{"id":8498,"date":"2026-06-11T09:00:00","date_gmt":"2026-06-11T08:00:00","guid":{"rendered":"https:\/\/uplastech.com\/silicone-tensile-tear-testing\/"},"modified":"2026-11-02T02:28:03","modified_gmt":"2026-11-02T02:28:03","slug":"silicone-tensile-tear-testing","status":"publish","type":"post","link":"https:\/\/uplastech.com\/nl\/silicone-tensile-tear-testing\/","title":{"rendered":"Silicone Tensile and Tear Testing: Two Numbers That Do Not Track Each Other"},"content":{"rendered":"<style>\n.upl-blog{font-size:17px;line-height:1.78;color:#1f2937}\n.upl-blog p{margin:0 0 18px}\n.upl-blog h2{font-size:26px;line-height:1.3;color:#0b2b33;margin:46px 0 14px;font-weight:700;letter-spacing:-.015em}\n.upl-blog h3{font-size:19.5px;color:#0d3b47;margin:28px 0 10px;font-weight:700}\n.upl-blog ul,.upl-blog ol{margin:0 0 20px;padding-left:22px}\n.upl-blog li{margin:0 0 9px}\n.upl-blog figure{margin:0 0 34px}\n.upl-blog figure img{width:100%;height:auto;display:block;border-radius:10px}\n.upl-blog figcaption{font-size:13px;color:#6b7280;margin-top:10px;line-height:1.5}\n.upl-blog .toc{background:none;border:0;border-radius:0;padding:0;margin:0 0 34px}\n.upl-blog .toc .lwptoc{margin:0}\n.upl-blog .toc h4{margin:0 0 10px;font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#0d5563}\n.upl-blog .toc ol{margin:0;padding-left:18px;font-size:14.5px}\n.upl-blog .toc li{margin-bottom:6px}\n.upl-blog table{width:100%;border-collapse:collapse;font-size:14.5px;margin:0 0 10px}\n.upl-blog th{background:#0d3b47;color:#fff;text-align:left;padding:11px 13px;font-weight:600;font-size:13.5px;border:0}\n.upl-blog td{padding:11px 13px;border:0;border-bottom:1px solid #e8ebed;vertical-align:top}\n.upl-blog tbody tr:nth-child(even){background:#fafbfc}\n.upl-blog .tablecap{font-size:12.5px;color:#6b7280;margin:0 0 30px}\n.upl-blog .myth{background:#fff8ef;border:1px solid #f6ddbd;border-radius:8px;padding:16px 20px;margin:0 0 26px;font-size:15.5px}\n.upl-blog .myth b{color:#a85c10}\n.upl-blog .callout{background:#f2f8f9;border-radius:8px;padding:18px 22px;margin:0 0 26px;font-size:15.5px;border-left:3px solid #14707f}\n.upl-blog .faq h3{border-top:1px solid #eceff1;padding-top:22px;margin-top:0;font-size:18px}\n.upl-blog .faq h3:first-of-type{border-top:0;padding-top:0}\n.upl-blog .cta{background:linear-gradient(135deg,#0b2b33,#0d5563);color:#fff;border-radius:12px;padding:34px;margin:48px 0 30px}\n.upl-blog .cta h2,.upl-blog .cta .cta-h{color:#fff;margin:0 0 10px;font-size:24px;font-weight:700;line-height:1.3}\n.upl-blog .cta p{color:#c9dee3;margin:0 0 20px;font-size:16px}\n.upl-blog .btn{display:inline-block;background:#e07a1f;color:#fff;text-decoration:none;font-weight:700;padding:13px 26px;border-radius:8px;font-size:15.5px}\n.upl-blog .rel{border-top:1px solid #e8ebed;margin-top:40px;padding-top:26px}\n.upl-blog .rel h4{font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#6b7280;margin:0 0 14px}\n.upl-blog .rel ul{list-style:none;padding:0;margin:0}\n.upl-blog .rel li{padding:11px 0;border-bottom:1px dashed #e8ebed}\n.upl-blog .rel a{text-decoration:none;font-weight:600;font-size:15.5px}\n@media(max-width:640px){.upl-blog h2{font-size:22px}.upl-blog table{font-size:13px}.upl-blog .cta{padding:24px}}\n\/* \u5355\u7bc7\u9875\u9690\u85cf WhatsApp \u95ee\u5019\u5361\uff0c\u53ea\u4fdd\u7559\u5706\u5f62\u6c14\u6ce1\uff0c\u907f\u514d\u906e\u6321\u4fa7\u680f\u8be2\u76d8\u63d0\u4ea4\u6309\u94ae\u3002\n   \u6ce8\u610f\uff1aClick to Chat \u7684\u70b9\u51fb\u903b\u8f91\u662f\u300c\u95ee\u5019\u5361\u5143\u7d20\u5b58\u5728\u5c31\u4e0d\u8df3\u8f6c\u300d\uff0c\u53ea\u9760 CSS \u9690\u85cf\u4f1a\u8ba9\u6c14\u6ce1\u53d8\u6210\u6b7b\u94fe\u63a5\u3002\n   Code Snippets #9\u300cUPL single post: WhatsApp bubble jumps straight to chat\u300d\u8d1f\u8d23\u628a\u8be5\u8282\u70b9\u4ece DOM \u79fb\u9664\uff0c\n   \u4e0b\u9762\u8fd9\u6761 CSS \u53ea\u662f\u79fb\u9664\u524d\u7684\u89c6\u89c9\u515c\u5e95\u3002\u5220 #9 \u524d\u5fc5\u987b\u5148\u5220\u8fd9\u6761\u89c4\u5219\u3002 *\/\nbody.single-post .ht_ctc_chat_greetings_box{display:none !important}\n<\/style>\n<div class=\"upl-blog\">\n<figure>\n<img fetchpriority=\"high\" decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/11\/silicone-tensile-tear-testing.jpg\" alt=\"Dumbbell shaped silicone test pieces clamped in a tensile testing machine on a laboratory bench, with a stack of untested specimens beside it\" width=\"1536\" height=\"909\"><figcaption>The dumbbell geometry is fixed by standard for a reason. A different cutter gives a different number.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"what\">What the tensile test actually measures<\/h2>\n<p>A tensile test pulls a dumbbell shaped specimen at a constant rate until it breaks, and records the force and the extension. From that record come three numbers: the tensile strength, which is the stress at break; the elongation at break, which is the strain at break; and the modulus at a stated strain, which is the slope of the early part of the curve.<\/p>\n<p>For silicone, the tensile strength of a general purpose compound is between 6 and 11 MPa, and the elongation at break is between 100 and 600 percent. Those ranges are wide because the numbers depend on the filler system far more than on the polymer. A fumed silica filled compound with a high loading is strong and short; a lightly filled compound is weak and stretchy.<\/p>\n<p>The test is quasi-static, and that matters. Silicone is viscoelastic, so the stress at a given strain depends on how fast the strain is applied. A test at 500 mm per minute gives a different curve from one at 50, and the standard fixes the rate so that results are comparable. A result quoted without the rate is not a result.<\/p>\n<p>The tensile test is also the test most often quoted for a property it does not measure. A seal does not fail in tension; it fails in compression set, in tear, or in adhesion. Tensile strength is a quality indicator for the compound, not a prediction of service performance.<\/p>\n<h2 id=\"curve\">Reading the stress strain curve<\/h2>\n<p>The chart on the left shows three silicone compounds at 40, 60 and 80 Shore A. All three start with a steep rise, then bend into a long plateau, and then rise again before breaking. The plateau is the region where the polymer chains are straightening out; the final rise is strain crystallisation, which is what gives silicone its toughness.<\/p>\n<p>The 40 Shore A compound reaches 550 percent strain at 8.1 MPa. The 60 Shore A compound breaks at 400 percent and 9.6 MPa, and the 80 Shore A compound at 300 percent and 11.6 MPa. Harder means stronger in tension and much shorter in extension, and the relationship is roughly linear across the range.<\/p>\n<p>That trade is the single most useful thing to understand about silicone specifications. A customer who asks for a harder compound to resist compression is also asking for a compound that will crack at a lower elongation. If the part is a diaphragm that has to flex, the harder compound will fail earlier, and the drawing that specified it will look correct.<\/p>\n<p>The shape of the curve also tells you about the compound. A curve with no strain crystallisation rise, one that just flattens and breaks, indicates a resin with a low vinyl content or a heavily plasticised compound. A curve that rises very steeply at low strain indicates a high filler loading, which usually means a high compression set as well.<\/p>\n<figure>\n<img decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/11\/silicone-tensile-tear-testing-chart.jpg\" alt=\"Stress strain curves for three silicone compounds at 40, 60 and 80 Shore A breaking at 550, 400 and 300 percent, and a line chart of tear strength rising with hardness\" width=\"1536\" height=\"909\"><figcaption>Left: stress against strain for three hardnesses. Right: tear strength against hardness, which is a different relationship.<\/figcaption><\/figure>\n<h2 id=\"tear\">Tear strength is a different failure<\/h2>\n<p>Tear strength measures the force required to propagate a cut through a specimen. It is expressed in kilonewtons per metre of thickness, and it is measured on a trouser, angle or crescent specimen depending on the standard. The number it produces is not a stress and cannot be compared with tensile strength.<\/p>\n<p>The chart on the right shows tear strength against hardness for the same family of compounds: 18 kN\/m at 30 Shore A, 24 at 40, 30 at 50, 36 at 60, 42 at 70 and 48 at 80. It rises with hardness in an almost straight line, which is convenient but also misleading, because the tear resistance of a part is dominated by its geometry rather than by the compound.<\/p>\n<p>A sharp internal corner concentrates stress, and a tear starts there at a fraction of the nominal tear strength. That is why a silicone gasket with a square corner tears at the corner while the same compound in a rounded section lasts for years. The compound number tells you how bad the geometry has to be before it matters.<\/p>\n<p>The two tests diverge most on compounds with high tear strength additives. A compound can be formulated for tear, with a vinyl rich polymer and a specific filler treatment, and gain 40 percent in tear strength for a 5 percent loss in tensile. If the part is a seal that is assembled over a sharp edge, tear is the number to specify, not tensile.<\/p>\n<h2 id=\"sample\">Specimen preparation dominates the result<\/h2>\n<p>The specimen has to be cut from a moulded plaque with a die that is sharp and free of nicks. A dull die produces a specimen with a micro-crack at the edge, and the specimen breaks at that crack rather than at the gauge section. The result is a tensile strength 20 to 30 percent below the true value and an elongation that is similarly short.<\/p>\n<p>The plaque itself has to be cured under the same conditions as the production part. A plaque that is press cured for 10 minutes and a part that is injection moulded with a 30 second cycle are not the same material, even from the same batch of compound. The moulded part usually has a higher state of cure at the surface and a lower one in the core.<\/p>\n<p>Thickness has to be measured and used in the calculation. A 2 mm nominal plaque that is actually 1.85 mm gives a stress that is 8 percent low, because the cross section is smaller than assumed. On a specification with a plus or minus 10 percent tolerance, that alone can decide whether a batch passes.<\/p>\n<p>Conditioning matters as well. Silicone absorbs very little water, so humidity is less critical than for other elastomers, but temperature is not. A specimen tested at 18 C in an unheated laboratory in winter reads differently from one tested at 23 C, and the difference on a soft compound can be 10 percent.<\/p>\n<h2 id=\"age\">The tests that predict service life<\/h2>\n<p>Tensile and tear describe the material as delivered. What decides whether a part lasts is heat ageing, compression set and, for dynamic parts, flex fatigue. Those three tests are the ones that should be on a drawing for any part that sees temperature or a sustained load.<\/p>\n<p>Heat ageing is a tensile test after a period at elevated temperature. The specimen is aged at 200 C for 72 hours, or 225 C for 24, and then tested. The acceptance criterion is usually that the tensile strength and elongation retain 70 to 80 percent of their original values. A compound that starts at 10 MPa and retains 50 percent is worse than one that starts at 8 and retains 85.<\/p>\n<p>Compression set is the test that matters for seals. A specimen is compressed by 25 percent, held at temperature for 22 or 70 hours, released and measured after 30 minutes. The permanent deformation as a percentage of the applied compression is the set. A good general purpose silicone is under 25 percent; a high temperature grade is under 15.<\/p>\n<p>Flex fatigue is rarely specified and frequently the cause of field failure on diaphragms and bellows. A dynamic part that flexes a million times will fail at a fold, and the fold location is set by geometry. The test is slow and expensive, which is why it is usually replaced by a design rule: keep the flexing section thin and avoid sharp transitions.<\/p>\n<h2 id=\"spec\">Writing a specification that means something<\/h2>\n<p>A silicone specification needs the hardness with its tolerance, the tensile strength as a minimum, the elongation at break as a minimum, the tear strength as a minimum if the part is assembled over an edge, the compression set with its test condition, and the heat ageing retention. Anything less and two suppliers can both comply while delivering different materials.<\/p>\n<p>The tolerances matter more than the nominal values. A hardness of 60 plus or minus 5 Shore A covers compounds that behave quite differently; plus or minus 3 is achievable and worth asking for on a seal. A tensile minimum of 7 MPa with an elongation minimum of 300 percent is a reasonable general purpose specification for a moulded part.<\/p>\n<p>The specification should also state the test standard, because the numbers are not interchangeable. ASTM D412 and ISO 37 use different specimen geometries and different test speeds, and a result quoted to one cannot be compared with a result quoted to the other without a conversion that is approximate at best.<\/p>\n<table>\n<thead>\n<tr>\n<th>Eigendom<\/th>\n<th>Test<\/th>\n<th>Typical range<\/th>\n<th>What it predicts<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Hardness<\/td>\n<td>ASTM D2240 Shore A<\/td>\n<td>30 to 80<\/td>\n<td>Stiffness, sealing force<\/td>\n<\/tr>\n<tr>\n<td>Tensile strength<\/td>\n<td>ASTM D412<\/td>\n<td>6 to 11 MPa<\/td>\n<td>Compound quality<\/td>\n<\/tr>\n<tr>\n<td>Elongation at break<\/td>\n<td>ASTM D412<\/td>\n<td>100 to 600 %<\/td>\n<td>Flexibility, toughness<\/td>\n<\/tr>\n<tr>\n<td>Tear strength<\/td>\n<td>ASTM D624 Die B<\/td>\n<td>18 to 48 kN\/m<\/td>\n<td>Resistance to a cut or edge<\/td>\n<\/tr>\n<tr>\n<td>Compression set<\/td>\n<td>ASTM D395 Method B<\/td>\n<td>15 to 30 %<\/td>\n<td>Sealing life under load<\/td>\n<\/tr>\n<tr>\n<td>Heat ageing retention<\/td>\n<td>ASTM D573<\/td>\n<td>70 to 90 %<\/td>\n<td>Service life at temperature<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 The six numbers that describe a silicone compound<\/p>\n<h2 id=\"inspect\">Incoming inspection in practice<\/h2>\n<p>A full tensile and tear test takes about two hours including specimen preparation and conditioning, and it destroys the specimen. That is too slow for every delivery, so most plants test a cured plaque from each batch and rely on the supplier's certificate for the rest.<\/p>\n<p>The cheapest useful check is hardness plus a visual and dimensional check on a moulded sample. Hardness takes a minute per point and catches the most common batch error, which is a filler loading that drifted. A batch that is four points off nominal will show it immediately, and it will also show the tensile and tear differences that follow.<\/p>\n<p>The second check is a compression set on a production part, held in a simple fixture. It is not a standard test, because the geometry is not standard, but it is directly relevant and it is repeatable within a plant. A part that sets 40 percent in the fixture will leak in service, whatever the certificate says.<\/p>\n<table>\n<thead>\n<tr>\n<th>Check<\/th>\n<th>Time<\/th>\n<th>Frequency<\/th>\n<th>Catches<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Hardness on a moulded sample<\/td>\n<td>1 minute<\/td>\n<td>Every batch<\/td>\n<td>Filler loading drift<\/td>\n<\/tr>\n<tr>\n<td>Visual and dimensional<\/td>\n<td>5 minutes<\/td>\n<td>Every batch<\/td>\n<td>Flash, short shots, cure<\/td>\n<\/tr>\n<tr>\n<td>Compression set in a fixture<\/td>\n<td>24 hours<\/td>\n<td>Monthly or on change<\/td>\n<td>Under cure, wrong compound<\/td>\n<\/tr>\n<tr>\n<td>Tensile and tear on a plaque<\/td>\n<td>2 hours<\/td>\n<td>New supplier or new batch of compound<\/td>\n<td>Compound substitution<\/td>\n<\/tr>\n<tr>\n<td>Heat ageing<\/td>\n<td>4 days<\/td>\n<td>New compound only<\/td>\n<td>Wrong base polymer<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 A practical inspection plan, cheapest first<\/p>\n<p>The order is deliberate. The first two checks cost minutes and catch most of what goes wrong. The expensive tests are for qualifying a compound, not for routine acceptance, and running them on every delivery is a way of spending money without buying information.<\/p>\n<div class=\"faq\">\n<h3>Is a higher tensile strength always better?<\/h3>\n<p>No. In silicone, tensile strength and elongation trade against each other, and a harder, stronger compound is also a shorter one. If the part has to flex, a compound that is 20 percent stronger and 25 percent shorter will fail sooner. Specify both numbers, and specify the one the application actually needs.<\/p>\n<h3>Why do my test results differ from the supplier's certificate?<\/h3>\n<p>Usually specimen preparation. A dull cutting die, a plaque cured differently from the supplier's, or a thickness measured at the wrong point will each move the result by 10 to 30 percent. Check the die first, then the cure, then the thickness.<\/p>\n<h3>What is a good tear strength for a silicone seal?<\/h3>\n<p>Above 25 kN\/m for a seal that is stretched over a metal edge during assembly, and above 35 kN\/m if the edge is sharp or the seal is thin. Below 20 kN\/m the seal will nick during installation and fail from that nick, regardless of its tensile strength.<\/p>\n<h3>What does compression set actually tell me?<\/h3>\n<p>How much of the sealing force the material loses permanently under sustained compression at temperature. A 25 percent set means a quarter of the deflection is gone and cannot be recovered. It is the single best predictor of whether a gasket will still seal after a year.<\/p>\n<h3>Can I test a finished part instead of a plaque?<\/h3>\n<p>For hardness and compression set, yes, and it is often more relevant. For tensile and tear, no, because the specimen geometry is fixed by the standard. A part tested in tension gives a number that cannot be compared with anything.<\/p>\n<h3>Why does the test speed matter?<\/h3>\n<p>Silicone is viscoelastic, so a faster pull produces a higher stress at the same strain and often a shorter elongation. The standards fix the speed for that reason. A result quoted without the speed and the standard cannot be compared with another result.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Specifying a silicone compound?<\/p>\n<p>Send the application, the temperature and whether the part flexes or seals. We will recommend the hardness and the two or three numbers that actually decide whether it works.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/nl\/custom-injection-molding\/\">Ask about silicone testing<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/nl\/silicone-hardness-testing\/\">Silicone Hardness Testing: Shore A, IRHD and the Sample Thickness<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/nl\/silicone-surface-treatment\/\">Silicone Surface Treatment: Getting Adhesion to Stick<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/nl\/silicone-laser-marking\/\">Silicone Laser Marking: Marking a Surface That Repels Everything<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/nl\/silicone-printing-pad\/\">Silicone Printing Pad: Transferring Ink Onto a Low Energy Surface<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/nl\/silicone-degassing-vacuum\/\">Degassing Silicone: Why the Bubbles Are Still There<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>A silicone compound can have a high tensile strength and tear like paper. The two tests measure different failure modes, and a specification that quotes only one of them is a specification for a material that may not survive the application.<\/p>","protected":false},"author":1,"featured_media":8496,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[39],"tags":[],"class_list":["post-8498","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-silicone-rubber-products"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/nl\/wp-json\/wp\/v2\/posts\/8498","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/nl\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/nl\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/nl\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/nl\/wp-json\/wp\/v2\/comments?post=8498"}],"version-history":[{"count":1,"href":"https:\/\/uplastech.com\/nl\/wp-json\/wp\/v2\/posts\/8498\/revisions"}],"predecessor-version":[{"id":8873,"href":"https:\/\/uplastech.com\/nl\/wp-json\/wp\/v2\/posts\/8498\/revisions\/8873"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/nl\/wp-json\/wp\/v2\/media\/8496"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/nl\/wp-json\/wp\/v2\/media?parent=8498"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/nl\/wp-json\/wp\/v2\/categories?post=8498"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/nl\/wp-json\/wp\/v2\/tags?post=8498"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}