Let’s explain the notes from the tension test specimen dimensions chart in simple terms:
### Notes Breakdown
#### NOTE 1:
– For the 1.5-inch (40-mm) wide specimens:
– Punch marks (small indentations) for measuring elongation (stretch) after breaking should be made on the flat or the edge of the specimen within the reduced section (the narrower middle part).
– For an 8-inch (200-mm) gauge length:
– Use nine or more punch marks, spaced 1 inch (25 mm) apart.
– Alternatively, use one or more pairs of punch marks spaced 8 inches (200 mm) apart.
– For a 2-inch (50-mm) gauge length:
– Use three or more punch marks, spaced 1 inch (25 mm) apart.
– Alternatively, use one or more pairs of punch marks spaced 2 inches (50 mm) apart.
#### NOTE 2:
– For the 0.5-inch (12.5-mm) wide specimen:
– Punch marks for measuring elongation after breaking should also be made on the flat or the edge of the specimen within the reduced section.
– Use three or more punch marks, spaced 1 inch (25 mm) apart.
– Alternatively, use one or more pairs of punch marks spaced 2 inches (50 mm) apart.
#### NOTE 3:
– For all four specimen sizes:
– The ends of the reduced section (narrow part) should not differ in width by more than specific small amounts:
– 0.004 inches (0.10 mm) for the largest specimens.
– 0.001 inches (0.025 mm) for the smallest specimens.
– There may be a gradual decrease in width from the ends to the center, but the width at either end should not be much larger than at the center.
#### NOTE 4:
– For all specimens:
– The radius of all fillets (curved parts) should be the same with a tolerance of 0.05 inches (1.25 mm).
– The centers of curvature of the two fillets at each end should be directly opposite each other within a tolerance of 0.10 inches (2.5 mm).
#### NOTE 5:
– If the material is narrower than the standard widths (W and C), narrower specimens can be used.
– The width of the reduced section should be as large as possible.
– The elongation requirements may not apply for narrower specimens.
– If the width is less than 1.5 inches (38 mm), the sides can be parallel throughout the specimen length.
#### NOTE 6:
– Specimens can have parallel sides throughout their length.
– The width and tolerances should be the same as specified.
– If necessary, a narrower specimen may be used, with the width being as large as the material permits.
– For widths of 1.5 inches (38 mm) or less, sides may be parallel throughout the length.
#### NOTE 7:
– The thickness (T) of the test specimen is specified in the product specification.
– Minimum nominal thickness for 1 to 1.5-inch (40-mm) wide specimens is 3/16 inches (5 mm).
– Maximum nominal thickness for 0.5-inch (12.5-mm) and 0.25-inch (6-mm) wide specimens is 1 inch (25 mm) and 0.25 inches (6 mm), respectively.
#### NOTE 8:
– For 0.25-inch (6-mm) wide specimens:
– The overall length should be as large as the material allows to help achieve axial loading during testing.
#### NOTE 9:
– Ideally, the grip section should be long enough to allow the specimen to extend into the grips by two-thirds or more of the grip length.
– For 0.5-inch (13-mm) wide specimens thicker than 0.375 inches (10 mm), longer grips and grip sections might be needed to prevent failure in the grip section.
#### NOTE 10:
– For standard sheet-type and subsize specimens:
– The ends should be symmetrical with the centerline of the reduced section within:
– 0.01 inches (0.25 mm) for standard sheet-type.
– 0.005 inches (0.13 mm) for subsize specimens.
– For steel, if the ends of the 0.5-inch (12.5-mm) wide specimen are symmetrical within 0.05 inches (1.0 mm), it is usually acceptable except for referee testing.
#### NOTE 11:
– For standard plate-type specimens:
– The ends should be symmetrical with the centerline of the reduced section within 0.25 inches (6.35 mm).
– For referee testing, the symmetry should be within 0.10 inches (2.5 mm).
These notes help ensure that the specimens are prepared and tested consistently, providing reliable data on the mechanical properties of the material.
Let’s explain the notes from the ASTM A370/ASME SA-370 tension test specimen dimensions chart in simple terms:
### Notes Breakdown
#### NOTE 1:
– The reduced section (the narrower middle part) of the specimen can have a gradual taper from the ends toward the center.
– The ends should not be more than 1% larger in diameter than the center.
#### NOTE 2:
– If needed, the length of the reduced section can be increased to fit an extensometer of any convenient gauge length.
– However, the reference marks for measuring elongation should still be spaced according to the specified gauge length.
#### NOTE 3:
– The gauge length and fillets (curved parts) should be as shown in the diagram.
– The ends of the specimen can be shaped in any way to fit the holders of the testing machine, ensuring the load is applied axially (straight along the length).
– If the specimen is held in wedge grips, the grip section should be long enough to allow the specimen to extend into the grips by at least two-thirds of the grip length.
#### NOTE 4:
– For the round specimens shown in Figures 5 and 6, the gauge lengths are four times the nominal diameter.
– In some product specifications, other specimen sizes may be used.
– However, if the 4-to-1 ratio (gauge length to diameter) is not maintained within dimensional tolerances, the elongation values may not be comparable to those from standard test specimens.
#### NOTE 5:
– Specimens smaller than 0.250 inches (6.25 mm) in diameter should only be used if:
– The material is too small to make larger specimens.
– All parties involved agree to use smaller specimens for acceptance testing.
– Smaller specimens require appropriate equipment and greater skill in both machining and testing.
#### NOTE 6:
– There are five commonly used specimen sizes with diameters approximately 0.505, 0.357, 0.252, 0.160, and 0.113 inches.
– These sizes are chosen for easy stress calculations from loads because their cross-sectional areas are approximately 0.200, 0.100, 0.0500, 0.0200, and 0.0100 square inches, respectively.
– When the actual diameters match these values, the stresses (or strengths) can be computed using simple multiplying factors of 5, 10, 20, 50, and 100, respectively.
– The metric equivalents of these diameters do not result in similarly convenient cross-sectional areas and multiplying factors.
These notes help ensure that specimens are prepared consistently and tested accurately, providing reliable data on the mechanical properties of the material.
14.1.1 Drop of the Beam or Halt of the Pointer Method
1. **Apply Load**: Gradually increase the load (force) on the specimen.
2. **Balance the Beam**: If using a machine with a lever and poise (balance weight), keep the beam balanced by moving the poise at a steady rate.
3. **Observe the Yield Point**: When the material reaches its yield point:
– The load increase will temporarily stop.
– Move the poise a bit further, causing the beam to drop briefly.
– If using a machine with a load-indicating dial, the pointer will pause or hesitate.
4. **Record the Load**: Note the load at the moment the beam drops or the pointer halts. This load corresponds to the yield point stress.
### 14.1.2 Autographic Diagram Method
1. **Use a Recording Device**: A machine with an autographic recording device will plot a stress-strain diagram.
2. **Identify the Knee**: Look for a sharp change in the curve (called the knee) or where the curve drops.
3. **Record the Stress**: The stress at the top of the knee or where the curve drops is the yield point.
### 14.1.3 Total Extension Under Load Method
1. **Use an Extensometer**: Attach a Class C or better extensometer to the specimen. This device measures how much the material stretches.
2. **Increase Load**: Gradually increase the load on the specimen.
3. **Measure Extension**: When the specimen reaches a specified extension (how much it has stretched), note the load.
4. **Record the Stress**: The stress corresponding to this load is considered the yield point, especially for materials that don’t show a clear yield point with other methods.
### Additional Notes:
– **Automatic Devices**: Devices that automatically measure the load at the specified extension can be used if their accuracy is proven.
– **Class C Extensometer**: Ensures accurate measurement of extension.
– **Practice E83**: Reference for accurate extensometer use.
– **Specified Extension for Steel**: For steel with a yield point up to 80,000 psi (550 MPa), an extension of 0.005 inches per inch of gauge length is appropriate.
– **Curve Interpretation**: The initial part of the stress-strain curve can be influenced by factors like how the specimen is seated in the grips or its residual stresses. These irregularities should be ignored when determining the extension-under-load yield.
### Summary
These methods help determine the yield point, the stress at which a material begins to deform permanently. Each method provides a way to observe and record this critical stress level accurately, ensuring the material’s performance is well understood.
### Specimen Dimensions and Types
The diagram shows five types of specimens (labeled Specimen 1 to Specimen 5) used in mechanical testing. Each type has specific dimensions and features for different testing needs.
#### Key Parts of the Specimen
1. **Gauge Length (G)**
– This is the central part of the specimen where measurements are taken. For all specimens, this length is 2 inches (50 mm) with a small tolerance of ±0.005 inches (0.10 mm).
2. **Diameter (D)**
– The thickness of the specimen at the gauge length. It is 0.5 inches (12.5 mm) with a tolerance of ±0.010 inches (0.25 mm).
3. **Radius of Fillet (R)**
– This is the curved part connecting the gauge length to the wider ends of the specimen. It should be at least 3/8 inches (10 mm) for all specimens.
4. **Length of Reduced Section (A)**
– This is the length of the narrower middle part where measurements are taken. It should be at least 2 1/4 inches (60 mm) for all specimens.
5. **Overall Length (L)**
– This is the total length of the specimen. It varies for each type:
– Specimen 1: 5 inches (125 mm)
– Specimen 2: 5 1/2 inches (140 mm)
– Specimen 3: 5 1/2 inches (140 mm)
– Specimen 4: 9 1/2 inches (240 mm)
– Specimen 5: 12 inches (300 mm)
6. **Grip Section (B)**
– The part of the specimen that is held by the testing machine’s grips. The lengths are approximate:
– Specimen 1: 1 3/8 inches (35 mm)
– Specimen 2: 1 inch (25 mm)
– Specimen 3: 3/4 inch (20 mm)
– Specimen 4: 1/2 inch (13 mm)
– Specimen 5: 3 inches (75 mm)
7. **End Section Diameter (C)**
– Diameter at the ends of the specimen. It’s 3/4 inch (20 mm) for Specimens 1, 2, and 3, and varies slightly for others.
8. **Shoulder and Fillet Section (E)**
– The length of the shoulder and fillet part which helps in gripping the specimen properly:
– Specimen 4: 7/8 inch (22 mm)
– Specimen 5: 3/4 inch (20 mm)
9. **Diameter of Shoulder (F)**
– The thickness at the shoulder part:
– Specimen 4: 5/8 inch (16 mm)
– Specimen 5: 19/32 inch (15 mm)
### Important Notes
1. **Gradual Taper**:
– The middle part of the specimen (reduced section) may taper slightly towards the center, but the ends should not be more than 0.005 inches (0.10 mm) larger than the center.
2. **Grip Length**:
– For Specimen 5, try to make the grip section long enough so that it extends into the grips by at least two-thirds of the grip length.
3. **Threaded Ends**:
– For high-strength brittle materials, use UNF series threads (like 3/4 by 16, 1/2 by 20, etc.) to avoid breaking in the thread portion.
### Understanding Yield Point Methods
1. **Drop of the Beam or Halt of the Pointer Method**:
– Increase the load on the specimen steadily. When the material yields, the increase in load stops, causing a momentary drop in the beam or a halt in the pointer. Record the load at this point as the yield point.
2. **Autographic Diagram Method**:
– Use a device that plots the stress-strain diagram. The yield point is the stress at the sharp change or drop in the curve.
3. **Total Extension Under Load Method**:
– Attach an extensometer to measure how much the specimen stretches. Increase the load until a specified extension is reached. Record the stress at this load as the yield point.
By understanding these dimensions and testing methods, you can prepare specimens correctly and accurately measure their mechanical properties.