3. 1.1 Impact load test
Impact load is the main reason for rail head damage,
crack in bolt hole and crack in sleeper of the joint. It
may also cause a very large vibration acceleration in
the ballast bed, which will lead to crushing of the
ballast, subsidence of the ballast bed and slope failure,
therefore it is a key indicator to measure the quality of
the rail joint.
7. The patch and bridge circuit for measuring
value of P1 and the strain wave when
dropping the wheel-set
8. According to the impulse theorem:
m is mass of the wheel-set acting on one rail
g is acceleration of gravity
H is height of dropping wheel-set
t is time of rising stage in the wave of
measuring force P1
9. 1.2 Quasi static vertical load test
Quasi static load may affect the derailment
caused by load reduction and rail climbing, and
its action on rail is similar to static load, transfer
function of load transfer from rail to subgrade is
approximately 1,leading to the bending of rail
and sleeper, and stress and strain of subgrade
beneath sleeper.
12. 1.2.1 Shear method
Both shear stress method and
bending moment difference method
can be used to measure Sr and SL
and sum them up
13. 1.2.1 Shear method
In shear stress method:
τ is shear stress
Sr is shear force
J is moment of inertia of rail cross-section relative to
horizontal neutral axis
G is static moment of area of rail cross-section distal to
calculating point of shear stress relative to horizontal
neutral axis
b is section thickness
14. 1.2.1 Shear method
The patch and bridge circuit for measuring value of
P2 by shear stress method and the waveform
20. 1.2.2 Rail web compression method
Paste the patch
symmetrically and vertically
on both sides of the rail web
near neutral axis, forming
the work arm of outer half-
bridge by series connection,
then paste two
compensation plates as
temperature compensation.
21. 2.Wheel-rail lateral horizontal force test
Wheel-rail horizontal force is an important parameter
that determines derailment coefficient which influences
the stability of running vehicles, it is also the main
reason for transverse damage and instability of the rail
Shear stress method is widely used to measure
horizontal force in China, its principle is similar to the
measurement of P2,namely measuring transverse force
on the sections of both sides at the same time, then
superimposing them according to the characteristics of
bridge.
22. The patch and bridge circuit for measuring
value of H with strain gauge and the waveform
24. The patch for measuring wheel-rail longitudinal
horizontal force and method of organizing the
bridge
25. L is longitudinal force in the rail
εL is longitudinal strain of the rail
E is modulus of elasticity of the rail
F is sectional area of the rail
εL can be read directly from the wave, then
27. 1.Stress and displacement test on
track components
Track components stress tests provides an
important reference for assessment of the strength of
track components.
Resistance strain gauges are pasted to the surface
of the structure, and rail stresses can be determined
by measuring the deformation.
28. 1.1 Leaf-spring displacement sensor
Leaf-spring displacement sensor
The structure of the displacement sensor is very
simple, by adjusting stiffness of the leaf-spring,
displacement sensor suitable for different
measurement range and different natural
frequency can be made.
29. 1.1 Leaf-spring displacement sensor
h is leaf-spring(cantilever) thickness
L1 is the distance between the middle point of the strain
gauge and the fixed end.
P is the force acting on the contact point, its value equals
the product of the stiffness K of beam at contact point
and the displacement y0
ε is the strain of one strain gauge, when using half-bridge
(2 pieces) complementary connection, the output of bridge
circuit ε2=2ε,when using full-bridge(4 pieces) connection,
ε4=4ε
32. 1.2 Combined spring displacement sensor
Combined spring displacement sensor
When measuring transverse displacements of
rail head and switch rail, the combination of
spring and cantilever beam, namely combined
displacement sensor can be used to reduce the
deformation of the elastic part of the leaf-
spring(cantilever).
34. y0= y1+ y2 K1y1=K2y2=P
1.2 Combined spring displacement sensor
35. Factors that should be considered:
(1) Range of the displacement sensor should meet the
requirements of the measured displacement. (mm)
1.3 Parameter selection of the displacement
sensor in the track test
36. Factors that should be considered:
(2) Displacement accuracy.
(3) Frequency response.
(4) Basic performance of the sensor.
(5) Sturdiness of the sensor.
(6) Resistance to electrical noise interference
(7) Good insulation property between the
sensor and the rail.
1.3 Parameter selection of the displacement
sensor in the track test
37. 1.3 Parameter selection of the displacement
sensor in the track test
Factors that should be considered:
(8) Transverse sensitivity of the displacement
sensor should be low.
(9) Easy to calibrate on the spot.
(10) Protection from environmental factors.
(11) Low cost.
38. 1.4 Installation of the displacement sensor
Whether it is for the measurement of absolute
displacement or relative displacement, the
installation quality of the sensor has a direct
influence on the reliability and accuracy of
the test results.
39. 2. Pressure test on the sleeper
There are two ways to measure the pressure
on the sleeper, one is putting the pressure
sensing component between rail and sleeper,
namely backing plate for force measurement ,
the other is taking the rail itself as sensing
component.
40. 2.1 Backing plate for force measurement
Ideal backing plate for sleeper pressure measurement
should meet the following conditions:
① Thin thickness, when installed under the rail, better
not changing the height of the rail surface or with
little change.
② Less structural components, not easy to loose and
damage under vehicle load.
③ Less changes of the elastic characteristic of rail and
sleeper.
41. 2.1 Backing plate for force measurement
Ideal backing plate for sleeper pressure measurement
should meet the following conditions:
④ A good linear relationship between load and
deformation, less changes of the elastic modulus
under static and dynamic load, a high modulus of
resilience.
⑤ Transfer point of the load should be accurate and
constant, avoiding changing the contact condition
between rail and sleeper.
⑥ Sensitive elements should be well protected, not
easy to damage.
43. 2.1 Backing plate for force measurement
Problems that may occur:
(1)It is not ideal to take rubber material as the elastic
component of the pressure sensor. General requirements
for the materials of elastic component are:
①Stress and strain should be proportional under the action
of external force.
②The value change of elastic modulus should be little
under the action of static and impact loads.
③After the cancellation of the load, it can quickly return to
the undeformed shape and size and have no residual
deformation.
44. 2.1 Backing plate for force measurement
Problems that may occur:
(2) It’s hard to improve the smooth degree and
friction property of the supporting surface.
(3) Change of sensitivity of plate for force
measurement.
(4) Sensitive elements are easy to damage due to
friction and overload.
45. 2.2 Take the rail as a force measuring element
Principle of measuring the pressure
on the sleeper by shear method
47. 2.2 Take the rail as a force measuring element
The patch and bridge circuit for measuring the
pressure on sleeper by shear method and the
waveform
48. 2.2 Take the rail as a force measuring element
The patch and bridge circuit for measuring the
pressure on sleeper by bending moment
difference method and the waveform
55. 3.1 Structure of earth pressure cell
Earth pressure sensor single oil cavity and
double oil cavity
56. 3.2 Burying of earth pressure cell
Earth pressure cell should be pre-buried
one to one and a half months earlier before
the test, to make the loose ballast bed and
subgrade surface come back to working
conditions as possible by operation effect
of the vehicles.
57. 3.3 Compressive stress test
Strip the end of the wire, connect the
assembled half-bridge(or full-bridge)
circuit with strain gauge, test the strain
output of the earth pressure cell, then
obtain earth pressure according to
sensitivity of earth pressure cell.
59. 1.Track vibration acceleration and track
damage
Simple harmonic vibration:
Maximum values of amplitude,
velocity and acceleration: A,Aω,Aω2
60. 1. Track vibration acceleration and track
damage
Vibrations due to different interferences:
A1＞A2,ω1＜ω2, A1ω1＜A2ω2
Now analyze which one is worse to the structure
