Nail pull resistance

Data will be presented to show that the constant strain rate method of testing can give equally precise results with a very substantial saving in lime and physical effort. Eor flexurid strength, nail pull resistance, and core hardness there is a simple linear correlation between the results with the two machines. The ctmsiani strain rale machine can more accurately determine the maximum load causing failure than the constant stress rate machine. Correlation between the results of tests on either machine shows that the core hardness and nail pull resistance tests tend lo duplicate information on core properties. 

Figure 4 shows the accessories used for nail pull resistance, and core, end. 

The constant strain machine can be readily adapted for running the nail pull resistance test. No change in sample size is required. The only change made in the equipment was the slot in the sample holder referred to previously. This makes inserting and removing a sample quicker and more convenient but is not absolutely necessary. 

The stress-strain curves also show that there can be numerous small-scale variations in core hardness. Most likely these represent small voids or lumps in the core. We believe that these local variations can cause some of the extreme variation between specimens that can occur in the nail pull resistance test. While these variations can affect the shape of the curve, in most cases the final value is quite consistent. 

In practice we believe that the test is not used very widely because a sample that meets the nail pull resistance specification will substantially exceed the core and end hardness specification. Further study and development of this test is warranted particularly if it is done on a constant strain machine. 

Consideration of what is done to the core when conducting the two tests indicates that they are somewhat similar. True, the pin used for the nail pull resistance test has a larger diameter and must tear through the paper before it crushes the core, but the basic action is to crush the core by pushing a pin into it. 

An additional evaluation was made by running a three-variable correlation using nail pull resistance as the dependent variable and core hardness and flexural strength as independent variables. The correlation coefficients are shown in Table 8. 

The combined correlation coefficient does increase significantly showing that nail pull resistance can be predicted reasonably well from core hardness and flexural strength. Since the major component of flexural strength variation is thickness, the correlation is really with core hardness and thickness. There may be a small effect of paper strength, but it is confounded with the effect of thickness. 

A logical conclusion is that the core hardness and nail pull resistance tests give essentially duplicate information. The core hardness test has the potential... 

Consideration should also be given to what the tests tell a user about the utility of a product. The nail pull resistance and core hardness tests give very similar infonnation. Possibly other types of tests should be devised to measure other properties of gypsum board. 

About 1975 the ASTM specifications for gypsum board were changed to eliminate arbitrary weight limits and substitute performance tests. The tests added were humidified sag resistance core, end, and edge hardness and nail pull... 

This standard consists of 22 test methods, some of which are used in evaluating high-density rigid polyurethane foams for furniture applications. These methods are concerned with fastener-holding properties Lateral Nail Resistance Test, Nail Withdrawal Test, Nail-Head Pull-through Test, and Direct Screw Withdrawal Test. 

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