Select a Penetrometer

Selecting the most appropriate penetrometer with which to test a particular material depends on sample form or shape, sample porosity, and the quantity of sample.

Penetrometers are available with three sample volumes, with five intrusion capacities, and in configurations for either solid pieces or powders. Refer to the Penetrometer Selection Guide in this section.

Ensure the sample nearly matches the size of the sample bulb and that the capillary volume is large enough to satisfy intrusion.

Penetrometer Selection Guide


Bulb
Volume (cc)


Sample
Type

Maximum
Measurable
Volume (cc)

Total
Stem
Volume
(cc)
Maximum
Head
Pressure

Physical Dimensions

Part
Number
(psia) (kPa) I (mm) H (mm)

D (mm)
3 Solid 0.387 0.412 4.68 32.3 227 242 1.473 950-61713-00
3 Solid 1.116 1.190 4.68 32.3 227 242 2.502 950-61715-00
3 Powder 0.387 0.412 4.68 32.3 227 242 1.473 950-61714-00
3 Powder 1.116 1.190 4.68

32.3

227 242 2.502 950-61716-00
5 Solid 0.366 0.392 4.45 30.7 215 230 1.473 950-61707-00
5 Solid 1.057 1.131 4.45 30.7 215 230 2.502 950-61709-00
5 Solid 1.716

1.836

4.45 30.7 215 230 3.188 950-61711-00
5 Powder 0.366 0.392 4.45 30.7 215 230 1.473 950-61708-00
5 Powder 1.057 1.131 4.45 30.7 215 230 2.502 950-61710-00
5 Powder 1.716 1.836 4.45 30.7 215 230 3.188 950-61712-00
15 Solid 0.366 0.392 4.45 30.7 215 230 1.473 950-61701-00
15 Solid 1.057 1.131 4.45 30.7 215 230 2.502 950-61703-00
15 Solid 1.716 1.836 4.45 30.7 215 230 3.188 950-61705-00
15* Solid 3.007 (3.263) 4.45 30.7 215 230 4.813 950-61724-00
15* Solid 3.857 (4.185) 4.45 30.7 215 230 4.813 950-61725-00
15 Powder 0.366 0.392 4.45 30.7 215 230 1.473 950-61702-00
15 Powder 1.057 1.131 4.45 30.7 215 230 2.502 950-61704-00
15 Powder 1.716 1.836 4.45 30.7 215 230 3.188 950-61706-00

* The first 3 mm of stem on these penetrometers have an inside diameter (D) of 1.5 mm. In computing maximum measurable (intrusion) volume, the value of I should be reduced by 3 mm.

  • Maximum measurable volume = [(3.14)(D2)(I)/4] × [0.001 cm3/mm3]
  • Total Stem (Capillary) volume = [(3.14)(D2)(H)/4] × [0.001 cm3/mm3]
  • Maximum Head Pressure (psia) = [H] × [0.01934 psia/mmHg]
  • Maximum Head Pressure (MPa) = [H] × [0.000133 MPa/mmHg]

A powder penetrometer should be used when the sample consists of small grains or particles. Chunks of material or formed objects (maximum size is 25 mm OD × 25 mm long) should only be installed in a “solid” penetrometer.

Best results, generally, are obtained when the bulb of the selected penetrometer is nearly filled by the minimum amount of sample that is representative. Next, the estimated pore volume of the sample should not exceed 90% nor be less than 25% of the total stem volume (see column 4 of the Penetrometer Selection Guide). Once materials of similar characteristics have been tested, it will usually be possible to select the optimum penetrometer almost without fail.

As an example, suppose the sample consists of a single sintered pellet of nickel (density 8.9 g/cc) weighing 29 g and having an estimated pore volume of 20% of the true sample volume to analyze. The following characteristics are calculated:

Volume of sample = mass/density = (29g)/(8.9g/cc) = 3.26 cc

Approximate pore volume = fractional pore volume × sample volume =
0.20 (3.26 cc) = 0.652 cc

Approximate total volume = volume of pores + volume of sample
(3.26 + 0.652) cc = 3.91 cc

Hence, the penetrometer listed sixth in the Penetrometer Selection Guide as solid, 5 cc sample volume, 1.131 cc total stem volume would be the appropriate choice unless the pellet shape dictates use of a larger one. The percent of maximum measurable intrusion volume required by this sample is (0.652 cc/1.131 cc) × 100% = 58%, which falls below the suggested 90% maximum.

The penetrometer for powdered or granular materials is chosen similarly, but remember that the spaces among the material grains are likely to constitute a void of about 40%. As another example, assume that 15 g of a granular material (density 3.5 g/cc) had been determined the minimum quantity for representation. Assume the powder has low porosity: 3%.

Volume of sample = mass/density = (15 g)/(3.5 g/cc) = 4.29 cc

Approximate pore volume of material = fractional porosity x sample volume =
0.03 (4.29 cc) = 0.13 cc

Approximate volume of interstice = (4.29 cc + 0.13 cc) (40/60) = 2.95 cc

Total volume of powdered sample = 4.29 cc + 0.13 cc + 2.95 cc = 7.37 cc

Three powder penetrometers listed in the Penetrometer Selection Guide will contain 7.37 cc of sample. Considering the sample size, the one having a total stem volume of 0.392 cc is most appropriate. The sample requires approximately 33% [0.13/0.39] of the stem capacity of the penetrometer. Optimum performance would be achieved if, instead of merely using the minimum 15 g of sample, the penetrometer were filled to capacity, which is approximately 30.5 g [15 × 15/7.37]. The penetration volume would then be about 0.26 cc [0.13 × 15/7.37] or nearly 66% [0.26/0.39] of the total stem volume.

  The previous calculations assume that all interstitial volume will be filled with mercury at the filling pressure. A minimum fill pressure of 0.5 psia will fill cavities of approximately 500 mm diameter, whereas a filling pressure of 1.5 psia will fill cavities as small as 120 mm diameter. If some interstitial volume remains unfilled at this point, allowance for this additional volume must be made in choosing the appropriate stem volume.

The percentage of the maximum intrusion (stem) volume utilized in each station is displayed on the Status Display as a guide for the operator. A % STEM reading of less than 25% or more than 90% suggests the need for a procedural change. The first instance suggests a larger quantity of sample might give better resolution and the second indicates that the capillary is on the verge of being depleted.

 
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