JP2009047596A - Impact strength evaluating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an impact strength evaluating method capable of easily and accurately evaluating the impact strength of a product or the like. <P>SOLUTION: In this method, the impact strength is evaluated using drop test data obtained by previously measuring the relation between the drop height of a dropping weight to a buffer material and the maximum acceleration and velocity variation regarding a plurality of kinds of buffer materials. The method includes a first step (step S3) of repeating the drop of a sample of each buffer material while gradually raising the drop height and acquiring a limit drop height for breaking the sample, a second step (step S4) of acquiring maximum acceleration and velocity variation corresponding to the limit drop height for each buffer material based on the drop test data, and a third step (step S5) of deriving a breakage boundary curve of the sample based on the acquired maximum acceleration and velocity variation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an impact strength evaluation method.

  The impact strength of a product is evaluated in order to understand what kind of shock pulse causes the product to break. For example, a shock-absorbing package design for protecting the product from a drop impact generated during the transportation of the product. It is used in the product design of portable devices that may fall during use.

As a method for evaluating product impact strength, it is generally performed to grasp a damage boundary curve of a product as standardized in JIS Z0019. For example, in Patent Document 1, in order to evaluate the impact resistance performance of a cathode ray tube, a cathode ray tube is attached to a drop table of an impact tester via a dedicated fixing jig, and a sine half wave and a trapezoidal wave are respectively used as shock waves. A method of acquiring data necessary for creating a damage boundary curve by sequentially performing a speed change test and an acceleration test is disclosed.
JP 2002-110045 A

  However, the conventional method using an impact tester is not only complicated to create and attach a dedicated jig, but also has a large configuration of the device itself to generate a desired shock pulse. It was not easy to use at development sites, and a simple evaluation method was needed.

  Accordingly, an object of the present invention is to provide an impact strength evaluation method capable of easily and accurately evaluating the impact strength of a product or the like.

  The object of the present invention is a method for evaluating impact strength using test data obtained by measuring in advance a plurality of types of the buffer material, the relationship between the falling height of the falling weight with respect to the buffer material and the maximum acceleration and speed change. The first step of repeatedly dropping the test sample with respect to each of the buffer materials while gradually increasing the drop height to obtain a limit drop height at which the test sample is damaged, and based on the test data The second step of acquiring the maximum acceleration and speed change corresponding to the limit fall height for each buffer material, and the damage boundary curve of the test sample is derived based on the acquired maximum acceleration and speed change. And an impact strength evaluation method comprising the third step.

  In this impact strength evaluation method, it is preferable that the third step includes a step of converting a reference curve obtained by standardizing a damage boundary curve into the damage boundary curve based on a preset condition.

  In addition, the first step may include a step of acquiring, for a plurality of parts of the specimen, the limit drop height at which the part is damaged, and deriving the damage boundary curve This can be done for each part.

  According to the present invention, the impact strength of a product or the like can be evaluated easily and with high accuracy.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a flowchart for explaining an example of the impact strength evaluation method of the present invention. Impact strength evaluation targets include all products and products that may be damaged by a drop impact, such as home appliances such as mobile phones, laptop computers, digital cameras, watermelons, peaches, strawberries, etc. Can be mentioned.

  First, as a premise for evaluating the impact strength, drop tests are performed on various cushioning materials using a falling weight in advance (step S1). In the drop test, a general-purpose drop tester can be used, but it is not always necessary to use a drop tester as long as the posture of the falling specimen can be maintained in a desired state. Alternatively, the specimen may be dropped manually.

  The drop surface that causes a drop impact on the specimen is a ground having sufficient rigidity in a normal drop test, but in the present invention, a drop test of the specimen is performed by placing various cushioning materials on the drop surface. To obtain drop test data for each cushioning material. As the cushioning material, in addition to a certain degree of cushioning, it is preferable that the change in performance against repeated impacts is small and the shape of the generated impact pulse is stable. For example, foamed rubber, rubber, gel, felt mat And rubber pads. It is preferable that the cushioning material has a thickness sufficient to obtain a stable waveform of the shock pulse, and a plurality of materials having different elastic coefficients and the like are prepared so that the acceleration at the time of breakage is dispersed over a wide range. It is preferable. Further, as the cushioning material, it is possible to select a strong ground having almost no cushioning action.

  In the drop test, an acceleration sensor is fixed to the top surface of the falling weight, etc., the falling weight is dropped onto the buffer material from various heights, and a sine half-wave shock pulse is applied. calculate. An outline of the sine half-wave shock pulse waveform is shown in FIG.

  The drop test is preferably performed by changing the mass of the falling weight, the shape of the collision surface, and the like so as to be compatible with various products and making them into a database. As an example, the impact surface of the falling weight is 2 types of spherical shell surface (radius 50 mm) and flat surface (30 mm square), and the weight of falling weight is 2 types of 5.8 kg and 11.6 kg. Fig. 3 shows the results of measuring the relationship between impact energy and maximum impact load when a rubber pad is used as a cushioning material. In any pattern, the relationship between the impact energy and the maximum impact load is almost linear, and can be approximated by a linear expression. Since the impact energy is the drop height × mass, and the maximum impact load is the maximum acceleration × mass, FIG. 3 shows the relationship between the drop height and the maximum acceleration.

  The relationship between the drop height and the speed change can be clarified from the drop test in the same manner as described above. For example, if the change in speed is ΔV, the restitution coefficient with the buffer material is e, and the drop height is h, the following formula 1 is established. Therefore, the drop height and speed are calculated from the restitution coefficient e with each buffer material measured in the drop test. The relationship with change can be determined.

[Equation 1]
ΔV = (1 + e) √ (2gh)
In this way, the relationship between the falling height of the falling weight with respect to a certain buffer material and the maximum acceleration and speed change can be obtained, and by performing this for other buffer materials, the drop test data for a plurality of types of buffer materials is stored in the database. (Step S2).

  Next, the limit drop height that leads to breakage is measured for the specimen to be evaluated. One of the buffer materials used in the drop weight drop test described above is placed on the drop surface, and the sample is dropped on this buffer material. This measurement can also be performed using a drop tester, or can be performed manually without using a tester.

  Set the initial drop height of the specimen to the highest value that does not appear to break, gradually increase the drop height, repeatedly drop the specimen, and end when the specimen is damaged . The limit drop height is the limit drop height at which a specific fragile part of the specimen will be damaged.For example, when the drop height is increased stepwise, the maximum drop height at which the specimen does not break In addition, an average value of the drop height at which the test sample is damaged and the maximum drop height at which the test sample is not damaged can be set as the limit drop height.

  Thus, after obtaining the limit drop height for a certain buffer material, the other buffer materials are similarly tested, and the limit drop height is obtained for each of a plurality of types of buffer materials (step S3).

  Next, based on the drop test data generated in step S2, the maximum acceleration and speed change corresponding to the limit drop height for each buffer material are acquired (step S4). The drop test data stored in the database organizes the relationship between drop height, maximum acceleration, and speed change according to characteristics such as the shape and mass of the drop weight for each cushioning material. The best drop test data is selected to extract the maximum acceleration and velocity changes corresponding to the critical drop height. For example, in the drop test data shown in FIG. 3, when the collision surface of the specimen is flat and the mass of the specimen is 5.8 kg, the corresponding straight line is extracted and the maximum impact load corresponding to the impact energy is extracted. The maximum acceleration can be obtained from Further, the change in speed can be calculated by the above formula 1 after obtaining the restitution coefficient e from the drop test data. In FIG. 3, the relationship between the impact energy and the maximum impact load can be expressed by the same approximate straight line regardless of the mass, as shown in FIG. 5, if the shape of the collision surface of the falling weight is the same. Thus, it is possible to facilitate the extraction operation of the maximum acceleration and the speed change corresponding to the limit drop height.

  The limit fall height is obtained in the same manner for other cushioning materials, and the maximum acceleration and speed change are obtained for each of them (step S5). That is, assuming that the maximum acceleration is A and the speed change is ΔV, (A (1), ΔV (1)), (A (2), ΔV (2)),... , (A (N), ΔV (N)). Here, the numbers 1 to N are given in order of increasing speed.

  Thereafter, a damage boundary curve of the specimen is derived based on the maximum acceleration and speed change for each buffer material (step S5). In the present embodiment, a reference curve obtained by standardizing a damage boundary curve based on a preset condition is used for this derivation. For example, the damage boundary curve for a sinusoidal half-wave shock pulse assuming that the natural frequency of the response system is 1 Hz and the transmission acceleration exceeds 1 is as follows. The speed change Δv can be obtained from a theoretical formula as shown in FIG. 4 and can be used as a reference curve.

  The reference curve described above is a curve that depends only on the natural frequency and the transmission acceleration. If the natural frequency and the transmission acceleration are clarified, a damage boundary curve can be obtained from the reference curve. That is, if the maximum input acceleration of the damage boundary curve to be obtained is A and the input speed change is ΔV, the specific acceleration a and the specific speed change Δv in the reference curve are expressed by the following formulas 2 and 3.

[Equation 2]
a = A / _ac
[Equation 3]
Δv = ΔV · (f _c / a _c )
Here, a _c is the strength (transmission acceleration) of the most vulnerable part of the product, and f _c is the natural frequency of the product.

Since the specific acceleration a approaches 1 when the specific speed change ΔV increases as shown in FIG. 4, the reference curve has the N types (A (1), ΔV (1)), (A (2)) described above. , ΔV (2)),..., (A (N), ΔV (N)), the corresponding (a (1), Δv (1)), (a (2), Δv ( 2)),..., (A (N), Δv (N)), a (N) corresponding to ΔV (N) in which the speed change is maximum is 1 in Equation 2 above. Assuming that there is, a _c = A (N).

Further, if the apparent value of _{a c,} from the equation 2, a (1) = A (1) / a that can be obtained as _c, the reference curve, a Delta] v corresponding to (1) (1) Can also be sought. Thus obtained _{a c,} the value of Delta] v (1) and [Delta] V (1) are substituted into the equation 3, it is possible to calculate the _{f c.}

Once a _c and f _c are obtained, the reference curve can be converted into a damage boundary curve from the above equations 2 and 3 using these values as initial values. Since the values of (A (1), ΔV (1)), (A (2), ΔV (2)),..., (A (N), ΔV (N)) are clear, they were obtained. A damage boundary curve with a minimum error can be obtained by applying a least square method to the damage boundary curve.

  Thus, according to the impact strength evaluation method of the present embodiment, by obtaining in advance drop test data of falling weights for a plurality of cushioning materials, from the limit fall height of the specimen for each cushioning material. Damage boundary curve can be obtained. Therefore, it is not necessary to use an expensive and large impact tester, and the damage boundary curve of the product can be easily derived.

In order to derive a highly accurate reference curve, it is preferable that there are drop test data for a large number of shock absorbing materials with a wide range of coefficient of restitution at the time of falling weight collision. Damage boundary curve can be obtained. As the two types of cushioning material, for example, a solid ground and a cushioning mat can be selected, and the acceleration A (1) for the former cushioning material is regarded as infinite, and the speed change ΔV (1) at this time is defined as Allowable speed change. The specific speed change Δv (1) corresponding to ΔV (1) can be assumed to be the minimum value in the reference curve, and is about 0.08 in the graph of FIG. Therefore, the value of Delta] v (1) and [Delta] V (1) is known, the value of _f c / _{a c} are obtained from the above equation 3. Using this value and the speed change ΔV (2) for the latter cushioning material, the specific speed change Δv (2) can be obtained from Equation 3 above, and a ( 2) can be obtained. As a result, since the values of a (2) and A (2) are known, the value of a _c can be obtained from the above equation 2, and the value of f _c can be obtained from the above equation 3. In this way, a damage boundary curve for the specimen can be derived.

  In this embodiment, drop test data and a reference curve for a sine half-wave shock pulse are created to derive a damage boundary curve. However, the shape of the shock wave is not limited to a sine half-wave. There may be a trapezoidal wave, a square wave, or the like.

  In the present embodiment, one fragile part of the product is selected, and the damage boundary curve is derived from the limit drop height of this part. However, a plurality of fragile parts that may be damaged are selected. It is also possible to select and derive a damage boundary curve for each part.

It is a flowchart for demonstrating an example of the impact strength evaluation method of this invention. It is a schematic diagram of a sine half wave shock pulse waveform. It is a figure which shows an example of the result of having measured the relationship between impact energy and the maximum impact load. It is a figure which shows an example of a reference | standard curve. It is the figure which redrawn the approximate straight line of the measurement result shown in FIG.

Claims (3)

A method of evaluating impact strength using drop test data measured in advance for a plurality of types of the cushioning material and the relationship between the falling height of the falling weight with respect to the cushioning material and the maximum acceleration and speed change,
A first step of repeatedly dropping the test piece with respect to each of the buffer materials while gradually increasing the drop height to obtain a limit drop height at which the test piece is damaged;
A second step of obtaining a maximum acceleration and speed change corresponding to the limit drop height for each of the buffer materials based on the drop test data;
And a third step of deriving a damage boundary curve of the specimen based on the acquired maximum acceleration and speed change. The impact strength evaluation method according to claim 1, wherein the third step includes a step of converting a reference curve obtained by standardizing a damage boundary curve into the damage boundary curve based on a preset condition. The first step includes, for a plurality of vulnerable parts of the specimen, obtaining the limit drop height at which the vulnerable parts are damaged,
The impact strength evaluation method according to claim 1, wherein the damage boundary curve is derived for each fragile site.