I saw a post on ELU about a more general question, Softened pronunciation of consonants, such as “t” or “s” followed by “y”. The question was answered in regard to palatalization, especially for phrases like "but you", where /t/ is followed by a palatal glide, /j/.
But does "palatalization" also explain the affrication of /t/ and /d/ when they're followed by /ɹ/, instead of by a front vowel or a palatal consonant? E.g. in 'tram' or 'address' (but not necessarily in 'string'?)
I could see how the affricates are closer to the palatal position than the stops, but the trigger for the change doesn't seem to be a following palatal consonant. (Typical English /ɹ/'s place of articulation is described as alveolar rather than palatal.)
Is this an example of a case where "tongue-raising typically affects apical and coronal consonants", i.e. palatalizes them?
This question is explored some at http://literalminded.wordpress.com/2010/03/17/chricky-affrication/ and its follow-up blog posts, but I didn't see a definitive answer for what causes the change, or what the process is called.
P.S. See also John Well's post how do we pronounce train ?, which is interesting: the "allophonic rule that retracts t and d when followed by r" - what rule is that and what causes it?
Strangely, when asked about "the shift of any alveolar plosive preceding a rhotic consonant to a post alveolar affricate," Wells concludes "I don’t believe there is any such phonological change in progress." I really don't understand how that conclusion is justified.