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Chapter 3 199 Material Properties Appendix B Apparent Elastic Modulus B.1—Apparent Elastic Modulus for the Condition of Either a Sustained Constant Load or a Sustained Constant Deformation B.1.1— Design Values for the Base Temperature of 73°F(23°C) TABLE B.1.1 Apparent Elastic Modulus for 73°F(23°C) Duration of4 ,. �� ...� Sustained Loading PE 2XXX PE3XXX PE4XXX 0.5hr 1 62,000 428 78,000 538 82,000 565 1"R IN 2hr 57,000 393 71,000 490 74,000 510 12hr 48,000 331 60,000 414 63,000 434 1 00h 42,000 290 52,000 359 55,000 379 1 FU ��x 1 year 30,000 207 38,000 262 40,000 276 77, ,<F � 50 years 22,000 152 28,000 193 29,000 200 (1) Although there are various factors that determine the exact apparent modulus response of a PE,a major factor is its ratio of crystalline to amorphous content—a parameter that is reflected by a PE's density.Hence,the major headings PE2XXX,PE3XXX and,PE4XXX,which are based on PE's Standard Designation Code.The first numeral of this code denotes the PE's density category in accordance with ASTM D3350(An explanation of this code is presented in Chapter 5). (2) The values in this table are applicable to both the condition of sustained and constant loading(under which the resultant strain increases with increased duration of loading)and that of constant strain(under which an initially generated stress gradually relaxes with increased time). (3) The design values in this table are based on results obtained under uni-axial loading,such as occurs in a test bar that is being subjected to a pulling load.When a PE is subjected to multi-axial stressing its strain response is inhibited,which results in a somewhat higher apparent modulus.For example,the apparent modulus of a PE pipe that is subjected to internal hydrostatic pressure—a condition that induces bi-axial stressing—is about 25%greater than that reported by this table.Thus,the Uni-axial condition represents a conservative estimate of the value that is achieved in most applications. It should also be kept in mind that these values are for the condition of continually sustained loading.If there is an interruption or a decrease in the loading this,effectively,results in a somewhat larger modulus. In addition,the values in this table apply to a stress intensity ranging up to about 400psi,a value that is seldom exceeded under normal service conditions.