High temperature extensometer system

A high temperature extensometer system carries specimen contact rods of substantial length which pass through openings in a furnace to engage a specimen in such furnace. The rods are supported at the exterior of the furnace on a paralleogram linkage support frame made to provide an output indicating specimen strain as the contact rods separate and also made with parallel beams which shift so the rods can move differentially in longitudinally axial direction. The rods shift axially when the specimen and test loading grips shift in position, for example when the grips and specimen are initially heated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a support system for a high temperature 
extensometer which must accommodate shifts in the specimen contact rods 
used for sensing strains in a specimen as the specimen and test assembly 
are subjected to high temperatures. 
2. Description of the Prior Art 
High temperature extensometers have been used for years, and generally are 
used in connection with a furnace that will heat a specimen to a desired 
level, and which specimen is then subjected to loads to determine specimen 
properties. The strain is sensed by having long ceramic rods which engage 
the specimen at contact points and extend to sensor system supports that 
are remote and shielded from the furnace. The extensometers provide an 
indication of the amount of strain in the specimen. In the prior art, the 
elongated rods and sensor systems were supported on the specimen and 
cantilevered outwardly. The rods were shorter than those now required with 
new higher temperature furnaces. 
With longer rods external supports for the extensometer are needed. The 
supports have to be shielded from heat, and be made to avoid placing loads 
on the sensing rods, and thus must permit substantially unrestrained 
movement in several degrees of freedom to accommodate shifts in the 
specimen during the process of heating up. 
SUMMARY OF THE INVENTION 
The present invention relates to a high temperature extensometer support 
system which supports an extensometer assembly having specimen contact 
rods of substantial length, and which support system accommodates movement 
of these rods during initial warm-up of the specimen and testing apparatus 
in a furnace for the high temperature test and yet provides accurate 
measurements of specimen strain. The specimen contact rods are also called 
extension rods, and are of substantial length so they pass through 
openings in the furnace to engage a specimen in the furnace. The rods are 
supported on the exterior of the furnace. Shifts in the specimen position 
as it heats up, due to thermal expansion of various parts, including the 
grips holding the specimen, are accommodated by providing a parallelogram 
linkage support frame for the specimen contact rods. One of the specimen 
contact rods is supported relative to the parallelogram linkage support 
frame through a sensing system which senses differential movement between 
the outer ends of the specimen contact rods when the specimen is under 
strain. The other of the rods is supported independently of the sensing 
system with respect to the parallelogram linkage support frame. 
The parallelogram linkage support frame is made so the rods can move 
differentially in their longitudinal axial direction without causing any 
undue loads on the rods and without placing any unwanted strains in the 
sensing system, itself. The specimen contact rods are urged axially toward 
the specimen under a spring load. The linkage or hold down flexure system 
for providing this axial load on the specimen contact rods in direction 
toward the specimen permits the rods to move differentially in axial 
direction and twist relative to each other generally about an axis lying 
in the direction of the longitudinal axis of one of the rods without 
causing the rods to slip off the specimen and without causing unwanted 
signals from the sensing system. 
The entire parallelogram linkage support frame is supported relative to a 
load frame supporting the specimen through a flexure link which permits 
the entire support frame to move easily in direction parallel to the 
longitudinal axes of the elongated specimen contact rods. 
The parallelogram linkage support frame is made up of first and second 
spaced, parallel beams, parallel to the specimen contact rods, and third 
and fourth connecting beams joining the first and second beams. The third 
and fourth beams are connected at their ends through spring flexures (no 
friction, zero clearance hinges) to the first and second beams. The 
parallelogram linkage support frame will permit movement of the first and 
second beams in direction of their longitudinal axes (which remain 
parallel). The flexure link for the support frame is connected to one of 
the beams and extends upwardly to where it is supported relative to the 
main test load frame. The flexure link can be adjusted in vertical 
direction so that the parallelogram support frame is supported at a 
reference position when the specimen contact rods are properly located. At 
this position the parallelogram linkage support frame is a rectangle, that 
is the first and second beams are perpendicular to the third and fourth 
beams. Suitable stops are provided to prevent extensive pivoting movement 
of the parallelogram linkage support frame. 
In the form shown, the plane of the parallelogram linkage support frame is 
vertical and parallel to the specimen axis (or loading axis) so the first 
and second beams are at the top and bottom of the support frame. The first 
and second specimen contact rods are connected to the first and second 
beams of the parallelogram support frame, and the supports are made rigid 
in direction of the axes of the contact rods and the axes of the first and 
second beams, which are mutually parallel to the rods at reference 
position. 
The first contact rod is coupled to the first (top) beam and the axes of 
the first rod and first beam are parallel. The mounting is such that the 
first rod axis will not move or tilt about an axis perpendicular to the 
specimen axis. 
The second specimen contact rod is supported on the second beam through a 
sensing system mounting for sensing differential movement between the 
outer ends of the first and second specimen contact rods. The sensing 
system measures strain in direction of the specimen axis and as the second 
contact rod pivots at its base end relative to the second (bottom) beam 
about an axis perpendicular to the end specimen axis. The support of the 
base of the second specimen contact rod is rigid against pivoting about an 
axis parallel to the specimen axis relative to the second beam of the 
support frame. 
In a preferred embodiment, the mounting of the first specimen contact rod 
is, however, made to permit movement of the first rod about an axis 
parallel to the specimen axis to accommodate some twisting of the 
specimen. 
The hold down flexure system for providing an axial load on the elongated 
specimen contact rods comprises a prebent spring, and a selected 
arrangement of laterally extending spring straps that will permit the 
outer ends of the specimen contact rods to separate relative to each 
other, and to twist in torsion as permitted by the base end mounting of 
the rods, and also to permit the entire parallelogram linkage support 
frame to move as needed. 
Suitable counterweights are provided to counterbalance the moments created 
by gravity on the second specimen contact rod about the mounting axis of 
the second rod, which is coupled through a sensing system to tee second 
beam. The sensing system mounting for the second or bottom specimen 
contact rod is used to provide a signal indicating differential movement 
between the outer ends of the specimen engaging ends of the specimen 
contact rods. 
The parallelogram linkage support frame also is counterweighted to avoid 
unwanted moments and balance the support frame in its reference position. 
The parallel linkage support frame is adapted to suit a wide variety of 
extensometer arrangements, particularly for high temperature operation. 
The plane of the parallelogram linkage support frame can be positioned 
perpendicular to a plane defined by the axes of the specimen contact rods 
if desired, rather than parallel to such plane, as shown.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings and the numerals of reference thereon, an 
extensometer assembly is indicated generally at 10 in FIG. 3, and it is of 
a type that is used to test a specimen indicated at 11 that is mounted 
adjacent to a heat source, such as being in a furnace represented in 
dotted lines at 12 in FIGS. 2 and 3 and schematically represented in FIG. 
1. The furnace 12 has suitable openings for operation with the 
extensometer and with a test load frame or testing machine. The furnace 12 
is mounted with respect to a load frame comprising a pair of columns 14, 
one of which is shown only fragmentarily in FIGS. 1 and 2. A first 
specimen grip 13 (FIG. 3) is mounted on the load frame and a second load 
grip 16 is attached to an actuator 17 (FIG. 3) for loading the specimen 11 
along its central axis 18 in the load frame. The extensometer assembly 10 
is supported so that the strain sensing is accurate and so that the 
specimen contact rods that contact the specimen are not likely to slip 
when the specimen 11 and the grips 13 and 16 move as the furnace is 
heated, or when the specimen 11 is loaded. In FIGS. 1 and 2, the main 
support is illustrated, fragmentarily. The column 14 forming part of the 
test load frame is used as a mounting member, and a split clamp indicated 
generally at 22 is clamped onto the column 14 and can be adjusted up and 
down. The split clamp in turn is used to support a support arm 23 that 
extends radially from the column. The arm 23 would be at an angle with 
respect to a line extending between a pair of columns 14 that are normally 
used in a load frame because the furnace 12 and specimen 11 are positioned 
between the load frame columns and the main part of the extensometer 
assembly 10 is outside the furnace. 
The arm 23 in turn supports an upright support block 24 that is attached to 
the arm 23 at its outer end as seen in FIGS. 1 and 2. The support block 24 
is suitably attached to a unitary heat shield indicated at 25. The heat 
shield 25 is made of a suitable heat conducting material such as copper, 
and has internal passageways for cooling water. The heat shield 25 is made 
with a relatively thick side block 26, and a heat shield plate 27 that is 
attached to the block 26. The plate 27 has upper and lower flanges 28 and 
28A, respectively (see FIGS. 5 and 6 also). The plate 27 is also shown in 
FIG. 2 in partial section, and the lower flange 28A can be seen where the 
upper flange 28 is broken away. 
Additionally, an extensometer main support arm assembly indicated generally 
at 33 is mounted to the upper end of the block 26 with suitable cap screws 
34. The extensometer support arm assembly 33 has an upright portion 35, 
and a laterally extending portion 36 that extends above the adjacent plate 
27. A laterally extending arm 38 forming part of the arm assembly 33 is 
fixed to portion 36 and extends in a direction generally perpendicular to 
the plate 27. The arm 38 is positioned in alignment with a pair of 
apertures indicated at 40 and 41 in plate 27, which are used for 
permitting elongated specimen contact rods 50 and 51 (FIGS. 2, 3, 5, 6 and 
7) to pass through the heat shield into the furnace 12 to contact the 
specimen 11 being tested. The outer end of arm 38 has a horizontal slot 42 
milled in it (FIG. 1). A knurled thumb wheel or nut 43 is placed in the 
slot 42, and a screw 44 is threaded in the knurled nut. The screw 44 has 
flat sides, and passes through openings in the arm 38 on opposite sides of 
the slot in which the knurled nut 43 is mounted. The screw 44 therefore 
will not rotate, but can be moved axially up or down by rotating the 
knurled nut. The lower end of the screw 44 is bifurcated to receive a thin 
flexure support strap 46. The strap 46 is held on the end of the screw 44 
with a cross pin 47 (FIG. 1). This also can be seen in FIG. 5, where the 
flexure strap 46 is shown along with the screw 44 and the knurled nut 43. 
The arm assembly 33 including the upright section 35 and the lateral 
section 36 is a unitary member that stably support overhead support arm 
38. 
The heat shield 25, which is supported stably on support block 24 and arm 
23 from the load frame column 14 thus provides the main support for 
supporting the extensometer assembly 10. 
Referring to FIG. 3, it can be seen that the extensometer assembly 10 
includes a pair of elongated specimen contact rods 50 and 51. The first 
rod 50 is the upper rod as shown, and the second rod 51 is the lower rod. 
The outer ends 50A and 51A of the rods contact a specimen with an edge 
line or knife edge formed by suitably shaping the ends. 
The lower specimen contact rod 51 is supported through a measuring sensor 
or sensing system indicated generally at 53 that is of substantially 
conventional design utilizing a cross flexure arrangement so that the rod 
51, and in particular its outer end 51A, which is the specimen contact 
end, can pivot and move along the axis 18 of the specimen 11 relative to 
the outer end 50A of the rod 50 about a flexure pivot axis indicated 
generally at 54. The upper specimen contact rod 50 is supported on a 
contact rod support system 55, which comprises a cross-flexure arrangement 
for mounting the base end of the rod 50 for permitting movement of the 
outer end 50A of the specimen contact rod 50 about an axis generally 
parallel to the axis 18 of the specimen to be tested. 
The support system 55 and the sensing system 53 which support the inner or 
base ends of the rods 50 and 51 are supported by a parallelogram linkage 
support frame indicated generally at 60, which includes a first link or 
beam 61 which as shown is an upper beam, and a second (lower) link or beam 
62. The first and second beams 61 or 62 have beam sections 61A and 62A 
which are mounted parallel to each other, and which are held together with 
a third link or beam 63 and a fourth link or beam 64, which is parallel to 
the third beam 63. The third and fourth beams are joined to the first and 
second beams 61 and 62 to form the parallelogram linkage support frame 60. 
The beams 61 and 62 are to the third link 63 through a first flexure strap 
set 66 that comprises a pair of spaced apart coplanar spring straps that 
are flexible and which are joined at first ends to an end of first beam 
section 61A, and at second ends to the end of third beam 63. The opposite 
end of the third beam 63 is connected with a pair of flexible straps or 
flexures 67 to the outer end of the second beam section 62A Straps 67 are 
fastened at their ends to the second beam section 62A and the third beam 
63, respectively. The fourth beam 64 is connected with suitable flexure 
straps 68 to ears 61D integral with the first beam section 61A at an 
intermediate portion of the beam 61. The ears form the end of the first 
parallel link or beam section 61A. The lower end of the fourth link or 
beam 64 is connected with a pair of coplanar flexure straps 69 to a pair 
of ears 62D at an intermediate portion of the beam 62, which ears are at 
the end of second beam section 62A. 
It can be seen therefore that the first and second (upper and lower) beams 
61 and 62 can move axially independently of each other in direction 
parallel to the longitudinal axes 5OB and 51B of the elongated specimen 
contact rods 50 and 51 as permitted by the hinging or pivoting action of 
the flexure straps 66, 67, 68 and 69. The straps form friction free, zero 
clearance (or looseness) hinges. 
The upper beam section 61A forms the actual parallel beam or link that is 
connected to the third and fourth beams 63 and 64. A second arm or beam 
section 61B of beam 61 is integral with the parallel beam section 61A and 
extends toward the specimen and heat shield from the beam section 61A. The 
beam or arm section 61B has a substantially greater lateral width than the 
beam section 61A, as shown perhaps best in FIG. 6, and has a central 
opening therethrough indicated at 70. 
It should be noted that the beams of the parallelogram linkage support 
frame 60 have cross holes formed therein for weight reduction. These holes 
are seen in FIG. 3, for example. 
The flexure support strap 46 passes through this opening 70, and the lower 
end of strap 46 is mounted to a parallel linkage support frame arm 73 with 
a suitable clamp block 74 held in place with cap screws. The arm 73 has a 
base portion 75 (FIG. 3) which passes through an opening in the fourth 
beam or link 64. The arm 73 is positioned between the beams or links 63 
and 64 as can be seen and is near the center of gravity of the 
extensometer assembly 10, so the assembly can be balanced when suspended 
from the support strap 46. The strap 46 bends very easily about a 
transverse or horizontal pivot axis. The upper end of the support arm 73 
is fixed to the first beam section 61A with suitable cap screws. 
The flexure straps 68 are mounted on the ears 61D that are integral with 
the beam section 61B and on the lower side of the beam section 61B. The 
ears 61D extend laterally from the width of the beam section 61A. Flexure 
strap 46 permits relatively free movement of the entire parallelogram 
support frame linkage and the supported specimen contact rods 50 and 51 in 
direction parallel to the axes 50B and 51B of the specimen contact rods. 
The support strap 46 also will twist easily about its longitudinal axis 
which is parallel to the plane of the parallelogram linkage support frame. 
The second beam section 62A corresponds to and is parallel to and aligned 
with the first beam section 61A of the first beam 61, and an arm section 
62B of beam 62 extends outwardly toward the heat shield 25 and specimen 
beyond the fourth beam 64. The end of second beam section 62B adjacent the 
heat shield 25 supports the sensing system 53, which in turn supports the 
elongated specimen contact rod 51. 
The sensing system 53 has two relatively movable members joined by a 
separate, pivot forming cross-flexure of substantially conventional 
design. The sensing system 53 includes a base member 80 that is fixedly 
connected to the beam section 62B and is spaced slightly thereabove. The 
base member 80 has a pair of ears 81 extending laterally of the beam 
section 62B (see FIG. 7) and each of these ears 81 supports a separate 
flexure strap 82. First ends of the straps 82 are fastened to the ears 81 
with suitable cap screws 83. As can be seen in FIG. 7 these straps 82 are 
spaced apart. The upper ends of the straps 82 are connected with cap 
screws 85 to a lower specimen contact rod support arm 86, which has a wide 
portion 86A on which the flexure straps 82 are attached with the cap 
screws 85. The specimen contact rod support arm 86 has an upright column 
portion 86B extending in direction toward the specimen contact rod 51. A 
V-shaped receptacle 86C is formed on a side of column 86B for centering 
and receiving the base end of specimen contact rod 51, and clamping the 
rod 51 in place with a suitable clamp plate 86D. 
Additionally, the specimen contact rod support arm 86 has a lower center 
portion 87 that is substantially centered between the flexure straps 82, 
and extends down below the attachment points of the cap screws 85. This 
center portion 87 supports one end of a flexure strap 88 that is a single 
strap that passes generally horizontally between the straps 82, so that 
the planes of the straps 82 and straps 88 intersect along the pivot axis 
indicated at 54. One end of the flexure strap 88 is connected to the block 
or center portion 87 of the arm assembly 86, and the opposite end of the 
flexure strap 88 is supported on a center support 89 formed on the arm 80, 
positioned between the ears 81, and thus extending between the flexure 
straps 82,82, back over a portion of the arm section. 62B. The end of the 
flexure strap 88 that is attached to the center support 89 is held in 
place with a suitable clamp block 92 and cap screws 92A. 
The specimen contact rod 51 thus can pivot about axis 54 relative to the 
arm section 62B and the rest of the parallelogram linkage support frame. 
The flexure strap 88 has strain gages thereon to measure the bending of 
the strap and provide an output signal indicating movement of the over end 
of rod 51 relative to the arm (and relative to rod 50 in direction of the 
loading axis) 62B using known circuitry. Thus, the sensing system 53 is 
used to indicate relative movement of the rods 50 and 51 in direction of 
the loading axis of the specimen. 
The support arm 86 also has a counterweight arm 94 mounted thereto on the 
top portion of a center block 95 fixed on the arm 86. The block 95 extends 
rearwardly above the clamp block 92 and is positioned so that it can move 
between the cap screws 92A that hold the block 92 in position to permit 
the required pivotal movement of arm 86 and rod 51 about pivot axis 54. 
The counterweight arm 94 extends through an opening in the fourth beam 64 
of the parallelogram linkage support frame and can move a limited amount 
up and down as the specimen contact rod 51 moves, which will in turn cause 
pivoting at axis 54 and thus movement of the block 95 and the 
counterweight arm 94. A counterweight 97 is provided at the outer end of 
the arm 94, and the counterweight 97 can be adjustable in size or mass, as 
well as in position in longitudinal direction, to properly counterweight 
the elongated specimen contact rod 51. 
A secondary heat shield indicated generally at 100 in FIGS. 3 and 7 is 
attached to the contact rod support arm 86, at junction line 101, and 
extends upwardly above the end of the support arm past the specimen 
contact rod 51. The heat shield 100 has a transverse receptacle 102 formed 
at the upper end which provides an interface with a secondary mating heat 
shield for the upper specimen contact rod. The heat shield 100 has an 
opening through which the specimen contact rod 51 extends. This opening in 
heat shield 100 for rod 51 can closely clear the rod 51 because the rod 51 
does not move relative to the opening or heat shield 100. This close fit 
helps block heat being radiated through the opening in the main heat 
shield wall 27 that is provided for the specimen contact rod 51. 
The upper or reference specimen contact rod 50 is mounted on a flexure 
support that permits rod 50 to pivot about an axis parallel to axis 18 of 
the specimen 11, but rod 51 is rigidly mounted to the parallel linkage 
support frame 60 in relation to movement parallel to the axis 18. Thus 
specimen movement along axis 18 will cause movement of rod 51 relative to 
rod 50. 
The specimen contact rod 50 is supported by the support flexure assembly 
55, which perhaps can be best seen in FIGS. 3, 5, 6, 7 and 9. The arm or 
beam section 61B of beam 61 extending from the parallel beam section 61A 
has a depending support block 105 that is fixed to the end of the arm 
section 61B and extends therefrom toward second beam 62. As can be seen in 
FIG. 9, this support block 105 has a head portion held with cap screws 106 
onto the end of the arm section 61B, and has a narrow leg 107 depending 
downwardly from the head portion. The leg 107 has a surface 111 that is 
approximately at the center of the beam 61. The leg 107 supports a pair of 
vertically spaced flexure straps 110 against surface 111, and these 
flexure straps are held clamped against the surface 111 with suitable 
clamp blocks 112 held in place with cap screws. The flexure straps 110 
extend forwardly (toward heat shield 25) as shown in FIG. 3 and are 
clamped onto an arm 115 with suitable clamp blocks 116. 
The arm 115 has a lower end portion 117 that has a V-block surface 118 
(FIG. 7) for receiving the specimen contact rod 50, and the rod 50 is 
clamped in place with a suitable clamp plate 120 held in place with cap 
screws. The arm 115 is thus supported on the flexure straps 110 with 
respect to the surface 111 of the leg portion 107 of the support block 
105. The arm 115 is L-shaped as viewed from the top, as can be seen in 
FIG. 6, and has a leg portion 115A that provides a surface at right angles 
to the surface 111. Leg 115A supports a pair of flexure straps 122 
thereon. The straps 122 are positioned between straps 110 as can be seen 
in FIG. 7, and also in FIG. 9. The flexure straps 122 have planes at right 
angles to the planes of flexure straps 110. The flexure straps 122 are 
clamped to leg 115A with clamp blocks 123. 
FIG. 7 and FIG. 9 are taken on sight lines in opposite directions along 
substantially the same plane. The flexure straps 122 are mounted with 
respect to a forward surface of the leg 107 with suitable clamp blocks 124 
as can be seen in FIG. 9, as well as being supported with respect to the 
rearwardly facing surface of the leg 115A with suitable clamp blocks 123. 
Thus, the two sets of flexure straps 110 and 122 intersect along a pivot 
axis shown in FIG. 6 at 130 and this permits the specimen contact rod 50 
to move or pivot about axis 130 in directions as indicated by the arrow 
131 in FIG. 6. 
The amount of pivoting about axis 130 is to accommodate slight torsional 
movement of the specimen or the parallelogram linkage support frame 60. 
The weight of the specimen contact rods 50 and 51, the supports for the 
specimen contact rods, and the parallelogram linkage support frame 60 is 
supported from the flexure strap 46. The strap 46 restrains any tendency 
of the support frame 60 and other portions of the extensometer assembly to 
pivot about an axis that is generally parallel to the contact rods 50 and 
51 and at their base ends is midway therebetween, and which is shown by 
the dot 132 in FIGS. 1 and 4. The axis of torsion or twist actually is 
about on a line from the point of contact of rod 51 with specimen 18 at 
end 51B to the point 132 midway between the rods at the base ends of the 
rods. The flexure strap 46 has a width that is adequate to resist movement 
about the axis 132. 
The support block 105 and the arm 115 carry cooperating stops that will 
prevent excessive movement of specimen contact rod 50 about axis 130. The 
two stops are mirror images of each other and are indicated at 135 and 
136, respectively. These stops are generally channel-shaped as perhaps can 
best be seen in FIG. 6, and each one has a narrow stop leg 135A and 136A, 
respectively, and a wider stop leg 135B and 136B, respectively. The stop 
135 is clamped onto the outer side surface of the leg 107 of the block 105 
with suitable cap screws 138, and the stop 136 is clamped onto the side 
surface of the arm 115 with suitable cap screws shown at 139 in FIG. 6. 
The stop legs 136A and 135B are spaced slightly at the rear, underneath 
the arm section 61B and the legs 136B and 135A are spaced slightly apart 
at the forward side of the arm 115. The adjacent pairs of legs contact 
after limited pivotal movement of the specimen contact rod 50 about axis 
130. 
A secondary heat shield 140 is clamped with cap screws 141 to the arm 115. 
Heat shield 140 has a lip 142 at its lower end that fits into the 
receptacle 102 of the heat shield 100, to provide an overlap for heat 
shielding. Again, the heat shield 140 has a relatively close fitting 
opening for the specimen contact rod 50 because the heat shield 140 is 
directly and fixedly attached to the arm supporting the rod 50 so that it 
moves with the rod. 
A stop assembly 150 is provided at the rear portion of the parallelogram 
linkage support frame, and in particular extends between the first beam or 
link section 61A, and the second beam link section 62A. The stop assembly 
150 includes an upright column 151 that is fixed to the second beam 
section 62A with suitable cap screws, and the upright column 151 has a 
recess or receptacle 152 formed therein at the upper ends. A second stop 
column 153 is fixed to the first beam section 61A, and depends therefrom. 
The second stop column is in alignment with the stop column 151 as can be 
seen in FIG. 4. The stop column 153 has a lug 154 which fits into the 
receptacle 152, and thus the lug 154 will strike the front or rear surface 
defining the receptacle 152 if the parallelogram linkage support frame 
moves too far out of a rectangular configuration, which is when right 
angles are formed between the axis of first and second parallel beam 
sections 61A and 62A and the third and fourth beams 63 and 64. 
Additionally, there are scribe marks 155 on the lug 154, and a 
corresponding center line scribe mark 156 on the column 151 adjacent 
receptacle 152, which will align when the parallelogram linkage support 
frame comprising the four beams 61A, 62A, 63 and 64 is forming a rectangle 
and in its reference position. The beams 61A and 62A can move in direction 
parallel to the axes of the specimen contact rods 50 and 51 relative to 
each other as the parallelogram linkage support frame parallelograms. The 
beams of the parallelogram linkage support frame then remain parallel, but 
the frame moves out of a rectangular shape. 
It also should be noted that the openings that are formed in the beams 61 
and 62 are for weight reduction, and one such opening 62C is shown in FIG. 
7 in cross-section. The weight reduction openings also are provided in the 
stop members 151 and 153. The parallelogram linkage support frame carries 
a counterweight 157 to balance the extensometer assembly relative to the 
support strap 46. 
It can thus be seen that the support strap 46 provides a vertical support 
for the entire parallelogram linkage support frame 60, the sensing system 
53 and rod 51, and the support for the upper specimen contact rod 50. The 
support frame 60 is free to move in direction of the axes 50B and 51B of 
the specimen contact rods 50 and 51. The specimen contact rods 50 and 51 
are urged toward the specimen 11, through a hold down flexure assembly 
indicated at 170 that provides a spring or biasing load against the base 
ends of the specimen contact rods 50 and 51, tending to move them toward 
the specimen. Hold down flexure assembly 170 is also made to accommodate 
differential axial movement of the specimen contact rods 50 and 51 without 
substantial restraint (as can the parallelogram linkage support frame), 
and also twisting of the rods about the axis 132, which axis is also 
represented in FIG. 1. The parallelogram linkage support frame is urged 
toward the specimen 11 as well by the hold down flexure assembly 170. 
The hold down flexure assembly 170 is supported to one side of the plane of 
the parallelogram linkage support frame 60 on a removable support slide 
171, that is mounted on the upright block 26 of the heat shield 25, as can 
be seen in FIGS. 1 and 2. Slide 171 supports a first prebent spring 172 at 
a first end, and as can be seen the spring edges taper outwardly toward 
its outer end. The lines along the edges of spring 172 preferably converge 
to a point at axis 132. The outer end of the spring 172 supports a block 
173 that extends laterally from spring 172 and has a horizontal shoulder 
surface 174 on one end and on which a laterally extending base flexure 
spring 175 is mounted. This base flexure spring 175 is relatively thin, 
but has a substantial width as can be seen in FIG. 2. The base flexure 
spring 175 has a long flat flexure spring 176 attached thereto with a 
suitable clamp block arrangement 177. The ends of springs 175 and 176 are 
overlapped, and the long flexure spring 176 is positioned to be generally 
on a plane substantially midway between the specimen contact rods 50 and 
51. The planes of springs 175 and 176 are perpendicular to the plane of 
spring 172. 
Elongated flexure 176 is thicker than the base section 175 and it extends 
laterally toward the parallelogram linkage support frame 60. The outer end 
of the spring 176 is coupled with a clamp block arrangement 180 to a thin 
flat flexure spring 182 that is supported on a plane substantially midway 
between the specimen contact rods 50 and 51, and the spring 182 extends 
laterally across the plane that is defined by the axes 50B and 51B of the 
specimen contact rods 50 and 51. An outer end of spring flexure 182 is 
extended so that the spring flexure 182 extends substantially equal 
distances on opposite sides of the axis 132 as shown in FIG. 1 between the 
end that is supported by the support blocks 180 and its outer end. A pair 
of arm members 183 and 184 are clamped to the outer end of spring flexure 
182. The arm members 183 and 184 extend vertically from the plane of the 
spring flexure 182, and suitable cap screws are used for clamping the two 
arm sections 183 and 184 together with the spring flexure 182 sandwiched 
between these arm sections. The arm section 183 in turn supports a 
specimen rod end contact arm 185 that extends laterally back toward the 
upper specimen contact rod 50, and it has an end adapter 186 that is 
provided with an internal conical socket that receives and centers a 
conical end 50C of the upper specimen contact rod 50. 
The lower arm section 184 has a laterally extending flexure strap or spring 
190 fixed thereto with a suitable block 191, and which extends back toward 
the lower specimen contact rod 51. The flexure strap 190 has an adapter 
192 at the end thereof adjacent the specimen contact rod 51, and this 
adapter 192 also has a conical interior socket that receives and centers 
on a conical end 51C of the specimen contact rod 51. The conical surfaces 
50C and 51C are on the remote side of the respective clamps that hold the 
specimen contact rods on their support arms. Flexure spring 182, arm 185 
and flexure strap 190 are positioned between the respective arms 
supporting the specimen contact rods and the fourth beam 64 of the 
parallelogram linkage support frame. The lateral arm 185 can be replaced 
with a flexure strap similar to strap 190, if desired. 
The conical seats or sockets in end adapters 186 and 192 have conical 
surfaces that have a substantially greater included angle than the 
included angle of the end surfaces 50C and 51C to permit the rods to pivot 
easily in the sockets. The tips of the conical surfaces on the rods also 
are rounded rather than a sharp point to aid pivoting of rods 50 and 51. 
It can thus be seen that if the rods 50 and 51 simultaneously move up and 
down, the flexure spring 175 in particular will bend about an axis 
generally parallel to the axes of the rods 50 and 51 to permit this 
movement without substantial load resisting such movement. It also can be 
seen that there will be an axial load on the specimen contact rods, for 
example, in the range of 200 grams total, provided by the adapters 186 and 
192, under load from the flexure spring 172, which is prebent so it 
provides a force when it is planar as shown for urging the specimen 
contact rods against the specimen 11. The resilient force from spring 172 
can be selected to insure proper contact between the rods and the specimen 
across a wide range of movements. 
If the specimen contact rods 50 and 51 tend to move together or apart (as 
rod 51 pivots for measuring specimen loads, or as support frame 60 
parallelograms), the flexure strap 190 will accommodate this movement, and 
if there is any differential axial movement of the rods 50 and 51, the 
flexure strap 182 will twist to accommodate it. The flexure strap 182 is 
centered on the axis 132, and the twisting will be accommodated in this 
flexure strap (the strap 176 is substantially thicker than the strap 182) 
so there will not be any substantial unwanted loads encountered. 
Thus, the hold down flexure assembly 170 accommodates movements of the 
specimen contact rods without causing erroneous readings or loads. 
The flexure spring 176 passes between a pair of arms indicated at 200,200 
which are mounted onto the slider block 171, and the arms 200 have aligned 
openings 201 therethrough through which a pin can be dropped so that the 
entire flexure assembly of the flexure can be pulled away from the ends of 
a specimen contact rod by moving the unit out to a point where the spring 
172 is bent from planar configuration, and shows the spring section 176 
assumes the position in dotted lines in FIG. 2. Then a pin can be dropped 
through the openings as shown in dotted lines in FIG. 1, to hold the 
flexure assembly 170 from engaging the specimen contact rods. 
The slider assembly 171 permits in and out (lateral) movement for removal 
and replacement of the flexure assembly 170 as indicated by the arrow 205. 
As can be seen in FIGS. 1 and 8, respectively, slide 171 has a center boss 
171A, forming a pair of slide ears 171B that are slidably fitted into a 
receptacle in a mounting block 210. The block 210 is clamped onto the 
block portion 26 of the heat shield 25. The block 210 is clamped in place 
with cap screws indicated at 211, and as can be seen the block 210 has a 
slightly recessed forward surface forming spaces 212 at the top and bottom 
of the main receptacle in which slide 171 is mounted. The recesses 212 are 
generally U-shaped spaces so that there are legs extending down along the 
sides of the block 210 as shown in dotted lines in FIG. 1, to form a 
center recess 212. Spring blades 214 are supported on the legs formed at 
the ends of the recess 212 above and below the boss 171A of slide 171, 
using cap screws 215. 
It can be seen that the spring blades 214 extend upwardly so that they will 
retain the flanges or ears 171B in the receptacle formed in the block 210, 
and yet will permit the boss 171A to slide between these blades. The 
blades 214 are then clamped down onto the ears 171B by deflecting the 
blades into the recesses 212 through the use of clamp cap screws shown in 
FIG. 1 at 220. This will deflect the spring blades 214 to clamp onto the 
flanges or ears 171B to hold the slide 171 in position as adjusted. 
The hold down flexure assembly 170 is pulled away from the ends of the 
specimen contact rods in axial direction of the rods, and a pin is 
inserted through the aligned openings 201. The entire flexure assembly 170 
can then be moved to the right in mounting block 210 as shown by arrow 205 
so that the hold down flexure assembly 170 can be entirely removed from 
the mounting block 210 and moved to a location clearing the extensometer 
assembly. The extensometer assembly 10 then may be removed from its 
mounting bolt 44 by removing pin 47 and withdrawing the rods 50 and 51 
from the furnace and heat shield 25, if desired. 
As a summary of the operation, then, as the specimen is heated up, and the 
specimen supporting grips are also heated the specimen can shift 
substantially relative to the support of flexure strap 46. The shifting 
will be accommodated without adding bending strain to the ceramic rods 50 
and 51 because the parallelogram linkage support frame can parallelogram 
in its plane through the flexures 66, 67, 68 and 69 that hingedly connect 
the parallel beams of the parallel linkage support frame 60 together. 
Other motions of the specimen contact rods other than relative movement 
along the loading axis of specimen 11 are also accommodated in the hold 
down flexure assembly 170, such as differential axial movement of the 
rods. Torsion of the specimen or twisting of the frame is accommodated by 
the upper contact rod support system 55 that supports the upper contact 
rod 50 relative to the first beam 61. An adequate and controlled spring 
force can be applied axially on the specimen contact rods, without 
incurring any other loads on specimen contact rods that are unwanted. 
Additionally, as the specimen shifts, so that, the rods 50 and 51 are at an 
angle relative to their supports and the parallelogram linkage support 
frame 60 has moved out of its rectangular arrangement, as indicated by the 
scribe marks 155 and 156, the nut 43 can be threaded to adjust the axial 
position of the support screw 44 and the support strap 46 to bring the 
scribe marks on the stop column 151 and 153 back into registry, meaning 
that the parallel linkage frame 60 is rectangular and the test is ready to 
be conducted. The amount of relative axial movement between the beams 61 
and 62 is small. The first and second beam sections 61A and 62A remain 
parallel, but shift axially to accommodate differential axial movement of 
the specimen contact rods 50 and 51. 
The support frame 60 couples the reference specimen contact rod 50 to the 
movable rod 51 through a measuring sensor system 53 to provide for strain 
measurement. The sensing system 53 can be any desired form that permits 
relative pivoting movement of the rod 51 and provides an output signal 
indicating such movement. For example, capacitive sensing may be used 
between counterweight arm 94 and beam section 62A, because there is 
relative movement between these members, or an LVDT also could be used to 
sense movement caused by strain in the specimen. 
The changing of spacing between the outer ends of the rods 50 and 51 which 
is the movement in direction along the specimen axis is the movement to be 
sensed, thus is adequately sensed without having unwanted strains placed 
on the measuring sensor system 53. 
The parallelogram linkage support frame can be rotated 90.degree. from the 
position shown and the specimen contact rods oriented as shown, that is, 
spaced apart along the axis 18 of a specimen. The coupling members between 
rod 50 and beam 61 and the measuring system between rod 51 and beam 62 
would be reoriented as needed, but the support frame would still 
parallelogram to permit differential axial movements of the specimen 
contact rods. 
The rod 50 could also be rigidly coupled to the beam 61 if desired, 
particularly if the gauge length (the distance between the ends 50B and 
51B) was relatively long. Then, the support strap 46 would be replaced 
with a thin wire or line that would permit twisting of the support frame 
60 about both horizontal and vertical axes to accommodate torsional 
shifting. 
The upper specimen contact rod support system 55, which permits movement of 
the rod 50 caused by torsion in the specimen, can have strain gages or 
other sensors associated therewith to provide torsional strain 
measurements. The external support for frame 60 would be modified to 
insure that the torsional strain loads are reacted properly for accurate 
measurements. 
The heat shields adequately shield the members from excessive heat from the 
furnace, and suitable cooling can be used in passageways in the heat 
shields as desired. While a furnace for the specimen is disclosed, other 
sources of heat can be used and the support system can be used with any 
specimen, whether heated or not, where shifts or movements of the type 
described may be a problem. 
Preferably, the spacing between the first and second beams of the 
parallelogram linkage support frame will be equal to, or greater than the 
spacing between the specimen contact rods. 
Although the present invention has been described with reference to 
preferred embodiments, workers skilled in the art will recognize that 
changes may be made in form and detail without departing from the spirit 
and scope of the invention.