CN113959328B - In-situ measurement method for internal strain of flexible foam - Google Patents
In-situ measurement method for internal strain of flexible foam Download PDFInfo
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- CN113959328B CN113959328B CN202111254557.4A CN202111254557A CN113959328B CN 113959328 B CN113959328 B CN 113959328B CN 202111254557 A CN202111254557 A CN 202111254557A CN 113959328 B CN113959328 B CN 113959328B
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/16—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge
- G01B7/18—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge using change in resistance
Abstract
An in-situ measurement method for internal strain of flexible foam comprises the steps that the flexible foam is of a regular porous structure, the internal strain of the flexible foam is measured by an in-situ strain sensor, the in-situ strain sensor is an elastic sensing material doped with reduced graphene oxide, the in-situ strain sensor is directly embedded into one or more positions to be measured in the foam structure through an in-situ direct writing process, and the in-situ measurement method is used for measuring tensile strain and compressive strain of the specified position of the foam structure; the flexible foam and the in-situ strain sensor are integrally formed by fully utilizing the designability of a three-dimensional direct writing process to a forming structure and material components, so that the accurate in-situ embedding of the miniature sensor and the accurate strain parameter measurement of any position in the flexible foam material are realized, the internal mechanical response parameters of the flexible material can be directly measured, the integrity of the foam structure is ensured, and the blank in the field of foam material internal mechanical behavior detection is filled.
Description
Technical Field
The invention relates to the technical field of in-situ measurement, in particular to an in-situ measurement method for internal strain of flexible foam.
Background
Due to its excellent flexibility, high-energy impact resistance, stress isolation, and sound and heat insulation properties, flexible foams are often used as sealing and shock absorbing materials, and are widely used in the fields of biomedical, automotive electronics, weaponry, aerospace, and the like. The research on the mechanical behavior of the internal microscopic pore structure of the flexible foam has important significance for real-time working condition monitoring, damage process analysis, material failure mechanism research and optimal design of the pore structure. For strain measurements at a given location inside a structure, the most straightforward, efficient and cost-effective method is to embed a high-precision sensor in situ. Different from the traditional solid material, the force transmission path of the elastic porous material is more complex, and the strain transmission is mainly carried out through the flexible pore wall on the microscopic scale, however, how to measure the internal strain of the flexible foam in situ is a problem to be solved urgently.
Disclosure of Invention
The applicant provides an in-situ measurement method for internal strain of flexible foam aiming at the defects in the prior art, so that the flexible foam and an in-situ sensor are integrally and precisely manufactured by means of an in-situ direct writing process, and accurate measurement of the in-situ strain of a specified position in the flexible foam is realized.
The technical scheme adopted by the invention is as follows:
an in-situ measurement method for internal strain of flexible foam comprises the steps that the flexible foam is of a regular porous structure, the internal strain of the flexible foam is measured by an in-situ strain sensor, the in-situ strain sensor is an elastic sensing material doped with reduced graphene oxide, the in-situ strain sensor is directly embedded into one or more positions to be measured in the foam structure through an in-situ direct writing process, and the in-situ measurement method is used for measuring tensile strain and compressive strain of the specified position of the foam structure;
the specific operation steps are as follows:
the first step is as follows: preparing a flat plate of polytetrafluoroethylene;
the second step: completely soaking the dust-free paper in HPLC acetone, taking out, wiping a polytetrafluoroethylene flat plate to remove impurities on the surface of the flat plate, and evaporating the acetone for 15min at normal temperature to take the treated polytetrafluoroethylene flat plate as a manufacturing substrate;
the third step: fully mixing the flexible polymer and the vulcanizing agent and removing bubbles by a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare flexible slurry;
the fourth step: mixing graphene oxide powder, a flexible polymer and ethyl acetate in a proportion of 1:49:150 by mass ratio, and fully mixing by mechanical stirring;
the fifth step: adding hydroiodic acid into the mixture obtained in the fourth step, wherein the mass ratio of hydroiodic acid to graphene oxide is 10:1, heating the mixture to 90 ℃ while stirring for 12 hours;
and a sixth step: adding a vulcanizing agent after the mixture obtained in the fifth step is cooled to room temperature, fully mixing the vulcanizing agent and removing bubbles through a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare elastic sensing slurry;
the seventh step: respectively filling the flexible slurry and the elastic sensing slurry into corresponding screw valves;
eighth step: installing a printing nozzle on the two screw valves;
the ninth step: setting a printing path plan according to a flexible foam structure to be manufactured and an in-situ strain measurement position;
the tenth step: setting the voltage of a screw valve corresponding to the flexible slurry to be 4V, the corresponding rotating speed to be 50rpm, the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, printing the flexible slurry on a polytetrafluoroethylene flat plate to form a flexible foam structure, and stopping printing after the flexible slurry is operated to a strain measurement position;
the eleventh step: switching to a screw valve corresponding to the elastic sensing slurry, setting the voltage of the screw valve to be 4V, setting the corresponding rotating speed to be 50rpm, setting the feeding air pressure of the screw valve to be 500kPa, setting the moving speed of a printing nozzle to be 10mm/s, and printing the elastic sensing slurry at a specified strain measurement position;
a twelfth step: switching to a screw valve corresponding to the flexible slurry, setting the voltage of the screw valve to be 4V, setting the corresponding rotating speed to be 50rpm, setting the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, and continuously printing the flexible foam structure until the next strain measurement position;
and a thirteenth step of: repeating the eleventh step and the twelfth step until the flexible foam structure is manufactured;
a fourteenth step of: heating the finished flexible foam structure to 180 ℃ and holding for 24 hours until fully cured;
the fifteenth step: separating the cured flexible foam structure from the polytetrafluoroethylene slab;
sixteenth, step: connecting the positive pole and the negative pole of the resistance tester with the two ends of the in-situ strain sensor, recording the resistance value, and calibrating the zero point of the in-situ strain sensor;
seventeenth step: obtaining a corresponding relation between the resistance and the strain of the in-situ strain sensor according to the zero resistance and the strain coefficient of the in-situ strain sensor;
eighteenth step: applying an external force to the flexible foam, and measuring the resistance change of the in-situ strain sensor through a resistance tester;
the nineteenth step: and obtaining a corresponding in-situ strain value according to the measured resistance value of the in-situ strain sensor and by combining the corresponding relation between the resistance and the strain of the in-situ strain sensor.
The further technical scheme is as follows:
in the first step, the flatness of the plate was 0.01mm and the surface roughness was Ra0.2.
In the first step, the polytetrafluoroethylene flat plate is a flat plate made of pure polytetrafluoroethylene or a metal flat plate with a polytetrafluoroethylene coating on the surface.
In the third step and the fourth step, the flexible polymer is one or more of thermosetting flexible polymers, including silicon rubber, butadiene-acrylonitrile rubber, butadiene rubber and chloroprene rubber.
In the eighth step, the inner diameter of the printing nozzle is 100 and 600 μm.
In the ninth step, the flexible foam structure is a regular porous structure.
And in the ninth step, the flexible foam structure adopts a grid-shaped hole structure, a triangular hole structure or a honeycomb-shaped hole structure.
And sixthly, directly connecting the positive and negative poles of the resistance tester with the two ends of the in-situ strain sensor by using conductive clips.
And sixthly, connecting the positive and negative poles of the resistance tester with the two ends of the in-situ strain sensor through conductive adhesive.
In the nineteenth step, the strain measurement range of the in-situ strain sensor is-70% -150%.
The invention has the following beneficial effects:
the flexible foam and in-situ strain sensor integrated forming device is compact and reasonable in structure and convenient to operate, the designability of a three-dimensional direct writing process to a forming structure and material components is fully utilized, the flexible foam and the in-situ strain sensor are integrally formed, the accurate in-situ embedding of the micro sensor and the accurate strain parameter measurement of any position inside the flexible foam material are realized, the internal mechanical response parameters of the flexible material can be directly measured, the integrity of the foam structure is ensured, the blank of the field of the detection of the internal mechanical behavior of the foam material is filled, and important theoretical basis and technical support are provided for the manufacturing of the intelligent porous material and the research of the mechanical behavior of the microscopic structure.
Drawings
FIG. 1 is a process diagram of a manufacturing method of embedding a single in-situ strain sensor in the cell wall of a third layer (eight layers in total) of honeycomb-shaped flexible foam and a corresponding in-situ strain measurement method.
FIG. 2 is a graph showing the in situ strain measurements (tensile strain) of the present invention on the cell walls of the third (total eight) layer of honeycomb-shaped flexible foam.
FIG. 3 is a graph of the in situ strain measurements (compressive strain) of the present invention on the cell walls of a third (total of eight) layer of honeycomb flexible foam.
FIG. 4 is a process diagram of a manufacturing method of embedding a single in-situ strain sensor in the hole wall of the third layer (eight layers in total) of triangular flexible foam and a corresponding in-situ strain measurement method according to the present invention.
FIG. 5 is a graph of the in situ strain measurements (tensile strain) of the triangular flexible foam third layer (eight layers total) cell walls according to the present invention.
FIG. 6 is a graph of the in situ strain measurements (tensile strain) of the triangular flexible foam third layer (eight layers total) cell walls according to the present invention.
FIG. 7 is a process diagram of the manufacturing method of embedding a single in-situ strain sensor in the hole wall of the second layer (eight layers in total) of the grid-shaped flexible foam and the corresponding in-situ strain measurement method according to the present invention.
FIG. 8 is a graph of in situ strain measurements (tensile strain) of the cell walls of a third (eight total) layer of reticulated flexible foam according to the present invention.
FIG. 9 is a graph of in situ strain measurements (compressive strain) of the cell walls of a third (eight total) layer of reticulated flexible foam according to the present invention.
Fig. 10 is a process diagram of the manufacturing method of embedding two staggered in-situ strain sensors in the second and third (eight layers in total) hole walls of the grid-shaped flexible foam and the corresponding in-situ strain measurement method according to the present invention.
FIG. 11 is a graph of in situ strain measurements (tensile strain) of the present invention on the cell walls of the second, third (eight total) layers of a reticulated flexible foam.
FIG. 12 is a graph of in situ strain measurements (compressive strain) for the second, third (eight total) cell walls of a reticulated flexible foam of the present invention.
FIG. 13 is a graph showing the relationship between the rate of change of resistance and the tensile strain of the in-situ strain sensor according to the present invention.
FIG. 14 is a graph showing the relationship between the rate of change of resistance and the compressive strain of the in situ strain sensor of the present invention.
Detailed Description
The following description of the embodiments of the present invention refers to the accompanying drawings.
As shown in fig. 1 to 14, the in-situ measurement method for internal strain of a flexible foam of the present embodiment includes a flexible foam, where the flexible foam has a regular porous structure, the internal strain of the flexible foam is measured by an in-situ strain sensor, the in-situ strain sensor is an elastic sensing material doped with reduced graphene oxide, the in-situ strain sensor is directly embedded into one or more positions to be measured in the foam structure through an in-situ direct writing process, and the in-situ measurement method measures tensile and compressive strains at specified positions of the foam structure;
the specific operation steps are as follows:
the first step is as follows: preparing a flat plate of polytetrafluoroethylene;
the second step is that: completely soaking the dust-free paper in HPLC acetone, taking out, wiping a polytetrafluoroethylene flat plate to remove impurities on the surface of the flat plate, and evaporating the acetone for 15min at normal temperature to take the treated polytetrafluoroethylene flat plate as a manufacturing substrate;
the third step: fully mixing the flexible polymer and the vulcanizing agent and removing bubbles by a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare flexible slurry;
the fourth step: mixing graphene oxide powder, a flexible polymer and ethyl acetate in a proportion of 1:49:150 by mass ratio by mechanical stirring;
the fifth step: adding hydriodic acid into the mixture obtained in the fourth step, wherein the mass ratio of hydriodic acid to graphene oxide is 10:1, heating the mixture to 90 ℃ while stirring for 12 hours;
and a sixth step: adding a vulcanizing agent after the mixture obtained in the fifth step is cooled to room temperature, fully mixing the vulcanizing agent and removing bubbles through a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare elastic sensing slurry;
the seventh step: respectively filling the flexible slurry and the elastic sensing slurry into corresponding screw valves;
eighth step: installing a printing nozzle on the two screw valves;
the ninth step: setting a printing path plan according to a flexible foam structure to be manufactured and an in-situ strain measurement position;
the tenth step: setting the voltage of a screw valve corresponding to the flexible slurry to be 4V, the corresponding rotating speed to be 50rpm, the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, printing the flexible slurry on a polytetrafluoroethylene flat plate to form a flexible foam structure, and stopping printing after the flexible slurry is operated to a strain measurement position;
the eleventh step: switching to a screw valve corresponding to the elastic sensing slurry, setting the voltage of the screw valve to be 4V, setting the corresponding rotating speed to be 50rpm, setting the feeding air pressure of the screw valve to be 500kPa, setting the moving speed of a printing nozzle to be 10mm/s, and printing the elastic sensing slurry at a specified strain measurement position;
a twelfth step: switching to a screw valve corresponding to the flexible slurry, setting the voltage of the screw valve to be 4V, setting the corresponding rotating speed to be 50rpm, setting the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, and continuously printing the flexible foam structure until the next strain measurement position;
the thirteenth step: repeating the eleventh step and the twelfth step until the flexible foam structure is manufactured;
the fourteenth step is that: heating the finished flexible foam structure to 180 ℃ and holding for 24 hours until fully cured;
the fifteenth step: separating the cured flexible foam structure from the polytetrafluoroethylene slab;
sixteenth step: connecting the positive pole and the negative pole of the resistance tester with the two ends of the in-situ strain sensor, recording the resistance value, and calibrating the zero point of the in-situ strain sensor;
seventeenth step: obtaining a corresponding relation between the resistance and the strain of the in-situ strain sensor according to the zero resistance and the strain coefficient of the in-situ strain sensor;
eighteenth step: applying an external force to the flexible foam, and measuring the resistance change of the in-situ strain sensor through a resistance tester;
the nineteenth step: and obtaining a corresponding in-situ strain value according to the measured resistance value of the in-situ strain sensor and the corresponding relation between the resistance and the strain of the in-situ strain sensor.
In the first step, the flatness of the plate was 0.01mm and the surface roughness was Ra0.2.
In the first step, the polytetrafluoroethylene flat plate is a flat plate made of pure polytetrafluoroethylene or a metal flat plate with a polytetrafluoroethylene coating on the surface.
In the third step and the fourth step, the flexible polymer is one or more of thermosetting flexible polymers, including silicone rubber, nitrile rubber, butadiene rubber, and chloroprene rubber.
In the eighth step, the inner diameter of the printing nozzle is 100-600 μm.
In the ninth step, the flexible foam structure is a regular porous structure.
And in the ninth step, the flexible foam structure adopts a grid-shaped hole structure, a triangular hole structure or a honeycomb-shaped hole structure.
And sixteenth step, the positive and negative poles of the resistance tester can be directly connected with the two ends of the in-situ strain sensor by conductive clamps.
And sixthly, connecting the positive pole and the negative pole of the resistance tester with the two ends of the in-situ strain sensor through conductive adhesive.
In the nineteenth step, the strain measurement range of the in-situ strain sensor is-70% -150%.
The first embodiment is as follows:
preparing a polytetrafluoroethylene flat plate, wherein the flatness of the flat plate is 0.01mm, and the surface roughness is Ra0.2;
completely soaking the dust-free paper in HPLC acetone, taking out the dust-free paper, wiping a polytetrafluoroethylene flat plate to remove impurities on the surface of the flat plate, and evaporating the acetone for 15min at normal temperature to take the treated polytetrafluoroethylene flat plate as a manufacturing substrate;
thirdly, fully mixing polysiloxane and vulcanizing agent according to the mass ratio of 10:1 and removing bubbles by a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare flexible slurry;
(IV) fully mixing the graphene oxide powder, polysiloxane and ethyl acetate in a mass ratio of 1:49:150 by mechanical stirring;
fifthly, adding hydriodic acid into the mixture, wherein the mass ratio of the hydriodic acid to the graphene oxide is 10:1, and heating the mixture to 90 ℃ while stirring for 12 hours;
sixthly, after the mixture is cooled to room temperature, adding a vulcanizing agent (the mass ratio of the vulcanizing agent to polysiloxane in the mixture is 1:10), fully mixing the vulcanizing agent and removing bubbles through a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare elastic sensing slurry;
respectively filling the flexible slurry and the elastic sensing slurry into corresponding screw valves;
(eight) installing a printing spray head on the two screw valves, wherein the inner diameter of the spray head is 100 mu m;
(ninthly) setting the voltage of a screw valve corresponding to the flexible slurry to be 4V (corresponding to the rotating speed of 50rpm), the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, printing the first layer and the second layer of the honeycomb-shaped flexible foam structure on the polytetrafluoroethylene flat plate by the flexible slurry, and stopping printing after the flexible slurry is operated to a strain measurement position when the third layer is printed;
(ten) switching to a screw valve corresponding to the elastic sensing slurry, setting the voltage of the screw valve to be 4V (corresponding to the rotating speed of 50rpm), setting the feeding air pressure of the screw valve to be 500kPa, setting the moving speed of a printing spray head to be 10mm/s, and printing the elastic sensing slurry at a specified strain measurement position;
switching to a screw valve corresponding to the flexible slurry, setting the voltage of the screw valve to be 4V (corresponding to the rotating speed of 50rpm), setting the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, and continuously printing third to eighth layers of the triangular flexible foam structure;
(twelfth) heating the completed flexible foam structure to 180 ℃ and holding for 24 hours until fully cured;
(thirteen) separating the cured flexible foam structure from the polytetrafluoroethylene slab;
connecting the positive and negative poles of the resistance tester with the two ends of the in-situ strain sensor through the conductive clamp, recording the resistance value, and calibrating the zero point of the in-situ strain sensor;
(fifteen) according to the zero point resistance and the strain coefficient of the in-situ strain sensor, obtaining the corresponding relation between the resistance and the strain of the in-situ strain sensor (figures 13 and 14);
(sixthly) applying an external force to the flexible foam, and measuring the resistance change of the in-situ strain sensor through a resistance tester;
seventhly, according to the measured resistance value of the in-situ strain sensor and the corresponding relation between the resistance and the strain of the in-situ strain sensor, a corresponding in-situ strain value is obtained, and the measurement result is shown in fig. 2.
The second embodiment:
preparing a polytetrafluoroethylene flat plate, wherein the flatness of the flat plate is 0.01mm, and the surface roughness is Ra0.2;
completely soaking the dust-free paper in HPLC acetone, taking out the dust-free paper, wiping a polytetrafluoroethylene flat plate to remove impurities on the surface of the flat plate, and evaporating the acetone for 15min at normal temperature to take the treated polytetrafluoroethylene flat plate as a manufacturing substrate;
thirdly, fully mixing polysiloxane and vulcanizing agent according to the mass ratio of 10:1 and removing bubbles by a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare flexible slurry;
(IV) fully mixing graphene oxide powder, polysiloxane and ethyl acetate in a mass ratio of 1:49:150 by mechanical stirring;
fifthly, adding hydriodic acid into the mixture, wherein the mass ratio of the hydriodic acid to the graphene oxide is 10:1, and heating the mixture to 90 ℃ while stirring for 12 hours;
sixthly, after the mixture is cooled to room temperature, adding a vulcanizing agent (the mass ratio of the vulcanizing agent to polysiloxane in the mixture is 1:10), fully mixing the vulcanizing agent and removing bubbles through a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare elastic sensing slurry;
respectively filling the flexible slurry and the elastic sensing slurry into corresponding screw valves;
(eight) installing a printing nozzle on the two screw valves, wherein the inner diameter of the nozzle is 200 mu m;
(ninthly) setting the voltage of a screw valve corresponding to the flexible slurry to be 4V (corresponding to the rotating speed of 50rpm), the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, printing the first layer and the second layer of the triangular flexible foam structure on a polytetrafluoroethylene flat plate by the flexible slurry, and stopping printing after the flexible slurry is operated to a strain measurement position when the third layer is printed;
(ten) switching to a screw valve corresponding to the elastic sensing slurry, setting the voltage of the screw valve to be 4V (corresponding to the rotating speed of 50rpm), setting the feeding air pressure of the screw valve to be 500kPa, setting the moving speed of a printing spray head to be 10mm/s, and printing the elastic sensing slurry at a specified strain measurement position;
switching to a screw valve corresponding to the flexible slurry, setting the voltage of the screw valve to be 4V (corresponding to the rotating speed of 50rpm), setting the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, and continuously printing third to eighth layers of the triangular flexible foam structure;
(twelfth) heating the completed flexible foam structure to 180 ℃ and holding for 24 hours until fully cured;
(thirteen) separating the cured flexible foam structure from the polytetrafluoroethylene slab;
connecting the positive and negative poles of the resistance tester with the two ends of the in-situ strain sensor through the conductive clamp, recording the resistance value, and calibrating the zero point of the in-situ strain sensor;
fifteenth, obtaining a corresponding relation between the resistance and the strain of the in-situ strain sensor according to the zero point resistance and the strain coefficient of the in-situ strain sensor (figures 13 and 14);
(sixthly) applying an external force to the flexible foam, and measuring the resistance change of the in-situ strain sensor through a resistance tester;
seventhly, according to the measured resistance value of the in-situ strain sensor and by combining the corresponding relation between the resistance and the strain of the in-situ strain sensor, a corresponding in-situ strain value is obtained, and the measurement result is shown in fig. 5 and 6.
Example three:
preparing a polytetrafluoroethylene flat plate, wherein the flatness of the flat plate is 0.01mm, and the surface roughness is Ra0.2;
completely soaking the dust-free paper in HPLC acetone, taking out the dust-free paper, wiping a polytetrafluoroethylene flat plate to remove impurities on the surface of the flat plate, and evaporating the acetone for 15min at normal temperature to take the treated polytetrafluoroethylene flat plate as a manufacturing substrate;
thirdly, fully mixing polysiloxane and vulcanizing agent according to the mass ratio of 10:1 and removing bubbles by a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare flexible slurry;
(IV) fully mixing graphene oxide powder, polysiloxane and ethyl acetate in a mass ratio of 1:49:150 by mechanical stirring;
fifthly, adding hydroiodic acid into the mixture, wherein the mass ratio of the hydroiodic acid to the graphene oxide is 10:1, and heating the mixture to 90 ℃ while stirring for 12 hours;
sixthly, after the mixture is cooled to room temperature, adding a vulcanizing agent (the mass ratio of the vulcanizing agent to polysiloxane in the mixture is 1:10), fully mixing the vulcanizing agent and removing bubbles through a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare elastic sensing slurry;
respectively filling the flexible slurry and the elastic sensing slurry into corresponding screw valves;
(eight) installing a printing spray head on the two screw valves, wherein the inner diameter of the spray head is 600 mu m;
(ninth), setting the voltage of a screw valve corresponding to the flexible slurry to be 4V (corresponding to the rotating speed of 50rpm), the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, printing the first layer and the second layer of the grid-shaped flexible foam structure on a polytetrafluoroethylene flat plate by the flexible slurry, and stopping printing after the flexible slurry is operated to a strain measurement position when the third layer is printed;
(ten) switching to a screw valve corresponding to the elastic sensing slurry, setting the voltage of the screw valve to be 4V (corresponding to the rotating speed of 50rpm), setting the feeding air pressure of the screw valve to be 500kPa, setting the moving speed of a printing spray head to be 10mm/s, and printing the elastic sensing slurry at a specified strain measurement position;
switching to a screw valve corresponding to the flexible slurry, setting the voltage of the screw valve to be 4V (corresponding to the rotating speed of 50rpm), setting the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, and continuously printing third to eighth layers of the grid-shaped flexible foam structure;
(twelfth) heating the completed flexible foam structure to 180 ℃ and holding for 24 hours until fully cured;
(thirteen) separating the cured flexible foam structure from the polytetrafluoroethylene slab;
connecting the positive and negative poles of the resistance tester with the two ends of the in-situ strain sensor through the conductive clamp, recording the resistance value, and calibrating the zero point of the in-situ strain sensor;
fifteenth, obtaining a corresponding relation between the resistance and the strain of the in-situ strain sensor according to the zero point resistance and the strain coefficient of the in-situ strain sensor (figures 13 and 14);
(sixthly) applying an external force to the flexible foam, and measuring the resistance change of the in-situ strain sensor through a resistance tester;
seventhly, according to the measured resistance value of the in-situ strain sensor and by combining the corresponding relation between the resistance and the strain of the in-situ strain sensor, a corresponding in-situ strain value is obtained, and the measurement result is shown in fig. 8 and fig. 9.
Example four:
preparing a polytetrafluoroethylene flat plate, wherein the flatness of the flat plate is 0.01mm, and the surface roughness is Ra0.2;
completely soaking the dust-free paper in HPLC acetone, taking out the dust-free paper, wiping a polytetrafluoroethylene flat plate to remove impurities on the surface of the flat plate, and evaporating the acetone for 15min at normal temperature to take the treated polytetrafluoroethylene flat plate as a manufacturing substrate;
thirdly, fully mixing polysiloxane and vulcanizing agent according to the mass ratio of 10:1 and removing bubbles by a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare flexible slurry;
(IV) fully mixing the graphene oxide powder, polysiloxane and ethyl acetate in a mass ratio of 1:49:150 by mechanical stirring;
fifthly, adding hydriodic acid into the mixture, wherein the mass ratio of the hydriodic acid to the graphene oxide is 10:1, and heating the mixture to 90 ℃ while stirring for 12 hours;
sixthly, after the mixture is cooled to room temperature, adding a vulcanizing agent (the mass ratio of the vulcanizing agent to polysiloxane in the mixture is 1:10), fully mixing the vulcanizing agent and removing bubbles through a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare elastic sensing slurry;
respectively filling the flexible slurry and the elastic sensing slurry into corresponding screw valves;
(eight) installing a printing spray head on the two screw valves, wherein the inner diameter of the spray head is 400 mu m;
(ninth), setting the voltage of a screw valve corresponding to the flexible slurry to be 4V (corresponding to the rotating speed of 50rpm), the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, printing the first layer of the grid-shaped flexible foam structure on a polytetrafluoroethylene flat plate by the flexible slurry, and stopping printing after the first layer is moved to a strain measurement position when the second layer is printed;
(ten) switching to a screw valve corresponding to the elastic sensing slurry, setting the voltage of the screw valve to be 4V (corresponding to the rotating speed of 50rpm), setting the feeding air pressure of the screw valve to be 500kPa, setting the moving speed of a printing spray head to be 10mm/s, and printing the first piece of elastic sensing slurry at a specified strain measurement position;
switching to a screw valve corresponding to the flexible slurry, setting the voltage of the screw valve to be 4V (corresponding to the rotating speed of 50rpm), setting the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, continuously printing the second layer and the third layer of the triangular flexible foam structure, and stopping printing after the third layer is printed and is operated to a strain measurement position;
(twelfth) switching to a screw valve corresponding to the elastic sensing paste, setting the voltage of the screw valve to be 4V (corresponding to the rotating speed of 50rpm), setting the feeding air pressure of the screw valve to be 500kPa, setting the moving speed of a printing nozzle to be 10mm/s, and printing a second elastic sensing paste at a specified strain measurement position;
(thirteen) switching to a screw valve corresponding to the flexible slurry, setting the voltage of the screw valve to be 4V (corresponding to the rotating speed of 50rpm), setting the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, and continuously printing third to eighth layers of the triangular flexible foam structure;
(fourteen) heating the completed flexible foam structure to 180 ℃ and holding for 24 hours until fully cured;
(fifteen) separating the vulcanized flexible foam structure from the teflon plate;
sixthly, connecting the positive pole and the negative pole of the resistance tester with two ends of the two in-situ strain sensors through the conductive clamp respectively, recording the resistance value, and calibrating the zero point of the in-situ strain sensors;
seventhly, obtaining a corresponding relation between the resistance and the strain of the in-situ strain sensor according to the zero resistance and the strain coefficient of the in-situ strain sensor (figures 13 and 14);
(eighteen) applying an external force to the flexible foam, and measuring the resistance change of the two in-situ strain sensors by using a resistance tester;
(nineteenth) according to the measured resistance value of the in-situ strain sensor, and by combining the corresponding relationship between the resistance and the strain of the in-situ strain sensor, a corresponding in-situ strain value is obtained, and the measurement results are shown in fig. 11 and 12.
The above description is intended to be illustrative, and not restrictive, the scope of the invention being indicated by the claims, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (9)
1. An in-situ measurement method for internal strain of flexible foam is characterized by comprising the following steps: the in-situ strain sensor is directly embedded into one or more positions to be measured in the foam structure through an in-situ direct writing process, and the in-situ measurement method is used for measuring the tensile strain and the compressive strain of the specified position of the foam structure;
the specific operation steps are as follows:
the first step is as follows: preparing a flat plate of polytetrafluoroethylene;
the second step: completely soaking the dust-free paper in HPLC acetone, taking out, wiping a polytetrafluoroethylene flat plate to remove impurities on the surface of the flat plate, and evaporating the acetone for 15min at normal temperature to take the treated polytetrafluoroethylene flat plate as a manufacturing substrate;
the third step: fully mixing the flexible polymer and the vulcanizing agent and removing bubbles to prepare flexible slurry by a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa;
the fourth step: fully mixing graphene oxide powder, flexible polymer and ethyl acetate in a mass ratio of 1:49:150 by mechanical stirring;
the fifth step: adding hydroiodic acid into the mixture obtained in the fourth step, wherein the mass ratio of the hydroiodic acid to the graphene oxide is 10:1, and heating the mixture to 90 ℃ while stirring for 12 hours;
and a sixth step: adding a vulcanizing agent after the mixture obtained in the fifth step is cooled to room temperature, fully mixing the vulcanizing agent and removing bubbles through a vacuum planetary mixer at the rotating speed of 2500rpm and the vacuum degree of-99.5 kPa to prepare elastic sensing slurry;
the seventh step: respectively filling the flexible slurry and the elastic sensing slurry into corresponding screw valves;
eighth step: installing a printing nozzle on the two screw valves;
the ninth step: setting a printing path plan according to a flexible foam structure to be manufactured and an in-situ strain measurement position;
the tenth step: setting the voltage of a screw valve corresponding to the flexible slurry to be 4V, the corresponding rotating speed to be 50rpm, the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, printing the flexible slurry on a polytetrafluoroethylene flat plate to form a flexible foam structure, and stopping printing after the flexible slurry is operated to a strain measurement position;
the eleventh step: switching to a screw valve corresponding to the elastic sensing slurry, setting the voltage of the screw valve to be 4V, setting the corresponding rotating speed to be 50rpm, setting the feeding air pressure of the screw valve to be 500kPa, setting the moving speed of a printing nozzle to be 10mm/s, and printing the elastic sensing slurry at a specified strain measurement position;
a twelfth step: switching to a screw valve corresponding to the flexible slurry, setting the voltage of the screw valve to be 4V, setting the corresponding rotating speed to be 50rpm, setting the feeding air pressure of the screw valve to be 350kPa, setting the moving speed of a printing nozzle to be 10mm/s, and continuously printing the flexible foam structure until the next strain measurement position;
and a thirteenth step of: repeating the eleventh step and the twelfth step until the flexible foam structure is manufactured;
the fourteenth step is that: heating the finished flexible foam structure to 180 ℃ and holding for 24 hours until fully cured;
the fifteenth step: separating the cured flexible foam structure from the polytetrafluoroethylene slab;
sixteenth, step: connecting the positive pole and the negative pole of the resistance tester with two ends of the in-situ strain sensor, recording the resistance value, and calibrating the zero point of the in-situ strain sensor;
seventeenth step: obtaining a corresponding relation between the resistance and the strain of the in-situ strain sensor according to the zero resistance and the strain coefficient of the in-situ strain sensor;
and eighteenth step: applying an external force to the flexible foam, and measuring the resistance change of the in-situ strain sensor through a resistance tester;
the nineteenth step: and obtaining a corresponding in-situ strain value according to the measured resistance value of the in-situ strain sensor and the corresponding relation between the resistance and the strain of the in-situ strain sensor.
2. The method of claim 1, wherein the in situ measurement of the internal strain of the flexible foam comprises: in the first step, the flatness of the plate was 0.01mm and the surface roughness was Ra0.2.
3. The method of claim 1, wherein the in situ measurement of the internal strain of the flexible foam comprises: in the first step, the polytetrafluoroethylene flat plate is a flat plate made of pure polytetrafluoroethylene or a metal flat plate with a polytetrafluoroethylene coating on the surface.
4. A method according to claim 1 for in situ measurement of the internal strain of a flexible foam, wherein: in the third step and the fourth step, the flexible polymer is one or more of thermosetting flexible polymers, including silicon rubber, butadiene-acrylonitrile rubber, butadiene rubber and chloroprene rubber.
5. A method according to claim 1 for in situ measurement of the internal strain of a flexible foam, wherein: in the eighth step, the inner diameter of the printing nozzle is 100-600 μm.
6. The method of claim 1, wherein the in situ measurement of the internal strain of the flexible foam comprises: in the ninth step, the flexible foam structure adopts a grid-shaped hole structure, a triangular hole structure and a honeycomb-shaped hole structure.
7. A method according to claim 1 for in situ measurement of the internal strain of a flexible foam, wherein: and sixteenth step, the positive and negative poles of the resistance tester can be directly connected with the two ends of the in-situ strain sensor by conductive clamps.
8. The method of claim 1, wherein the in situ measurement of the internal strain of the flexible foam comprises: and sixthly, connecting the positive pole and the negative pole of the resistance tester with the two ends of the in-situ strain sensor through conductive adhesive.
9. The method of claim 1, wherein the in situ measurement of the internal strain of the flexible foam comprises: in the nineteenth step, the strain measurement range of the in-situ strain sensor is-70% -150%.
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