Developing Standardization Procedures & Conducting Product Testing For Veterinary-Use Hypodermic Devices

NPPC Project #00-146
Steven J. Hoff, PhD, PE Associate Professor
Iowa State University, Department of Agricultural and Biosystems Engineering
206B Davidson Hall, Ames, Iowa 50011, hoffer@iastate.edu

 

Abstract

 

Needles from six manufacturers were either donated or purchased for evaluating overall static and dynamic strength. Needle assemblies ranging in gauge from 22, 20, 18, and 16 and needle lengths ranging from 0.50, 0.75, 1.00, and 1.50 inches were acquired. Hub materials consisting of polypropylene only, polypropylene with an aluminum insert, aluminum, stainless steel, and brass/nickel/chrome composite were tested. In total, 83 needle assemblies were tested.

 

Specialty testing equipment was developed to conduct the trials for this study. Three basic tests were completed, two designed to test overall static strength and one designed to test strength with simulated animal movement. Three replications of both static tests were conducted and twelve replications of the dynamic test were conducted. The over-riding goal was to provide a series of guidelines that could be used to assess needle/hub assembly performance in the field based on data collected in a controlled laboratory setting.

 

The major focus of this study was to determine characteristics of needle/hub assemblies that result in both desirable and undesirable failure modes in the field. An undesirable needle failure is one where the needle physically fractures after a single needle-bending event, or, a failure that involves a permanently deformed needle that could be straightened and reused. A desirable needle failure is one where, upon failure, no possibility exists for reusing the needle.

 

A procedure was developed that relates static testing results to anticipated failure modes expected in the field. This procedure, using a newly developed variable called the Rigidity Rating (RR) can then be used, it is hypothesized, to predict “desirable” or “undesirable” field failure conditions. Using this procedure, 100 percent of the desirable failures actually observed during simulated animal movement testing were predicted using the RR. More work is needed to further develop and refine this technique.

 

Introduction

 

The swine industry is quickly recognizing the importance of broken needles present in swine carcasses as they are processed at the packer. There is a wide spread interest in the industry to rid all processed cuts from broken needle hazards. Two forces are at work in this issue. First, what causes needles to break and ultimately end up in swine carcasses, and second, if a needle is present in a swine carcass, what ability do we as an industry have to identify and remove the needle?

 

Several different needles and needle/hub assemblies have been tested at Iowa State University. Assemblies from North America (United States and Canada) and Asia (Japan) have been tested. Through all testing procedures conducted prior to this current research project, needles remained intact with all or a portion of the hub assembly except when a needle that was permanently deformed was straightened and reused. Our conclusion to-date has been that needles left in swine carcasses are the result of needle misuse at the farm and not a result of needle strength limitations.

 

The ultimate failure condition for a needle/hub assembly is one in which upon excessive loading, as would be present during pig movement at the time of injection, the hub assembly permanently deforms, without detachment from the needle thereby preventing repeated use of the needle. In this manner, no choice exists but to discard the needle since re-use is impossible. Several needle manufacturers have a vested interest and desire to develop a needle/hub assembly that meets this criterion.

 

A set of strength tests for veterinary-use needle/hub assemblies has been developed at Iowa State University for evaluating the ultimate strength of needle assemblies during both static and dynamic testing. A specific standardization procedure and a complete assessment of current strength characteristics for all veterinary-use hypodermic needles used in the United States and Canada is urgently needed as the swine industry works diligently to eliminate broken needle hazards from entering the food chain.

 

Objectives
 
Two objectives guided this research project;

1. Provide to the industry a complete document outlining ultimate strength, load-to-failure, and the failure modes for all veterinary-use hypodermic needles used in the United States and Canada. Testing includes 16, 18, 20, and 22 gauge needles varying from 2 to 1 2 inches in length and with all combinations of needles and hub material currently available.
2. Finalize a standardization procedure for testing and evaluating veterinary-use hypodermic needles identifying specific strength characteristics that result in undesirable and desirable failure modes using both static and dynamic testing procedures.

 

The outcome from this research project will be a consumers-report statement of the strength and failure modes for every manufactured veterinary-use needle used in the United States and Canada. A specific set of load limits and conditions of failure required for standardized use of needle assemblies in the swine industry will be determined.

 

Procedures

 

This research project was intended to build upon past needle research conducted with funds provided by NPPC. In past needle research, a series of testing equipment was developed to test and simulate static and dynamic forces subjected to veterinary-use needles. This previously developed equipment worked very well and allowed for several important conclusions to be made regarding needle strength characteristics. In particular, it was concluded that most all needle fragments found in swine carcasses was the result of needle misuse. That is, if a needle was permanently deformed straightened and reused, the probability of fracturing a needle was high leaving a difficult-to-find needle fragment in the animal.

 

For this current funded research effort, it became apparent that the testing equipment used in the past would not suffice for a project of this magnitude. Therefore, to accomplish the objectives of this research project, a completely new set of equipment was designed and manufactured to ensure that every needle tested was being tested under identical conditions. The equipment developed to accomplish the objectives of this research project is described below:

 

Static Test Stand: The first device developed was one that could test needle/hub strength under static (ie. no animal movement) conditions. The static test stand developed is shown in Figure 1. This device, made entirely of aluminum, can precisely control the loading point on each needle/hub assembly. This device contains a highly accurate load cell and is completely computer controlled for conducting all desired tests. All load data and the position of the load point are stored in real-time during each test.

 

From this static testing unit, two basic loading conditions were tested:

 

Full-Embedment Test: The load point was placed at a location 1 mm from the needle/hub joint as shown in Figure 2. This static test was intended to simulate the load that would be applied to a needle if just after full embedment of the needle into the animal, the animal suddenly moved laterally away. In all discussion of the results, this test is referred to as “Test 1”.

 

Tip-Bending Test: The load point was placed at a location 80% of the distance from the needle/hub joint to the end of the needle tip as shown in Figure 3. This static test was intended to simulate the load that would be applied to a needle if just upon injection, the animal suddenly moved laterally away before actually being injected. In all discussion of the results, this is referred to as “Test 2”.

 

Dynamic Test Stand: A second device was developed to simulate the dynamic loads applied to a needle/hub assembly if the animal moves during and after the injection process, or, the load that might be applied with a user that violently injects an animal while in motion. The dynamic test stand, called the Animal Movement Simulator (AMS), is shown in Figure 4. This device, made entirely of aluminum, can precisely control the simulated animal speed and the point at which animal movement begins relative to the injection process. The actual needle injection zone consists of rigid polystyrene insulation board with two layers of common chamois material, intended to simulate the hide. Tests conducted on this injection area indicate a puncture force that closely matches that of a typical finishing pig. The AMS testing has no load sensing capabilities. Instead, the failure mode, if any, is categorized and compared among manufacturers. In all discussion of the results, this test is referred to as “Test 3”.

 

AMS testing was devised to better reflect actual field condition loading situations. The failure modes recorded during this testing procedure were compared to the static loading tests to determine if any correlation could be made between these relatively simple static tests and the failures observed during AMS testing. In other words, it is entirely possible that a needle/hub assembly is superior in strength characteristics during static testing, but which has a failure mode during AMS testing that is unacceptable to the industry. Likewise, some needle/hub assemblies might not exhibit superior strength characteristics during static testing, but are resilient to unacceptable failure modes during AMS testing. AMS and static testing results were used to make these comparisons in the hope of providing useful design guidelines for the industry.

 

Needles Acquired: A complete search of the veterinary-use needle industry was conducted and various needles were acquired. Donations were requested and if a donation was not made, arrangements were made to purchase the required needles for testing. A total of six manufacturers were identified with a total of 83 combinations of needle gauge, needle length, and hub material acquired.

 

Needle gauges of 22, 20, 18, and 16 were received with lengths that varied between 0.5, 0.75, 1.00, and 1.50 inches. Hub materials varied between aluminum (A), polypropylene (P), polypropylene with an aluminum insert (PA), stainless steel (SS), and brass/nickel/chrome (BNC) composite. Within the polypropylene-only hubs, some manufacturers clearly used an epoxy bond between the needle and the hub in excess of what would be required to simply join the needle to the hub and these were identified as polypropylene with epoxy (PE). The complete listing of manufacturers, brand names, needle gauge, needle length, and hub materials tested are shown in Tables 1a to 1d, organized by gauge from 22, 20, 18, and 16 gauge, respectively.

 

Testing Procedures: For each of the 83 needle/hub combinations tested, a separate container was filled with up to 50 randomly selected needles. All testing was then conducted from needles in these containers.

 

For Test 1 and Test 2, three replications were conducted. Tests were conducted to ensure that three replications was sufficient for conducting valid statistical tests. Using prior equipment from prior tests, it was determined that 5 replications were required. Three replications for the new equipment developed for conducting Test 1 and Test 2 indicates improvement in the equipment design and reproducibility. For test 3, twelve replications were conducted to yield an acceptable determination of the percent times that needle/hub assemblies would fail under various categories. For a few needle/hub assemblies supplied, it was not possible to conduct 12 replications during Test 3. For these cases, three replications were conducted.

 

For all 83 needle/hub assemblies tested, a second container was made to collect and store all tested needles for future reference. Therefore, 83 containers were made for each untested needle and 83 containers were made for Test 1, Test 2, and Test 3 experiments (249 after-test containers).

 

Failure Mode Designations: Throughout all of the testing, a description of the failure mode (if any) was made. Each failure mode designation is given below and these are referred to quite often in the results. The designations are listed in order of needle/hub failure preference. As one moves down the list of failure modes, the severity to the industry worsens.

 

 

 

For example, if a needle/hub fails (i.e. not Category 0), failure categories 1 and 2 are preferred to the industry. For these failures, the assembly remains intact but can not be reused and therefore no choice exists but to discard.

 

A Category 3 failure implies that upon failure, the bottom portion of the hub completely fractures leaving the needle and a portion of the hub with the animal. This type of failure does allow for relatively easy needle removal since the hub portion remaining with the needle can be easily found.

 

A Category 4 failure will result whenever the needle is weaker than the hub material itself. That is, if the hub is very strong and resilient to deformation, as might be the case for metal hub needles, the needle will absorb most all of the load applied to it and will permanently deform. This type of failure could be considered acceptable if and only if a strict adherence to discarding these types of failures is observed. However, as was mentioned before, it is clear that these types of failures are being ignored and therefore once straightened and resused, result in a high probability of needle fracture inside the animal.

 

Category 5 and 6 failures are completely unacceptable to the industry. With these failures, the needle will fracture upon initial bending leaving the needle directly in the animal with little hope of retrieval.

 

All seven failure categories listed above were observed with this research project and the characteristics that resulted in each will be discussed at great length below.

 

Results and Discussion

 

The results are summarized in two basic tables. Table 2 summarizes all Test 1 and Test 3 results together and Table 3 summarizes all Test 2 and Test 3 results together. The reason for including Test 3 results along with both Test 1 and Test 2 was to see if any comparisons could be made between the static tests conducted (Tests 1 and 2) and the failure modes observed during Test 3. For both Tables 2 and 3, the results are grouped by gauge.

 

Test 1 Results: Tables 2a to 2d summarize the results for Test 1 (Full Embedment) for the 22, 20, 18, and 16 gauge needles tested, respectively. Also given are the failure modes recorded during AMS testing (Test 3). A summary description of results is given below, organized by gauge.

 

22 Gauge Results: All metal hub needles (A or BNC) had a higher maximum load capability relative to all polypropylene (P, PE, or PA) hub needles tested. Metal hub needles all had maximum loads greater than 10 lbs where all P, PE, or PA hub assemblies were similar and less than 10 lbs. In all cases, Category 4 failures were observed for 100 percent of the trials.

 

20 Gauge results: All metal hub needles (A, BNC, or SS) had a higher maximum load capability relative to all polypropylene (P, PE, or PA) hub needles tested. Metal hub needles all had maximum loads greater than 10 lbs where all P, PE, or PA hub assemblies were similar and less than 10 lbs. With the exception of one assembly tested, Category 4 failures were observed for 100 percent of the trials. In one case, the Harvard Brand SS hub, 0.75 inch needle supplied by Jorgenson Laboratories, needle fracture was observed. The needle fractured but remained intact (Category 5 failure).

 

18 Gauge results: All metal hub needles (A, BNC, or SS) had a higher maximum load capability relative to all polypropylene (P, PE, or PA) hub needles tested. Metal hub needles all had maximum loads greater than 20 lbs where all P, PE, or PA hub assemblies were similar and less than 12 lbs. All metal hub needle assemblies had Category 4 failures for 100 percent of the trials with all P, PE, or PA hub assemblies having Category 1 failures for 100 percent of the trials.

 

16 Gauge results: All metal hub needles (A, BNC, or SS) had a higher maximum load capability relative to all polypropylene (P, PE, or PA) hub needles tested. Metal hub needles all had maximum loads greater than 30 lbs where all P or PE hub assemblies were similar and less than 10 lbs. All metal hub needle assemblies had Category 4 failures for 100 percent of the trials with all P or PE hub assemblies having Category 1 failures for 100 percent of the trials.

 

Test 2 Results: Tables 3a to 3d summarize the results for Test 2 (Tip Bending) for the 22, 20, 18, and 16 gauge needles tested, respectively. Also given are the failure modes recorded during AMS testing (Test 3). A summary description of results is given below, organized by gauge.

 

22 Gauge Results: For Test 2, length of needle played a dominant role in strength characteristics. The longer the needle, the lower the ultimate strength since the torque on the hub itself was higher. Maximum loads sustained were all less than 1.4 lbs.
 
20 Gauge results: Results for the 20 gauge needles were similar to the results for the 22 gauge needles. Maximum loads sustained were predominantly a function of needle length. Maximum loads sustained were all less than 2.7 lbs.

 

18 Gauge results: The general trend for 18 gauge needles was similar to the 22 and 20 gauge needles. As needle length increases, maximum load sustained decreases. Maximum loads sustained were all less than 6.3 lbs.

 

16 Gauge results: The general trend for 16 gauge needles was similar to the 22, 20 and 18 gauge needles. As needle length increases, maximum load sustained decreases. Maximum loads sustained were all less than 11 lbs.

 

Test 3 Results: Test 3 data was summarized in general terms along with the strength data given for Tests 1 and 2 in Tables 2 and 3. Table 4 summarizes, in more detail, the failure conditions observed for Test 3, grouped by gauge and by needle manufacturer. Shown in Table 4 is the observed percent failures in each of the seven categories listed previously.

 

In general, failure Categories 5 and 6 (PNFI, PNF) are unacceptable failure modes. Failure Category 4 (PND) by itself could be considered an acceptable failure mode if and only if a strict adherence to not straightening a permanently deformed needle is adopted. However, as has been determined in past studies, this appears to be the main cause of needle breakage and subsequent needles left in carcasses. Therefore, from strictly a theoretical point of view, Category 4 in this report is considered unacceptable to the industry. What follows is a discussion of the results, listed in order by gauge.

 

22 Gauge Results: All needle/hub assemblies tested resulted in a Category 3 or 4 failure. If the hub was metal (A or BNC), a Category 4 failure was observed. If the hub was polypropylene and supported internally with an aluminum insert (PA), a Category 4 failure was observed. If the hub was polypropylene only, a Category 3 failure was observed for at least 92 percent of the cases.

 

20 Gauge results: For one manufacturer, a Category 6 failure was observed. A Category 4 failure was observed for 100 percent of the cases for all metal hub needles tested. If the hub was polypropylene only, a Category 3 failure was observed for 100 percent of the cases. If the needle was less than or equal to 1.00 inches long and the hub was made of polypropylene with an aluminum insert, a Category 1 failure mode was observed for at least 92 percent of the cases. For this PA assembly at 1.50 inch needle length, a Category 4 failure was observed. Clearly, the aluminum insert added support to the hub and allowed for a more desirable failure mode up to a 1.50 inch needle length.

 

18 Gauge results: A Category 5 failure was observed for one manufacturer using the aluminum hub needle assembly. For another manufacturer, it’s SS hub resulted in a high incidence of Category 5 failures. For this manufacturer, this occurred with their “economy” line of needles. This same manufacturer, using non-economy brand needles resulted in no apparent failure. For all other cases involving metal hub needle assemblies, a Category 4 failure was observed. If the hub was made of polypropylene only, a Category 3 failure was observed. Adding an aluminum insert to the polypropylene hub moved the failure mode towards a Category 1 or 3 failure.

 

16 Gauge results: A Category 5 failure was observed for one assembly tested for 8 percent of the trials. This same manufacturer had a Category 5 failure at the 18 gauge level as well. A high incidence of Category 0 failures was observed and these were in all cases for needles less than or equal to 1.00 inches. One polypropylene manufacturer had an assortment of Category 1, 2, or 3 failures with the predominant mode at Category 2.

 

Relationship of Test 3 to Test 1 Failures Observed: Test 3 represents the types of failure that would be expected in the field and therefore would be considered to be a more accurate representation of clinical findings. However, from an engineering point of view, it is desirable to be able to predict clinical findings using results collected from static testing and therefore to find features in static strength characteristics that could be used to predict the failures observed in Test 3.

 

Characteristic Failures in Test 3 Relative to Test 1: Category 5 or 6 failures recorded during Test 3 are unacceptable to the industry. The following needle assemblies resulted in these types of failures:

 

 

These results, gathered using Test 3, were only found during Test 1 trials for the 20 gauge, 0.75 inch long SS hub needle from Jorgensen Laboratories (Harvard Brand). For the remaining cases given above, Category 5 or 6 failures were never observed during Test 1 conditions.

 

The conclusion is made that as a minimum, needle/hub assemblies must “pass” Test 1 conditions. Passing Test 1 implies that after loading, the needle should deform without experiencing a Category 5 or Category 6 failure. Ultimate strength is not as important as is the ability of the needle to bend without fracturing. In other words, if the needle fractures at all during Test 1 conditions, it will surely fracture when an abrupt animal movement event is experienced during the injection process. Conversely though, if a needle does not fracture during Test 1 conditions, this does not imply that it will not fracture during animal movement conditions.

 

For all 22 and 20 gauge needles, and if the hub material was made of metal (A, BNC, SS) or if a polypropylene hub had an aluminum insert (PA), the failure category recorded from Test 1 matched the failure category recorded for Test 3. If the hub was made of polypropylene only (P or PE), the failures observed during Test 1 did not agree with the failures observed during Test 3. In all cases of P or PE hub 20 or 22 gauge needles, regardless of length, a Category 3 failure was observed 100 percent of the time during Test 3 while a Category 1 failure was observed 100 percent of the time during Test 1.

 

The conclusion is made that for 22 or 20 gauge metal hub needle assemblies, regardless of length, the failures observed in Test 1 agreed with the failures observed in Test 3. This was not the case however for any of the 22 or 20 gauge unsupported polypropylene needles.

 

No obvious trends like those observed for the 22 and 20 gauge needles were found for the 18 and 16 gauge needles. A large range of differences were observed between observed Test 1 and Test 3 failures.

 

Desirable Traits: If one scans the Test 3 results, there appears to be a series of needle/hub characteristics that always resulted in a failure Category between 0 and 3, without 100 percent of the failures falling into Category 3. These would be considered desirable needle/hub traits based on needle/hub failure. What follows is an analysis to try and determine what strength characteristics resulted in these traits.

 

From Test 3 results, the following needle/hub assemblies always resulted in a Category 0 to 3 failure, without 100 percent of the failures in Category 3:
 

 

To help and determine what made these assemblies more desirable, an additional strength indicator was collected during all Test 1 and Test 2 trials in the hope that it would allow additional useful information. In Tables 2 and 3, this additional strength indicator is listed as “Max Mod E”. This designation corresponds to a strength characteristic called the Modulus of Elasticity.

 

The Modulus of Elasticity can be interpreted as the rigidity of the needle/hub assembly. The higher the Modulus of Elasticity, the more rigid a needle/hub assembly is. The smaller the Modulus of Elasticity, the more “plastic” or spring-like the needle/hub assembly is. The Max Mod E measured during Tests 1 and 2 was defined as the maximum load versus distance of needle deformation. Again, the higher the Max Mod E, the larger the load required to deform the needle (vica versa). The table below describes the maximum load sustained for each of the desirable failures observed and the Max Mod E associated with each:

 

Several comparison tests were conducted to try and relate either Test 1 or Test 2 results with the failure categories observed in Test 3. The hope was to find meaningful static testing data that could be used to relate clinical observations on needle/hub failures. Several comparison tests involving Test 1 and Test 2 static results were made to try and attempt this goal. Finally, the following variable, defined as the Rigidity Rating (RR) was found to predict closely the failure categories observed in Test 3:
 

Rigidity Rating (RR) = {Max Mod E / (A * Max Load * 10,000)}Test 1

 
Where
Max Mod E = maximum Load/Distance measurement recorded during Test 1 (lbs/in)
A = cross-sectional area of the needle (in2)
Max Load = maximum load sustained by the needle/hub during Test 1 (lbs)
10,000 = simple multiplier

 

The RR results are listed below for the “desirable” cases listed above:

 

Using the RR concept defined above, the following limits were found for 20, 18, and 16 gauge needles that yield acceptable failure conditions (Category 0, 1, 2, or 3) during Test 3 (animal movement):
 
If the hub is metal (A, SS, or BNC) or the hub is polypropylene with a metal inset (PA), then:
RR < 2.00 for 20 gauge needles
RR < 1.20 for 18 gauge needles
RR < 0.75 for 16 gauge needles

 

If the hub is polypropylene only (P or PE), then:
 
RR < 1.40 for 20 gauge needles
RR < 1.00 for 18 gauge needles
RR < 0.55 for 16 gauge needles

 

Using this criteria, 100 percent of the observed “desirable” failures found during Test 3 would have been predicted using the RR concept gathered using Test 1 results only. In addition however, two added “desirable” cases would have been predicted but these were not observed during actual Test 3 experiments. The two added cases that would have been predicted using this RR concept that were not observed are listed below:

 

A complete summary of all 22, 20, 18, and 16 gauge needles and all RR values determined were given in Table 4.

 

Summary: Needles from six manufacturers were either donated or purchased for evaluating overall static and dynamic strength. Needle assemblies ranging in gauge from 22, 20, 18, and 16 and needle lengths ranging from 0.50, 0.75, 1.00, and 1.50 inches were acquired. Hub materials consisting of polypropylene only, polypropylene with an aluminum insert, aluminum, stainless steel, and brass/nickel/chrome composite were tested. In total, 83 needle assemblies were tested.

 

Specialty testing equipment was developed to conduct the trials for this study. Three basic tests were completed, two designed to test overall static strength and one designed to test strength with simulated animal movement. Three replications of both static tests were conducted and twelve replications of the dynamic test were conducted. The over-riding goal was to provide a series of guidelines that could be used to assess needle/hub assembly performance in the field based on data collected in a controlled laboratory setting.

 

The major focus of this study was to determine characteristics of needle/hub assemblies that result in both desirable and undesirable failure modes in the field. An undesirable needle failure is one where the needle physically fractures after a single needle-bending event, or, a failure that involves a permanently deformed needle that could be straightened and reused. A desirable needle failure is one where, upon failure, no possibility exists for reusing the needle.

 

The findings from this study are as follows:

1. Needle fracture was found for some brands of needles currently being marketing after one needle bending event. These were found for Test 1 conditions, representing full-embedment loading. If a needle fractured during Test 1 conditions, it also fractured during Test 3 conditions (animal movement simulation).
2. For all 22 and 20 gauge needles, and if the hub material was made of metal (A, BNC, SS) or if a polypropylene hub had an aluminum insert (PA), the failure category recorded from Test 1 matched the failure category recorded for Test 3. In other words, expected failures in the field could be gathered from Test 1 failures.
3. If the hub was made of polypropylene only (P or PE), the failures observed during Test 1 did not match the failures observed during Test 3. In all cases of P or PE hub 20 or 22 gauge needles, regardless of length, a Category 3 failure was observed 100 percent of the time during Test 3 while a Category 1 failure was observed 100 percent of the time during Test 1.
4.  No obvious trends like those observed for the 22 and 20 gauge needles were found for the 18 and 16 gauge needles. That is, Test 1 failures did not match the failures observed in Test 3 and therefore could not be used directly to predict field performance.
5.  A procedure was developed that related the strength characteristics measured during Test 1 and the failures, if any, observed during Test 3. This procedure resulted in a Rigidity Rating (RR) for needles based solely on Test 1 measurements. Using RR, a prediction could be made on the type of failure to be expected in the field, with animal movement present during an injection process. For the data collected for this study, the results look promising and indicate a reasonable method for “qualifying” needle/hub assemblies based on strength. More replications however are needed to further develop and refine this procedure.
6. It appears as though laboratory measured static strength data could be used to predict field failure conditions. Currently and preliminarily, the guidelines could be stated as follows:

 

First, a needle must be able to be loaded during Test 1 conditions without fracture of the needle itself. If a needle fractures during Test 1, it will fracture during field conditions leaving a portion of the needle without a portion of the hub embedded in the animal’s tissue. Ultimate strength during Test 1, by itself, is not an important indicator of projected field performance. Needle integrity after Test 1 loading is the first and foremost criteria.

 

Second, during Test 1 conditions, two very important measurements need to be made. First, the maximum load (Max L, lbs) supported by the needle/assembly needs to be measured. Second, the maximum load versus distance of movement needs to be recorded. For this study, this was referred to as the Modulus of Elasticity (Max Mod E).

 

Third, a new variable, called the Rigidity Rating (RR), needs to be determined and calculated as:

Rigidity Rating (RR) = {Max Mod E / (A * Max L * 10,000)}Test 1

 

Fourth, the RR can then be used, it is hypothesized, to predict “desirable” or “undesirable” field failure conditions. As an example, and based on the results collected to date, if the following conditions are met for metal or metal supported polypropylene hub needles;
RR < 2.00 for 20 gauge needles
RR < 1.20 for 18 gauge needles
RR < 0.75 for 16 gauge needles

 

Or the following conditions are met for polypropylene hub needles;
RR < 1.40 for 20 gauge needles
RR < 1.00 for 18 gauge needles
RR < 0.55 for 16 gauge needles

 

then the predictions are that the needles will fail in the field “desirably” implying a Category 0, 1, 2, or 3 failure without 100 percent of the failures falling into Category 3.

 

Table 1a: Listing of all 22 gauge needles tested.

¹No Brand Name means it is sold under the manufacturer’s name.
²A = aluminum; P = polypropylene; PA = polypropylene with aluminum insert;
PE = polypropylene with an epoxy adhesive; SS = stainless steel; BNC = brass/nickel/chrome plated

 

Table 1b: Listing of all 20 gauge needles tested.

 

Table 1c: Listing of all 18 gauge needles tested.

 

Table 1d: Listing of all 16 gauge needles tested.

 

Table 2a: 22 Gauge Test 1 (Full Embedment) and Test 3 (Animal Movement Simulation) Data

³ PND = permanent needle deformation; PND/NFI = permanent needle deformation/needle fracture (intact); PNF = permanent needle fracture; PHD = permanent hub deformation; PHF = permanent hub fracture; PHFI = permanent hub fracture (intact)

 

Table 2b: 20 Gauge Test 1 (Full Embedment) and Test 3 (Animal Movement Simulation) Data

 

Table 2c: 18 Gauge Test 1 (Full Embedment) and Test 3 (Animal Movement Simulation) Data

 

 

Table 2d: 16 Gauge Test 1 (Full Embedment) and Test 3 (Animal Movement Simulation) Data

 

Table 3a: 22 Gauge Test 2 (Tip Bending by Gauge) and Test 3 (Animal Movement Simulation) Data

 

Table 3b: 20 Gauge Test 2 (Tip Bending by Gauge) and Test 3 (Animal Movement Simulation) Data

 

Table 3c: 18 Gauge Test 2 (Tip Bending by Gauge) and Test 3 (Animal Movement Simulation) Data

 

 

Table 3d: 16 Gauge Test 2 (Tip Bending by Gauge) and Test 3 (Animal Movement Simulation) Data

 

Table 4a: Rigidity rating results versus 22 gauge needle failures observed for Test 1 and 3.

* No data for PHD, PHFI, PNFI or PNF

 

Table 4b: Rigidity rating results versus 20 gauge needle failures observed for Test 1 and 3.

* No data for PHFI, or PNFI

 

Table 4c: Rigidity rating results versus 18 gauge needle failures observed for Test 1 and 3.

* No data for PHFI, or PNF

 

Table 4d: Rigidity rating results versus 16 gauge needle failures observed for Test 1 and 3.

 

 

 

Dr. Steve Hoff
Dr. Hoff is an Associate Professor at Iowa State University in the Agricultural and Biosystems Engineering Department. He received a B.S. in Agricultural Engineering Technology from the University of Wisconsin-River Falls, a B.S., M.S. and Ph.D. in Agricultural Engineering from the University of Minnesota. Dr. Hoff holds five U.S. Patents and three copyrighted software logic methods for animal housing climate control. His areas of teaching and research include environmental climate control for animal housing, sensor development, controller development, and air emission measurement and control technologies for animal production systems.