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  ETK59 - Mechanics and Strength of Materials

Bristol Community College

 

Department of Engineering

 

77 Elsbree Street

 

Fall River, Ma 02720

 

 

 

Adhesive Testing

 

 

 

 

Course Number: ETK59

 

Course Name: Mechanics and Strength of Materials  

Written By: Strength of Materials Class

    Lab Day: Monday Lab Time: 1:00 Dates Performed: September 10, October 10, and November 13, 2001

Date Submitted: December 4, 2001

Objective:

The purpose of this experiment is to familiarize the student with the testing techniques used to measure the strength of the important types of adhesives and adhesive joints, the interaction of forces and the resulting failure types.

The effects of saltwater submerged fixture assembly, short-term exposure of adhesives to refrigerated saltwater and the long-term exposure of adhesives to open ocean saltwater will also be investigated.

The three sets of samples are an air assembled, air cured control group with minimal aging, a sea water submerged assembled and cured group with 4 weeks of aging in refrigerated sea water and a sea water submerged assembled and cured group with 8 weeks of aging in open ocean sea water.

The adhesives being evaluated are Fastweld, Epoxo 88, Bio-Fix 911 (w/ Kevlar Additives), Epoxy 10-3070 and RepairitQuik.

The materials being bonded are aluminum (for both peel and tension lap tests), carbon and stainless steels (tension lap test only) and oak wood (compression lap test only)

 

 

Background:

Adhesives:

An adhesive is a material that may be applied between adjacent surfaces of members to hold them together. Adhesives include materials such as glue, paste, and cement.

Glue is the term generally used to include all adhesives used on wood.

Paste is usually a preparation from starch and water.

Cement (excluding Portland cement) is usually a thermoplastic resin dissolved in a solvent, such as household or airplane cement.

Nature of Adhesion

The exact mechanism of adhesion is not entirely understood. At one time it was believed to involve a mechanical action. According to this, adhesion resulted from the fluid adhesive penetrating pores or voids in the material and hardening to form an interlocking mechanical action. This concept has been largely replaced by one of chemical adhesion, which is based on molecular attraction forces between the adhesive and the material being joined. This explains why it is possible to join materials having perfectly smooth surfaces with no possibility of mechanical interlocking. Mechanical adhesion may be involved in joining some porous materials, but it is not important in most adhesive joints.

Chemical adhesion requires that materials be selected that will develop strong molecular attraction between each other; this means that the adhesive must be matched to materials being joined. A good adhesive for one material may not be effective with another material.

Clean surfaces are essential, to allow the molecules of the adhesive to directly contact the surface. A layer of oil only one molecule thick can prevent adhesion. Even a fingerprint on a polished metal surface can greatly reduce the strength of a joint. A few special adhesives have been developed, however, that can dissolve or absorb oil films on sheet metal surfaces and provide a good joint without cleaning.

Classes of Adhesives:

Adhesive are classified by their application:

Structural adhesives - produce high strength in shear tension or pull, to hold structural members securely.

Holding adhesives for attaching materials with low stress such as masking tape.

Sealing adhesives are for closing a joint to provide a fluid-tight seal.

Structural Adhesives

Practically all structural adhesives used for joining metals are some type of synthetic resin. These materials react chemically to form a strong bond and have high internal strength. The chemical reaction may result from mixing two separate components together or from heating a single component material.

Epoxies are the most versatile and well known of the structural adhesives, and they represent characteristics of many others. They form a strong bond with a great variety of materials, including metal, wood, glass, and ceramics. They are available as two component liquids or pastes that require mixing just prior to use and will set at room temperatures. Other pre-mixed forms are available in liquid, paste or tape that may be stored and placed at room temperature and cured by heating.

Other structural adhesives include; Silicones, Phenolics, Polysulfides, Vinyls and Polyurethane

 

Joints:

This experiment demonstrates testing of structures or assemblies of several parts. Often the weakest portion of an assembly is where two pieces of material are joined together. These joints can be joined at their ends with a butt joint or where they overlap in a lap joint. In adhesive joints the most common type of bond is the lap joint. Each joint represents a structure for which it is difficult to determine load-carrying capacity by simple calculations from available data. It often requires multiple calculation for different types of loading and failures. These joints can fail in two primary modes: shear or peel, or in combinations of these modes. The peel mode is a combination of the two simple stresses, tension and shear. These stresses have been studied in previous labs.

Adhesives frequently do not have physical properties equal to that of the parts they are used to join. By proper design, however, a joint can be made to develop full strength of the parts. This requires a large joint area, with the material loaded uniformly. The adhesive should be loaded in shear whenever possible.

Joint Types:

The butt joint has limited area and is not usually effective. The multiple tongue and groove, or finger joint is commonly used instead in laminated wood beams and places much adhesive in shear rather than straight tension.

The simple lap joint is very effective. Any practical strength can be obtained by varying the width of lap.

The scarf joint provides very high strength in a member of uniform thickness. The tapered ends are very difficult to repair.

The "L" and 'T" joints are used frequently with metal construction. Applied loads tend to cause "peeling" stress, or a localized stress which can cause progressive failure.

 

Testing Adhesive Joint Strength

The common strength properties of adhesive joints include tensile, peel and shear. Of these, shear strength is most important for most joints in wood and metal. Shear tests have become, therefore, the most common for rating adhesives and glues. Although shear test are the most common, adhesives are actually weakest in the peel mode. Due to this peeling is the most probable mode of failure and must be considered in evaluating adhesives.

 

Equipment Required:

    • Universal Testing Machine (w/ Hardened compression discs/blocks & Tensile jaws)
    • Adhesive Joint Fixtures: Wood (Oak) Compression Lap Joint Fixtures

(2" wide, 0.25" Thick)

Aluminum Tension Lap Joint Fixtures

(2" wide, 0.080" Thick)

Carbon Steel Tension Lap Joint Fixtures

(2" wide, 0.025" Thick)

Stainless Steel Tension Lap Joint Fixtures

(1.5" wide, 0.025" Thick)

Aluminum Peel Test Fixture

(2" wide, 0.025" Thick)

Note: One complete set of fixtures is used to test each adhesive

 

Procedure

Compression Lap Test

  1. Configure UTM for compression mode with test Hardened compression discs.
  2. Select a bonded wood fixture
  3. Measure the actual length and width of the joint area visible from the exterior
  4. Place the specimen in the machine and gradually apply load
  5. Observe the behavior of the specimen
  6. Continue to load to failure
  7. Record the maximum load reached.
  8. Examine the broken specimen
  9. Determine whether failure occurred at the adhesive or in the wood fixture
  10. Estimate the % of adhesive coverage of the bonded area.
  11. Determine the bond strength based on measured area and based on estimated coverage area
  12. Repeat Procedure for each Adhesive

Tensile Lap Test

  1. Configure UTM for Tensile mode with tensile jaws.
  2. Select a bonded metal lap test fixture
  3. Determine the material, Measure the actual length and width of the joint area visible from the exterior
  4. Place the specimen in the machine and gradually apply load
  5. Observe the behavior of the specimen
  6. Continue to load to failure
  7. Record the maximum load reached.
  1. Examine the broken specimen
  2. Determine whether failure occurred at the adhesive or in the metal fixture
  3. Estimate the % of adhesive coverage of the bonded area.
  4. Determine the bond strength based on measured area and based on estimated coverage area
  5. Repeat Procedure for each Fixture type and each Adhesive

 

Tensile Peel Test

  1. Configure UTM for Tensile mode with tensile jaws.
  2. Select a bonded metal peel test fixture
  3. Measure the actual length and width of the joint area visible from the exterior
  4. Prepare specimen by bending back free ends for jaws to grip
  5. Place the specimen in the machine and gradually apply load
  6. Observe the behavior of the specimen
  7. Continue to load to failure
  8. Record the maximum load reached.
  9. Examine the broken specimen
  10. Determine whether failure occurred at the adhesive or in the metal fixture
  11. Estimate the % of adhesive coverage of the bonded area.
  12. Determine the bond strength based on measured area and based on estimated coverage area
  13. Repeat Procedure for each Adhesive

 

 

 

Data & Results

Data:

Table 1: Control / Air Cured Adhesive Sample Testing Data

 

 

Sample

Code

Test Type

Dimensions (in x in)

Area (in2)

Coverage (estimated)

Max. Force (Lb)

010913 911C-AL

Tension Peel

1.98 x 2.04 *

4.04

90%

<5

010913 911C-AH

Tension Lap

1.97 x 1.09 *

2.16

60%

520

010913 911C-SS

Tension Lap

1.55 x 1.43 *

2.22

90%

790

010913 911C-CS

Tension Lap

2.13 x 2.00 *

4.27

80%

1310

010913 911C-OW

Compression Lap

2.00 x 1.66

3.31

**

>2410

010913 RIQC-AL

Tension Peel

1.88 x 1.96

3.69

100%

2

010913 RIQC-AH

Tension Lap

1.98 x 2.02

4.04

100%

564

010913 RIQC-SS

Tension Lap

1.52 x 1.48

2.25

100%

460

010913 RIQC-CS

Tension Lap

2.02 x 2.00 *

4.04

90%

1530

010913 RIQC-OW

Compression Lap

2.00 x 2.01

4.02

100%

1080

010913 FWC-AL

Tension Peel

***

***

***

***

010913 FWC-AH

Tension Lap

2.01 x 2.01 *

4.03

60%

620

010913 FWC-SS

Tension Lap

1.46 x 1.43 *

2.09

40%

140

010913 FWC-CS

Tension Lap

1.97 x 2.01 *

3.96

30%

456

010913 FWC-OW

Compression Lap

2.02 x 2.00 *

4.04

90%

745

010913 3070C-AL

Tension Peel

2.08 x 2.06 *

4.28

80%

0

010913 3070C-AH

Tension Lap

1.85 x 2.18

4.25

100%

1990

010913 3070C-SS

Tension Lap

1.46 x 1.65

2.41

100%

2750

010913 3070C-CS

Tension Lap

1.97 x 2.29 *

4.51

60%

1930

010913 3070C-OW

Compression Lap

2.02 x 2.00

4.04

**

>2550

010913 88C-AL

Tension Peel

2.00 x 2.21 *

4.42

90%

1

010913 88C-AH

Tension Lap

***

***

***

***

010913 88C-SS

Tension Lap

***

***

***

***

010913 88C-CS

Tension Lap

2.00 x 1.97 *

3.94

60%

884

010913 88C-OW

Compression Lap

2.02 x 2.29

4.63

100%

2070

* Incomplete Bond – Coverage Estimated After Failure ** Fixture Failure (Before Bond Failure) *** Bond Failure (Separated Fixture)

 

 

Table 2: Refrigerated Adhesive Sample Testing Data

 

 

Sample

Code

Test Type

Dimensions (in x in)

Area (in2)

Coverage (estimated)

Max. Force (Lb)

010918 911REF-AL

Tension Peel

****

****

****

****

010918 911REF-AH

Tension Lap

1.92 x 2.53

4.86

100%

1116

010918 911REF-SS

Tension Lap

1.47 x 1.55

2.28

100%

332

010918 911REF-CS

Tension Lap

2.01 x 2.09

4.20

100%

675

010918 911REF-OW

Compression Lap

2.48 x 2.09 *

5.18

90%

65

010918 RIQREF-AL

Tension Peel

1.96 x 2.34 *

4.59

80%

<1

010918 RIQREF-AH

Tension Lap

1.99 x 2.14 *

4.27

80%

78

010918 RIQREF-SS

Tension Lap

1.45 x 1.89

2.73

100%

25

010918 RIQREF-CS

Tension Lap

2.01 x 2.08 *

4.18

90%

340

010918 RIQREF-OW

Compression Lap

***

***

***

***

010918 FWREF-AL

Tension Peel

2.15 x 1.94 *

4.17

50%

0.5

010918 FWREF-AH

Tension Lap

2.63 x 2.04 *

5.34

40%

440

010918 FWREF-SS

Tension Lap

1.56 x 1.46 *

2.27

90%

193

010918 FWREF-CS

Tension Lap

1.95 x 1.98 *

3.85

20%

112

010918 FWREF-OW

Compression Lap

2.09 x 2.16 *

4.50

60%

25

010918 3070REF-AL

Tension Peel

2.42 x 1.87 *

4.53

90%

1

010918 3070REF-AH

Tension Lap

***

***

***

***

010918 3070REF-SS

Tension Lap

1.64 x 1.68 *

2.76

80%

384

010918 3070REF-CS

Tension Lap

2.25 x 1.67 *

3.76

70%

124

010918 3070REF-OW

Compression Lap

2.16 x 2.14 *

4.62

90%

1006

010918 88REF-AL

Tension Peel

2.08 x 2.01 *

4.19

90%

<1

010918 88REF-AH

Tension Lap

2.03 x 1.95 *

3.94

90%

818

010918 88REF-SS

Tension Lap

1.57 x 1.42 *

2.23

90%

454

010918 88REF-CS

Tension Lap

1.90 x 1.89

3.59

100%

720

010918 88REF-OW

Compression Lap

2.15 x 2.17 *

4.67

70%

<5

* Incomplete Bond – Coverage Estimated After Failure ** Fixture Failure (Before Bond Failure) *** Bond Failure (Separated Fixture) **** Misaligned Sample

Table 3: Sea Water Life Test Adhesive Sample Testing Data

 

 

Sample

Code

Test Type

Dimensions (in x in)

Area (in2)

Coverage (estimated)

Max. Force (Lb)

010918 911SEA-AL

Tension Peel

***

***

***

***

010918 911SEA-AH

Tension Lap

2.00 x 2.00

4.00

100%

2000

010918 911SEA-SS

Tension Lap

***

***

***

***

010918 911SEA-CS

Tension Lap

***

***

***

***

010918 911SEA-OW

Compression Lap

***

***

***

***

010918 RIQSEA-AL

Tension Peel

***

***

***

***

010918 RIQSEA-AH

Tension Lap

***

***

***

***

010918 RIQSEA-SS

Tension Lap

1.57 x 1.51

2.36

100%

16

010918 RIQSEA-CS

Tension Lap

1.90 x 2.42

4.70

80%

195

010918 RIQSEA-OW

Compression Lap

2.30 x 2.17

4.98

90%

51

010918 FWSEA-AL

Tension Peel

2.03 x 2.10

4.25

50%

2.5

010918 FWSEA-AH

Tension Lap

***

***

***

***

010918 FWSEA-SS

Tension Lap

2.03 x 1.58

3.20

100%

832

010918 FWSEA-CS

Tension Lap

***

***

***

***

010918 FWSEA-OW

Compression Lap

2.12 x 1.58

3.37

60%

67.5

010918 3070SEA-AL

Tension Peel

***

***

***

***

010918 3070SEA-AH

Tension Lap

***

***

***

***

010918 3070SEA-SS

Tension Lap

***

***

***

***

010918 3070SEA-CS

Tension Lap

***

***

***

***

010918 3070SEA-OW

Compression Lap

***

***

***

***

010918 88SEA-AL

Tension Peel

2.20 x 1.96

4.31

100%

1

010918 88SEA-AH

Tension Lap

***

***

***

***

010918 88SEA-SS

Tension Lap

***

***

***

***

010918 88SEA-CS

Tension Lap

***

***

***

***

010918 88SEA-OW

Compression Lap

***

***

***

***

* Incomplete Bond – Coverage Estimated After Failure ** Fixture Failure (Before Bond Failure) *** Bond Failure (Separated Fixture) **** Misaligned Sample     Results:    

Table 4: Air Cured Adhesive Sample Strengths

Sample

Code

Test Type

Bond Strength

Measured Area (psi)

Bond Strength

Estimated Area (psi)

Bond Strength

Specified Value (psi)

Deviation from Specified Value (%)

010913 911C-AL

Tension Peel

1.24

1.37

*

*

010913 911C-AH

Tension Lap

241

401

*

*

010913 911C-SS

Tension Lap

356

396

*

*

010913 911C-CS

Tension Lap

307

384

*

*

010913 911C-OW

Compression Lap

**

**

*

*

010913 RIQC-AL

Tension Peel

.542

.542

800-1000

010913 RIQC-AH

Tension Lap

140

140

800-1000

010913 RIQC-SS

Tension Lap

204

204

800-1000

010913 RIQC-CS

Tension Lap

379

421

800-1000

010913 RIQC-OW

Compression Lap

269

269

800-1000

010913 FWC-AL

Tension Peel

**

**

*

010913 FWC-AH

Tension Lap

154

256

2800

010913 FWC-SS

Tension Lap

67

167

2800

010913 FWC-CS

Tension Lap

115

384

2800

010913 FWC-OW

Compression Lap

184

205

2800

010913 3070C-AL

Tension Peel

0

0

*

010913 3070C-AH

Tension Lap

468

468

2800

010913 3070C-SS

Tension Lap

1140

1140

2800

010913 3070C-CS

Tension Lap

42

713

2800

010913 3070C-OW

Compression Lap

631

631

2800

010913 88C-AL

Tension Peel

.226

.251

*

010913 88C-AH

Tension Lap

**

**

2800

010913 88C-SS

Tension Lap

**

**

2800

010913 88C-CS

Tension Lap

224

374

2800

010913 88C-OW

Compression Lap

447

447

2800

* No Specified Value for Peel or Lap Shear Strength provided by manufacturer ** Test Failure (see data)

Table 5: Refrigerated Adhesive Sample Strengths

Sample

Code

Test Type

Bond Strength

Measured Area (psi)

Bond Strength

Estimated Area (psi)

Bond Strength

Specified Value (psi)

Deviation from Specified Value (%)

010913 911REF-AL

Tension Peel

**

**

*

010913 911REF-AH

Tension Lap

230

230

*

010913 911REF-SS

Tension Lap

146

146

*

010913 911REF-CS

Tension Lap

161

161

*

010913 911REF-OW

Compression Lap

12.5

13.9

*

010913 RIQREF-AL

Tension Peel

< .218

< .275

*

010913 RIQREF-AH

Tension Lap

18.3

22.8

*

010913 RIQREF-SS

Tension Lap

9.16

9.16

*

010913 RIQREF-CS

Tension Lap

81.3

90.4

*

010913 RIQREF-OW

Compression Lap

**

**

*

010913 FWREF-AL

Tension Peel

.120

.240

*

010913 FWREF-AH

Tension Lap

82.4

206

2800

010913 FWREF-SS

Tension Lap

85.0

94.5

2800

010913 FWREF-CS

Tension Lap

29.1

145

2800

010913 FWREF-OW

Compression Lap

5.56

9.26

2800

010913 3070REF-AL

Tension Peel

.221

.245

2800

010913 3070REF-AH

Tension Lap

**

**

2800

010913 3070REF-SS

Tension Lap

139

174

2800

010913 3070REF-CS

Tension Lap

33.0

47.1

2800

010913 3070REF-OW

Compression Lap

218

242

2800

010913 88REF-AL

Tension Peel

.240

.265

2800

010913 88REF-AH

Tension Lap

208

231

2800

010913 88REF-SS

Tension Lap

204

226

2800

010913 88REF-CS

Tension Lap

200

200

2800

010913 88REF-OW

Compression Lap

1.07

1.53

2800

* No Specified Value for Peel or Lap Shear Strength provided by manufacturer ** Test Failure (see data)

Table 6: Sea Water Life Test Adhesive Sample Strengths

Sample

Code

Test Type

Bond Strength

Measured Area (psi)

Bond Strength

Estimated Area (psi)

Bond Strength

Specified Value (psi)

Deviation from Specified Value (%)

010913 911SEA-AL

Tension Peel

**

**

    

010913 911SEA-AH

Tension Lap

**

**

    

010913 911SEA-SS

Tension Lap

500

500

    

010913 911SEA-CS

Tension Lap

**

**

    

010913 911SEA-OW

Compression Lap

**

**

    

010913 RIQSEA-AL

Tension Peel

**

**

    

010913 RIQSEA-AH

Tension Lap

6.78

6.78

    

010913 RIQSEA-SS

Tension Lap

33.2

41.5

    

010913 RIQSEA-CS

Tension Lap

9.22

10.2

    

010913 RIQSEA-OW

Compression Lap

.294

.588

    

010913 FWSEA-AL

Tension Peel

**

**

    

010913 FWSEA-AH

Tension Lap

261

261

    

010913 FWSEA-SS

Tension Lap

**

**

    

010913 FWSEA-CS

Tension Lap

12.0

20.0

    

010913 FWSEA-OW

Compression Lap

**

**

    

010913 3070SEA-AL

Tension Peel

**

**

    

010913 3070SEA-AH

Tension Lap

**

**

    

010913 3070SEA-SS

Tension Lap

**

**

    

010913 3070SEA-CS

Tension Lap

**

**

    

010913 3070SEA-OW

Compression Lap

.232

.232

    

010913 88SEA-AL

Tension Peel

**

**

    

010913 88SEA-AH

Tension Lap

**

**

    

010913 88SEA-SS

Tension Lap

**

**

    

010913 88SEA-CS

Tension Lap

**

**

    

010913 88SEA-OW

Compression Lap

**

**

    

* No Specified Value for Peel or Lap Shear Strength provided by manufacturer ** Test Failure (see data)

Reference Information

Fastweld - Lap Shear Strength (Alum to Alum w/ 24 hr cure at Rm. Temp.) = 2,800 psi

Epoxo 88 - Tensile Strength = 2,000 psi

Bio-Fix 911 (w/o Kevlar Additives) - Tensile Strength = 7,600 psi

Compression Strength = 10,000 psi

Epoxy 10-3070 - Tensile Strength = 5,510 psi

Compression Strength = 13,050 psi

FastSteel - Lap Tensile Shear (1/16" thick on Steel) 800 – 1,000 psi

RepairitQuik - Lap Tensile Shear (1/16" thick on Steel) 800 – 1,000 psi

 

 

 

 

 

 

 

 

 

Table 1: Air Cured Sample Bond Strength

 

 

 

 

 

 

Table 2: Refrigerated Sea Water Cured Sample Bond Strength

 

 

 

 

 

 

 

 

Table 3: Sea Water Cured Sample Bond Strength

 

 

 

 

 

 

Table 4: Average Bond Strength

 

 

 

 

 

 

 

 

DISCUSSION

Comparison of Results (dry/control environment):

In the control environment portion of the testing, bond strengths were determined for five different commercially available epoxies. Since the values for the tension lap tests of the different adhesives were similar, an average was taken to get a more accurate representation of the true adhesive strengths.

Epoxy 10-3070, by far, supplied the best results, with a strength of 774 PSI in the tension lap tests. Bio Fix 911 and Epoxo88 were also relatively strong, providing bond strengths of 394 PSI and 374 PSI respectively, although there was only one Epoxo88 sample to test. The two weakest adhesives were FastWeld and RepairitQuik, only providing strengths of 269 PSI and 255 PSI respectively. This may be due to the nature of the two adhesives. FastWeld is a thick, clay type adhesive that is not engineered only for adhesive qualities, but also for its ability to fill holes, while RepairitQuik is a putty type adhesive that is better suited for repairing cracks and fissures, rather than providing a consistent source of practical strength. In fact, in three of the five samples for RepairitQuik, it was noted that the adhesive was not fully cured. The adhesive material was still slightly moist and pliable.

The oak wood specimens all performed very well, with an average strength of 388 PSI. This can be attributed to the added benefit of having a rough, organic mating surface that the adhesive could penetrate. These samples benefited from mechanical adhesion, as well as chemical adhesion. In one case, the oak wood fixture failed before the adhered bond did, while another sample failed prematurely due to the wood shearing off, rather than the failure of the bond itself. Upon further inspection of the failed specimen, it was noted that the adhesive was still intact.

All tension peel test samples were extremely weak-with the strongest specimen having a strength of only ½ PSI. These joints are very weak due to the load being concentrated over a very small area, and should be avoided in engineering applications. Since these results were so consistently low, no comparison between them was warranted.

The material type used in the tension lap tests seemed to have little effect on the overall strength of these bonds. The aluminum samples averaged 316 PSI; the carbon steel samples averaged 455 PSI; the stainless steel samples averaged 477 PSI. These materials all seem to lend themselves well to chemical adhesion.

All adhesives were far weaker than the manufacturer supplied reference data. The reference data was highly idealized and assumed a perfect bond-adhesive cured at the proper temperature, correct amount of adhesive used, a degreased and abraded mating surface, and a precise amount of pressure applied during the curing process. Because of these assumptions, the reference data given mean very little to the validity of the tests. Epoxy 10-3070, being so much stronger than the other adhesives, suggests that this type of adhesive relies less on idealized conditions than the other adhesives.

 

 

DISCUSSION

Comparison of Results (refrigerated seawater environment):

All adhesives showed a considerable decrease in bond strength after being exposed to the refrigerated seawater, although some handled it a lot better than others.

Epoxo88 (219 PSI) withstood the exposure to this environment the best, retaining 58.6% of its original strength of 274 PSI. This commercially available adhesive is actually marketed as a marine adhesive, suggesting that it is engineered for these conditions. FastWeld, one of the weakest adhesives in the control environment, also handled these conditions fairly well, retaining 55.4% of its initial strength. Bio Fix 911 retained 45.4% of its strength.

Interestingly, the Epoxy 10-3070-the strongest adhesive in the control tests-suffered the greatest decline in strength after being exposed to this environment. Samples bonded with this adhesive averaged only 72.7 PSI after supplying 774 PSI in the dry tests-a decrease in strength of 90.6%. This shows a general trend of strong adhesives in a dry environment becoming very weak in seawater, while weak adhesives in the dry environment seemed to retain a greater percentage of its bond strength.

RepairitQuik (40.8 PSI) was another adhesive that performed poorly, declining in strength by 84%. As in the control samples of this adhesive, most showed signs of incomplete curing. The lack of curing of this adhesive in the tests suggests that it is highly dependent on perfect conditions in order for it to properly cure.

Predictably, the oak wood samples dramatically lost strength when exposed to the seawater, losing 86.3% of its strength. The wood seemed to absorb the water, softening the wood fixture, as well as helping to deteriorate the bond from the inside out. This kind of fixture is definitely not desirable under these conditions.

As was the case in the control environment, the material used to create the joint seemed to make little difference in this test. The aluminum samples averaged 172 PSI; the carbon steel samples averaged 128 PSI; the stainless steel samples averaged 130 PSI. If these samples were left in the water for a longer duration of time, these numbers could be greatly affected by oxidation of the carbon steel and the aluminum.

No reference information was available for bond strength of these adhesives when in this type of environment. Consequently, no comparison could be made to given reference values.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DISCUSSION

Comparison of Results (seawater life test environment):

Compared to the refrigerated seawater test, all adhesives placed in this life test showed an even larger decrease in bond strength. These specimens were in the seawater environment 2 weeks longer than the refrigerated samples, undoubtedly having a huge effect on the overall results. Out of the 25 total samples, only 8 survived to be tested. This suggests that compared to the cold refrigerated seawater in the previous test, the relatively warm ocean water combined with the slight temperature changes of the coastal waters and the movement of the water from the currents and tides to prematurely fail these adhered joints.

Although their strength was relatively weak, RepairitQuik (16.1 PSI) and FastWeld (87 PSI) seemed to hold up the best in this test. Each adhesive provided 3 of the 8 total samples, leaving only 2 samples remaining for the other 3 adhesives. The Bio Fix and Epoxo88 adhesives each had 1 sample remaining, which accounted for all of the samples.

The strongest adhesive in the control environment, the Epoxy 10-3070, had no test specimens survive. Considering that this epoxy lost all of its strength in these tests, as well as lost 91.6% of its strength in the refrigerated sea water test, it shows that Epoxy 10-3070 does not hold up well in a marine environment and should be avoided in the field.

The oak wood samples lost virtually all of their practical strength, averaging only 6.04 PSI. The only samples that remained were bonded with RepairitQuik and FastWeld, which suggests that the "putty/paste" type nature of these two adhesives worked better than the other types with the rough mating surface of the wood.

Possibly due to the its resistance to oxidation, the stainless steel samples faired much better than other materials in the life test. 3 stainless steel samples survived; 1 carbon steel sample survived; no aluminum samples survived. When zero strength was used for prematurely failed samples, the averages of the bond strengths were 154 PSI for the stainless steel, 8.3 PSI for the carbon steel, and since no aluminum samples remained, the strength was 0 PSI. Predictably, the carbon steel and the aluminum samples were very oxidized, which helped to break apart and fail the bonded joints on these materials.

Sources of Error

 

There could have been two main types of errors, sample and instrumental. Sample errors in this lab would be that the samples weren’t perfectly aligned with one another, which would change its area and change the amount of adhesive used in the sample. The coverage of the adhesive used wasn’t 100%, causing it to break earlier than expected. There weren’t enough samples to use as an average when comparing it to its reference value. Instrumental errors in this lab would be the measuring equipment used wasn’t precisely accurate, causing error in the samples area. The force measured from the universal testing machine could have been misread because it had increments of ten pounds per square inch. The reference value given to use may have been incorrect. All of these possibilities would result in the cause of error.

 

CONCLUSION

The experiment was successful in familiarizing the experimenters with the testing techniques used to measure bond strength in adhesives on various materials using a uni-axial tension test. The experiment was useful in the familiarization of a Universal Testing Machine operating in compression mode as well as tension mode while performing tension peel, tension lap, and compression lap testing, which are the primary ways of testing adhesive joints. In general, the experiment showed that adhesives have the weakest bond strength in a peel test, and that the greatest bond strengths were seen in the tension lap test. The experiment also showed that the greatest bonding or coverage area yielded the greatest strength. Practical experience with various measuring tools such as a micrometer and a dial caliper was also gained. A good working knowledge of the various equations and terminology used in engineering fields to determine the bonding strength of adhesives in tension peel, tension lap, and compression lap testing was obtained.

The air-cured samples had the greatest strength of all the samples with average tension lap strength of 413 psi. 23 out of the 25 samples, or 92 % survived. The strongest tension lap sample in this group was the 3070-SS at 1141 psi and the weakest was the RIQ –AH at 140 psi. The 3070 samples had the highest tension lap average at 774 psi while the RIQ had the lowest at 255 psi.

The refrigerated samples averaged 132 psi in tension lap strength, which is 42.4 % of the air-cured sample strength. 22 out of the 25 samples, or 88 % survived. The strongest tension lap samples in this group were the 911-AH at 230 psi and the 88-AH at 231 psi; the weakest was the RIQ–SS at 9.16 psi. The 88 samples had the highest tension lap average at 219 psi while the RIQ had the lowest at 40.8 psi.

The seawater samples had the lowest strength of all the samples with an average tension lap strength of 54 psi, which is 17.3 % of the air-cured sample strength. 8 out of the 25 samples, or 32 % survived. The strongest tension lap sample in this group was the FW-SS at 261 psi and the weakest was the RIQ–SS at 6.78 psi. The FW samples had the highest tension lap average at 87 psi while the RIQ had the lowest at 16.1 psi.

Note: The broken samples were accounted for and were factored in the calculations for average strengths.

Improvement of this lab could be obtained by testing several of the same type specimens, as this has the potential to improve the results of the bonding strength of a given adhesive. Another reason for testing multiple samples of each type is that adhesive bonds lack consistency and some of the samples were separated or missing on arrival. Some specimens were not completely bonded over the whole lap area forcing an estimation of the coverage area, and therefore, a less than desirable strength. A better understanding of the similarities and differences of the various epoxies used would be helpful: for example, 88 versus 3070. Improvements could also be obtained by knowing the type of aluminum, stainless steel, or carbon steel used in the samples. A better comparison can be made if values for tension lap, tension peel, and compression lap strengths are found.