It is crucial to understand the significant impact that even minor changes in ceramic purity and overall armor plate size have on plate weight.
To really understand what you are buying and to really comprehend the details so that you can compare armor products between manufacturers, you need to become familiar with two basic rules:
- The higher the ceramic purity, the greater the quality and the greater the weight.
- Given the same ceramic purity and thickness, an increase in the size of the ceramic armor strike face will have a significant impact on weight.
It is absolutely imperative that you know the dimensions of the ceramic strike face, if you want to make an "apples to apples" comparison between similar armor plates.
This is a technical, complicated (but not difficult subject) and most people may not care to dig down quite this deep. But, as designers and armor builders - you always want to make your armor is a balanced blend of affordability, performance and weight.
Let's start with the concept of ceramic purity. We will use aluminum oxide (alumina) as an example, since there are greater fluctuations in purity for alumina than other types of ceramic. The higher level of purity, the greater the content of alumina... and therefore, the greater density, homogenous material distribution, quality and stopping power (for a given thickness).
99.7% alumina is about as pure as we can find. Its density can be between 3.95-3.98 g/cm3.
Given the shape below - let's calculate the weight of the ceramic strike face at an industry standard (RF3 protection level) of 10mm thickness:
To estimate the weight of the object, we need to calculate its volume and then multiply by the density of aluminum oxide ceramic (3.98 g/cm³). The object is 10 mm thick, and the dimensions provided are in mm (based on the previous context). Let's convert them to cm for consistency with the density unit (1 cm = 10 mm).Step 1: Calculate the AreaThe shape is a trapezoid with the following dimensions:
- Top base = 139.00 mm = 13.9 cm
- Bottom base = 251.00 mm = 25.1 cm
- Height = 305.00 mm = 30.5 cm
The area of a trapezoid is given by:
\text{Area} = \frac{(\text{top base} + \text{bottom base}) \times \text{height}}{2}
\text{Area} = \frac{(13.9 + 25.1) \times 30.5}{2}
\text{Area} = \frac{39 \times 30.5}{2}
\text{Area} = \frac{1190.5}{2}
\text{Area} = 595.25 \, \text{cm}^2
Step 2: Calculate the VolumeThe thickness is 10 mm = 1 cm. The volume is the area multiplied by the thickness:
\text{Volume} = \text{Area} \times \text{thickness}
\text{Volume} = 595.25 \, \text{cm}^2 \times 1 \, \text{cm}
\text{Volume} = 595.25 \, \text{cm}^3
Step 3: Calculate the WeightThe weight (mass) is the volume multiplied by the density:
\text{Weight} = \text{Volume} \times \text{Density}
\text{Weight} = 595.25 \, \text{cm}^3 \times 3.98 \, \text{g/cm}^3
\text{Weight} = 2368.595 \, \text{g}
\text{Weight} \approx 2369 \, \text{g} \text{ or } 2.369 \, \text{kg}
Final AnswerThe estimated weight of the object is approximately 2.37 kg (rounded to three significant figures).
So, the weight of the SAPI armor plate in the dimensions above is 2.37 kg or 5.22 pounds (just for the strike face).
Many armor plates by big names are made with 90% alumina. How does that impact weight? 90% alumina has a density of 3.6 g/cm3. Let's recalculate the weight:
To recalculate the weight of the object with a density of 3.6 g/cm³, we’ll use the previously determined volume. The object is 10 mm thick, and the dimensions are in mm (converted to cm as before).Step 1: Use the Previously Calculated VolumeFrom the earlier calculation, the volume of the object is:
\text{Volume} = 595.25 \, \text{cm}^3
Step 2: Calculate the WeightThe weight (mass) is the volume multiplied by the density:
\text{Weight} = \text{Volume} \times \text{Density}
\text{Weight} = 595.25 \, \text{cm}^3 \times 3.6 \, \text{g/cm}^3
\text{Weight} = 2142.9 \, \text{g}
\text{Weight} \approx 2143 \, \text{g} \text{ or } 2.143 \, \text{kg}
Final AnswerThe estimated weight of the object is approximately 2.14 kg or 4.72 pounds (rounded to three significant figures).
5.22 pounds - 4.72 pounds = .5 pounds! By using more high quality ceramic, builders/manufacturers increase the weight of the above SAPI plate shape by 8 ounces (1/2 pound).
I hope that it's beginning to be clear that use of higher quality alumina ceramic creates more weight than using lighter, less dense ceramic.
Here is where we are so far in our comparison: For the given plate dimensions above, we have seen an 8 ounce difference in the plate weight just based on purity.
Now, let's take a look at minor size differences. Many manufacturers will tell you (or advertise as such) that they are selling you a certain size, but the actual measured size is slightly less. For example, a manufacturer might advertise a 10" x 12" armor plate but use a 9.5" x 11.5" strike face. They may add a rubber edge to the outside and that brings the total finished size to approximately 9.75" x 11.75" Other manufacturers use a full 10" x 12" ceramic strike face. This extra 1/2" along the perimeter of the armor plate has a drastic impact on weight.
For 99.7% alumina, reducing the outer perimeter of the strike face by 1/2", the total weight of the armor is reduced by 1.06 pounds!
Small fluctuations in purity and weight have a tremendous impact on armor total weight and performance. It's important for consumers to understand these differences so that they can truly compare armor systems.
In our example, we have seen that a 10" x 12" alumina armor plate, utilizing a full 10" x 12" strike face (10mm) and 99.7% alumina is more than 1.5 pounds heavier that a lower quality plate using lower purity ceramic and a smaller strike face. Most consumers would not know this at the onset of their purchase decision. It's best to go with a company you can trust to be honest and transparent.
