When should the subject agree with the object of the preposition?

Question

Quite often while I'm looking through research articles, I see sentences that start like this one:

The tensile strengths of the composites changed...

I generally change strengths to strength in this case. My thinking is that because "strength" refers to a singular property, rather than multiple different types of tensile strength, I should change it. However, there is a strength associated with each of the composites tested.

Are there any rules that say I shouldn't change the plurality of the subject when it would disagree with the plurality of the object of the prepositional phrase attached to the subject?

Answer 1

It's a fine point, and I doubt many would even notice if OP got it "wrong", but consider...

1: The age of the children was unknown.
2: The ages of the children were unknown.

I think #1 would often (perhaps, usually) be taken to imply the children were all of the same age, where #2 strongly implies a variety of ages. But from OP's perspective, age is a "singular property".

Obviously there are multiple composites, with different tensile strengths. So if OP wants to play strictly by the "rules", he should pluralise strengths.