Testing dart drop test

There are other types of impact tests for shock loading where energy is required to cause complete failure is reported. Each has their specific behaviors that can be related to specific product performance requirements. Tests include ball burst, ball or falling dart using different weights and heights, bag drop, bullet-type instantaneous impact, Charpy, dart drop, Mullen burst, tear resistance, and tub (2). 

We test the impact resistance of polymer plaques using the configuration shown in Fig. 8.8. We subject circular injection molded plaques to the shock of a falling weight with a hemispherical impacter. This test is also known as the Dart Drop Test . Samples can fail in a brittle or a ductile manner. Brittle samples often shatter. Ductile samples can split or a small disk may be punched out of their center. This test provides results that are analogous to those obtained from un-notched impact beam testing. 

The flaw spectrum approach may be capable also of correlating failure data obtained under conditions which appear to give different material behavior. For example, tensile, Izod, and dart drop impact tests all give different impact energies or toughness measures. In part, this may be explained by the simple idea that a different fraction of flaws is active in each test. Equal biaxial loading (as in dart drop) and uniaxial tension (as in tensile impact) give rise to different flaw activities thus it is to be expected that the number of crazes produced in each test will be different. 

Polymers which yield extensively under stress exhibit nonlinear stress-strain behavior. This invalidates the application of linear elastic fracture mechanics. It is usually assumed that the LEFM approach can be used if the size of the plastic zone is small compared to the dimensions of the object. Alternative concepts have been proposed for rating the fracture resistance of tougher polymers, like polyolelins, but empirical pendulum impact or dart drop tests are deeply entrenched forjudging such behavior. 

The dart drop impact test, ASTM D1709 and ASTM D4272, is often used for film samples. In D1709, a sample of the film is subjected to an impact by a round-... 

ASTM D 4272 Standard test method for total energy impact of plastic films by dart drop... 

Fig. 18.24 Results of the dart drop test showing the increased energy absorption due to decoupling with a hydrophobic fiber surface (weak interphase)...

This effect is fully corroborated by a dart drop test (DIN EN ISO 6603-2) with a 100 J dart and injection molded plates of 2 mm thickness, as shown in Fig. 18.24. In particular, the absorbed energy during the puncture event for the weak PP-g-MAH interphase is more than doubled compared to the normal composite without decoupling (moderate interphase). 

A free-falling dart method for polyethylene films is described in ASTM D1709. Unlike low-speed uniaxial tensile tests, the pendulum impact test measures the resistance of film to impact puncture, simulating high-speed end use application. Dart drop measures the energy lost by a moderate velocity blunt impact passing through... 

Fig. 5. T5rpical results of a dart-drop test using the staircase method of analysis (12). To convert J to ft-lbf, divide by 1.35. Courtesy of the Society of Plastics Engineers.

The falling weight or dart drop test method simulates actual day-to-day abuse and can be carried out either on standard laboratory specimens or on the articles themselves. Failure may occur in various ways ranging from brittle to ductile failure (Figure 14). Particular care must be taken to avoid the brittle failure by proper selection of grade. At temperatures below -20 °C, elastomer-modified PP is more impact resistant than PP copolymer and homopolymer. 

As far as the mechanical properties are concerned, the tear (test name Elmendorf tear), impact (test name dart drop), and tensile strengths give an indication of the mechanical strength of the tubular film. Some of these properties and the effect the processing parameters have on them were discussed in Section 1.2. The amorphous as well as the crystalline orientation developments during the blowing process depend on... 

Free Falling Dart Drop Test Instrumented Dart Test... 

Impact tests were performed using a dart-drop impact tester (DDI/TE, Model DDL 120, Qnalitest Ine., Ft. Lauderdale, Florida, USA) as per ASTM D 4272 standard testing conditions and procedures using a 38.1 mm dart. Ten specimens were tested for eaeh N and average impaet energy was calculated. Barrier property measurements are in progress and will be reported in the ftiture. 

Tables 4—6 Ust ASTM methods used for the characterization of PB and PMP. A number of specialized methods were developed for testing particular articles manufactured from polyolefins several of these determine the performance of PB and PMP film, including the measurement of the film s dart impact strength and tear strength. Dart impact strength is measured by dropping a heavy dart with a round tip on a stretched film. Tear resistance, which reflects the film s resistance to tear propagation, is measured with the Ehnendorf tear tester. Two values for the tear strength are usually reported, one in the machine dkection of the film and the other in the transverse dkection. Pipes manufactured from PB are tested by pressurizing them internally with water the time-to-burst failure is determined at various temperatures (46). The standard test method for haze and luminous transmittance (ASTM D1003) is used for the measurement of PMP optical characteristics.

Cold impact was measured by the falling dart test in which a 3" x 6" x 0.125" sample is positioned in an inverted U shape, conditioned four hours at -30°C., and impacted at the highest point of the specimen by a weighted two-inch diameter rod-shaped plunger rounded on the end to a one-inch radius. The plunger is dropped from a predetermined height to give 5 mph impact velocity. 

Impact Resistance of Plastic Film by the Free-Falling Dart Method. Primary Film Test Method ASTM D1709 Additional Test Method ISO 7765-1. A weighted dart is dropped from a standard height onto a taut sample. Depending upon the expected impact strength of the test sample, either method A or method B is chosen. The method defines the dart size and the drop height for the dart. Test method A specifies a dart with a 38 mm diameter dropped from 0.66 m. Test method B specifies a dart with a 51 mm diameter dropped from 1.5 m. 

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