Press, 1987
37. J.D. Burton, W.B. Jones, and M.L. Williams, Trans. Soc. Rheol, Vol 15, 1971, p 39
38. G. Danneberg, J. Appl. Polym. Sci., Vol 5, 1961, p 125
39. F. Erdogan, Eng. Fract. Mech., Vol 4, 1972, p 811
40. T.R. Guess, R.E. Allred, and F.P. Gerstle, J. Test. Eval., Vol 5 (No. 2), 1977, p 84
41. G.R. Hamed, Energy Conservation During Peel Testing, Treatise on Adhesion and Adhesives, Vol 6, R.
L. Patrick, K. L. DeVries, and G. P. Anderson, Eds., Marcel Dekker, 1988, p 233
42. R.W. Hertzberg and J.A. Manson, Fatigue of Engineering Plastics, Academy, 1980
43. G.R. Irwin, Fracture Mechanics Applied to Adhesive Systems, Treatise on Adhesion and Adhesives, Vol
1, R. L. Patrick, Ed., Marcel Dekker, 1966, p 233
44. W.S. Johnson, J. Test. Eval., Vol 15 (No. 6), 1987, p 303
45. D.H. Kaelble, Physical Chemistry of Adhesion, Wiley-Interscience, 1971
46. H.H. Kaush, Polymer Fracture, Springer-Verlag, Berlin, 1978
47. W.G. Knauss and K.M. Liechti, Interfacial Crack Growth and Its Relation to Crack Front Profiles, ACS
Organic Coatings and Applied Polymer Science Proceedings, Vol 47, American Chemical Society,
Washington, DC, 1982, p 481
48. K.M. Liechti and C. Lin, Structural Adhesives in Engineering, Institute of Mechanical Engineering,
London, 1986, p 83
49. J.C. McMillan, Developments in Adhesives in Engineering, 2nd ed., Applied Science, London, 1981, p
243
50. D.R. Mulville, D.L. Hunston, and P.W. Mast, J. Eng. Mater. Technol., Vol 100, 1978, p 25
51. J.R. Rice and G.C. Sih, J. Appl. Mech., Vol 32, 1965, p 418
52. E.F. Rybicki and M.F. Kanninen, Eng. Fract. Mech., Vol 9, 1974, p 921
53. G.B. Sinclair, Int. J. Fract., Vol 16, 1980, p 111
54. J.D. Venables, D.K. McNamara, J.M. Chen, T.S. Sun, and R.L. Hopping, Appl. Surf. Sci., Vol 3, 1979, p
88
55. S.S. Wang, J.F. Mandell, and F.J. McGarry, Int. J. Fract., Vol 14, 1978, p 39
56. J.G. Williams, Fracture Mechanics of Polymers, Ellis Horwood, Chichester, 1984
57. M.L. Williams, J. Adhes., Vol 5, 1973, p 81
58. R.J. Young, in Structural Adhesives: Developments in Resins and Primers, A.J. Kinlock, Ed., Applied
Science, London, 1986, p 163
59. J.R. Rice, A Path Independent Integral and the Approximate Analysis of Strain Concentration by
Notches and Cracks, J. Appl. Mach., 1979, p 379–386h
60. J.W. Hutchinson and P.C. Paris, Stability of J-Controlled Crack Growth, STP 668, ASTM, 1979, p 37–
64
61. K.L. DeVries and P.R. Borgmeier, Fracture Mechanics Analyses of the Behavior of Adhesion Test
Specimens, Mittal Festschrift, W.J. Van Ooij and H.R. Anderson, Jr., Ed., 1998, p 615–640
62. R.R. Despain, R.D. Luntz, K.L. DeVries, and M.L. Williams, J. Dental Res., Vol 52, 1973, p 742
Mechanical Testing of Welded Joints
William Mohr, Edison Welding Institute
Introduction
IN WELDED STRUCTURES, the welds typically have a mechanical purpose. Loads must be carried across the
weld joint. Standard mechanical tests have been devised to demonstrate that not only the base metals but also
the entire welded joint can fulfill this mechanical purpose (Ref 1, 2). This article primarily discusses standard
test methods that can be applied to many types of welds. These include tension, bending, impact, and toughness
testing.
Residual stress measurement techniques and weldability testing also are discussed. Residual stress can be
imposed by the welding itself, as well as by cutting and forming processes. The presence of high-tension or
compression residual stresses can affect the ability of the welded structure to carry the mechanical loading.
Cracking due to welding can also affect the load-carrying capacity of welded joints, and weldability testing
techniques that combine welding and mechanical loading to test the resistance to cracking are available. Many
other testing techniques can be applied to weld joints and welded structures. Fatigue and creep are both
important areas where mechanical tests on welded joints have indicated properties different from those of the
base metal. Testing of welded structure properties can also be done on structures that more closely model the
service structure than the standard specimens described below.
References cited in this section
1. “Standard Welding Terms and Definitions,” AWS 3.0, American Welding Society
2. L.P. Connor, Ed., Welding Handbook, 8th ed., Vol 1, American Welding Society, 1991
Mechanical Testing of Welded Joints
William Mohr, Edison Welding Institute
Reasons to Measure Properties of Welds
The mechanical properties of welded joints, the properties related to stress and strain, are most often measured
to show that such a weld and other similar welds will serve their purpose under loading. More rarely, several
welds are compared to see which welding techniques, processes, or chemistries provide the best combination of
mechanical properties.
Four stages in the qualification process for the weld joint can use standard mechanical test methods. The weld
metal can be chosen based on the mechanical properties from standard tests. The base metal, in some situations,
may also need to be qualified to demonstrate that its mechanical properties will not be substantially degraded
by welding. Once base metal and weld metal are chosen, the other weld process parameters, such as weld shape
or heat input, can be qualified by standard mechanical testing. Finally, after the weld is made, it may require
qualification by mechanical testing.
Each of the four qualification stages requires different types of tests and different approaches. These approaches
are described in the next four sections.
Weld Material Qualification
Weld metals are qualified by making welds that pass mechanical property tests on the weld metal itself. Such
tests can be used to qualify filler materials, such as welding wire or electrodes. Mechanical tests for such
qualification are described in the individual specifications of the filler metals, such as those in American
Welding Society (AWS) Specification A5.1 (Ref 3) and others of the AWS A5 series.
Mechanical property tests applied to weld qualification are designed to determine a small number of standard
values to check whether the weld metal passes or fails. This approach will not reveal the entire range of
properties that the weld metal can achieve. For instance, weld metal toughness in AWS A5.1 is measured by a
Charpy test specimen taken from the weld centerline. Other locations, which may have different toughnesses,
are not checked.
Base Material Qualification for Welded Service
The heat of welding will modify the structure and properties of the region of the base metal adjacent to the weld
in the heat-affected zone (HAZ). To prevent this modification in properties from causing service failures, some
standards require that a sample of the base material be tested after undergoing a representative heat treatment.
American Petroleum Institute standard (API) RP2Z is an example of a standard that requires base-material
qualification for welded service (Ref 4). Multipass welding provides the heat treatment. The welding
parameters are chosen to represent the most severe heat treatment of the base material that may occur during
fabrication. The parameter of interest is the fracture toughness, commonly measured by crack tip opening
displacement (CTOD). Particular regions of the HAZ are the most likely to show low toughness (the local
brittle zones, or LBZs), so there is also a requirement that the crack sample the required portion of that kind of
microstructure.
Weld Procedure Qualification
Weldment properties are dependent not only on the materials used to make the joint but also on the other
parameters of the welding process. Weld metal properties may be modified by the admixture of base material
melted by the heat of welding. The region where the base metal was only partially melted, at the fusion line,
may have local mechanical properties differing from those of the neighboring weld metal and HAZ regions. In
addition, the welding processes and procedures may induce specific imperfections, such as slag inclusions,
blowholes, or cracks.
Because the issues described cannot be resolved by either weld metal or base material tests alone, test
procedures that use specimens containing weld metal, base metal, and HAZ are used to determine mechanical
properties of welded joints in weldment procedure qualifications.
Weld procedure qualification tests may be less quantitative than weld metal qualification tests and often
provide only a “yes-or-no” answer. They are often capable of being completed in a shop floor environment
rather than a testing laboratory with calibrated equipment.
While many of the weld procedure qualification tests in wide use are discussed subsequently in this article,
several are not, because they are not properly mechanical tests; that is, neither a loading parameter, such as
stress, or a displacement parameter, such as strain, is measured. This group includes visual examination for
surface flaws and the breaking of fillet welds to examine the weld root.
Weld Service Assessment
Assessment of existing welds to determine if they meet the needs of future service may require that material
properties be obtained from representative weldments. In some cases, new weldments can be made with the
same materials and process parameters, so that sections from these weldments can be tested to find
representative properties for the existing welds. Generally, neither the original materials nor full information is
available to allow replication of existing weldments. Instead, a sample must be taken from the existing
weldments.
Taking a sample requires trading the advantage of obtaining mechanical property data for the disadvantage of
damaging the existing structure. Choices often are made that limit the damage to the existing structure by
limiting the amount of material to be tested. Tests such as macrohardness or microhardness, which damage a
small surface volume, may be appropriate. Smaller-scale test specimens may also be used, for instance, subsize
Charpy specimens. Alternatively, specimens can be taken from regions where subsequent repair is easiest or
from an area that is being removed as part of a modification.
References cited in this section
3. “Specification for Carbon Steel Electrodes for Shielded Metal Arc Welding,” ANSI/AWS A5.1-91,
American National Standards Institute/American Welding Society, Miami, 1991
4. “Recommended Practice for Preproduction Qualification for Steel Plates for Offshore Structures,” API
2Z, 2nd ed. (includes November 1998 addenda), American Petroleum Institute, Washington DC, 1998
Mechanical Testing of Welded Joints
William Mohr, Edison Welding Institute
Mechanical Testing for Weldment Properties
Tensile Strength and Ductility of Weldments
Testing for mechanical properties of strength and ductility for welded joints is somewhat more complicated
than it is for base metal, because these properties vary across the weld metal, the adjacent HAZ, and the base
metal. Several different tests may be used or combined to assess the strength of the overall welded joints.
Tensile testing is widely used to measure the strength and ductility of the weld metal alone. Tensile testing of
welds in place, with weld metal, HAZ, and base metal, allows an overall strength to be determined but usually
cannot provide the strengths of the individual parts of the weldment.
Tensile tests of welds can also measure elastic modulus. However, except in rare cases of dissimilar metal
joining, the elastic modulus is not sensitive to the differences between weld, HAZ, and base metal. So,
measurement during weld tensile tests is not usually required. Also, most tensile testing procedures for weld
joints cannot be relied upon to provide accurate values of elastic modulus. The specific procedures for testing of
elastic modulus distributed by ASTM should be used if required (Ref 5).
Testing of Weld Material. Deposited weld metal can be tested for the mechanical properties of strength and
ductility using the same test methods used for base metals (Ref 6, 7). However, a sufficient volume of deposited
weld metal is required to remove a test specimen made entirely of weld metal. Often, arc welds are long only in
one direction (the longitudinal direction), while the through-thickness and cross-weld directions are much
smaller. This encourages all-weld-metal tensile test specimens to be removed with the long direction of the
specimen corresponding to the longitudinal direction of the weld. Such longitudinal tensile test specimens are
standard for all-weld-metal tests.
All-weld-metal tests are most commonly done on specimens with round cross section. The diameter of the
specimen may need to be reduced from that used for base metal so that the specimen can be taken entirely from
weld metal. Rectangular cross-section specimens also are used occasionally.
Ultimate tensile strength, yield strength (usually based either on yield point or a specified offset), elongation,
and reduction of area are all commonly recorded.
While the specimen surface should be smooth, without deep machining marks, imperfections within the gage
length due to welding should not be removed. This requirement may increase the variability of results within a
group of similar specimens.
If the data required are for a class of weld material such as an electrode lot, the material can be taken from
specimens that reduce the possibility of dilution of base metal into the weld, such as a built-up weld pad. If the
data required are for a particular weldment, the geometry as well as the welding process and procedure should
model those of the weldment as closely as possible. Some modifications of the weldment may be allowed, such
as increasing the root opening by 6 mm ( in.) or buttering the groove faces with the weld metal to be tested.
The surface of the tested section, in the gage length, is recommended to be 3 mm ( in.) or more from the
fusion line.
Testing of Welds in Place. When the weld metal extends over only part of the tested gage length, tensile tests
can be performed similar to those performed on the round and rectangular specimen tests of weld metal. The
nonuniformity of deformation or stresses of the weld, HAZ, and base metal combination limits the information
normally recorded.
For transverse tests, ultimate strength and the location of fracture are the only commonly recorded parameters,
because strength, elongation, and reduction in area will all be affected by the constraint of the adjacent differing
materials. If the weld is undermatched, the yield strength tends to be higher than it is for an all-weld-metal
specimen, while the elongation over the gage length and reduction in area are smaller. If the weld yield strength
exceeds that of the base material, that is, it is overmatched, the failure tends to occur not in the adjacent HAZ,
but in the base material closer to the end of the gage length, because of the constraint provided by the high-
strength weld metal.
Local strain measurements, such as those made by strain gages, can add useful information to the results of
transverse testing. The local strain information can be correlated to the load and displacement information to
allow local strengths to be determined.
For longitudinal tests, the strain will be nearly uniform across the weld metal, HAZ, and base metal.
Differences in response to the applied strain may result in stresses varying across the cross section. Only
ultimate strength is commonly measured.
Testing standards may need to be varied for some specific geometries. For instance, girth welded tubes of less
than 75 mm (3 in.) diameter are commonly tested in the form of tubes with central plugs at the grips. The weld
is placed at the center of the gage length between the grips. The additional constraint induced by the hoop
direction continuity tends to increase the measured strengths and decrease the measured ductilities for tube
welds tested in this manner compared to a similar joint between flat sheets.
Shear Testing of Fillet Welds
Shear strength tests for fillet welds are described in AWS B4.0 for two orientations of fillet welds (transverse to
the tension loading and longitudinal to the tension loading) (Ref 8, 9). The transverse specimen is a double lap
specimen with loaded fillet welds, as shown in Fig. 1. The longitudinal specimen is a combination of two