US Student debt volume and default rate data source I would like to see data for private and public student loans and their default rate over time
With regard to your title, I assume you're looking for data for the US. This report from the U.S. Department of Education presents data and selected findings about the repayment of federal student loans using data from the 2015 Federal Student Aid Supplements to two Beginning Postsecondary Students Longitudinal Studies (BPS). 

The report focuses on two cohorts of borrowers: those who began their postsecondary education in the 1995–96 academic year (BPS:96/01) and those who began in the 2003–04 academic year (BPS:04/09). 

The report presents estimates of both cohorts' cumulative borrowing, repayment, and default statuses as of June 30, 2015, some 20 years after the 1995–96 cohort and 12 years after the 2003–04 cohort began postsecondary education.

Interesting key findings


Some 55% of students in the 1995–96 cohort and 63% of the 2003–04 cohorttook out federal education loans within 12 years of entering postsecondary education.
Overall, 25% of borrowers in the 1995–96 cohort had defaulted on at least one loan within 20 years of beginning postsecondary education, and 14% defaulted on their most recent loan.
Among borrowers in the 2003–04 cohort, 45% of those who had never attained a credential and were not enrolled in 2009 had defaulted on a loan within 12 years. Among those who attained undergraduate certificates, the rate of defaulting within 12 years was 44%; for associate's degree recipients, it was 22%; and for bachelor's degree recipients, it was 8%.