Creep
Creep turns up in 3 fields: adhesives, refractories, geosynthetics. Here is what it means to the people in each one.
Creep in adhesives
Slow, continuing deformation of an adhesive under a constant load, which can end in failure over time.
Even below its short-term strength, a bonded joint under sustained load slowly stretches. PSAs, hot melts, PVA and flexible adhesives creep most, especially as temperature rises toward Tg. Creep is tested by hanging a weight and measuring slip or time to failure. Designs carrying permanent loads use a fraction of the short-term strength or a more crosslinked adhesive.
"Sign panels have slid half an inch down the wall, the tape is creeping in the afternoon sun."
Creep in refractories
Slow, permanent deformation of a refractory under steady load at high temperature over hours to years.
Time-dependent deformation of a material held under constant stress at high temperature, measured in compression as percent change over tens of hours under methods such as ASTM C832. Creep matters wherever refractories carry weight hot for long periods: hot blast stove domes and checkers, glass furnace crowns, coke oven walls and tall stacks. Glassy bonds creep; well-sintered, low-impurity materials such as silica brick and mullite resist it.
"Checkers in stove 2 are showing creep, the bottom courses are bulging and the flues are pinching shut."
Creep in geosynthetics
Slow, continuing stretch of a geosynthetic under a constant load over time.
Polymers keep deforming under sustained load, so a geogrid holding a wall for decades keeps elongating after construction and can rupture at loads well below its short-term strength. Creep is measured in long-term load tests, often accelerated with temperature, and turned into a creep reduction factor for design. Polyester creeps much less than polypropylene or HDPE, which is why it is favored for heavily loaded reinforcement.
"Creep factor on the HDPE grid is close to 3, so the polyester grid works out cheaper per unit of design strength."