All to Know about Elmendorf Tear Test

Definition of Elmendorf Tear

Elmendorf tear strength or tear resistance refers to the measure of the ability of a material such as Polyethylene Film to withstand the effects tearing by the Elmendorf tear test method, also known as the pendulum method.

The Elmendorf test  is very similar to another method known as the tongue-tearing method, and in addition, it also belongs to the group of fast tear strength techniques.  The Elmendorf tear test is one of the methods that is widely used globally to test resistance. It can be used to test the tear resistance of woven fabrics and also other types of fabrics that are built using similar technique. This method, however, cannot be used to test the resistance of woven elastic fabrics, knitted fabrics, or other types of fabrics with the probability of tearing transfer and having a greater difference of weft and warp.

 

Purpose of the Elmendorf Tear Test Method

The main aim of the Elmendorf tear test is to determine the ability of a material to resist the progression of the first tear or the tear resistance. The value of a material’s tear resistance, such as fabric or a thin film, is normally accepted to be the force required to complete that material’s tear so that it has gone totally through the sample material and in the process becoming separated into two parts. The use of flexible materials that may suffer a fractional split intentionally, should be used for this test in order to achieve the best outcomes possible.

 

Types of Materials Used for Tear Testing

Tear testing is usually done on flexible materials since they are more susceptible to intentional fractures and punctures as well as partial tearing. Other materials that are commonly used in tear testing are the textiles, elastomers, polymers, rubbers, packaging and paper products. These materials are widely used in industries dealing with clothing, biomedical, dental and medical.

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Tear Tests and Standards

However, there are other different types of tear testing which are in common with the Elmendorf tear test in their purpose, and it is important just to mention a few for you so that you grasp the whole idea of tear testing completely. Most tear resistance tests are executed statically and they generally take three forms in most cases. These forms are different from each other in configuration and in the preparation of the sample to be used, the rate of experimenting and the grip placement.

• Trouser shape tear test is the first form of tear testing, and it involves the use of a rectangular sample which is cut in a way to resemble the shape of trousers, actually two legs are formed. Placed in to the test grips, each leg is pulled apart which causes a tear between them.
• Tongue tear test is the second type of tear testing methods. It requires that a tab be cut in the middle of the sample. This tab is then placed in the top and bottom grips. The top grips moves upward leading to an incision on the sample.
• Trapezoid tear test is the third form of tear testing. The experiment sample is cut in the form of an isosceles trapezoid, with a small incision being made in one side. The sample is placed in a position where the grips move apart propagating the incision- the sample is positioned to produce a horizontally extending tear.

 

The Elmendorf tear test testing parameters have diverse national testing standards, as shown in Table 1 below.

Table 1: Elmendorf tear test – tear strength comparison of technical parameters

N/B: The humidifying time of all these models is 4 hours.[/su_table]

 

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Elmendorf Tear Test Procedure

The current GB / T 3917.1-2009 steps for detection methods are as follows:

① Preparation of the sample：

When preparing the sample for the Elmendorf tear test procedure, you require two sets of specimens. Take two samples, cut them at a distance of 150mm from the edge of the cloth. One specimen is for the warp sample and the other for the weft sample. The left side of the specimen should be parallel to the warp or weft samples to make sure that the tear is made alongside the incision. A minimum of five samples is required for each group. The tear length, however, remains the same, 43 ± 0.5mm.

Take great care when doing the sampling preparation as the sample is the main representative. Take the longitudinal direction of the sample, the sample should be parallel to the short side of the weft, do not cut-off incision weft. After cutting the sample, ensure you place in into a constant temperature and humidity laboratory, but the humidity conditioning treatment should be done before testing. Remember, if the sample is prepared wrongly and carelessly, not according to procedure, the results intended will be inaccurate which will lead to wrong conclusions being made for the Elmendorf tear test.

② Preparation of the Instrument：

To ensure that the Elmendorf tear test outcomes of the samples fall within the range of 15%-85% of the corresponding scale, make sure the calibration equipment is working properly and the select the proper quality of the pendulum. With the calibration instrument at zero, the pendulum is supposed to rise to the starting position, and ensure that the pointer is placed at zero.

③ Clamping the Specimen：

The sample should be slotted in between the clamps to make sure that the sample’s longer side is centered, with the lower side touching the base of the clamp head. The upper side of the sample should be parallel to the top of the clamp head, with both clamps clamping the sample in an even manner. In the center of the opposite side of the sample’s groove, make a cut of 43 ± 0.5 mm incision with the use of a shearing device according to the procedure, and ensure you leave a length of 43 ± 0.5mm to be torn.

④ Measurement Performance：

For this step, you should start the instrument and letting go of the device for tearing. Hold the tear testing device at a high position so as to avoid damaging the position of the pointer. Note and record the data indicated by the pointer. The test outcome should fall within a range of 15% to 18% of the scale used.

During the testing period, great care should be taken to ensure that the tear is in the direction of the force. Check whether the yarn slides off the fabric instead of being torn. Important to note is that, if the fabric does not slip from the jaws of the clamps, the tear should be in the 15mm wide groove region, and this indicates that the test is normal and correct.

If the yarn slips up then the outcome will be inaccurate, and should be disregarded. The Elmendorf tear test does not apply in situations where more than three of the five specimens are rejected- there be no enough specimens to bring a standard conclusion or outcome.

 

1. Fabrics Using Elmendorf Tear Test — Falling Pendulum Apparatus

 

Significance and use

Note any disputes arising from the test outcomes, and conduct several tests for comparison so as to determine any statistical bias. These tests should be performed in the same laboratories they were prepared in at the same temperature and humidity.

Conduct the test in two laboratories in order to get average results which should bring an accurate conclusion. You can also use the microprocessor systems to automatically collect data, it is very efficient is providing economical and consistent data.

Scope

This method also applies to fabrics like woven, layered blankets, blanket, airbags and napped pile, just to mention a few, provided the fabric tears only in the longwise direction to the direction of the force applied during the experiment. These fabrics may be heavily-sized, untreated, resin-treated, coated, or treated.

This tear test technique is appropriate only for the warp direction experiments of warp-knit fabrics. It is not, however, appropriate for the course direction of warp knit fabrics of lots of other knitted fabrics.

The values for this test method are stated either in SI units or U.S. customary units, which are to be viewed as standard, but you should use them independently of each other.

 

2. Plastic Film and Thin Sheeting

 

Significance and use

This test technique also is of importance in classifying relative tearing strengths or resistance of several plastic films and thin sheet of different thicknesses. This test uses relatively less extensible films and sheeting in order to acquire highly reliable outcomes.

This test method has used widely as a one index of the tearing resistance of thin sheeting and plastic films utilized in packaging applications. This test method’s apparatus is used to provide a controlled means for tearing these specimens at straining speeds, despite the fact that its not always possible to compare film tearing statistics with the materials toughness or mechanical properties.

Plastic films and sheeting indicate constantly indicate marked anisotropy in their resistance to tearing, which is even further complicated by the fact that some types of film stretch greatly than others when tearing. The degree of this stretching is highly reliant on the film positioning and the in-built mechanical properties of the polymer, from which it is built.

The specimen in this test method is provides data which may supplement that of other relevant tests such as the Test Method D1004. The tearing rate in this test method,  while varying as a function of resistance to splitting, is in the range of 7.6 to 46m/min.

There is no direct, linear connection between tearing force and the thickness of the specimen. The data obtained from this tear test method is expressed as tear force in millinewtons or grams-force, with the thickness comparisons of specimen being reported. However, you cannot be able to compare data from different specimens which have different thicknesses. In short, you can only compare data from samples with the same range of thickness for accurate conclusion.

Scope

This test for tearing resistance covers the determination of the strength to propagate the tearing through a specified length of a flexible sheeting or a plastic film after the test has been initiated by the tear testing apparatus. Two specimens should be prepared properly, one should be a rectangular shape and the other one should have a constant radius experimenting length.

It may be highly unlikely to achieve constant and reliable outcomes from the test method due to several factors. The first one is the difficulty in choosing a uniformly indistinguishable set of specimens, then the unpredictable degree of positioning in several plastic films and lastly is the difficulty found in testing highly extensible or highly oriented materials. This leads to misleading and unreliable results.

The values are stated in SI units, which are to be regarded as standard.

 

Elmendorf Tear Test of Polyethylene Film

This is one of the perfect examples of how the Elmendorf tear test method works and I have provided a full procedure of how the tearing resistance was measured, testing the tear resistance capabilities of various materials such as polyethylene film. I have chosen this type of film due to its properties, which are very appropriate for this type of tear test method.

Experimentation Process

Elmendorf tear experiments of some Polyethylene film specimens were conducted on 25-38 mm blown film, in accordance with the standard procedure. Mechanical measurements are made for several commercial films such as E/B, E/H LLDPE and LDPE films and various resins, on a Universal Testing Machine at stretching rates of 21.2 mm·s^-1 (50″·min^-1) and 8.5 mm/s (20″·min^-1). Samples required for this testing are prepared appropriately.

 

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The Outcomes

Phenomenological Explanation of Elmendorf Tear Test

The Elmendorf tear test is performed in accordance to ASTM D1922 and ISO 6383-2 standards on a special tool following the standard method. Some rectangular specimens, with the following dimensions; 76 mm in width and 63 mm in length, are cut from a roll of film in two directions of that roll, the machine direction (MD) and the transverse direction (TD).

The major part of the Elmendorf tear test apparatus is the pendulum with the arm length measuring 40.6 cm. The weight of this pendulum can be adjusted from or between 200 to 1600 g contingent on the ETR of the film. The pendulum is placed in a horizontal placement and the long edge of the PE film is fastened between two clamps as shown in Figure 1A, one attached to the pendulum and the other to the body part of the testing apparatus.

An incision is made in the center of the wide side of the film, leaving a length equal to 43mm of the uncut film. The point where the tear begins, that is, the end of the cut, stretches 5 mm beyond external edges of the clamps.  Upon the pendulum being released, the swinging motion produced by it causes a rapid tear to the film’s uncut length, as indicated in Figures 1B and 1C.

As a result of the Elmendorf’s apparatus geometry, it causes the film to be torn completely upon the pendulum reaching the lowest part of its swing. However the speed of the pendulum would be very high if there were no film, but the impact of the film tearing causes the pendulum’s swinging speed to slow down. The duration of the single test is not more than 0.5 seconds.

The energy loss experienced by the pendulum is used to measure the Elmendorf’s tear rate. The experiment outcomes for several specimen of the same film are calculated and the average is determined, which is afterwards presented as equivalent to the pendulum’s weight, in gram, which is enough to bring the pendulum to a complete standstill when the film is totally torn.

 

However, always make sure that you state your goals before carrying out the analysis of the tear testing process. For instance, the first goal should be to observe all the phases occurring during the film tearing process in the terms usually used to define standardized mechanical testing of semi-crystalline plastics.

 

Mechanical processes that take place during the Elmendorf tear test can be evidently seen when the high quality LLPDE film is torn. As Figure 1B depicts, the tearing is followed by short-term winding of the still intact part of the PE film, which is now placed upright to the plane of the clamp movement.  The temporary winding in an apparent turning of the x coordinate by 90º whereas the direction of y coordinate remains the same. The original direction of the x coordinate is returned at the time when the film becomes wholly torn. See Figure 1C.

During the Elmendorf tear test, the rate of the film tearing is very rapid, in a blink of an eye, and it is very difficult as well to observe its direction. You will be able to notice a few features during these experiment. One of the features you are likely to observe is the establishment of border fringes, strongly strained thin regions along the tear line, which is schematically displayed in Figure 1C.

The micrograph of a typical fringe is depicted in figure 2, which are usually smaller with their length varying from 0.3 to 1 mm, which relies on the variety of film and the direction of the tear. The second evident feature is straining of the region in the film between the x axis and the diagonal line depicted in Figure 1B.

For the convenience of the observation, three lines marked A, B and C, were drawn on the film horizontally to the direction of the tear before the test (See Figure 1-A). The straining ends up causing a winding of these lines. The bending increases with the length of the tear as depicted in Figure 1C. The shape of the bent lines can be measured in torn film specimens after the experiments.

 

It should be observed that during the Elmendorf tear test on any of the film samples produced by the film blowing technique, a common aberration in the experiment might occur. Despite the knowledge that the tear is supposed to propagate along the x coordinate, it sometimes changes its direction and ends up propagating y coordinate. The explanation for the alteration is highly due to vast no-uniformity in the film’s orientation pattern.

As discussed before, several types of blown film are rather strongly MD or TD positioned. As a result of this, the strengths of their tears in the two directions is evidently different and the direction of the tear may change by following the direction of minimum resistance.

When the tear tests are performed by hand at a slow rate, various other of its significant feature becomes clear. First is the very strong warping of the film regions around the tear borders. The directions of the warping line are shown clearly in Figures1B and 1C. The second one is the great stress evident in several parts of the film during the experiment.

The stress is observable in the regions between the tear border and the last warping line, depicted as the diagonal line in figure C, while the rest of the film parts have not experienced any stress. It should be keenly noted that the gentle tearing of a polymer film, while making observations of the involved processes likely, heavily overestimates the resistance of the film to tearing.

Figure 1. (A, B & C)  Schematics of Elmendorf tear test (see text).

 

Figure 2.  Microphotograph of oriented fringes in TD-torn LLDPE film; magnification ´100, length of fringes ~0.7 mm.

 

Mechanical Details of the Test

Figure 3 below depicts the scheme of an interfered tear test. Only the segments of the films that are strained are shown. The diagram is same with that of Figure 1B but has more details. The tearing involves three parts of the film as shown in Figure 2-A.  Region 1, which is the middle part, is the strongly affected part. Observations of Region 1 are very convenient, but only if the film is covered with paint or colored with a permanent stain before the tear test begins. The positioning and dimensions of this region are very vital for the total understanding of the Elmendorf tear test outcomes. The area is in the form of an isosceles triangle, with its base placed along the x axis and y =0, and in addition, this area of the film is twisted with respect to the x coordinate. Though, this region is smaller and its thickness is normally less than 3 to 4 mm.

 

 

Figure 3.  A) Stressed/stretched film regions during Elmendorf tear test; B) Transformation of Region I during passage of tear point along its altitude.

 

Figure 3B depicts clearly what occurs with one half of Region 1 when the tear point continues travelling along its altitude, that is, along the x coordinate. The forms of all these features are deliberately distorted to show the alterations more clearly. At the period when the tear point stretches to the positions illustrated at left in figure 3-B, the height of Region 1, which is the altitude’s length, is h′; it can be roughly projected experimentally (see above). As the tear point travels along the altitude toward the vertex of Region I, the altitude h′ becomes slightly stretched out and progressively splits into two “halves” h″ situated along the x coordinate.  This change is shown in the right part of Figure 3-B after the tear point moves far ahead (x_tear″ >> x_tear′).  Some significant visual observations become probable if such slow tearing is halted midway and the sample is held under stress only slightly below s_br:

1. The size of Region 1 in the strained specimen, both its base and its altitude, change moderately slightly when the entire length of the tear increases.
2. In some tests, a short distance along the x axis was marked (like h′ in Figure 3-B), and the tear was allowed to propagate along the marked distance. Measurements of its both halves (h″) showed that after the torn film was subsequently relaxed, h″ were only slightly higher than h′.

Figure 3-A displays that two other regions of the film are strained during the tear test, Regions 2, orthogonal trapezoids with huge bases equal to the width of one clamp, Y, and small bases corresponding to h′ of Region 1. The strains and the stresses in any point of Regions II along the x coordinate are very irregular and rely on the position along the y coordinate.  The greatest stresses are along the tear line, at y = 0

Model of Elmendorf Tear Test

Significant complications ascend when one tries to find an analytical answer describing stretching of a combination of Region 1 and two adjacent Regions 2 shown in Figure 3.  One reason is strong twisting and warping of all the stress-affected parts of the film obvious from Figure 3-A and 3-B.  The second explanation is a very uneven spreading of stresses and strains in Region 1.  Clearly, the midpoint of the base in Region 1 is under the breaking stress.

Conclusion of the Elmendorf tear test

A physical model of the Elmendorf tear test is created for the film developed from semi-crystalline PE resins, LDPE and LLDPE.  This model treats the Elmendorf tear test as a distinct case of a cascade of high-speed straining/breaking of a very great quantity of thin polymer strips which have cross-sections of different variations. This physical model defines the ETR of a specific film as a complex function of six constraints that illustrate the standard stress-strain curve of the respective PE resin- strains and stresses at the necking, the yield and the breaking points, as shown in Figure 4.

Many comparisons of experimental and calculated ETR for films made from different kinds of PE resins illustrate that the model accurately predicts ETR ranges for different varieties of film and is appropriate for semi-quantitative characterization and grading of PE resins for film application.

This model aids in the evaluation of the relative significance of various mechanical properties of PE resins for their behavior trends in the tests for the tearing of the films. As an instance, this model provides a clear explanation regarding the physical reasons for commonly known differences between various kinds of film manufactured from E/B and E/H copolymers, the outcome of molecular orientation in the film on its tear properties, differences between PE films produced from LLPE and LLDPE resins, among others.

 

Figure 4.  Idealized stress-strain curve of ductile polymer

 

However, the Elmendorf tear test should be performed using a special apparatus known as the Elmendorf tear tester, which is perfectly tailored to test the tear strengths or tear resistance of various materials. Perhaps one of the best tools to conduct a tear test with, as it has zero sample slip-ups, as well as high accuracy which provides consistent results leading to very reliable conclusions. Here, the important aspects of this machine will be discussed clearly allowing you to grasp how it works and acquire more knowledge about how tear testing works.

 

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Elmendorf Tear Tester

Elmendorf  tear tester, falling-pendulum instrument, controlled by a computer, is used to determine the ballistic tearing strength of textiles, paper, plastics, or board. Tear Strength Tester complies with the main standards.

The tearing tester is additionally improved and supported by the easy to use computers to control them, which has made it easy to operate when doing tearing tests and also has enabled faster tests to be done. You are more likely to get accurate results that are more reliable and consistent. Elmendorf Tear Resistance Tester will display its impressive performance when you perform the Elmendorf tear test. Below, we have discussed how this tear testing apparatus can be applied, its features, specifications, included accessories, weight, dimensions and power supply needed to run this tool.

Application of the Elmendorf Tear Tester

• Auto Elmendorf Tear Tester,

This is a patented device, which is used to test the ballistic tearing strength of textiles, plastics, paper or board.

• Elmendorf type tear tester

This tear testing apparatus is not applied to thin fabric or materials that stretch easily which the direction of the tearing might be shift in test.

Important to note is that compressed air of 0.4~ 0.7 mPa is essential.

Features of the Elmendorf Tear Tester

The following are the features of the Elmendorf tear tester:

• Operates in accordance with the commonly implemented test standards.
• Automatic clamping and notching of the sample.
• The Elmendorf tear tester is the solitary one that covers the most finalized test range from 0 to 12800cN.
• Repeatable, pneumatic sample gripping system warranties satisfactory clamping force to evade all slipping events, thus guaranteeing seamless reproducibility of the experimental circumstances.

Specifications

• Accuracy: 0.2% of pendulum range
• Unit: GF, MN, CN, CP, LB

 

Included Accessories

• TESTEX Elmendorf Tearing Test software
• Complete with working pendulums

1600cN/g (3.5lb), 3200cN/g (7.0lb), 6400cN/g (14.0lb), 12800cN/g(28.0lb) 1 pc of Specimen cutting template

Weight

The Elmendorf tear test apparatus has a standard weight of 105 kg

Power

The Elmendorf tear tester uses a power supply of up to 220/110 V, 50/60 Hz, 0.5-0.7 Mpa

 

What Factors to Pay Close Attention to When Determining the Tearing Strength?

1. The specimens should be cut according to the sizes in the following chart.

Project	Trapezoid Method	Single-tongue method	Hammer-drop method
Sample Length（mm）	≥200 (approximately 150）	≥200	75 （approximately 63）
Sample Width（mm）	50（After repairing the edge yarn）	75	100
Cut Length（mm）	10	80	20
Tear Length（mm）	10	75	13
Holding Distance（mm）	100	75	＜2
Stretching Rate（mm）	200	200（Hair Length 50）	Hammer Drop

 

2. The direction of the test refers to the direction in which the yarn is torn, that is, the direction vertical to the cut, such as the warp yarns of the warp specimen in the single tongue tear in the width direction, and the trapezoid technique in the opposite direction.
3. The cut should be cut along the warp or weft direction, otherwise the tear may stray from the cut during the tearing process.
4. When the sample is clamped, the yarn at the incision cannot be stressed.
5. Drop the weight of the bezel in order to determine the pressure, full, not with the fan hem friction.

Elmendorf tear tester is an impressive machine for measuring tear resistance, one that you will find very reliable and effective in its use. Finding the right tool is very crucial when you are considering doing a test on tear resistance of various materials such as yawn, fabrics or paper. Finding the perfect developer of this tools is also a crucial thing, that’s where TESTEX comes in. One of the well-known companies that produce state of the art Tear testing machines such as the Elmendorf Tear Tester TF140C. Very impressive machines in their function. We have used these machines to draw lots of accurate conclusions on tear testing of various materials. The tear testing apparatus are in high demand now! Welcome to contact us for Elmendorf tear tester price or more information.

Elmendorf Tear Tester TF140C