*KEYWORD *comment Just from observation, it seems what really happens is that the actual unloading retraces the loading curve if the maximum loaded state is still to the left of where the unshifted input unloading curve intersects the input loading curve. However, if the maximum loaded state is to the right of where the unshifted input unloading curve intersects the input loading curve, the unloading curve is shifted to the right soas to intersect the maximum load point and then the unloading path follows the shifted unloading curve. This may result in nonzero deflection at zero load. In the attached jpeg, the actual force vs. engineering strain is plotted as curve A; curves B and C are the input loading curve and input unloading curve. The jpeg was created using the LS-PrePost command file "pcom", i.e, lsprepost c=pcom *MAT_SEATBELT $# mid mpul llcid ulcid lmin $ 1 3.4843E-8 500007 500008 0.194000 1 3.4843E-8 500007 500009 0.194000 *load_node_point 17,1, 200 *define_curve 200 0,0 $0.02, 1100 0.02, 1500 0.15, 0 *control_timestep ,.3 *ELEMENT_SEATBELT $# eid pid n 1 n 2 sbrid slen n 3 n 4 1 1 16 17 0 0.000 0 0 *control_solution ,,,1000 *BOUNDARY_SPC_NODE $# nsid cid dofx dofy dofz dofrx dofry dofrz 16 0 1 1 1 0 0 0 *CONTROL_TERMINATION $# endtim endcyc dtmin endeng endmas $ 0.040000 0 0.000 0.000 0.000 0.15 *DATABASE_SBTOUT $# dt binary lcur ioopt 2.0000E-4 0 0 1 *DATABASE_BINARY_D3PLOT $# dt lcdt beam npltc psetid 4.0000E-4 0 0 0 0 $# ioopt 0 $*boundary_prescribed_motion $17,1,2,100, 0.6 *define_curve 100 0,0 0.01,20 0.02,0 *SECTION_SEATBELT $# secid 1 *DEFINE_CURVE $# lcid sidr sfa sfo offa offo dattyp 500007 0 1.000000 1.000000 0.000 0.000 0 $# a1 o1 0.000 0.000 0.0196800 50.0000000 0.0355966 100.0000000 0.0510621 150.0000000 0.0657083 200.0000000 0.0793641 250.0000000 0.0919952 300.0000000 0.1036559 350.0000000 0.1144497 400.0000000 0.1245021 450.0000000 0.1339400 500.0000000 0.1428779 550.0000000 0.1514097 600.0000000 0.1596034 650.0000000 0.1675034 700.0000000 0.1751303 750.0000000 0.1824855 800.0000000 0.1895545 850.0000000 0.1963138 900.0000000 0.2027359 950.0000000 0.2087924 1000.0000000 0.2144621 1050.0000000 0.2197297 1100.0000000 0.2245897 1150.0000000 0.2290510 1200.0000000 0.2331317 1250.0000000 0.2368607 1300.0000000 0.2402772 1350.0000000 0.2434241 1400.0000000 0.2463497 1450.0000000 0.2490972 1500.0000000 0.2517076 1550.0000000 0.2542110 1600.0000000 0.2566262 1650.0000000 0.2589566 1700.0000000 0.2611897 1750.0000000 0.2632986 1800.0000000 0.2652421 1850.0000000 0.2669710 1900.0000000 0.2684366 1950.0000000 0.2696000 2000.0000000 0.2705517 2050.0000000 0.2711034 2100.0000000 0.2714483 2150.0000000 0.2717931 2200.0000000 0.2720690 2250.0000000 *DEFINE_CURVE $# lcid sidr sfa sfo offa offo dattyp 500008 0 1.000000 1.000000 0.000 0.000 0 $# a1 o1 0.000 0.000 0.2335445 95.0000000 0.2455085 100.0000000 0.2502941 106.0000000 0.2550797 115.0000000 0.2584224 125.0000000 0.2620116 140.0000000 0.2646509 160.0000000 0.2670437 185.0000000 0.2680008 200.0000000 0.2693096 230.0000000 0.2701471 260.0000000 0.2709846 300.0000000 0.2714632 350.0000000 0.2719417 500.0000000 0.2720690 2250.0000000 *DEFINE_CURVE $# lcid sidr sfa sfo offa offo dattyp 500009 0 1.000000 1.000000 0.000 0.000 0 $# a1 o1 0.000 0.000 0.2335445 95.0000000 0.24 2500. *NODE $# nid x y z tc rc 16 350.0000000 0.000 400.0000000 0 0 17 400.0000000 0.000 400.0000000 0 0 *PART $# title Part for belt material 1 $# pid secid mid eosid hgid grav adpopt tmid 1 1 1 0 0 0 0 0 *END