Xi'an Heaven Abundant Mining Equipment CO.,LTD
When a PDC cutter comes out of the hole damaged, the cause is almost never slow wear. It is a sudden hit — a hard stringer, a pebble bed, or the moment the bit tags the bottom of the hole. That is why impact resistance is one of the first properties drilling teams should understand before choosing PDC cutters or a PDC drill bit. In this article, we explain what impact resistance means, how it is measured, what controls it, and how to pick cutters that can survive demanding formations.
Impact resistance is the ability of a PDC cutter’s diamond table to absorb sudden, concentrated loads without chipping, spalling, or breaking. It is different from wear resistance. Wear resistance describes slow, gradual material loss over time, like sandpaper rubbing away a surface. Impact resistance describes behavior under shock loading — a load applied in a fraction of a second.
In the factory, impact resistance is usually measured with a ｄｒｏｐ-weight test. A controlled mass is dropped onto the cutter table, and the energy, in joules, at which the first damage appears is recorded. Standard cutters typically survive 15 to 65 joules in this kind of test, while premium impact-graded cutters are rated from 40 to 80 joules. The higher the number, the more shock the cutter can absorb before it starts to chip.
Most PDC cutter failures happen in the same situations:
When a bit hits a hard stringer, the cutting structure stops suddenly while the drill string keeps pushing. The energy has to go somewhere, and it usually goes into the cutters. A cutter with low impact resistance chips or spalls on the first hit. A cutter with high impact resistance absorbs the shock and keeps cutting.
This matters for cost. Every time a cutter fails, the bit has to be pulled, which means non-productive time, extra trips, and higher cost per foot. Choosing cutters with adequate impact resistance for the formation is one of the most effective ways to keep a PDC drill bit in the hole longer.
Several design and material factors determine how much impact a PDC cutter can take:
1. Cobalt content. Cobalt is the metal binder that holds the diamond grains together. More cobalt means a tougher, more impact-resistant cutter, but it also means lower wear resistance. Typical cutters use 6% to 16% cobalt by weight. For hard, abrasive rock where wear is the main enemy, lower cobalt (6–8%) is preferred. For interbedded formations where impacts are frequent, higher cobalt (10–14%) gives better toughness.
2. Diamond table thickness. The four-digit code on a cutter tells you its size. The first two digits are the diameter in sixteenths of an inch, and the last two are the diamond table thickness in thousandths of an inch. A 1308 cutter is 13/16 inch (20.64 mm) in diameter with a 0.008 inch (0.203 mm) table, while a 1313 has the same diameter but a thicker 0.013 inch (0.330 mm) table. A thicker table absorbs more impact before the load reaches the carbide substrate, which is why 1313 cutters are often chosen for harder, more impact-prone drilling.
3. Diamond concentration. Concentration is the percentage of diamond in the table relative to the theoretical maximum. Higher concentration gives better wear life but makes the cutter more brittle. For hard rock where impact resistance matters more than wear life, a slightly lower concentration is often the better trade-off.
4. Chamfer design. The chamfer is the beveled edge where the diamond table meets the carbide substrate. A well-designed chamfer (typically 0.2–0.3 mm at 45 degrees) protects the cutting edge from early-life spalling and helps the cutter survive the initial impact when it first touches bottom.
5. Non-planar geometry. Modern cutters are no longer limited to flat, round tables. Ridge, axe, and tapered shapes concentrate cutting force on a smaller area and redirect impact stress away from the most vulnerable part of the edge. These shapes are especially useful in hard carbonate and interbedded formations.
6. Substrate hardness. The tungsten carbide substrate supports the diamond table. A softer substrate absorbs more impact but erodes faster, while a harder substrate resists erosion but is more brittle under shock. Most production cutters fall between 88 and 91.5 HRA.
7. Sintering quality and grain size. Mixing fine, medium, and coarse diamond grains together gives a denser table. Fine grains provide a sharp edge and good wear resistance, while coarse grains act as crack arrestors that stop microcracks from spreading through the diamond layer.
There is no single “best” impact rating. The right choice depends on the formation:
When you compare cutters from different suppliers, ask for numbers, not adjectives. A datasheet that says “high impact resistance” without a joule rating and a test method tells you very little. Ask for the ｄｒｏｐ-weight or pendulum test result and the sample size, and compare cutters on the same basis.
All three are reduced by choosing cutters with adequate impact resistance, proper chamfer design, and good thermal stability, and by matching the cutter to the formation.
Xi’an Heaven Abundant Mining Equipment Co., Ltd. (TY Drill Bits) has been manufacturing and supplying drilling tools since 2010. The company offers a full range of PDC cutters — including 1308, 1313, 0808, and 0804 sizes — as well as PDC drill bits in 3-blade, 4-blade, and matrix body designs for water well, mining, and geological drilling.
Whether you need cutters for a new PDC drill bit or replacement cutters for an existing bit, the TY Drill Bits team can help you ｓｅｌｅｃｔ the right size, cobalt content, and geometry for your formation. All products are backed by ISO9001 quality management, and the company supports OEM orders.
Q: What does the code 1308 mean?
A: The first two digits are the diameter in sixteenths of an inch (13 = 13/16 inch = 20.64 mm). The last two digits are the diamond table thickness in thousandths of an inch (08 = 0.008 inch = 0.203 mm).
Q: What is a good impact resistance value?
A: Standard cutters typically survive 15–65 joules in a ｄｒｏｐ-weight test, while premium impact-graded cutters are rated at 40–80 joules. For hard, impact-prone formations, look for cutters rated at 50 joules or higher.
Q: Is higher cobalt always better?
A: No. Higher cobalt improves impact resistance but reduces wear resistance. The right cobalt content depends on the formation — lower for abrasive hard rock, higher for interbedded formations.
Q: How is impact resistance tested?
A: The most common method is a ｄｒｏｐ-weight test, where a controlled mass is dropped onto the cutter table and the energy at which the first damage appears is recorded in joules. Some suppliers use a pendulum test instead.
Impact resistance is one of the most important properties of a PDC cutter, and it is often the difference between a bit that lasts and a bit that fails early. By understanding how it is measured and what controls it — cobalt content, table thickness, chamfer, geometry, and substrate — you can choose cutters that match your formation and keep your drilling on schedule. For help selecting PDC cutters or a PDC drill bit for your next project, contact the TY Drill Bits team.
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