CN114486577A - Test sample, device and method for I-type dynamic fracture toughness of UHPC - Google Patents
Test sample, device and method for I-type dynamic fracture toughness of UHPC Download PDFInfo
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Abstract
The invention discloses a test sample, a device and a method for I-type dynamic fracture toughness of UHPC (ultra high performance polycarbonate). The test sample is hemispherical as a whole, a semicircular groove is arranged on the end surface of the test sample, and a crack is also arranged at the bottom of the semicircular groove and extends to the hemispherical circle center of the test sample along the axial direction. The testing device comprises a test sample and a testing mechanism, wherein the testing mechanism comprises an impact load emission assembly, an incidence rod and a transmission rod; the test method is that the impact load emitting assembly is used for generating impact load on the incident rod, and dynamic compression load is applied to the end faces of the two sides of the test sample through the incident rod and the transmission rod, so that the relation between the dynamic stress intensity factor and the speed and acceleration in the crack unsteady expansion process is obtained. The invention can comprehensively research the I-type dynamic fracture process of UHPC, can research the relation between the speed, the acceleration and the dynamic fracture toughness in the crack propagation process, has accurate and reliable obtained result, and fills the blank in the research field.
Description
Technical Field
The invention relates to the technical field of material performance testing, in particular to a test sample, a device and a method for I-type dynamic fracture toughness of UHPC.
Background
Fracture toughness is an important parameter for evaluating mechanical properties of UHPC (ultra high performance concrete), including crack initiation, propagation, fracture mechanism and the like of UHPC. Therefore, obtaining an accurate fracture toughness value of the UHPC, designing a scientific testing device and a scientific measuring method are all very important.
Studying dynamic crack propagation in brittle materials, the crack propagation velocity is generally assumed to be constant, i.e. the crack propagates at a constant rate, a simplification that makes the mathematical model easier to handle, but is less suitable from a physical point of view. The severity of engineering disasters caused by dynamic fracture of the UHPC fault is influenced by the unsteady expansion speed and acceleration of the fracture. The dynamic crack initiation stage and the crack arrest stage are supposed to exist, but the measurement precision is insufficient or the calculation is simplified, so that many scholars consider the dynamic crack initiation stage and the crack arrest stage as the precision error of a measuring instrument, the crack still seems to be a constant-speed propagation in an average sense, although some mechanical property results can be obtained simply, the influence of key factors can be ignored, and the acceleration cannot be concerned.
Disclosure of Invention
Aiming at the defects in the prior art, the technical problems to be solved by the invention are as follows: how to provide a test sample, a device and a test method for the I-type dynamic fracture toughness of the UHPC, which consider the influence of the speed and the acceleration in the crack propagation process on the dynamic fracture toughness and greatly improve the measurement accuracy.
In order to solve the technical problems, the invention adopts the following technical scheme:
the test sample of the type I dynamic fracture toughness of the UHPC is wholly hemispherical, a semicircular groove extending towards the inside of the test sample is arranged on the end face of the test sample, the circle center of the semicircular groove and the circle center of the hemisphere of the test sample are located on the same horizontal line, a crack is further arranged at the bottom of the semicircular groove, and the crack extends towards the direction of the circle center of the hemisphere of the test sample along the axial direction.
Like this, the above-mentioned structural design of test sample for the test sample not only has the advantage of easily making, and the design of half slot has increased the profitable stress concentration in crackle point simultaneously, has obvious advantage to the crackle propagation speed change among the research brittle material I type dynamic fracture process, and in addition, still has the prefabricated crackle of being convenient for, does not need the advantage of loading anchor clamps, and the fracture area of test sample is effectively increased, makes things convenient for the research of test sample fracture overall process.
A test device for I-type dynamic fracture toughness of UHPC comprises the test sample and a test mechanism;
the test mechanism includes along impact load emission subassembly, incident pole and the transmission pole that the axial set gradually, impact load emission subassembly be used for to the incident pole provides impact load, the plane of test sample install in the incident pole orientation the one end of transmission pole still be equipped with first crack extensometer on the test sample, in order to be used for the monitoring the fracture process of crackle on the test sample be equipped with first foil gage on the incident pole, in order to be used for measuring incident wave and the back wave of test sample department be equipped with the second foil gage on the transmission pole, in order to be used for measuring the transmission wave of test sample department.
In the testing process, the first strain gauge and the second strain gauge collect real-time strain pulse signals of incident waves, reflected waves and transmitted waves in the testing process, and the first crack propagation meter calculates the speed and the acceleration of the crack passing through the first crack propagation meter under different impact loads so as to obtain the relation between the dynamic stress intensity factor and the speed and the acceleration in the crack unsteady number propagation process.
Preferably, the incident rod is used for installing a polytetrafluoroethylene gasket is arranged on the end face of the test sample, and the test sample is installed on the polytetrafluoroethylene gasket.
Therefore, the end face friction effect can be reduced, and the influence of the unevenness of the loading end face of the test sample on the experiment caused by the machining reason can be reduced, so that the successful crack initiation of the test sample is realized.
Preferably, the first crack propagation meter is positioned on the front side of the front crack tip of the test sample along the crack propagation direction, a plurality of third strain gauges are further arranged on the front side of the first crack propagation meter along the crack propagation direction at intervals, and a second crack propagation meter is further arranged on the back side of the test sample at a position corresponding to the crack tip along the crack propagation direction.
A test method of I-type dynamic fracture toughness of UHPC is characterized in that the test device of I-type dynamic fracture toughness of UHPC is adopted, an impact load emitting assembly generates an impact load on an incidence rod, dynamic compression loads are applied to two side end faces of a test sample through the incidence rod and a transmission rod, a first strain gauge and a second strain gauge collect real-time strain pulse signals of incidence waves, reflection waves and transmission waves in the test process, and a first crack expansion meter calculates the speed and the acceleration of a crack passing through the first crack expansion meter under different impact loads so as to obtain the relation between a dynamic stress intensity factor and the speed and the acceleration in the process of unsteady crack expansion.
Preferably, the method comprises the following steps:
step 1) preparing the test sample;
step 2) mounting the test sample at one end of the incident rod facing the transmission rod, and enabling the central lines of the test sample, the incident rod, the transmission rod and the impact load emission assembly to be located on the same horizontal plane;
step 3) adjusting the speed of the impact load transmitting assembly impacting the incident rod to change the impact load of the incident rod on the test sample, wherein the first strain gauge and the second strain gauge acquire real-time strain pulse signals of incident waves, reflected waves and transmitted waves in the test process, and the first crack propagation meter calculates the speed and the acceleration of cracks passing through the first crack propagation meter under different impact loads;
and 4) calculating by adopting an experiment-numerical value-analytic method to obtain the relation between the dynamic stress intensity factor and the speed and the acceleration in the crack unsteady number expansion process.
Preferably, the dynamic stress intensity factor in the crack unsteady number expansion process in the step 4)
With velocity v and acceleration
The relationship of (1) is:
in the formula: k isI 0The dynamic stress intensity factor is the dynamic stress intensity factor when the test sample speed is 0;
cRis the rayleigh wave velocity of the material;
cdis the expansion wave velocity of the material;
b is a dimensional factor related to the width of the test specimen.
Preferably, the first crack growth meter comprises a plurality of wires connected in parallel, and the wire closest to the crack abuts against the crack tip of the crack;
in step 3), when the impact load transmitting assembly impacts the incident rod, cracks on the test sample crack, so that the metal wires of the first crack propagation meter are broken and the resistance of the first crack propagation meter changes, the time for the crack to propagate to the position is determined by monitoring the jump point of the voltage step change monitored by the first crack propagation meter, the time difference between the crack to propagate to the two metal wires is calculated, and the crack propagation speed between the two metal wires is calculated according to the distance between the two metal wires.
Preferably, in step 3), the crack propagation velocity v is calculated by the following formula:
in the formula, delta l is the distance between two metal wires;
tn+1-tnthe time difference between crack propagation to two wires.
Preferably, in step 4), the Rayleigh velocity c of the materialRThe calculation formula of (2) is as follows:
cR＝cS(0.86+1.14μ)/(1+μ)；
cS＝[E/2ρ(1+μ)]1/2；
expansion wave velocity c of materialdThe calculation formula of (2) is as follows:
cd＝{E(1-μ)/[ρ(1+μ)(1-2μ)]}1/2；
in the formula: rho is the material density;
e is the elastic modulus of the material;
μ is the Poisson's ratio of the material.
Compared with the prior art, the invention has the following advantages:
1. the test method can comprehensively research the I-type dynamic fracture process of the UHPC, can research the relation between the speed, the acceleration and the dynamic fracture toughness in the crack propagation process, has accurate and reliable obtained results, fills the blank in the research field, and has the advantages of simple operation, strong practicability, accurate cutting and good application prospect.
2. The invention provides a large semi-cylindrical sample based on UHPC (ultra high performance polycarbonate), aims to comprehensively research the I-type dynamic fracture process of UHPC (ultra high performance polycarbonate), focuses on the research on the relation between the speed, the acceleration and the dynamic fracture toughness in the crack propagation process, predicts the fracture path of the sample through numerical calibration analysis, researches the crack speed, the acceleration and the dynamic fracture toughness of the UHPC, and has important significance for analyzing the rapid fracture phenomenon of a brittle material in the dynamic action.
3. The invention designs a UHPC sample with a specific geometric shape by utilizing the dynamic loading principle of a Hopkinson pressure bar device, and provides a test method and a test formula for testing the UHPC I type dynamic fracture toughness by focusing on the research on the relation between the speed, the acceleration and the dynamic fracture toughness in the crack propagation process. The method can accurately measure the important parameter of the dynamic fracture toughness of the UHPC, and has important reference value for the engineering properties of the UHPC.
Drawings
FIG. 1 is a schematic structural view of a test specimen of type I dynamic fracture toughness of UHPC of the present invention;
FIG. 2 is a schematic view of the dynamic impact of a test apparatus for type I dynamic fracture toughness of UHPC of the present invention;
FIG. 3 is a diagram showing the bonding positions and configurations of a third strain gage, a first crack propagation meter and a second crack propagation meter in the device for testing type I dynamic fracture toughness of UHPC according to the present invention;
FIG. 4 is a circuit diagram of a first crack propagation meter in an apparatus for testing type I dynamic fracture toughness of UHPC's of the present invention.
Description of reference numerals: the device comprises an impact load transmitting assembly 1, an incident rod 2, a first strain gauge 3, a polytetrafluoroethylene gasket 4, a test sample 5, a first crack propagation meter 6, a second strain gauge 7, a transmission rod 8, a buffer mechanism 9, a third strain gauge 10 and a second crack propagation meter 11.
Detailed Description
The invention will be further explained with reference to the drawings and the embodiments.
As shown in the attached figure 1, the test sample of the type I dynamic fracture toughness of the UHPC is wholly hemispherical, a semicircular groove extending towards the inside of the test sample is arranged on the end face of the test sample, the circle center of the semicircular groove and the circle center of the hemispherical shape of the test sample are positioned on the same horizontal line, and a crack is also arranged at the bottom of the semicircular groove and extends towards the direction of the circle center of the hemispherical shape of the test sample along the axial direction.
Concretely, the test sample is earlier cut into the hemispheroid of appointed radius by great stone, adopt small-size cutting machine to cut out the half slot again, set up the distance between two centre of a circle and the fracture area length of test sample, wherein, the half slot is seted up on the left side plane of test sample, it has the crackle to open on the centre of a circle extension line of half slot, the crackle width is less than 0.4mm, test sample thickness B is 30mm, outer radius R is 50mm, inner bore radius R is 10mm, prefabricate initial crackle length a0The dynamic impact load is 8mm, P (t) is the dynamic impact load which is a function of time, the distance between two circle centers is maximum c 30mm due to the limited diameter of the testing device adopted in the experiment, the length L of a fracture zone of a test sample is 70mm, and the length alpha of a dimensionless initial crack is a0/L＝0.1。
Like this, the above-mentioned structural design of test sample for the test sample not only has the advantage of easily making, and the design of half slot has increased the profitable stress concentration in crackle point simultaneously, has obvious advantage to the crackle propagation speed change among the research brittle material I type dynamic fracture process, and in addition, still has the prefabricated crackle of being convenient for, does not need the advantage of loading anchor clamps, and the fracture area of test sample is effectively increased, makes things convenient for the research of test sample fracture overall process.
As shown in fig. 2, the present invention further provides a testing apparatus for type I dynamic fracture toughness of UHPC, comprising the above test sample 5, and a testing mechanism;
the test mechanism comprises an impact load transmitting assembly 1, an incident rod 2 and a transmission rod 8 which are sequentially arranged along the axial direction, the impact load transmitting assembly 1 is used for providing impact load for the incident rod 2, the plane of a test sample 5 is installed at one end, facing the transmission rod 8, of the incident rod 2, a first crack extensometer 6 is further arranged on the test sample 5 and used for monitoring the fracture process of cracks on the test sample 5, a first strain gage 3 is arranged on the incident rod 2 and used for measuring incident waves and reflected waves of the test sample 5, a second strain gage 7 is arranged on the transmission rod 8 and used for measuring transmitted waves of the test sample 5, a buffer mechanism 9 is further arranged at the front end of the transmission rod 8, the buffer mechanism 9 is used for fixing the movement distance of the transmission rod 8 and balancing the impact load received by the transmission rod 8.
Thus, when carrying out the test of the I-type dynamic fracture toughness of UHPC, the test sample 5 is placed between the incident rod 2 and the transmission rod 8, the position of the test sample 5 is adjusted, the center of the semicircular groove of the test sample 5 is ensured to be aligned with the incident rod 2 and the transmission rod 8 in the horizontal direction, namely the center lines of the test sample 5, the incident rod 2, the transmission rod 8 and the impact load emission component 1 are adjusted to be on the same horizontal plane, the Hopkinson pressure bar dynamic impact test can be carried out after the parameters are adjusted, then the impact load emission component 1 generates impact load on the incident rod 2, in the specific embodiment, the impact load emission component 1 is a shuttle shell, the impact load forms dynamic compression load applied on the end surfaces at two sides of the test sample 5 through the incident rod 2 and the transmission rod 8, and simultaneously, when the incident rod 2 is impacted by the impact load emission component 1, a half-sine elastic stress wave is generated and is transmitted forwards, the strain signal, namely incident wave epsilon i (t), is measured through the first strain gauge 3, the stress wave continuously propagates forwards to reach the interface of the incident rod 2 and the test sample 5, and because the wave impedances of the incident rod 2 and the test sample 5 are different, part of the elastic stress wave is reflected back to the incident rod 2 and passes through the first strain gauge 3 again, and then the strain signal, namely reflected wave epsilon r (t), is measured; the other part of the elastic stress wave passes through the test sample 5 to cause high-speed deformation of the test sample 5, the elastic stress wave passes through the second strain gauge 7 on the transmission rod 8, a strain signal, namely a transmission wave epsilon t (t), is measured, and the speed of the crack passing through the adhering range of the CPG1 can be calculated by the CPG1 (the first crack propagation meter 6) according to the distance between the grid wires and the voltage change time difference. In the test process, the first strain gauge 3 and the second strain gauge 7 collect real-time strain pulse signals of incident waves, reflected waves and transmitted waves in the test process, and the first crack propagation meter 6 calculates the speed and the acceleration of the crack passing through the first crack propagation meter 6 under different impact loads so as to obtain the relation between the dynamic stress intensity factor and the speed and the acceleration in the crack non-constant number propagation process.
In this embodiment, the end face of the incident rod 2 for mounting the test sample 5 is coated with a lubricant and is padded with a teflon pad 4 having a small thickness, the test sample 5 is mounted on the teflon pad 4, and the lubricant is vaseline in this embodiment.
Therefore, the end face friction effect can be reduced, and meanwhile, the influence of the unevenness of the loading end face of the test sample 5 caused by machining on the experiment can be reduced, so that the successful crack initiation of the test sample 5 is realized.
As shown in fig. 3, in the present embodiment, the first crack growth meter 6(CPG1) is located on the front side of the front crack tip of the test specimen 5 in the crack growth direction, and a plurality of third strain gages 10 are further arranged at intervals on the front side of the first crack growth meter 6 in the crack growth direction, specifically, 3 third strain gages 10 are attached at intervals of 5mm at a position 5mm away from the right loading end face d of the first crack growth meter 6, and a second crack growth meter 11(CPG2) is further provided at a position on the back side of the test specimen 5 corresponding to the crack tip in the crack growth direction.
The invention also provides a method for testing the I-type dynamic fracture toughness of the UHPC, which is characterized in that by adopting the device for testing the I-type dynamic fracture toughness of the UHPC, the impact load emitting assembly 1 generates dynamic impact load P (t) on the incident rod 2, the dynamic impact load P (t) is a function of time, dynamic compression loads are applied to the end faces of two sides of the test sample 5 through the incident rod 2 and the transmission rod 8, the first strain gauge 3 and the second strain gauge 7 collect real-time strain pulse signals of incident waves, reflected waves and transmitted waves in the test process, and the first crack extensometer 6 calculates the speed and the acceleration of the crack passing through the first crack extensometer 6 under different impact loads so as to obtain the relationship between the dynamic stress intensity factor and the speed and the acceleration in the crack unsteady number extension process.
Thus, in the dynamic test, the dynamic load (or pulse) in the test process is accurately recorded by the test measuring instrument, and the dynamic response, such as dynamic strain, characteristic time parameter or crack propagation speed, on the sample is obtained by different test equipment (high-speed camera, CPG, SG and the like); in the numerical calculation: inputting the dynamic load obtained in the test into numerical software, and performing dynamic analysis by using the computing power of the software to obtain mechanical parameters and time histories thereof which are not easy to record in the dynamic test; in theoretical analysis, a time history of DSIF (dynamic stress intensity factor) in a dynamic crack propagation process is obtained by using a universal function; finally, the measurement of the propagation speed of the UHPC dynamic propagation toughness crack can be obtained by combining the characteristic time parameter.
In this embodiment, the method comprises the following steps:
step 1) preparing a test sample 5;
step 2) mounting the test sample 5 at one end of the incident rod 2 facing the transmission rod 8, and enabling the center lines of the test sample 5, the incident rod 2, the transmission rod 8 and the impact load emission assembly 1 to be located on the same horizontal plane;
step 3) adjusting the speed of the impact load transmitting assembly 1 impacting the incident rod 2 to change the impact load of the incident rod 2 on the test sample 5, acquiring real-time strain pulse signals of incident waves, reflected waves and transmitted waves in the test process by the first strain gauge 3 and the second strain gauge 7, and calculating the speed and the acceleration of the crack passing through the first crack extensometer 6 under different impact loads by the first crack extensometer 6;
and 4) calculating by adopting an experiment-numerical value-analytic method to obtain the relation between the dynamic stress intensity factor and the speed and the acceleration in the crack unsteady number expansion process.
In the present embodiment, the first crack growth meter 6 includes a plurality of wires connected in parallel, and the wire closest to the crack abuts against the crack tip of the crack;
in the step 3), when the impact load transmitting assembly 1 impacts the incident rod 2, cracks on the test sample 5 crack, so that the metal wires of the first crack propagation meter 6 are broken and the resistance of the first crack propagation meter 6 is changed, the time for the crack to propagate to the position is determined by monitoring the jump point of the voltage step change monitored by the first crack propagation meter 6, the time difference for the crack to propagate to the two metal wires is calculated, and the crack propagation speed between the two metal wires is calculated according to the distance between the two metal wires.
In the present embodiment, in step 3), the calculation formula of the crack propagation velocity v is:
in the formula, delta l is the distance between two metal wires;
tn+1-tnthe time difference between crack propagation to two wires.
Specifically, as shown in FIG. 4, when the crack propagates to the nth wire of CPG1, causing the wire to break, RC2And the total resistance of the parallel circuit of the CPG1 will change, the resistance of the whole CPG1 parallel circuit will become larger, and the expression is:
in the formula: rCPGIs the resistance of the entire CPG 1; riIs the resistance of the ith wire.
Once the crack is initiated, the wire is broken in turn as the crack propagates, and the total parallel resistance of the CPG1 increases by Δ R. The time when the crack propagates to the position can be determined by monitoring the jump point of the voltage step change, and the time difference delta t when the crack propagates to the two wires can be calculated. Knowing the distance Δ l between the two wires, the crack propagation velocity v between the two wires can be calculated, and the expression is:
v＝Δl/Δt(i＝1，2，3，...，n)
in the formula: v is the average velocity between the ith and (i + 1) th wires; Δ l is the distance between two adjacent wires; delta t is the time difference delta t between crack propagation and two filaments, namely ti + 1-ti; n is the total amount of the metal wires. The velocity time history of crack propagation in the CPG1 detection range can be obtained from the above formula.
And (3) measuring the dynamic strain of the sample:
as shown in fig. 3, in the dynamic experiment, 25 wires were selected from CPG1, and the total parallel resistance R was 1.5 Ω. In order to ensure the accuracy of the crack initiation time, when the CPG1 is pasted, the first metal wire of the CPG1 is close to the crack tip of the crack directlyMeasuring crack initiation time tfAnd then compared to the crack initiation time measured by the second crack growth plate CPG 2. The way and size of the attachment is shown in fig. 3.
In the conventional method, the average velocity v is obtained by CPG1 on the assumption that the crack is initiated and then propagates at a constant velocityaTime to crack initiation tf＝t1-l0/va。
Crack propagation velocity calculation:
in the formula: delta l is the distance between two metal wires, and delta l is 1.67mm when the length is equal to l/24;
tn+1-tnthe time difference between crack propagation to two wires.
In this embodiment, the dynamic stress intensity factor during the unsteady expansion of the crack in step 4)
With velocity v and acceleration
The relationship of (1) is:
in the formula: kI 0The dynamic stress intensity factor when the speed of the test sample 5 is 0 is adopted;
cRis the rayleigh wave velocity of the material;
cdis the expansion wave velocity of the material;
b is a dimensional factor related to the width of the test specimen 5.
Specifically, in order to systematically research the influence of the loading rate on the dynamic fracture toughness, the speed of the shuttle-shaped shell impacting the incident rod 2 is adjusted by controlling the air pressure of the chamber, and the loading rate is controlled in a range of (2.2 ℃.)5.0)×104MPa·m1/2·s-1When driving force KI d(tf) Exceeds UHPC resistance KIC DIn the meantime, cracks initiate.
Specifically, a calculation formula is obtained by combining characteristic time parameters according to a specific size structure of a large semi-cylindrical sample
Calculating the type I dynamic stress intensity factor of UHPC, wherein KI 0[t，a(t)]＝KI d[t，a(t)，v(t)＝o]The dynamic stress intensity factor for a stationary crack tip of the same size, representing the propagating crack size a (t) corresponding to time t, is related only to the applied dynamic load, the specimen configuration and the transient crack size. Time (t)f，tp) Corresponding to a propagation crack size of (a)0，ap)，(a0，ap) The corresponding static crack dynamic stress intensity factor time history is respectively KI 0(t，a0)、KI 0(t，ap) (ii) a K (v) is a universal function value related to the fracture velocity v only,
c is obtained according to the basic parameters of the sample adopted by the experiment and the calculation formula of the wave velocity of the materiald、csAnd cR：
Wherein, cd＝{E(1-μ)/[ρ(1+μ)(1-2μ)]}1/2；
cR＝cS(0.86+1.14u)/(1+μ)；
cs＝[E/2ρ(1+μ)]1/2；
In the formula: c. CsIs the shear wave velocity of the material, cRIs the Rayleigh wave velocity, c, of the materialdIs the expansion wave velocity of the material; ρ is the material density and E isThe elastic modulus of the material, mu, is the poisson's ratio of the material.
For a crack propagating at an unsteady velocity, the finite width of the band causes the crack tip to emit a stress wave that is reflected from the boundary and reacts with the crack tip to alter the crack propagation velocity and create an acceleration, the crack thus having an inertia that increases with increasing crack velocity. The invention then proposes:
in the formula: braces represent the inertia factor or term; subscripts us (unsteady) and s (steady) denote an unsteady and steady state, respectively; g is the energy release rate, i.e. the driving force, of the structure upon crack propagation, which is equal to the material resistance, i.e. the fracture toughness; v is the speed of the rotating shaft of the motor,
acceleration at which the crack propagates at an unsteady velocity; gs is the rate of energy release at steady velocity, and
according to the equivalence of the dynamic energy release rate G and the dynamic stress intensity factor K, the following results are obtained:
Kusis a stress intensity factor in a constant velocity state, KsIs as in the preceding
Finally combining the speed influence factor to obtain the stress intensity factor in the unsteady speed expansion process of the crack
The formula of (a):
in the formula: and KI 0The first term of multiplication is the velocity factor and the second term, shown in braces, is the acceleration factor, representing the inertial effect. And substituting different impact speeds into a dynamic stress intensity factor calculation formula to obtain the UHPC I type dynamic fracture toughness value.
Compared with the prior art, the test method can comprehensively research the I-type dynamic fracture process of the UHPC, and can research the relation between the speed, the acceleration and the dynamic fracture toughness in the crack propagation process. The obtained result is accurate and reliable, and the blank in the research field is filled. Meanwhile, the invention has the advantages of simple operation, strong practicability, accurate cutting and good application prospect. The invention provides a large semi-cylindrical sample based on UHPC (ultra high performance polycarbonate), aims to comprehensively research the I-type dynamic fracture process of UHPC (ultra high performance polycarbonate), focuses on the research on the relation between the speed, the acceleration and the dynamic fracture toughness in the crack propagation process, predicts the fracture path of the sample through numerical calibration analysis, researches the crack speed, the acceleration and the dynamic fracture toughness of the UHPC, and has important significance for analyzing the rapid fracture phenomenon of a brittle material in the dynamic action. The invention designs a UHPC sample with a specific geometric shape by utilizing the dynamic loading principle of a Hopkinson pressure bar device, and provides a test method and a test formula for testing the UHPC I type dynamic fracture toughness by focusing on the research on the relation between the speed, the acceleration and the dynamic fracture toughness in the crack propagation process. The method can accurately measure the important parameter of the dynamic fracture toughness of the UHPC, and has important reference value for the UHPC engineering property.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the technical solutions, and those skilled in the art should understand that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all that should be covered by the claims of the present invention.
Claims (10)
1. The test sample for the I-type dynamic fracture toughness of the UHPC is characterized in that the whole test sample is hemispherical, a semicircular groove extending towards the inside of the test sample is arranged on the end face of the test sample, the circle center of the semicircular groove and the circle center of the hemispherical shape of the test sample are positioned on the same horizontal line, a crack is further arranged at the bottom of the semicircular groove, and the crack extends towards the direction of the circle center of the hemispherical shape of the test sample along the axial direction.
2. A UHPC test apparatus for type I dynamic fracture toughness comprising the test specimen of claim 1 and a test mechanism;
the test mechanism includes along impact load emission subassembly, incident pole and the transmission pole that the axial set gradually, impact load emission subassembly be used for to the incident pole provides impact load, the plane of test sample install in the incident pole orientation the one end of transmission pole still be equipped with first crack extensometer on the test sample, in order to be used for the monitoring the fracture process of crackle on the test sample be equipped with first foil gage on the incident pole, in order to be used for measuring incident wave and the back wave of test sample department be equipped with the second foil gage on the transmission pole, in order to be used for measuring the transmission wave of test sample department.
3. The apparatus for testing type I dynamic fracture toughness of UHPC of claim 1, wherein said entrance rod is provided with a teflon spacer on an end surface for mounting said test specimen, said test specimen being mounted on said teflon spacer.
4. The apparatus for testing type I dynamic fracture toughness of UHPC according to claim 1, wherein said first crack propagation meter is located at the front side of the front crack tip of said test specimen along the crack propagation direction, and a plurality of third strain gages are further arranged at intervals at the front side of said first crack propagation meter along the crack propagation direction, and a second crack propagation meter is further arranged at the position of the back side of said test specimen corresponding to the crack tip along the crack propagation direction.
5. A method for testing the type I dynamic fracture toughness of the UHPC is characterized in that the device for testing the type I dynamic fracture toughness of the UHPC is adopted, the impact load emitting assembly generates impact load on the incident rod, dynamic compression load is applied to the two side end faces of the test sample through the incident rod and the transmission rod, the first strain gauge and the second strain gauge collect real-time strain pulse signals of incident waves, reflected waves and transmitted waves in the test process, and the first crack propagation meter calculates the speed and the acceleration of a crack passing through the first crack propagation meter under different impact loads so as to obtain the relation between the dynamic stress intensity factor and the speed and the acceleration in the crack unsteady number propagation process.
6. The method of testing type I dynamic fracture toughness of UHPC according to claim 5, characterized in that it comprises the following steps:
step 1) preparing the test sample;
step 2) mounting the test sample at one end of the incident rod facing the transmission rod, and enabling central lines of the test sample, the incident rod, the transmission rod and the impact load emission assembly to be located on the same horizontal plane;
step 3) adjusting the speed of the impact load transmitting assembly impacting the incident rod to change the impact load of the incident rod on the test sample, wherein the first strain gauge and the second strain gauge collect real-time strain pulse signals of incident waves, reflected waves and transmitted waves in the test process, and the first crack expansion meter calculates the speed and the acceleration of the crack passing through the first crack expansion meter under different impact loads;
and 4) calculating by adopting an experiment-numerical value-analytic method to obtain the relation between the dynamic stress intensity factor and the speed and the acceleration in the crack unsteady number expansion process.
7. The method for testing type I dynamic fracture toughness of UHPC according to claim 6, characterized in that the dynamic stress intensity factor during the unsteady expansion of cracks in step 4)
With velocity v and acceleration
The relationship of (1) is:
in the formula: k isI 0The dynamic stress intensity factor is the dynamic stress intensity factor when the test sample speed is 0;
cRis the rayleigh wave velocity of the material;
cdis the expansion wave velocity of the material;
b is a dimensional factor related to the width of the test specimen.
8. The method of testing the type I dynamic fracture toughness of a UHPC of claim 7 wherein the first crack propagation meter comprises a plurality of wires connected in parallel and the wire closest to the crack abuts the crack tip of the crack;
in step 3), when the impact load transmitting assembly impacts the incident rod, cracks on the test sample crack, so that the metal wires of the first crack propagation meter are broken and the resistance of the first crack propagation meter changes, the time for the crack to propagate to the position is determined by monitoring the jump point of the voltage step change monitored by the first crack propagation meter, the time difference between the crack to propagate to the two metal wires is calculated, and the crack propagation speed between the two metal wires is calculated according to the distance between the two metal wires.
9. The method for testing type I dynamic fracture toughness of UHPC according to claim 8, wherein in step 3), the crack propagation velocity v is calculated by the formula:
in the formula, delta l is the distance between two metal wires;
tn+1-tnthe time difference between crack propagation to two wires.
10. The method for testing type I dynamic fracture toughness of UHPC according to claim 7, wherein in step 4), the Rayleigh wave velocity c of the materialRThe calculation formula of (2) is as follows:
cR＝cS(0.86+1.14μ)/(1+μ)；
cS＝[E/2ρ(1+μ)]1/2；
expansion wave velocity c of materialdThe calculation formula of (2) is as follows:
cd＝{E(1-μ)/[ρ(1+μ)(1-2μ)]}1/2；
in the formula: rho is the material density;
e is the elastic modulus of the material;
μ is the Poisson's ratio of the material.
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