Edi Liberato blog

No need to say much about the classical ASTM D638 tensile test specimens AKA dogbones. Just a few remarks:

Type I, II, III, and V have the same shape but different dimensions.
Type I is usually injection molded.
Type V is usually cut using punch dies.
Type IV is intended for non-rigid plastics.
Thickness of 3.2 mm is recommended for injection molded specimens.

ASTMD638table

Figure above reference:ASTM D638, Standard Test Method for Tensile Properties of Plastics, ASTM International, West Conshohocken, PA, 2014, www.astm.org

Cadquery scripts:

import cadquery as cq

# ASTM D638 typeI dogbone

W = 13.0
L = 57.0
WO = 19.0
LO = 165.0
R = 76.0
thickness = 3.2

dogbone_typeI = (cq.Workplane("front").box(LO, WO, thickness).
    faces(">Y").workplane().rect(L, thickness).cutBlind(-(WO-W)/2).
    faces("<Y").workplane().rect(L, thickness).cutBlind(-(WO-W)/2).
    faces(">Z").workplane(centerOption='CenterOfBoundBox').
    rect(L, 2*R+W, forConstruction=True).vertices().hole(2*R))

show_object(dogbone_typeI)

import cadquery as cq

# ASTM D638 typeIV dogbone

W = 6.0
L = 33.0
WO = 19.0
LO = 115.0
R = 14.0
RO = 25.0
thickness = 3.2

dogbone_typeIV = (cq.Workplane("front").box(LO, WO, thickness).
    faces(">Y").workplane().rect(L, thickness).cutBlind(-(WO-W)/2).
    faces("<Y").workplane().rect(L, thickness).cutBlind(-(WO-W)/2).
    faces(">Z").workplane(centerOption='CenterOfBoundBox').
    rect(L, 2*R+W, forConstruction=True).vertices().hole(R*2).
    edges("|Z").edges("not <X or >X").fillet(RO))

show_object(dogbone_typeIV)

ASTM D638 Tensile Test Specimens