As the title asks, I wish it could be clear to me. Can someone give me a good characterization? Do you produce them differently on a cello than on a violin or viola?
Détaché – Simply meaning detached, it implies that each note is played in a separate bow stroke (as opposed to Legato where groups of notes should be smoothly played in the same stroke of the bow). The bowing should still be smooth without emphasis on the separation – this emphasis would imply a Détaché-lancé bow stroke.
Martelé – Hammered. Simply speaking, it's a more aggressive form of staccato, and usually used for individual dotted notes. Most of the time you'll want to use the entire length of the bow, and use the first finger on your bow hand to apply pressure to get a good initial "bite" which you'll then gradually release along the bow's length.
I can only speak for the violin in terms of application technique, but I would imagine they are similar (though the amount of pressure and the points you use on the bow may well be different).
'Martele' could be described as a long staccato. Staccato is a short stroke executed with very short bow length, biting the string at the beginning of the note, releasing the pressure and moving energetic but very short and biting again for the next note. Martele is executed in a similar way, only the energetic movement involves much longer bow and more energy. Now, 'detache' means separate strokes but smoothly connected with even bow speed and pressure.
The martelé and détaché bowing techniques are almost identical. Both originated in the military as close variations of a style of regimental playing. The word martelé is from the Latin root for military. In Napoleon's army the revolutionary ideal affected music and the concept of 'regiment' was considered too aristratic. Even the names of months and the calander year were changed in revolutionary France. For the revolutionary troops, they wanted a more 'democratic' reference than an entire regiment, so the style became known as 'détaché' as coming from a detachment.
This answer was delivered as an edit to the question from an anonymous visitor. I've made this post Community Wiki to reflect the fact that it is not my work, and I do not claim any credit for this information.